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P R O P E R T Y of T H E : - § § ** # 8 7 A R T E S S C E N T : A V E R T A S *... • rº, , g 4. : ;", r - ºr g;" t = ~~~ *** į Q. & . *~ ) /* . . ºf + PORTLAND CEMENT Its Composition, Raw Materials, Manu- facture, Testing and Analysis, º: * -º - * ; , , & * ** - *, BY * y § - A'. º, ſ six a RICHARD K. MEADE, M.S.: ; 3 * º 9 *s 2. * . . +. - *- : '* . . . - * .5°, - - º 2. - - Consulting Engineer and Chemist, Baltimore, Md., Director and Consulting Engineer of the National Cement Co., Montreal, Author of the Chemists Pocket Manual, etc. Formerly Gen. Manager of the Tidewater Portland Cement Co,. Chemist of the Dexter Portland Cement Co. Chemist and Superintendent of the Northampton Portland Cement Co., Chemist of the Edison Portland Cement Co., Consulting Chemist to the Giant Portland Cement Co., Consulting Chemist to the Allentown Portland Cement Co., Vice President of the American Institute of Chemical Engineers, Member Committee on Cement Manufacture, American Society of Mechanical Engineers, Etc., Etc. THIRD EDITION * ſº ; ; EASTON, PA. THE CHEMICAL PUBLISHING COMPANY 1926 LONDON , ENGLAND : TOKYO. JAPAN: MARUZEN COMPANY., LTD. WILLIAMS & NOR GATE, 11-16 NIHON BASH. To RI-SANCHC ME 14 HENRIETTA ST REET, COVENT GARD EN, W. C. : . COPYRIGHT, I.9 II, BY EDwARD HART. COPYRIGHT, 1926, BY EDwARD HART. wº- .* ** t v. -4 * * .* ** " … i •-A..."-- - - * * & * The present treatise upon Portland cement is really the second edition of a small manual by the writer, published some four years ago, called “The Chemical and Physical Examination of Portland Cement.” In preparing this new edition, it seemed wise to add a section on the manufacture of Porland cement, for the reason that the chemist who is to intelligently supervise the process of manufacture, as well as the chemist who is to report upon the raw materials and the engineer who is to inspect the product, should have a good, general knowledge of the technology of Portland cement. It was also found necessary to rewrite almost the entire section upon the physical testing of cement in order to give special promi- nence to the uniform methods of testing adopted by the American Society of Civil Engineers, and to the standard specifications of the American Society for Testing Materials. Much new matter has also been added to the section on the analysis of cement and its raw materials, and sections on the experimental manufacture of small lots of cement and on the history of the industry have been included. The analytical methods have all been used to some extent in the writer's laboratory and have been found satisfactory. Com- ments as to their accuracy and advice as to the best methods of manipulation will usually be found with each method under the heading, “notes.” The author again wishes to thank the many friends who have aided him in the preparation of both this and the former edition. NAZARETH, PA., July, IQO6. f $ -e PREFACE TO FIRST EDITION. sºlº PREFACE TO THE SECOND EDITION In the preparation of the present edition, the entire text of the book has been revised. Much new matter has been added, particularly to the section on “Manufacture,” which has been increased by 76 pages. Descriptions of the newer appliances for the Manufacture of Portland Cement have been added so that it is believed that this section represents fairly well the present state of the industry in this country. The section on “Analytical Methods” has been somewhat con- densed, so far as space goes, by the printing of the notes in smaller type but the actual matter has been increased. The section on “Physical Testing” has been revised to conform to the changes made in the standard specifications and methods of testing, and much new matter has been included here also. A chapter has been added to the book on the “Investigation of Materials for the Manufacture of Portland Cement.” The number of illustrations has been increased from IOO to 17O and among the new ones will be found many half-tones showing ac- tual installations of cement machinery, kilns, etc. BALTIMORE, M.D., October, IQII. PREFACE TO THE THIRD EDITION Originally this work was intended primarily for chemists and cement inspectors and described methods of test and analysis only. The section on the manufacture of cement has been increased with each edition, however, until now it is much the largest part of the book. It is hence believed that the work will prove fully as useful to engineers and others interested solely in the mechan- ical features of the process as to chemists and others engaged in inspecting and testing cement. In preparing the third edition of this book, the author has taken the opportunity to again thoroughly revise the entire text to make it conform to present day theory and practice. Much of the book has been rewritten. The subject matter has been in- creased by nearly two hundred pages, most of this new material being added to the section on “Manufacture.” Seventy new illustrations appear in this and it is believed that it covers all of the latest advances in the art of cement making, including the waste heat boiler, dust precipitation, etc. An effort has been made to present the manufacture of cement in as practical a manner as possible and much information is given as to the power and fuel requirements of the process, output of machines, cost data, etc. A few new methods of analysis have been added to the section on “Analytical Methods” and the section on “Physical Testing” has, of course, been revised to agree with the present American standard specifications and methods of test. Paragraphs have been added at the end of each chapter of this showing the in- fluence of manufacturing conditions, chemical composition, etc., upon those properties of cement covered by the tests. This has been done with a view to presenting in brief form methods for correcting faults in manufacture. Some information as to for- eign specifications, methods of test, etc., has also been added to this section. Once more, the author wishes to express to his many friends in the cement industry his appreciation and thanks for the assis- tance they have given him in the revision of this book. Their kindness in furnishing him with the results of their experience has done much to add to its value. BALTIMORE, MARYLAND, June, 1926. CONTENTS. INTRODUCTION Chapter I—Relation Between Mortar Materials and History of the Development of the American Portland Cement Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I–I 5 Relation Between Portland Cement and Other Mortar Materials, 1 ; History of the Development of Mortar Materials, 4; The Beginning of the Cement Industry in England, 4; Invention of Portland Cement, 6; Discovery of Cement Rock in the United States, 7; Manufacture of Natural Cement, 8; Beginning of the Portland Cement Industry in the United States, Io; Development in Other States, I I ; Production of Port- land Cement, 13. J. Chapter II—The Nature and Composition of Portland Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I6–50 Composition of Portland Cement, 16; Substances found in Cement, 17; Analyses of American Portland Cements, 19; Early Studies of Cement, 20; Le Chatelier's Investigations, 20; Newberry's Formula, 22; Törne- bohm's Investigations, 23; Richardson's Work, 24; Researches of Day, Shepherd and Rankin, 24; Use of Triangular Diagrams, 25; Ternary System, 27; Compounds in Cement, 29; Formation of Cement Clinker, 31 ; Experiments of Bates and Phillips, 33; Setting and Hardening of Cement, 34; Effect of Theory Upon Practice, 37; Lime, 38; Silica and Alumina, 41; Ferric Oxide, 43; Magnesia, 45; Alkalies, 47; Sulphur, 48; Carbon Dioxide and Water, 49; Other Compounds in Portland Cement, 50. MANUFACTURE v Chapter III—Raw Materials . . . . . . . . . . . . . . . . . . . . . . . 5I-74 Essential Elements, 51 ; Classification of Materials, 51 ; Limestone, 52; Cement Rock, 55; Marl, 58; Clay, 60; Shale, 61; Analyses of Materials Used for the Manufacture of Portland Cement at Various Plants, 62; Blast Furnace Slag, 68; Alkali Waste, 70; Gypsum, 70; Valuation of Raw Materials, 72. Chapter IV—Proportioning the Raw Materials . . . . . . . 75–95 Lime Ratio, 75; Newberry's Formula, 77; Formula Based on Bates and Rankin's Works, 78; Use of Formula, 79; Fixed Lime Standard, 81 ; Formulas for a Fixed Lime Standard, 82; Formulas for Correcting the Mix, 84; Formula for a Three-Component Mix, 86; Proportioning the Mixture in the Wet Process, 88; Correcting Slurry, 91; Calculating the Probable Analyses of Cement Clinker, 93. viii CONTENTS Chapter V–Quarrying, Mining and Excavating the Raw Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96–IIO Quarrying the Stone, 96; Stripping, 97; Blasting, 98; Loading, 99; Glory Hole Method of Quarrying, Ioo; Mining, Io2; Excavating Marl, IO2; Digging Clay and Shale, IO4; Hauling, 104. Chapter VI—Outline of Process, Mixing the Raw Ma- terials and Chemical Control . . . . . . . . . . . . . . . . e o e s e III–I3O Wet and Dry Process, III; Importance of Chemical Control, II2; Chemical Control, II4; Mixing the Raw Materials, II 7; Correcting the Mix, I 19 ; Storage of Raw Materials, I22; Weighing the Raw Materials, I27. Chapter VII—The Dry Process . . . . . . . . . . . . . . . . . . . . I31–I5O Outline of the Dry Process, I31; Crushing, 133; Drying and Dryers, 138; Capacity of Rotary Dryers, 141; Waste Heat Dryers, 143; Drying Clay, I45; Feeding the Dryer, 145; Pulverizing the Raw Material, i46; Degree of Fineness of the Raw Material, I46; Elevating and Conveying Machinery, I47; Complete Raw Mill, I49. Chapter VIII—The Wet Process . . . . . . . . . . . . . . . . . . . I5I–I72 History of the Wet Process, 151; Outline of Wet Process, 152; Ad- vantages and Disadvantages Claimed for the Wet Process, 153; Chemical Control of the Wet Process, 155; Grinding the Raw Materials, 157; Wash Mills, 158; Water, 161; Slurry Basins, 163; Dorr Slurry Mixer, 166; Handling Slurry, 168; Weight of Slurry, 171; Complete Grinding Plant, I72. Chapter IX—Crushing Machinery . . . . . . . . . . . . . . . . . . I73–189 Development of Grinding Machinery, 173; Gyratory Crusher, 175; Jaw Crusher, 178; Fairmount or Roll Jaw Crusher, 180; Hammer Mill, 182; Edge Runner Mill, 186; Rolls, 187. Chapter X—Grinding Machinery . . . . . . . . . . . . . . . . . . . . I90–243 The Ball Mill, 190; Kominuter, 195; Tube Mill, 197; Ball–Tube Mill, 2Io; Hardinge Mill, 2II; Rod Mill, 212; Compound Mill, 212; Compeb Mill, 213; Griffin Mill, 216; Bradley Hercules Mill, 219; Huntington Mill, 222; Raymond Roller Mill, 224; Fuller-Lehigh Mill, 226; Bonnot Mill, 232; Kent and Maxecon Mills, 233; Sturtevant Ring Roll Mill, 235; Newaygo Separator, 236; Hummer Screen, 237; Air Separators, 239; Capacity of Various Grinders, 242. Chapter XI-Burning—Kilns and General Description of the Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244–279 Shaft Kiln, 244; Rotary Kiln, 250; General Description of the Rotary Kiln, 251 ; Reactions which Occur in the Kiln, 254; The Four Zones, 255; Mechanical Details of Construction, 256; Stack and Dust Chamber, 259; CONTENTS ix Length and Diameter, 261 ; Feeding the Raw Material into the Kiln, 264; Kiln Lining, 267; Speed of Rotation, 272; Inclination of the Kiln, 273; Length of the Clinkering Zone, 273; Capacity of Cement Kilns, 274; Fuel Requirements, 276; Labor, 277; Degree of Burning, 278. Chapter XII—Burning—Scientific Consideration of the Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280–322 Chemical Changes Undergone in Burning, 280; Influence of Coal-Ash on Chemical Composition of Cement, 281 ; Relation Between Time Tem- perature and Fineness, 284; Temperature of Burning, 285; Thermo- Chemistry of Burning, 287; Heat of Decomposition, 290; Heat of Forma- tion of Clinker, 291 ; Heat Required to Burn Cement, 292; Application of Heat, 294; Air Required for Combustion, 296; Products of Combustion, 297; Excess Air Used in Burning, 298; Heat Carried out by the Waste Gases, 300; Heat Loss Due to Carbon Burned to Carbon Monoxide, 302; Heat Lost by Radiation, 303; Heat Balance, 305; Dust Losses, 309; Dust Collection, 312; Collection by Washing the Gases with Water, 315; Potash from the Cement Industry, 317; Water Soluble Potash, 319; Potash Salts from Dust, 32O. Chapter XIII—Burning (Continued)—Fuel and Prep- aration of Same . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323–361 Comparison of Fuels, 323; Cost of Pulverizing Coal, 325; Composi- tion of Coal for Cement Burning, 325; Preparation of Pulverized Coal, 327; Coal Crushers, 327; Drying the Coal, 329; Fuller-Lehigh Dryer, 330; Ruggles-Coles Dryer, 331 ; Direct Fired Coal Dryer, 333; Pulverizing the Coal, 334; General Coal Plant Arrangement, 336; Conveying the Coal, 337; Fuller-Kinyon Pump, 338; Distribution Line, 340; Equipment Em- ployed for Heating the Kiln with Powdered Coal, 341; Air for Carrying Coal, 342; Worm Feeder for Coal, 343; Equipment for Reducing and Varying Feed, 345; Burners, 347; Steam and High Pressure Air Burners, 349; Unit System and Aero Pulverizer, 351; Oil, 355; Storage of Coal, 356; Burning with Natural and Producer Gas, 357. º Chapter XIV—Cooling and Grinding the Clinker, Stor- ing and Packing the Cement, Etc. . . . . . . . . . . . . . . . . 362-391 Cooling the Clinker, 362; Utilization of Heat in Clinker for Other Purposes than Preheating Air for Kiln, 367; Storing and Seasoning Clinker, 368; Travelling Crane for Handling Clinker, 370; Revolving Cranes for Handling Clinker, 372; Properties of Seasoned Clinker, 374; Adding the Retarder, 375; Grinding the Clinker, 376; Factors Influencing Grinding of Clinker, 377; Conveying Clinker and Cement, 379; Stock Houses, 38o; Silo Stock Houses, 382; Pack House, 385; Packing, 387. X CONTENTS * Chapter XV-Power Equipment, General Arrangement of Plant, Cost of Manufacture, Etc. . . . . . . . . . . . . . . 392–432 Power Transmission, 392; Shaft Driven Mills, 392; Electric Drives, 393; Boiler Plant, 394; Power Required, 395; Waste Heat Boilers, 396; Air Leakage and Draft, 397; Heat in Gases, 398; Calculating Quantity of Gas and Heat in this, 400; The Boiler, 402; Air Seal and Dampers, 403; Economizer, Fan, Etc., 405; Auxiliary Departments, 407; Machine Shop, 408; Arrangement of Plant, 410; Mechanical Equipment of Plants, 41.1; Cost of Plant, 425; Cost of Raw Materials, 426; Labor, 427; Supplies and Fuel, 430; Administrative Expenses, Depreciation, Etc., 431; Present Cost of Manufacture, 432. ANALYTICAL METHODS Chapter XVI—The Analyses of Cement . . . . . . . . . . . . . 433–494 Preparation of the Sample, 433; Standard Specifications for Chemical Properties of Cement, 434; Standard Methods for Chemical Analysis, 434; Loss on Ignition, 434; Insoluble Residue, 435; Sulphuric Anhydride, 435; Magnesia, 436; Determination of Silica, Ferric Oxide, Alumina, Lime and Magnesia, 438; Volumetric Determination of Lime, 451 ; Rapid Determination of Lime, 456; Determination of Ferric Oxide, 457; Deter- mination of Sulphuric Anhydride, 466, Determination of Total Sulphur, 469; Determination of Sulphur Present as Calcium Sulphide, 470; Loss on Ignition, 473; Photometric Method for Magnesia, 474; Determination of Carbon Dioxide and Combined Water, 475; Determination of Carbon Dioxide Alone, 481 ; Rapid Determination of Carbon Dioxide, 483; De- termination of Hygroscopic Water, 485; Determination of Alkalies, 486; Determination of Phosphoric Acid, 491 ; Determination of Manganese, 492; Determination of Titanium, 493. Chapter XVII—Analyses of Cement Mixtures, Slurry, Etc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495–52O Sampling, 495; Rapid Method for Checking the Percentage of Cal- cium Carbonate in Cement Mixtures, 503; Determination of Silicates, 516; Complete Analysis of Cement Mixture or Slurry, 517. Chapter XVIII—Analyses of the Raw Materials . . . . 521-538 Methods for Limestone, Cement-Rock and Marl, 521 ; Rapid Deter- mination of Lime and Magnesia, 526; Methods for Clay and Shale, 529; Method for Gypsum or Plaster of Paris, 536. PHYSICAL TESTING Chapter XIX—Inspection of Cement . . . . . . . . . . . . . . . . 539–552 Standard Specifications and Tests for Portland Cement, 539; Methods of Inspection, 541; Inspection at the Mill, 542; Inspection on the Work, CONTENTS xi 545; Standard Methods of Sampling, 546; Samplers, 547; Uniform Speci- fications and Methods of Testing, 550; Tests to be Made, 551. Chapter XX—Specific Gravity . . . . . . . . . . . . . . . . . . . . . 553–564 Standard Specification for Specific Gravity, 553; Standard Method of Operating Test, 553; Notes on Standard Method, 555; Other Methods, 557; Observations on Specific Gravity, 558; Effect of Burning on Specific Gravity, 559; Effect of Adulteration on Specific Gravity, 560; Effect of Seasoning Cement or Clinker on Specific Gravity, 560; Specific Gravity Upon Dried and Ignited Samples, 562; Manufacturing Conditions Affect- ing Specific Gravity, 563. Chapter XXI-Fineness . . . . . . . . . . . . . . . . . . . . . . . . . . . 565-589 Standard Specification and Method of Test, 565; Foreign Specifica- tions for Fineness, 566; Errors in Sieves, 566; Methods of Sieving, Sieves, Etc., 568; Determining the Flour in Cement, 570; Suspension Method, 571 ; Griffin-Goreham Flourometer, 572; Pierson Air Analyser, 575; Gary-Lindner Apparatus, 577; Observations on Fineness, 578; Effect of Fineness on the Properties of Portland Cement, 578; Influence on Color, 578; Influence on Soundness, 579; Influence on Setting Time, 58o; Effect of Fineness on Strength, 582; Limitations of Sieve Test, 584; Effect of Fineness of Cement on the Resulting Concrete, 586; Effect of Manufac- turing Conditions on Fineness, 588. Chapter XXII—Time of Setting . . . . . . . . . . . . . . . . . . . . 590–612 Standard Specification and Method of Test, 590; Normal Consistency, 590; Determination of Setting Time, 592; Foreign Specifications for Setting Time, 594; Notes 594; Other Methods, 596; Observations on Setting Time, 598; Factors Influencing the Rate of Setting, 598; Rise in Temperature During Setting, 600; Influence of Sulphates on Setting Prop- erties, 601 ; Influence of Calcium Chloride on Setting Time, 605; Influence of Hydration, 606; Quickening the Setting Time, 607; Effect of Storage of Portland Cement on Its Setting Properties, 607; Influence of Slaked Lime on Setting Time, 610; Manufacturing Conditions Affecting Setting Time, 61 I. Chapter XXIII—Soundness . . . . . . . . . . . . . . . . . . . . . . . . 613–639 Standard Specification and Method of Test, 613; Notes, 616; Other Methods, 618; Normal Tests, 618; Boiling Test, 618; German Specifica- tions, 620; Le Chatelier Test, British Specifications, 62o ; French Specifica- tions, 621 ; High Pressure Boiling Test, 622; Faija's Test, 623; Kiln Test, 624; Calcium Chloride Test, 624; Bauschinger's Calipers, 625; Microscopic Test for Free Lime, 626; Observations, 629; Importance of Test, 629; Causes of Unsoundness, 630; Effect of Seasoning in Soundness, 631 ; Effect of Fine Grinding of the Raw Materials on Soundness, 632; Effect of Sulphates on Soundness, 633; Value of Accelerated Tests, 634; Manu- facturing Conditions Influencing Soundness, 637. xii CONTENTS Chapter XXIV—Tensile Strength . . . . . . . . . . . . . . . . . . 640–67I Specification, 640; Method of Operating Test, 640; Notes, 643; Stand- ard Sand, 643; Other Forms of Briquettes, 644; Molds, 645; Mixing, 647; Percentage of Water, 648; Storage of Briquettes, 650; Testing Machines, 652; Rate of Stress, 657; Clips, 658; Other Methods, 660; Foreign Speci- fications, 660; Lack of Uniformity in Tensile Tests, 661; Machines for Mixing the Mortar and Making Briquettes, 622; Observations, 663; High Tensile Strength of Unsound Cement, 663; Relation Between Neat and Sand Strength, 664; Effect of Seasoning and Hydration on Strength, 665; Drop in Tensile Strength, 667; Manufacturing Conditions Influencing Strength, 669. MISCELLANEOUS Chapter XXV-The Detection of Adulteration in Port- land Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672–678 Microscopic Test, 672; Tests of Drs. R. and W. Fresenius, 673; Le Chatelier's Test, 677. Chapter XXVI—The Investigation of Materials for the Manufacture of Portland Cement . . . . . . . . . . . . . . . . . 679–693 Prospecting Limestone and Cement Rock Deposits, 679; Clay and Shale, 683; Marl, 684; Trial Burnings, 685; Experimental Shaft Kilns, 687; Experimental Rotary Kilns, 690; Value of Experimental Burnings, 693. Appendix-Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694 Atomic Weights of the More Important Elements, 694; Factors, 694; For Converting Mg2P.O; to MgO, 695; For Calculating the Percentage of Lime or Carbonate of Lime with one-half Gram Sample, 695; Percentage of Water for Sand Mixtures, 698. INTRODUCTION CHAPTER I RELATION BETWEEN MORTAR MATERIALS AND HISTORY OF THE DEVELOPMENT OF THE AMERICAN PORTLAND CEMENT INDUSTRY Relation Between Portland Cement and Other Mortar Materials Mortar materials may be classified according to their proper- ties, methods of manufacture and materials from which they are made as follows:– I. Common Limes are made by burning relatively pure lime- stone. When mixed with water they slake and show no hydrau- lic properties. 2. Hydraulic Limes are made by burning impure limestone at low temperatures. They slake with water but show hydraulic properties. 3. Natural Cements are made by burning impure limestones at a low temperature (insufficient to vitrify). They do not slake with water but require to be ground in order to convert them into a hydraulic cement. 4. Portland Cement is made by heating to incipient vitrifac- tion an intimate mixture of an argillaceous substance, such as clay or shale, and a calcareous substance, such as limestone or marl, in which mixture the percentage of silica, alumina and iron oxide bears to the percentage of lime the ratio of approximately I : 2, which vitrified product does not slake with water but upon grinding forms an energetic hydraulic cement. 5. Puzzolan Cements are made by incorporating slaked lime with finely ground slag or volcanic ash or by incorporating a small proportion of Portland cement clinker with suitably treated slag and grinding intimately the mixture. PORTLAND CEMENT 6. Plasters are made by heating gypsum sufficiently to drive off three-fourths or all of the combined water which it con- tains and grinding finely the more or less dehydrated residue. Table I given below will explain the above classifications, while Tables II and VIII show the composition of these various materials. TABLE. I.-SHowING THE RELATION BETWEEN LIMEs, CEMENTS AND PLASTERs. mºus j | *...* | . classification Made from rel-| Burn ed at Slake on addi- Not h y - I. Common atively pure 1 o w tem- tion of water draulic lime limestones peratures, to burn ed 6oo°-12oo° product - e C. Hydraulic 2. Hydraulic Made from ar- limes gillaceous or impure lime- Stone Do not slake on 3. N at ural, addition of Roman or water but Rosendale m us t be Cement ground fine- Made from an Burned at '3' " "* 4. Portl and i n tim a t e high tem- cement mixture of p e ratures. argillace o us 1300°-6100° and cal car-l C. e o us sub- st a n c e s in proper pro- portions d e f b d 5. S 1 a g o r M * r J.' ; Not burlle Puzzo lan slaked 1 i me Cements a n d b l a st furnace slag or volc an ic ash M a d e from Burn ed at Not hy- gypsum from I65- draulic 6. Plasters 2OO° C. TABLE II.-CHEMICAI, CoM Position of MoRTAR MATERIALs. Analysis Material From SiO2 Fe2O3 Al2O3 CaO MgO SO3 CO2 H2O Lime. . . . . . . . . . . . . Glencoe, Mo. . . . . . . . . O. I 5 O.85 98.OI O. 45 O. 55 Lime . . . . . . . . . . . . . York, Pa. . . . . . . . . . . . . O.52 O.24 97. I4 I.28 O.96 Lime. . . . . . . . . . . . . McNeil, Tex . . . . . . . . . O.25 O. I5 97.46 O.73 I. 4 I Lime. . . . . . . . . . . . . Tiffin, O. . . . . . . . . . . . . I.6I O. I 7 57. 44 40.36 O. 4 I ge e Hydrated little . . . . . Carey, O. . . . . . . . . . . . . O. 34 O. I 8 45.37 3 I.2O 3.O2 2O.O7 Hydrated line . . . . Union Bridge, Md. . . . . o.38 o.O8 o.O6 72.59 O.74 ge tº 2. I O 23. II Hydraulic lime. . . . . Lafarge Ceinent . . . . . . 3 I. IO 2. I5 4.43 58.38 I.O.9 o,6o I. 28 tº º Hydraulic lime. . . . . Teil, France. . . . . . . . . I9 O5 O. 55 I.6o 65. IO O.65 O. 3O tº º I 2.45 Plaster of Paris. . . . Nova Scotia. . . . . . . . . O. I I O. O.I. O.O3 38.90 O. I4 54.81 O.54 5.33 Plaster of Paris. . . . Buffalo, N. Y. . . . . . . . 2.48 O.32 O.4O 37.8I o:39 53. I2 O.6 I 4.98 Natural cement. . . . Cumberland, Md. . . . . 29.92 4.78 II. 23 36.50 II.93 tº e 5.42 tº gº Natural cement. . . . Rosendale, N. Y. . . . . 27.75 4.28 5.5O 35.6 I 2 ſ. 18 O.5O 4. O5 Portland cement. . . Average American . . . . 22.56 2.85 7. 44 62.73 I.99 I.46 tº tº Portland cement. . . Average German . . . . . 2I.29 2.72 7.64 63.48 I.53 1.77 Portland cement. . English, “K. B. & S.”| 19.75 5. OI 7.48 61.39 I. 28 O.96 Portland cement. . . Belgian, “Josson” . . . . 22.92 2.46 7.98 63.39 trace I. 28 4 PORTLAND CEMENT History of the Development of Mortar Materials When lime mortar was first employed or what people dis- covered its binding properties no one knows, but it is certain that its use antedates written history. It has been found be- tween the stones of what remains of a very ancient temple on the Island of Cyprus, supposed to be the oldest ruin in the world. The Egyptians used, in place of lime, a mortar in which partially burned gypsum or plaster of Paris was the cementing factor and this was employed in the construction of the Pyr- amids, built over four thousand years ago. The Romans dis- covered that a mixture of lime and volcanic ashes would harden under water and hence might be used for the construction of aqueducts, cisterns, docks, etc. They used this mortar in many of their public buildings and temples, in the Phantheon, in the Baths of Caracalla and in the aqueduct which supplied Rome with water. From the period of the Romans, no advance was made in the technology of building materials until the latter part of the eighteenth century, when the modern cement industry had its beginning . The Beginning of the Cement Industry in England The cement industry proper dates from the researches of an English engineer, John Smeaton, who had been employed by par- liament to build a lighthouse upon a group of gneiss rocks, in the English Channel, just off the coast of Cornwall. These crags, known as Eddystone, were at high tide under water for some hours and many shipwrecks had occurred upon them. They were a menace to the navigation of this part of the channel and it was necessary to warn sailors of their whereabouts. Two wooden structures built upon them had been subjected to the fury of the elements and had each experienced a short life. When Smeaton attacked the problem, he determined to build a structure which would weather the fiercest storms of the chan- nel and would come out of these an enduring monument to his engineering skill. One of the greatest difficulties he had to over- come was the failure of ordinary lime mortar (the discovery of which dates back to antiquity) to harden under water. In order MORTAR MATERIALS AND CEMENT INDUSTRY - 5 that his foundations should be firm, it was necessary that some mortar be found which would meet this difficulty. To this end he undertook a series of investigations in 1756, the result of which was the discovery that the hard, white, pure limestones, hitherto considered best for lime making, were in reality inferior to the soft clayey ones;" for from these latter he succeeded in obtain- ing a lime far Superior to any then in use because it not only hardened better in air, but would also harden under water. Such a limestone Smeaton found near at hand, at Aberthaw, in Corn- wall, and the hydraulic lime formed by burning this stone was the basis of the mortar used in the construction of the Eddystone lighthouse. Smeaton in making his hydraulic lime, however, used only those layers of his quarry which after burning gave a product that would slake with water. The idea of burning the layers which would not slake readily and then by grinding, convert them into a very energetic hydraulic lime did not suggest itself to him and it was not until forty years later that this first improvement was made in the manufacture of hydraulic lime. - In 1796, one Joseph Parker, of Northfleet, in Kent Co., Eng., took out a patent for the manufacture of a hydraulic lime which he called “Roman Cement” and which he made by calcining or burning the argillocalcareous, kidney-shaped nodules called “sep- taria” and then grinding the resulting product to a powder.” In composition these nodules were very similar to what we now call Rosendale cement-rock. They occurred geologically in the Lon- don clay formation and were usually obtained from the shores of the Isle of Sheppy where they were washed up after a storm. This cement came rapidly into favor with the English engineers because much work could be done with it that was impossible with quicklime. In 1802 cement was produced from the same “septaria” at Boulogne, France, and this was the beginning of the cement industry in that country. In 1810, Edgar Dobbs, of Southwick, England, obtained a patent for the manufacture of an artificial Roman cement by * Smeaton—Narrative of the building, etc., of the Eddystone Lighthouse, Book IV. * Redgrave—Calcareous Cements. * 2 º 6 PORTLAND CEMENT mixing carbonate of lime and clay, in suitable proportions, mois- tening, molding into bricks, and burning sufficiently to expel the carbonic acid, without vitrifying the mixture. Soon after this, General Sir Wm. Paisley, in England, and L. J. Vicat, a French engineer, both independently of each other, made exhaustive ex- periments looking to the manufacture of an artificial Roman ce- ment by mixing clay with chalk, etc. In 1813 Vicat began the manufacture of artificial hydraulic cement in France, as did also James Frost in England, in 1822. & Invention of Portland Cement In 1824, Joseph Aspāin, a bricklayer of Leeds, England, took out a patent on an improved cement which he proposed to make from the dust of roads repaired with limestone, or else from lime- stone itself combined with clay, by burning and grinding. This cement he called “Portland Cement,” because when hardened it produced a yellowish gray mass resembling in appearance the stone from the famous quarries of Portland, England. Aspáin is usually credited with the invention of Portland ce- ment and while he certainly did originate the name “Portland Cement” he probably did nothing more than make an artificial Roman cement, which had been done before, since he apparently did not carry his burning to the point of incipient vitrifaction, which we now recognize as being an essential point in the manu- facture of Portland cement.” Aspdin erected a factory at Wake- field, England, for the manufacture of his cement, which was used upon the Thames Tunnel in 1828. At first Portland cement was sold at prices considerably lower than the Natural or Roman Cement of Parker and his successors, and it was not until John Grant, in 1859, decided to use Portland cement in the construction of the London drainage canal, of which he was chief engineer, and published his reasons for doing so in the transac- tions of the Institute of Civil Engineers, that the new cement began to come to the front. It is evident that by this time the value of burning the clinker to the point of incipient vitrifaction had been discovered and 1 Michaelis—Thonindustrie Zeitung, Jan. 16, 1904. MORTAR MATERIALS AND CEMENT INDUSTRY 7 made use of probably first in the famous old works of White & Bros., established by James Frost at Swanscombe, in 1825, and still existent. In 1852 the first German Portland cement works were established near Stettin. The Germans were quick to see the value of the new building material, and with their fine tech- nologists soon turned out a better product, by the substitution of scientific methods in place of rules of thumb. They were the first to appreciate the value of fine grinding of the cement, and until recently the German Portlands were the standards. To-day un- doubtedly the best Portland cement made in the world is turned out in America. Discovery of Cement-Rock in the United States In this country the cement industry began with the discovery in 1818, of a natural cement-rock near Chittenango, Madison Co., N. Y., by Mr. Canvass White, an engineer engaged in the con- struction of the Erie canal, who after some experimenting ap- plied to the State of New York for the exclusive right to manu- facture this cement for twenty years. The state denied his re- quest but gave him $2O,OOO in recognition of his valuable discov- ery." His cement was used in large quantities in the construc- tion of the Erie canal and brought a price of about twenty cents a bushel. t As the greatest users of cement in this country were the canals, and as they at that time furnished the only means for the trans- portation of bulky materials, there was naturally the sharpest lookout kept along their line of construction for limestone suit- able for the making of hydraulic cement. In consequence of this, nearly all the early cement mills were started along the line of, and to furnish cement for, the construction of some canal. In 1825, cement-rock was discovered in Ulster County, New York, along the line of the Delaware and Hudson canal and in the fol- lowing year a mill was started at High Falls in that county. In 1828, a mill was built at Rosendale, also in Ulster County. This soon became the center of the industry and the cement made here was called Rosendale. This name is still largely applied to Ameri- can natural cements. The first cement was made in small upright * Sylvester—History of Ulster County, N. Y. 8 PORTLAND CEMENT kilns. Wood was used as fuel and the burning continued for about a week. The clinker was then ground between mill stones by water-power. After these mills had been in operation several years continuous kilns were introduced which permitted the clinker to be drawn daily, coal being used as fuel. In 1829 cement-rock was discovered near Louisville, Ky., while constructing the Louisville & Portland Canal, and John Hulme & Co. almost immediately began the manufacture of Louisville ce- ment at Shippingport, a suburb of Louisville." During the construction of the Chesapeake and Ohio Canal, cement-rock was discovered, in 1836, in Maryland, at Round Top, near Hancock, and it has been manufactured there ever since. Other canals along whose lines cement-rock was discovered with the location and date, are the Illinois and Michigan Canal, at Utica, in 1838; James River Canal, at Balcony Falls, Va., in 1848; and Lehigh Coal and Navigation Co. Canal, at Siegfried, Pa., in 1850. At all of these points the manufacture of cement has been continuous. Other well known brands of cement began to be manufactured as follows: Akron, N. Y., 1840; Ft. Scott, Kan., 1868; Buffalo, N. Y., 1874; and Milwaukee, Wis., in 1875. Manufacture of Natural Cement The process for making natural cement is in general as follows: The rock is blasted down from the face of the quarry, broken by hand with sledges into sizes suitable for the kiln, loaded on dump cars and elevated to the mouth of the kilns. Here the rock is dumped into the kiln alternately with coal, a layer of rock and then a layer of coal. The charging is kept up continuously dur- ing the daytime but hardly ever at night. As the charge works its way down through the kiln it becomes calcined and the larger portion of its carbonic acid driven off. When it reaches the base of the kiln it is drawn out and conveyed to the grinding machin- ery. The kilns used for the manufacture of natural cement are usually made of iron plates riveted together and lined with fire- brick. They are circular in shape, upright, and their average dimensions are about 16 feet in diameter by 45 feet in height. * Lesley—Jour. Assoc. Eng. Socs., 15, 198. MORTAR MATERIALS AND CEMENT INDUSTRY 9 The clinker is usually ground by buhr-stones, the fine material in many mills being separated from the coarse by passing over Screens, so placed as to allow the fine particles to go to the store- house and to return the coarse ones to the grinders. The buhr- Stones are preceded by crushers or crackers to reduce the clinker to a suitable size for them to handle. In some instances ball and tube mills and Griffin mills have been installed in natural cement plants, particularly where these plants also make Portland, but the clinker from these kilns is usually so soft as to be easily ground by buhr-stones. There were at one time in this country between 60 and 70 mills manufacturing natural cement, now there are very few in opera- tion. The principal use of natural cement to-day is for laying brick and stone. The terms “masonry cement” and “brick ce- ment” and various trade names are now often applied to natural cement alone or to mixtures of natural cement with hydrated lime and other substances added to give plasticity. Below are some figures on the production of natural cement in this country. TABLE III.-PRODUCTION OF NATURAL CEMENT IN UNITED STATES, 1818–1915. (Mineral Resources of the United States, 1915.) Year Barrels Year Barrels Year Barrels 1818 to 1830 3OO,OOO I888 6,253,295 I902 || 8,044,305 1830 to 1840 I, OOO,OOO 1889 6,531,876 I903 7,030.27I 1840 to 1850 4,250,000 1890 7,082,204 I904 || 4,866,331 1850 to 1860 II, OOO,OOO 1891 7, 45 I ,535 I905 4,473, O49 1860 to 1870 I6,42O,OOO 1892 8,21 1, 181 I906 || 4,055,797 1870 to 1880 22, OOO,OOO I893 7.4II,815 I907 2,887,700 I88O 2,030, OOO 1894 7,563,488 I908 1,686,862 I88I 2,440,000 || 1895 7,741,077 I909 || I,537,638 I882 3, I65,OOO 1896 7,97O,450 I9 IO || I, I39,239 1883 4, IQO,OOO 1897 8.31 1,688 191 I 926,091 1884 4,OOO,OOO 1898 8,418,924 I912 821,231 1885 4, IOO,OOO I899 9,868, 179 I9 I3 744,658 I886 4, 186, 152 1900 8,383,519 I9 I4 751,285 1887 6,692,744 || 1901 7,084.823 I915 750,863 It will be noticed that there was but little increase in the pro- duction of natural cement from 1887 to 1903 and that since the IO PORTLAND CEMENT latter date there has been a steady decline. This is due to the fact that since about 1900 Portland cement has been fast dis- placing natural cement. The increase in production in 1900 was due to the strong demand for building materials that year; a demand that could not be supplied by the Portland cement manufacturers. Our imports in 1900 were over 3,000,000 bar- rels of Portland, in spite of the fact that the home mills pro- duced over 3,000,000 barrels more than in 1899. Beginning of the Portland Cement Industry in the United States As we have stated cement-rock was discovered in 1850 at Sieg- fried, in Northampton Co., Pa., on the line of the Lehigh Coal and Navigation Co.'s canal leading from Easton to Mauch Chunk. As the cement for the canal had to be brought from New York, the discovery was a valuable one and was put to immediate use by the erection of a mill at Siegfried. In the spring of 1866, Messrs. David O. Saylor, Esaias Rehrig and Adam Woolever, three gentlemen, of Allentown, Pa., formed the Coplay Cement Co., and located a mill at Coplay, near Allentown, and not far from Siegfried. Mr. Saylor was presi- dent and superintendent of the company. The plant made ex- cellent cement though its methods for doing so were crude. Early in the seventies Mr. Saylor began to experiment upon the manufacture of Portland cement from the rocks of his quarry. No Portland cement was made in this country then, and most of it in use here came from England and Germany. Its reputation was established and it was looked upon as superior to Rosendale Cement. Mr. Saylor was led to make his experiments by the fact that he noticed the harder burned portions of his Rosendale clinker gave a cement which for a short period would show a tensile strength equal to that of the best imported Portland; but he found this cement would crumble away with time. This was due to the raw materials not being properly proportioned. The result of these experiments taught him that if he mixed a certain amount of cement-rock high in lime with his ordinary cement-rock he could make Portland cement, and after many trial lots were burned the MORTAR MATERIALS AND CEMIENT INDUSTRY II company turned out its first Portland in 1875. This was the first Portland cement made in the Lehigh District, and it was made from a material totally different from that used in any of the European mills. The drawings for the first kilns were made by James Cabott Arch, an English engineer, and were bottle-shaped. Having solved the problem of how to make Portland cement, Saylor found another and equally difficult one awaiting him of how to sell it, after it was made. The labor cost of manufactur- ing his cement was great and he could not afford to offer it at prices much below the imported article. As the foreign cements had an established record, they fought the new cement with the argument that any brand of Portland cement required time to prove itself, and it was only by liberal advertising and an iron- clad guarantee of his product that Saylor secured a market. Among the first great engineering works upon whose construc- tion Saylor's Portland cement was used were the Eads jetties along the Mississippi River, and the first great sky-scraper in which American Portland cement was used was the Drexel Build- ing in Philadelphia. Slowly American Portland cement overcame the prejudice against it and it is now recognized as superior to that manufactured in any part of the world. Saylor's original plant turned out only 1,700 barrels of Portland cement a year. Since its inception, however, it has grown steadily and now has a capacity of considerably over this amount a day. Development in Other States While Saylor was conducting his experiments in the Lehigh Valley, a Chicago concern, known as the Eagle Portland Cement Co., built a plant near Kalamazoo, Mich., about 1872, to manu- facture Portland cement from marl and clay. This plant at first consisted of two bottle-shaped kilns, which number was after- wards increased to four. The product was known as “Eagle Portland Cement,” and its quality must have been excellent as some three or four miles of sidewalk put down in Kalamazoo are still in good condition. This mill, however was forced to shut down in 1882, for although its product sold at from $4 to $4.25 I 2 PORTLAND CEMENT per barrel, it could not manufacture cement at a figure below this. To-day no traces of even the kilns remain." At Wampum, Pa., a small plant was started to make cement from limestone and clay, in 1875. Thomas Millen found, at South Bend, Ind., a white marl and clay which resembled in com- position, the material used for cement making in England, and started a small plant there in 1877.* Both the plants at Wampum and South Bend, Ind., were for many years producers, though in a modest way. In Maine also a small plant was started by the Cobb Lime Co., at Rockport, in 1879, but this too failed to make cement at a figure below its selling price and closed down perma- nently as did also a small plant in the Rosendale district about the same time. Of the six works started prior to 1881 half that number were failures and represented a complete loss to their promoters. The cement made at Coplay and Wampum, however, was on exhibi- tion at the Philadelphia Centennial in 1876 and held its own with the imported article. About 1883, a small plant for the manufacture of Portland cement was inaugurated at Egypt, Pa., near Coplay, by Robt. W. Lesley, the first president of the, to be later formed, American Association of Portland Cement Manufacturers, John W. Eckert, Saylor's first chemist, and others. This plant progressed gradu- ally and developed into the American Cement Co., a large pro- ducer of both natural and Portland cement. From this time on plants sprung up rapidly in the Lehigh Valley Section, among the older ones being the Atlas, Bonneville, Alpha and Lawrence, all except the second now important producers. In other sections also, successful mills were built. In New York, Thomas Millen, who had previously built a works in In- diana, and his son, Duane Millen, started the Empire Portland Cement Co., at Warners, Onondaga Co., in 1886. In Ohio, at Harper, Logan Co., the Buckeye Portland Cement Co., put in operation their plant in 1889; and in 1890 the Western Portland Cement Co., of Yankton, S. D., began to make Portland cement. 1 Russell—Twenty-second Annual Report, U. S. Geological Survey, Part III. * Cement Age, July, 1905, contains an interesting account by Mr. Millen himself of how he came to go into the manufacture of Portland cement at South Bend. MORTAR MATERIALS AND CEMENT INDUSTRY I3 From this time on the Portland cement industry has taken rapid strides and plants have been built in almost every part of the country. The process of manufacture has been greatly improved, resulting in a considerable lessening of the cost of production. American Portland cement has practically displaced the imported article. New uses have been found for Portland cement and it is to-day, next to steel, our most important material of construc- tion. The Portland Cement Association formed in 1902, has done wonders for the industry. This association has published and distributed gratis to those interested valuable bulletins ex- plaining certain particular forms of concrete construction and the employment of cement by the farmer and artesan. The American Concrete Institute has also been a potent factor in popularizing the use of concrete. This society holds an annual meeting at which papers dealing with cement products and con- crete are read. In addition to the national association there are a number of local and state associations. Cement shows have been held at intervals at Chicago and in New York at which various appliances of use to cement workers were on exhibition as well as novel cement products, etc. At the present time, 1923, the United States produces about one-half the estimated produc- tion of the world. This is estimated as follows: Barrels United States º I37,OOO,OOO Germany and Austria 3O,OOO,OOO British Empire 35,000,000 France and Colonies I2,OOO,OOO Japanese Empire I2,000,000 Belgium IO,OOO,COO Others 3O,OOO,OOO Total 266,000,000 Table TV shows the growth of the American Portland cement industry from year to year. Table V the production by districts and states in 1922. Table VI the price from 1870 to 1922, and Table VII the growth of the per capita consumption. I4 PORTLAND CEMENT TABLE IV.-PRODUCTION OF PORTLAND CEMENT IN THE UNITED STATES, 1870-1923, IN BARRRELs. Year Quantity Value 1870-1879 82,000 $ 246,000 I88O 42,000 I26,000 I88I 60,000 I50,000 I882 85,000 IQI,250 1883 90,000 . I93,500 I884 IOO,OOO 2IO,OOO 1885 I50,000 292,500 I886 I50,000 292,500 1887 25O,OOO 487,500 I888 250,000 487,500 1889 3OO,OOO 500,000 1890 335,500 704,050 I891 454,813 967,429 1892 547,440 I, I53,600 1893 590,652 I, I58,138 I894 798,757 I,383,473 I895 990,324 I,585,830 I896 I,543,023 2,424,OII I897 2,677,775 4,315,891 1898 3,692,284 5,970,773 I899 5,652,266 8,074,371 I900 8,482,020 9,280,525 * Estimated. † Value of cement shipped. Year I90I I902 I903 I904 I905 I906 I907 I908 I909 I9IO I9II IOI2 I913 I9I4 I9I5 I9I6 I9I7 I918 I9IQ I92O I92I I922 I923* TABLE V.—PORTLAND CEMENT PRODUCED IN THE UNITED STATES, By DISTRICTS AND STATES IN 1922. Mineral Resources of the United States. Commercial District Eastern Pennsylvania, New Jersey, and Maryland New York tº tº º º Ohio, western Pennsylvania, and West Virginia Michigan Illinois, Indiana, and Kentucky Virginia, Tennessee, Alabama, and Georgia Eastern Missouri, Iowa, and Minnesota Western Missouri, Nebraska, Kansas, and Oklahoma Texas Colorado and Utah California Oregon, Washington, and Montana Quantity Value I2,7II,225 $ 12,532,360 I7,230,644 20,864,078 22,342,973 27,713,319 26,505,881 23,355, II9 35,246,812 33,245,867 46,463,424 52,466, 186 48,785,390 53,992,551 5I,072,912 43,547,679 64,991,431 52,858,354 76,549,95I 68,205,800 78,528,637 66,248,817 82,438,096 67,016,928 92,097, I31 92,557,617 88,230,170 81,789,368 85,914,907 73,886,820 9I,521,198 IOO,947,881 92,814,202 I25,670,430 71,081,663 II.3,730,661 80,777,935 I28,130,269 IOO,023,245 202,046,955 98,842,049 180,778,415f II4,789,984 207,170,43Of I37,377,000 /- Production -, Active Quantity plants (barrels) 22 3I, IQ5,617 9 5,922,706 IO IO,753,30I I2 6,243,805 IO I7,998,914 8 5,954,043 9 II,392,552 II 8,025,720 5 3,628,756 5 2,020,784 9 8,7II,515 9 2,942,271 II4,789,984 MORTAR MATERIALS AND CEMENT INDUSTRY I5 TABLE V.—PORTLAND CEMENT PRODUCED IN THE UNITED STATES, BY DISTRICTs AND STATES IN 1922. (Continued) /- Production—, Active Quantity State plants (barrels) Alabama 3 2,290,884 California 9 8,711,515 - Illinois 4 6,407, I29– Iowa 4 4,272,432 Kansas 7 4,634,287 Michigan I2 6,243,805 Missouri 5 6,170,633 New York 9 5,922,706 Ohio - 5 2,835,243 Pennsylvania 22 33,276,093– Texas 5 3,628,756 Washington 4 I,942,781 Other States (b) 29 28,453,720 * II8 II.4,789,984 (b) Colorado, Georgia, Indiana, Kentucky, Maryland, Minnesota, Montana, Nebraska, New Jersey, Oklahoma, Oregon, Tennessee, Utah, Virginia, and West Virginia. TABLE VH-AveRAGE PRICE PER BARREL OF PORTLAND CEMENT, 1870-1922. Year Price Year Price Year Price 1870-1880 $3.00 1897 $1.61 I9II $0.844 I88I 2.50 1898 I.62 I9I2 o.813 I882 2.OI I899 I.43 IQI3 I.OO5 1883 2. I5 I900 I.09 I9I4 O.927 1884 2. IO I90I O.99 I9I5 O.860 1885-1888 I.95 I902 I.2I I916 I.IO3 1889 I.67 I903 I.24 I917 I.354 I890 2.09 I904 O.88 1918 I.598 1891 2.I.3 I905 O.94 IQIQ I.7IO 1892 2. II I906 I. I3 I920 2.O2O 1893 I.91 I907 I. II I92I I.890 I894 I.73 1908 o.85 I922 I.760 I895 I.6o I909 o.813 1896 I.57 I9IO o,891 TABLE VII.-PER CAPITA Consum PTION OF CEMENT. Year Barrels Year Barrels I9I4 O.77 I919 O.77 I9I5 o.83 I92O 0.86 1916 0.89 * I92I O.87 I917 o.84 1922 I.06 1918 O.64 CHAPTER II THE NATURE AND COMPOSITION OF PORTLAND CEMENT Portland cement may be defined as “the product obtained by finely pulverizing clinker produced by calcining to incipient fusion an intimate and properly proportioned mixture of argillaceous and calcareous materials, with no additions subsequent to cal- cination excepting water and calcined or uncalcined gypsum.” When the fine powder is mixed with water chemical action takes place, and a hard mass is formed. The change undergone by the cement mortar in passing from the plastic to the solid state is termed “setting.” This usually requires but a few hours at most. On completion of the set a gradual increase in cohesive strength is experienced by the mass for some time, and the cement is said to “harden.” Cements usually require from six months to a year to gain their full strength. Cement differs from lime in that it hardens while wet and does not depend upon the carbon dioxide of the air for its hardening. It is very insoluble in water and is adapted to use in moist places or under water where lime mortar would be useless. Composition of Portland Cement The composition of Portland cement may be considered from two viewpoints, that of the analyst and that of the physical chem- ist. The analyst concerns himself with the quantities of certain elementary compounds such as silica, alumina, lime, etc., which are present in cement, while the physical chemist determines the relation which these compounds bear to each other, their physical form, state of equilibrium, etc. Cement is such a complex sub- stance that two lots having identically the same analysis, fineness, etc., may yet have quite different setting properties. This dif- ference is due to a difference in the chemical structure of the 1 Standard Specifications for Portland Cement, Amer. Soc. Test. Mat. THE NATURE AND COMPOSITION OF PORTLAND CEMENT 17 / two cements. A study of the latter is therefore necessary if the behavior of cement is to be understood. . . Turning our attention first to the Analysis of cement and the composition of the material as shown by this, we find that the present state of the art of cement analysis is by no means as satisfactory as it might be, and expert and careful chemists do not always agree upon even the analysis of cement. After the careful work' done by pºwo committees and one of the best chemists of the United States Geological Survey, it would seem as if the conditions foſ accurate work had been so fully estab- lished as to "...º. among skillful chemists. That this is not so the follºwing incident will show. Some years ago the author was associated with two prominent American chemists in the exam;iation of some thirty samples of cement. The aver- age respºts of the three sets of determinations are given below and, demonstrate clearly how unsatisfactory is the present state 9i analytical chemistry. Variation between Chemist A |B C extremies Lime 60.75 6I.I3 6I.I9 0.46 Silica 22.59 22.28 22. II O.48 Alumina 6.88 7.56 8.59 I.7.I Iron oxide 3.40 3.61 2.56 O.84 Magnesia I.20 O.92 I.58 O.66 Sulphur trioxide I.09 I.2O I.3.I O.22 Loss on ignition 2.22 2.22 2.37 O.25 Substances Found in Cement Whatever may be the nature of their combination with each other the essential elements of Portland cement are lime, silica, 1 Richardson, Schaffer and Newberry—J. Soc. Chem. Ind., 21, 830 and 1216; J. Am. Chem. Soc., 25, 1 180, and 26, 995. Meade, Newberry and McCready—Cement and Eng. News, Aug., 1904, Chem. Eng., I. Hillebrand—J. A. m. Chem. Soc., 24, 362. Peckham—J. Soc. Chem. Ind., 21, 831, and J. Am. Chem. Soc., 26, 1636. Blount—J. A. m. Chem. Soc., 26, 995. Gano—Chem. Eng., 9, 7. I8 . PORTLAND CEMENT \ and alumina. In the cements of commerce, iron replaces some alumina and magnesia some lime, since clays usually contain a considerable amount of the former, and limestones are rarely free from at least a few tenths of a per cent of the latter. Other elements which are found in one or the other or even both of the raw materials and which find their way into the final product are the alkalies, manganese, titanic acid, phosphoric acid, sulphuric acid and strontium. Sulphate of lime, either in the form of gyp- sum, CaSO4·2H2O, or of plaster of Yaris (CaSO4)2.H2O, is added to regulate the setting time, and carbon dioxide and water are absorbed from the air by the clinker, either before or after grinding. Of these elements, lime, silica, alumina, iron and sulphuric acid all exercise an important influence on the cement, and its properties will depend largely upon the relative amounts of these present. The alkalies, no doubt, if present in larger quantities, would affect to some degree at least the physical properties of cement, but in the small amounts found in American Portland cements the rôle they play is a very slight one. Table VIII gives the analyses of a larger number of American Portland cements from different parts of the country, and made from various raw materials. Referring to Table VIII, we see that the chemical composition of American Portland cements which pass the standard speci- fications for soundness, setting time and tensile strength falls within the following limits: Per Cent Silica I9–25 Alumina 5— 9 Iron oxide 2— 4 Lime 60–64 Magnesia I— 4 Sulphur trioxide * I— 2 The average is represented by the following: Per cent Silica 22.0 Alumina 7.5 Iron oxide 2.5 Lime 62.o Magnesia 2.5 Sulphur trioxide I.5 TABLE VIII. —ANALYS&S OF AMERICAN PORTLAND CEMENTS. (Made by the author with the exception of those marked *.) Made from Where 111ade SiO2 Nazareth, Pa. . . . . . . . . . . I 9.92 Nazareth, Pa. . . . . . . . . . . 2 I. I.4 Bath, Pa. . . . . . . . . . . . . . . 19.64 Alpha, N. J. . . . . . . . . . . . 2 I.82 cent. and §º. Pa. . . . . . . 2 I.94 11116 SLOne Coplay, Pa. . . . . . . . . . . . . 22.26 Omrod, Pa. . . . . . . . . . . . . 22. 2C) Martin's Creek, Pa. . . . . 2O.32 | Reading, Pa. . . . . . . . . . . 24. 16 | Bay City, Mich . . . . . . . . 2O.72 Wellston, O. . . . . . . . . . . . 2 I.84 Chanute, Kan . . . . . . . . . . 2O. 74 Ada, Okla . . . . . . . . . . . . . I 2.28 *Glens Falls, N. Y. . . . . . 2I.5O Limestone and clay 4 *::::: º ::::::: ;: roshale Davenport, Cal. . . . . . . . . 25.38 Cement, Cal. . . . . . . . . . . 22.34 *Baker, Wash. . . . . . . . . . . 24.63 St. Louis, Mo. . . . . . . . . . 23. I2 Demopolis, Ala . . . . . . . . I9.36 | *Portland, Colo. . . . . . . . . 2.I.88 *Middlebranch, O. . . . . . . 2.I. 24 *Coldwater, Mich. . . . . . . 2.I. 22 Sandusky, O. . . . . . . . . . . 2 I.93 Marl and clay *Bronson, Mich. . . . . . . . . 22.90 *Harper, O. . . . . . . . . . . . . 2 I.3O *Warners, N. Y. . . . . . . . . 22. O4 Limestone and ſ Chicage, Ill . . . . . . . . . . . . 22.4 I blast furnace slag i Chicago, Ill. . . . . . . . . . . . 23.06 | Fe2O3 || Al2O3 CaO | MgO K2O Na2O SO3 I, OSS 2.28 7.52 62.48 || 3. 19 O.52 o,66 I.51 I.46 2.30 | 6.94 63.24 3.26 O.36 O.5 I I. I2 I. 24 2.80 7.52 62.3.I 3. O4 11. d. I.6o I.48 2.5I 8.03 62. I9 2.71 n. d. I. O2 I.O5 2.37 6.87 6o. 25 2.78 o.61 O.87 | I.38 || 3.55 2. IO 5.36 63.32 - || 3.81 n. d. O.89 | 1.24 2.27 | 6.69 62.61 3.OO O.32 O.61 I.32 I.56 2.50 | 7. I2 62.94 | 3.38 11. d. I. 45 I. 25 I.45 5. IO 62.95 || 3. I2 O.2I O. 50 | I. 35 | I.4O 2.85 7. I7 62.64 1.97 || 0.48 O. I2 I.42 2.58 5.os | 6.77 62.66 | O.80 n. d. I.24 tº º 3.72 7.06 62.76 1.78 O.4I O.23 I. 12 | 1.40 3.2O | 6.36 59.66 3. II | O.80 O.25 I.40 || 2.82 IO.50 63.50 I.8o O. 40 1.50 | 11. d. 3.2O | 5.62 62.32 1.77 n.d. o.90 | 1.68 2.81 | 6.54 63.O I 2.7 I n. d. I.42 2.OI I.2O || 3.34 62.96 I. 2C) n. d. o.35 | 4.58 3.30 7.OO 6o.72 I .30 n. d. I.O.5 2.54 8.56 62.88 I.6O n. d. i.33 n.d. 2.49 || 6.18 63.47 o.88 n. d. 1.34 | 1.81 4. To 9. I8 63.20 I. 16 n. d. 1. 18 I. 12' 2.85 | 7. I4 64.94 trace I. 18 O.73 I.O8 4. I4 || 7.85 63.22 o. 28 O.68 I. I I I.32 3.83 || 7.5 I 63.75 o.82 n. d. 1.58 || I.O2 2.35 | 5.99 62.92 I. IO | O.63 O, 27 | I.55 2.92 3.60 6.8o 63.90 O.7O I. IO O.40 | O.6O 2.OO | 6.95 62.50 I. 2C) n. d. O.98 || 4.62 3.4I | 6.45 6O.92 3.53 n. d. I. 25 $ tº 2.5I 8. I2 62.or I.68 n. d. I.4O | I.O2 2.88 || 8, 16 62. Io 1.88 o.36 o.58 || 1.57 & º J 2O Y. PORTLAND CEMENT The Lehigh Valley cements (made from argillaceous lime- Stone) are characterized by high magnesia usually between 3 and 3.5 per cent, though Occasionally as low as 2.5 per cent and as high as 5 per cent. They contain about 2.5 per cent iron oxide and about twice as much silica as iron oxide and alumina com- bined. In those cements from the western end of the deposit, this ratio is somewhat higher, however, owing to the fact that the cement-rock found here is higher in silica and also to the fact that the limestone used with this rock is silicious. Most of the marl cements are low in magnesia, some of them containing as little as O.5 per cent. Some of the Michigan marl cements are high in iron oxide, 3 to 4 per cent. This comes from the clay, or shale, however, and hence is also characteristic of some cements made from limestone and clay or shale. The cements made from the Selma chalk at Demopolis, Ala., are high in iron and alumina, published analyses showing 12 to 14 per cent iron oxide and alumina and only about 2 per cent silica. Early Studies of Cement The scientific study of cements really began about the first quarter of the last century, and with the work of Collet-Des- cotils" and Vicat,” who showed that the hydraulic properties of cement were due to the fact that the burning of these materials converted the silica into a soluble form. The work of Vicat was especially noteworthy. Frémy” attributed the hardening to com- bined alumina, and A. Winkler” brought forward the theory that basic silicates were formed when cements were burned, and that these were hydrolysed when water was added, forming lime and hydrated less basic silicates. Le Chatelier's Investigations Le Chatelier" was the first chemist to apply to the study of cement the methods employed in petrography or the study of * Jour. des Mines, 1813, 34, 308. * Mortiers ct Ciments Calcaircs, Paris, 1828. * Compt. Rend., 1856, 60, 993. * J. Prakt. Chem., 1856, 67, 44. * Constitution of Hydraulic Mortars (Trans. by J. L. Mack), Ann. des Mines, 1887, p. 345. 22 72 $6/74. Aſ a £7/4 Sz. 101 wº, we wºrry //o/−/~E A* v.A. A 7"/c/74. Yoaka’ wa'ſ 6 & 7 AA awg &A HOPPETAz I Le 5c/7ZAF AZ/77"Aoarava 64 re- Coal' ve; XoA: A3& 4.7" /. T ~ / 7A7/4- fºLI (Yºr —é º AA’47/vi Ar S-->!” 2. V N Ana-ayscrazzavº Aſozz ATA: Z. A vaſ/75 vve"/47////vº Avo/, / ATA’ Fig. 17.-Poidometer.—Schaffer Poidometer Co. consists of a belt supported beneath a hopper by means of a series of fixed rollers. Following these latter and also supporting the belt is a roller which is suspended from a lever arm which in turn controls the opening by means of which the material flows from the hopper on to the belt. When the material runs from the hopper on to the belt, the latter will sag from its weight. The roller under the belt receives this weight and in turn pulls on the walking beam proportionately to the weight which it receives. This pull is offset by a weight which may be set in any desired position. When the flow of material is too great the roller falls cutting off the flow of material to the belt, etc. The poidometer I30 PORTLAND CEMENT is adjusted by means of the weight on the beam and may be made to feed material sufficiently evenly and accurately to answer the requirements of the cement mill. Two poidometers are em- ployed, one for limestone and one for shale (or clay) and these are set to give the desired amounts of material. The scales usually dump or feed simultaneously into a hopper, which in turn discharges on to a belt conveyor. This latter carries the material to the driers or to the bins above the grinding mills. Sometimes, but not often, a mechanical mixer is placed below the scales. This usually consists, when used for mixing crushed material, of drums fitted with flights similar in appear- ance and action to concrete mixers, or when employed for mix- ing partly ground materials of a cut flight conveyor. Usually, however, the driers and grinders are depended on for the mixing. CHAPTER VII THE DRY PROCESS Outline of the Dry Process Figure 18 shows in diagramatic form the steps of the dry process of cement manufacture. The methods employed for Limestone Clay, Shale Slag or Cement Rock ! *——3- <—º Mixed in Proper Proportions Crushed ! Dried Pulverized to a fineness of 95% to 98% passing a No. 1 oo test sieve Burned at a temperature of from 14oo° to 16oo°C Cooled 2% to 3% Gypsum ! --_ | Pulverized to a fineness of at least 78% passing a No. 200 sieve PORTLAND CEMENT Fig. 18.-Diagram showing steps in the manufacture of Portland cement by the dry process. I32 PORTLAND CEMENT mixing and storing the raw materials have been described in the preceeding chapter, while the various crushers and pulverizers commonly employed in both processes are described in detail in the next. The purpose of this chapter is, therefore, to present in Sequence the various steps of the dry process up to the burning. As has been previously stated, the raw materials may be mixed either before or after the primary crushing. The drying always follows the crushing but sometimes the mixing of the two ma- terials may be deferred until after the material is coarsely ground and just before final pulverization in the tube mills. We thus have four alternative schemes. (I) To crush, dry, pulverize, etc., the two materials together. (2) To crush sepa- rately and then mix, dry, pulverize, etc., together. (3) To crush and dry separately, mix and then pulverize the mixture. (4) To crush, dry and partially pulverize the two materials separately, mix and then finely pulverize the mixture, etc. The first method is entirely satisfactory where the raw ma- terials are two grades of cement-rock, or are cement-rock and limestone. The second and third methods are generally em- ployed when limestone and shale are used and the third and fourth methods when clay is to be mixed with limestone. The merits and demerits of these various schemes from a chemical standpoint have been quite fully discussed in the pre- ceeding section. From a mechanical standpoint, there is much in favor of mixing at as early a stage in the process as is possi- ble, as this evidently diminishes both the apparatus required and the attention necessary. When the two materials are kept sepa- rate, each must have its own crushing plant, storing bins, dryers, conveying System, etc. Crushing and pulverizing may, of course, be considered as two stages in the reduction of the material from the size brought to the mill to the fine powder necessary for burning. In modern cement mills, this reduction takes place in from three to five steps (depending on the apparatus employed), of which we usually speak of the first two or three as crushing and the last one or two as pulverizing. Drying is merely incident to grinding, as it is not practicable to grind damp or slightly moist materials. The drying THE DRY PROCESS I33 takes place after the crushing and not before, because, obviously, it is easier to handle crushed material in the dryer. Indeed if it were practicable to do so, there would be an advantage in dry- ing the rock before crushing, since even the crushers handle dry rock more satisfactorily than wet. By “crushing” is generally meant the reduction of the ma- terials from quarry size to pieces the largest of which are from say 94 to 2 inches, while by “pulveriging” we mean the reduction of this material from the above size to a fine powder. The crushing of hard materials is now always done in two stages and sometimes in three. The first or primary crushing may be done in I. Gyratory or Gates Crushers (Size No. 9 and larger)." 2. Jaw or Blake Crushers (36 inches x 24 inches opening and larger). 3. Roll Crushers, Fairmount Crushers (36 inches x 60 inches opening and larger). 4. Hammer Mills (Williams “Jumbo”). The secondary crushing is now done by I. Hammer Mills." 2. Crushing Rolls. 3. Gyratory Crushers (Size No. 6 and smaller). Crushing The work to be done by each crusher will depend upon cir- cumstances. When steam shovels are employed, the primary crushers take the rock as it comes from the quarry and reduce this to a maximum about 6 to Io inches. The secondary crushers receive the product of the primary crusher and reduce this to a product ranging from 34 to 2% inches and under, depending on the type of pulverizers employed. Ball mills and Hercules mills will take limestone crushed to 2% inches, but Conpeb, Griffin, Fuller, Kent and Sturtevant mills require a somewhat finer feed. The primary and secondary crushers should be so balanced as to handle the rock most efficiently. Sometimes where the primary crushing is only to Io inches, as is the case with very large crushers, and the type pulverizer employed requires a rock 1 All of these machines are described in the next chapter. IO I34 PORTLAND CEMENT crushed quite Small, the Secondary crushing is done in two steps —usually two hammer mills being employed. At most cement plants, however, two-stage crushing is all that is necessary. At a few small plants or plants built fifteen or twenty years ago, the crushing is done in one stage; one or more gyratory crushers (No. 5 to No. 7%) being employed, but this practice is now obsolete in America. In the early days, it was quite com- mon to install No. 5 or No. 6 gyratory crushers and to follow these directly by a ball mill. The No. 6 crusher may be set so as to crush to 2 inches and under, which is about as coarsely crushed material as the ball mill will handle with any degree of efficiency. The No. 6 gyratory is about as small a crusher of this type as will crush hand loaded stone, and even with this size crusher, con- siderable sledging in the quarry is necessary in order to break down the stone to a size which will pass into the opening (I2 x 46 inches) of this crusher. On the other hand, gyratory crushers larger than the No. 7% crusher, which has an opening 15 x 55 inches, can not be set to crush as Small as 2 inches. Consequently, when steam shovels were introduced into the cement industry, it was necessary to provide crushers which would handle very large pieces of stone. These large crushers, on the other hand, would not give a product small enough to go to the grinding mills, which made the intermediate crusher neces- Sary. Gyratory crushers were first employed for the secondary crushing simply because many plants, when they changed from hand loading to steam shovel loading, installed a large gyratory, jaw or roll crusher to do the primary crushing and then sent the product of this to the small (No. 5 or No. 6) gyratory crushers which they formerly used, etc. When new plants were built, however, these generally employed hammer-mills for the second- ary crushing. The most approved crushing plant at the present time is one in which the primary crushing is done by a large gyratory or jaw crusher and the secondary crushing by a hammer-mill. When the stone is soft, as in the case of cement-rock, a roll jaw crusher of the Fairmount type also gives excellent results for THE DRY PROCESS I35 primary crushing. The gyratory crusher should not be smaller than No. 18 and the jaw crusher should be at least 36 x 42 inches, if steam shovels are employed in the quarry. The product of the first crusher should preferably be fed by gravity into the Secondary one. This, of course, necessitates setting the primary crusher high up on massive concrete piers. When this is undesirable, a large bucket elevator or an inclined belt conveyor may be employed to take the stone from this crusher to the Smaller ones. In some instances, the primary crusher is located at the quarry and the secondary ones at the mill. At others, both the primary and secondary crushing is done at the quarry. In either case, the rock is conveyed to the mill in cars, by aerial tramway, or by a long belt conveyor. The hammer mill should be capable of taking the product or the primary crusher and delivering this in a proper condition for the pulverizers. The hammer mill should also have sufficient capacity to take practically the full quantity of material the pri- mary crusher delivers to it. In other words, no intermediate stor- age should be required, although it is advisable to discharge the primary crusher into a pocket or hopper of a few cubic yards capacity and to feed from this to the hammer mill by means of a pan conveyor or a belt conveyor, the latter acting as a feeder. This arrangement prevents choking the hammer mill, should a car of fine material be sent from the quarry. Material in such condition would need but little crushing and consequently might pass through the primary crusher in such volume that the hammer mill could not handle it. This is particularly true when jaw and roll crushers are employed ahead of the hammer mill. Sometimes the product of the primary crusher is passed through a rotary screen in order to separate from it any fully crushed material and allow only the big pieces to go to the second- ary crusher. While this relieves the latter of some work, the screen has to be revolved and the extra handling of the stone represents a source of trouble which more than balances the gain at the secondary crusher, so that in general it will be found more satisfactory to pass all the stone directly from the primary to to the secondary crusher. - 136 (One No. 9 and two No. 6 PORTLAND CEMENT Fig. 19.-Crushers—Tidewater Portland Cement Co. gyratory crushers). THE DRY PROCESS I37 At a few plants, the quarry cars are dumped into some form of feeder which feeds the stone into the crusher at a uniform rate. These consist of slow moving heavy pan or apron con- veyors, reciprocating feeders such as are described under Dryers or slow moving parallel chains. The general practice, however, is to dump the contents of the quarry cars directly into the crusher, a metal hopper or chute being built above the crusher to receive the stone. The machines are massive and repairs generally require handling large parts. It is well, therefore, to install a crane on a bridge beam moving over both crushers in order to handle the repair parts, etc. There should be a hook fastened to an iron cable and pulled by an air hoist installed above the crusher so that large pieces of — 42, -* -3 Fig. 20.-Crushing Plant—National Cement Co., Montreal, Que., Richard K. Meade & Co., Engineers. I38 PORTLAND CEMENT Stone which become wedged in the latter may be lifted out or turned around so as to go in. Figures 19 and 20 show two crushing plants. In each in- stance the equipment is evident from the drawing. § Drying and Dryers The dryers used for drying all cement raw materials may be classed under two heads—direct fired dryers and waste heat dryers. The former are heated by means of a fire box at one end of the dryer or by an oil or powdered coal jet and the latter by the hot waste gases from the rotary kilns. With both forms the rock is fed in at the upper end and works its way out at the lower. Direct fired dryers (Fig. 21) are cylindrical in shape, from 5 to 8 feet in diameter and from 50 to 80 feet in length. They are similar in construction to the rotary kiln described in Chapter XI. The form shown is heated by means of coal fired on grates in the fire box shown at the discharge end. The cylinder is in- clined from the horizontal at a pitch of from 9% to 34 inch to the foot and is usually provided with angle or channel irons bolted to the inside to act as shelves to carry the rock up and expose it to the hot gases. (See Fig. 22). Some dryers have their upper half divided into four compartments by means of plates in order to expose a greater surface of rock. (See Fig. 23). Until recently direct fired dryers were usually fired by means of hand stoking on grates. Now pulverized coal is much used. This not only saves labor but also increases the capacity of the dryer over hand firing. The temperature of a dryer is kept too low to admit of proper combustion of powdered coal in the dryer itself and this is usually secured by employing a fire box or combustion chamber at the end of the dryer. When it is desired to change a grate or stoker fired dryer to pulverized coal the installation is simple and nothing is neces- sary except to tear out the grate bars and protect the end of the dryer from burning out by a proper shield of fire brick, if this does not already exist. The fire-doors are then removed and the THE DRY PROCESS º ºutlºº. º -- I39 I40 PORTLAND CEMENT Fig. 22.—Rotary dryer shelver. Fig. 23.−Rotary dryer compartments. burners inserted in their place, the space around being stopped up with fire brick. If the furnace is small, it may be necessary to make a few openings in the side to protect the walls from scorifying, etc. Fig. 24 shows the installation of powdered coal in an old grate setting. #2 $ºś% *śº § § §§g: § % º ºğ § % te & ** * º x * * > . Sº, |- Fig. 24.—Method of installing pulverized coal firing in case of dryer previously fired by hand. Ø ŞNN * º º | s tº THE DRY PROCESS I4I With dryers a slow, lazy flame is desired; hence only a small amount of air is allowed to enter with the coal and the balance is drawn in through openings in the front and sides of the furnace. When a new dryer is to be installed, a combustion chamber of Special design may be employed, and such a combustion chamber will be somewhat cheaper than the ordinary dryer fire box. Fig. 25 gives the details of such a combustion chamber suitable for a 6 x 50 foot rotary dryer. Modification of this de- º - TF-8& g com/asſºon Cºamér Fig. 25.-Combustion chamber for heating dryer with pulverized coal–Meade system. sign to suit various other sizes can easily be made by allowing about the same proportion between the combustion space and the dryer. Capacity of Rotary Dryers The capacity of an ordinary rotary dryer, where the length is about ten times the diameter, is about 125 pounds (in the case of clay) to 150 pounds (in the case of hard limestone) of water evaporated per square foot of cross-section per hour. The area of cross-section of a 5-foot diameter dryer, for example, is 19.6 square feet. If this dryer is 50 feet long its capacity on limestone is therefore 2,940 pounds of water per hour. If the limestone to be dried contains say 5 per cent moisture, there would have to be evaporated IoS pounds of water per ton of material dried and the capacity of the dryer would be 28 tons of dried material per hour. TABLE XIII.-CAPACITIES OF AND Pow ER REQUIRED TO OPERATE DIRECT FIRED ROTARY DRYERS Material Limestone Shale Clay Tº .: E. É. .9 Moisture in wet material 3% 5% 5% 8% Iož I5% 20% 25% # ; *- O © $—e Pounds of water to be re- # g ‘s moved per ton of ma- 62 IO5 IO5 I 75 223 352 5OO 666 53 º terial dried : }. .S U) Approximate coal re- (ſ) quired per ton of mate- I I I8 I 2 O 7o IOO I rial dried in lbs. 9 3 5 33 P. M. . P. size of dryer Capacities in tons (2,000 lbs.) of dried material per hour Diam. Length 4 ft. X 40 ft. 3O I8 I6 IO 6% 4% 3 2% 7% 4 5 ft. X 50 ft. 47 28 26 I 5 IO 7 4% 3% IO 3 6 ft. X 60 ft. 67 42 38 22 I4 IO 6% 5 I5 2 7 ft. X 70 ft. 92 55 52 3O 2O I3 9 7 I 5 I34 8 ft. X 80 ft. I2O 72 67 4O 26 I8 I 2 9% 2O I}% # THE DRY PROCESS I43 The fuel requirements are about I pound of coal for every 5 or 6 pounds of water. The above dryer would, therefore, require about 490 pounds of coal per hour based on the higher ratio. Table XIII gives the capacities of various sizes of dryers on material of varying percentages of moisture, power to operate, etc. Waste Heat Dryers The waste heat dryers were the invention of the late Mr. Charles A. Matcham, of Allentown, Pa. These dryers are similar in every respect to the ordinary direct fired dryer described above except that they are made somewhat larger and have no fire box. The arrangement with reference to the kiln is shown in Fig. 26. The dryers, as will be seen from this, are immediately back of $ t º Y F- g ſ ~~~ *-ºs- t º g rº-º-> .* i *-*-*- ! *}ºve-. §ººr is ; ,” y i t t : g ! zer ; ," • *, A & : l, t f t - : & t O ; --~~~< * , f @ rºw was tº sw's w = * * * Arm rºw & a ºf “, viz “ - tº ºr sº ww.rº stºry wrvaruzziºrz ***ºry ºrwºrx Fig. 26.—Dryer arranged to utilize waste heat from kilns. and in a line with the kilns, so that they can receive the waste gases of the latter with as little impediment to the draft as pos- sible. Between the dryers and kilns is the customary dust- chamber (see Chapter XI) and on this rests a stack provided with a damper. When the dryers are in use, this damper is closed and the kiln stack is not used, all the gases from the kiln I44 PORTLAND CEMENT passing through the dryer. As the gases from a 125-foot rotary kiln are at about 900-1,600° F. and there are at least 250,000 B. t. u. (18 pounds of coal) in the gases entering the dryer per minute no difficulty is experienced in drying large quantities of material very thoroughly by means of these waste heat dryers. There is usually a movable housing between the dryers and dust- chamber to allow easy access to the former for repairs without shutting down the kiln. The stone from the dryer drops down through an opening in the housing into a pit, from which it is elevated to the storage or stock-bins by means of bucket elevators. In order not to effect the capacity of the kilns, these dryers must be of large diameter and must be provided with taller stacks than are ordinarily employed for kilns or direct fired dryers. These waste heat dryers save the coal used in heating the ordi- nary direct fired dryers and also the labor necessary to stoke them. This saving in the cost of manufacture approaches one to two cents per barrel, depending upon the moisture in the raw materials and the cost of coal. The waste heat dryers also dry very thoroughly, and sometimes even break down the structure of the rock, due to the high temperature of the gases passing through them, thus often effecting a saving in the cost of pul- verizing. It is doubtful if waste heat dryers will be employed to any extent in the cement industry in this country in the future ex- cept where power can be purchased cheaply, as the waste heat boiler offers a much more efficient method of utilizating the heat in the gases. The number of B. t. u. required for drying the raw materials at most dry process plants does not exceed 35,000 B. t. u. per barrel, whereas the requirements for steam raising with turbo-generators are say 31O,OOO B. t. u. per barrel of cement. Since the waste gases from burning one barrel of clinker contain between 40O,OOO and 500,000 B. t. u., the employment of waste heat dryers in place of boilers entails a loss of at least 365,000 B. t. u. per barrel. In a plant of 3,000 barrels per day output, this amounts to about 40 tons of coal per day. It will be seen, there- fore, that it pays better to employ direct heat dryers and waste heat boilers rather than to reverse the process. THE DRY PROCESS I45 Drying Clay Sometimes in drying clay, this latter balls up in the dryer. The outside of these clay balls bake hard but the inside, even after they have passed through the hottest part of the dryer, remains wet. In drying such clays, therefore, it is found most success- ful to do the drying in two stages, first passing the clay through a dryer, then through a set of rolls or other disintegrator to break open these balls and allow the heat to get at the moisture remaining in the center of the lumps and then through a second dryer in which the remaining moisture is driven off. The clays along the Hudson river used by the Alsen and other plants there are very plastic and ball up and bake in this way. Here this system of drying has proved very efficient. Clays often contain considerable moisture and when this is the case much coal is necessary to dry them, hence waste heat dryers will here often effect a great saving over direct fired dryers. Slag which has been granulated by water, as is always done when this material is used for Portland cement, is particularly hard to dry and the expense of drying granulated slag, often carrying as much as 20 per cent water, almost balances the fact that it is a waste product and may be obtained for nothing by the com- panies using it. Feeding the Dryer Dryers are sometimes fed directly from the stone storage and sometimes from the secondary crusher, in which case the dryer must take the stone as rapidly as it is fed from storage or as delivered by the crusher. A more approved method is to install a bin above the feed end of the dryer and to feed the material to be dried out of this at a regular and uniform rate suited to the capacity of the dryer and the moisture in the material. For feeding the material, a reciprocating table feeder is generally used. This consists simply of a table placed at a slight incli- nation from the horizontal. This table is moved backwards and forwards beneath the opening at the bottom of the bin by means of an arm and an eccentric, the material spilling over the end at each backward stroke. The amount of rock fed may be adjusted I46 PORTLAND CEMENT by either a slide in front of the opening or by varying the length of the stroke, which can be adjusted at the eccentric. Pulveriging the Raw Materials The final reduction of the raw material to the proper fineness for burning is usually effected in two stages, by one of the fol- lowing ways: I. Hercules Mills followed by Tube Mills. 2. Ball Mills followed by Tube Mills. 3. Kominuters followed by Tube Mills. 4. Griffin Mills followed by Tube Mills. 5. Kent Mills, Screen Separators and Tube Mills. 6. Sturtevant Mills, Screen Separators and Tube Mills. Or in one stage by one of the following mills: 7. Compeb Mills. 8. Griffin Mills. 9. Fuller Mills. IO. Sturtevant Mills and Air or Screen Separators. II. Kent Mills and Air or Screen Separators. I2. Raymond Mills. Most of the newer dry process plants are equipped with Her- cules mills and Tube mills. The older plants quite generally employ tube mills using either ball mills, Kominuters or Griffin mills to prepare for these. Griffin mills and Fuller mills are still used to some extent, while a few plants employ Sturtevant or Kent mills, either for full reduction or for preparing for the tube mill. Degree of Fineness of the Raw Materials Three variables enter into the production of Portland cement clinker, vig:—temperature of burning, length of time in the kiln and the fineness to which the raw materials have been reduced. This may be expressed mathematically as an equation thus: A X B X C = D, in which A represents time; B, temperature; C, fineness, and D, a constant namely, clinker. If we increase any one of the three variables A, B and C, it will decrease one or both of the other two. Thus by increasing the time in the kiln, THE DRY PROCESS I47 we decrease the temperature necessary to clinker, while if we grind the materials more finely we decrease either the tempera- ture or the length of time in the kiln and may thus increase the output of the kiln and decrease the fuel required per barrel. In Portland cement clinker, no actual fusion has taken place, merely sintering or diffusion between the elements of the lime- stone and clay. That is, the silica and alumina in the clay par- ticles diffuse into the lime of the limestone and vice versa. The rate or rapidity of diffusion as well as the temperature at which it takes place depend upon the surface exposed. This is a general law applicable to all solids and solutions, therefore, the finer the raw materials are ground, the greater area of surface is pre- sented and consequently the greater chance for diffusion. The actual degree of fineness to which the raw material should be ground depends largely upon conditions. It may be said, as a general rule, that it should never be ground coarser than 90 per cent through a IOO-mesh sieve and that in most cases 95 per cent to 98 per cent is required to produce a sound cement. The fine- ness of the raw material should be tested at least once a day and, if possible, two or three times a day in order to have a check upon the work of the mills and to keep them up to standard. The raw material can be tested on the IOO-mesh sieve by the method for fineness outlined in the section on “Physical Testing.” In general, it may be said that most of the trouble experienced in making a satisfactory product by cement mills is due to im- proper grinding of the raw materials. Fine grinding of the raw materials will always pay as it reduces not only the coal required for burning but also increases the output of the kilns and re- Sults in a greatly improved product. Elevating and Conveying Machinery The raw materials are carried from one stage in the process to the next by means of mechanical conveyors. The product of the large gyratory crushers is difficult to handle and where this must be conveyed, belt conveyors, may be employed to advantage. Probably the best method of elevating where space permits this is an inclined belt conveyor. Where this can not be used, con- I48 PORTLAND CEMENT tinuous steel bucket elevators employing buckets of very heavy construction and roller chain are often employed. The service on such elevators is very severe and they must be very sub- stantially made. Belt elevators of this type are not satisfactory and in fact belt elevators are seldom used in cement plants. The size of the bucket depends entirely on the size of the stone to be handled and on the quantity of this. The elevators are, of course, very slow moving and are driven by a pair of toothed sprockets at the head end. These large elevators should be pro- vided with some automatic brake so that if the motor driving them stops they will not reverse from the load in the buckets and dump the material in the boot of the elevator, making it necessary to clean the latter out before the elevator can be started again. The product of small gyratory crushers and hammer mills can be handled in any of the ways mentioned above. Owing to the size of the material, smaller and less rugged buckets may be em- ployed. The stone may also be conveyed horizontally by means of a drag chain with large links. The product of the ball mills, the Hercules mills and other granulators can be conveyed laterally by means of screw con- veyors or belt conveyors. The former are probably more gen- erally employed. Ordinary malleable iron single or double strand bucket elevators are generally used for elevating material of this type. The product of the tube mills and the finely ground raw ma- terial ready for the kiln can be handled to advantage by any of the methods described in the preceeding paragraph. The Fuller-Kinyon pump has also just come into use for con- veying finely ground raw material from the mills to the bins above the kilns. This pump is fully described in the section on Pulverized Coal, to which the reader is referred. In the older mills elevators and conveyors were usually driven by means of chain or belt drives and this generally made a counter- shaft necessary even when individual motor drives were used. Elevators and conveyors are now often driven directly from a THE DRY PROCESS I49 motor without belts or chains by means of some form of worm or spur-gear speed reducer. The spur-gear reducers of the Jones type were first employed for unit drives but in many of the newer mills worm-gear reducers such as the Hindley, Cleveland or De Laval are employed. The worm-gear reducers save room and therefore economize building space. In the case of either type of speed reducer, the motor is attached to the shaft of the worm by a flexible coupling, and the head shaft of the elevator or con- veyor to the shaft of the gear by the same means. Back-geared motors are also used to some extent to drive elevators and con- veyors, but the reduction of speed in the motor itself is seldom enough to allow them to be used without a counter-shaft or speed reducer. JAz-z-zo/v-23-5- ../ea .22s. 6: Arr zºo -a g- Fig. 27.-Raw mill—National Cement Co., Montreal, Que., Richard K. Meade & Co., Engineers. Complete Raw Mill Fig. 27 shows a section of the complete raw mill of a modern dry process cement plant. As will be noted this is equipped with Bradley Hercules mills and 7 x 26 foot tube mills. The ar- II I5O PORTLAND CEMENT : rangement is evident from the drawing. In this particular plant, there are four units all arranged as shown in one room. Two units are designed for grinding the raw materials and two for grinding the clinker, but by an extension of the conveying systems the mills are so placed that any mill can be used for grinding cement and any mill for raw materials. CHAPTER VIII THE WET PROCESS History of The Wet Process The first materials used in Europe were the soft chalks of England. These carried considerable water as excavated, and in the old shaft kiln process of burning it was also necessary to mold the material into bricks. The general method of opera- tion, therefore, was to grind the two materials together in a thick “slurry” and allow this to settle, drain the water off, and break up the resulting mass into blocks, which were dried and fed into the kiln. In northern Germany, these same soft chalks of the North Sea coast were used, and the process was quite similar to that employed in England. When plants were started in Southern Germany, these used hard materials, but, as the molding into bricks was necessary, the plants here naturally followed the method of those in the north. In America, the first successful plant employed the cement- rock of the Lehigh district. This was a solid and compact ma- terial, carrying only a very small quantity of moisture. Saylor and his co-workers knew nothing of foreign practice, except what they had been told, so they followed their own ideas, which consisted in grinding the rock dry and only incorporating with it sufficient water to mold it into the blocks necessary for charg— ing the vertical kiln. When the rotary kiln was introduced here, this material was still ground dry, but in the very early stages of the process, a small amount of water was added to it just before it was fed into the rotary kiln, under the belief that it would perhaps otherwise be blown away. The addition of water, however, was soon discontinued and all the subsequent cement plants of the Lehigh district employed a straight dry process. * See page 244 et seq. I52 PORTLAND CEMENT As rotary kiln plants were built in other parts of the country, when they employed dry materials, they followed quite closely the practice in the Lehigh district. The wet process plants in this country were, in the early days of the industry, confined exclusively to the manufacture of cement from marl and clay. This material, carrying as it did approximately 50 per cent to 60 per cent of water, was manifestly not adapted to drying before grinding, and very properly the manufacturers who were using it believed that the drying opera- tion could be most successfully carried out in the rotary kiln it- Self. With the introduction of the manufacture of cement in the West, difficulties were encountered in certain plants. What these difficulties were need not be gone into extensively here, but it is sufficient to say that they were connected with the quality of the product and occurred in a section where fuel (natural gas) was very cheap. Several of these plants were in charge of German chemists, and one of these believed that the difficulty that occurred with the quality of the product could be overcome by the introduction of the wet process. Working on this theory, the plant was changed to a wet process one, and the alteration did result in improving materially the quality of the product. This occurrence might have been sufficient to induce all manu- facturers who were having trouble with the quality of their product to adopt the wet process, had it not been for the fact that many plants employing similar raw materials were making perfectly satisfactory cement by the dry process and employing less fuel for doing this than were the wet process plants. Outline of the Wet Process The wet process of cement manufacture differs from the dry process only in that the materials are ground and burned wet. No drying of the raw materials is necessary. On the other hand, water must be actually added to the raw materials (except in the case of marl and shells dredged from under water and alkali- waste) at Some time before they are ground, usually after crush- ing and just before the raw materials are fed to the pulverizing THE WET PROCESS I 53 machines. Fig. 28 illustrates diagramatically the steps of the wet process where clay is employed as the argillaceous raw ma- terial. When limestone and shale are the raw materials, the wet process does not differ from the dry until the grinding is reached, here water is added, the proportion being from 40 to 60 per cent of the dry raw materials, and the mixture is pulverized. The resulting slurry will contain from 30 to 40 per cent water according to the amount added. It is of about the consistency of a thin mud. Only enough water is used to make the mixture sufficiently fluid to handle easily. Any excess over this is un- desirable as it increases the fuel requirements in the kiln. The same machines are used for crushing" as in the dry process and a storage” for rock is usually provided. The mix” may be made at any convenient point, as in the dry process. When clay is used, the limestone is crushed and handled as in the dry process, but the general practice is to dump the clay into a wash mill and work it up with water into a thin “slip” or slurry, which is fed into the grinding machines at a regular rate along with the limestone. At some plants the clay is mixed in with the limestone as it comes from the pits, either before or after the limestone is crushed. Marl is usually worked up with sufficient water to make it fluid either in a wash mill, a pug mill or a wet pan; the clay receiving the same treatment in the same apparatus with the marl; or else in a separate machine. In the latter case, the two slurrys are mixed in the required amounts and ground. Advantages and Disadvantages Claimed for the IWet Process The following are the advantages” claimed for the wet process: (I) That a better and more uniform cement can be manu- factured by the wet process than by the dry, owing to the fact * See pages 175 to 189. * See Chapter VI. “Those who desire to study the relative merits of the two processes will find a discussion of this by the author in Concrete-Cement Age, Cement Mill Edition, May, 1921. I54 - PORTLAND CEMENT Limestone, Marine-Shells, Clay Water Marl or Alkali Waste. – | Crushed Clay and water mixed to form a thin slurry free from lumps or pebbles Mixed in proper proportions | Water Pulverized in the form of a slurry containing from 33°/, 7% to 45% water to a fineness of 92 to 98% passing a No. IOO test sieve Burned at a temperature of from 14oo° to 16oo°C Cooled | 2% to 3% gypsum Pulverized to a fineness of at least 78% passing a No. 200 test sieve PORTLAND CEMENT Fig. 28.—Diagram showing steps in the manufacture of Portland cement by the wet process. THE WET PROCESS I55 that a more satisfactory mixture of the raw material can be made and a more constant composition can be maintained. (2) That wet materials can be more easily ground than dry, the operation requiring less power and the repair item being less. That the output of the mills is also greater, which decreases the investment in the plant and consequently lessens interest, de- preciation, etc. (3) That the raw materials do not need to be dried which effects a saving of the fuel and equipment necessary for this, with the labor, power, repairs, overhead, depreciation attendant on the latter, etc. (4) That the clinker of the wet process is more easily ground than that of the dry. . (5) That wet materials are more easily handled than dry. (6) That there is less dust connected with the wet process than with the dry. The admitted disadvantages of the wet process are: (I) That more fuel is required to burn a slurry than is re- quired to burn a dry mixture even when the coal necessary for drying is included. (2) That greater kiln and fuel grinding capacity is required than in the dry process. (3) That power is required to agitate and mix the slurry. For the evidence supporting these various claims the reader is referred to the chapter on burning, and to the following par- agraphs of this one. The relative fuel requirements of the wet and dry processes and the dust losses of each are quite fully dis- cussed under Burning, while the advantage in chemical control and grinding are discussed below. Chemical Control of the Wet Process Chemical control of the wet process is usually secured by some modification of the following system: From the tube mills, the finely ground slurry is emptied into “correcting basins.” These are fairly large, usually holding from 3 or 4 hours' run of material. The slurry is continually stirred and consequently is thoroughly mixed and of practically the same composition I56 PORTLAND CEMENT * throughout the basin. If found not to be of the proper com- position, it is possible to add to it a small quantity of clay slip, made by grinding clay and water; or what is more common prac- tice, a succeeding tank of slurry is ground of a slightly higher or lower composition, as the case may require, and the contents of the two basins are then mixed in the proper proportions and run into a still larger basin called the “mixing basin.” These latter are often made sufficiently large to hold a full day's run. Their contents also are constantly agitated and thoroughly mixed be- fore being sent to the kilns. In this way, the contents of the kiln basins are usually of correct and uniform composition. Examination of the records of Sev- eral wet process plants reveals the fact, however, that in spite of this theoretical opportunity to secure perfect composition, the contents of the kiln basins are often at least I per cent and some- times farther from the composition desired. Even in this process much is left to the skill and good judgment of the chemist. It is also a difficult matter to agitate the large kiln basins thor- oughly, and some settling always occurs where the arms of the agitator do not reach. * It will be seen that this system of slurry basins is well adapted to promote proper proportioning of the clay and limestone, but it must be remembered that uniformity of the cement depends very much on the uniformity of the raw materials also. If the cement is to be uniform in its setting and hardening properties there are two ratios which must be kept uniform, namely: CaO SiO, H- A1,O, + Fe, Os (I) and SiO, Al,O, (2) The first of these ratios will determine the soundness, strength, etc., of the cement, but the second will also play an important part in the hardening and setting qualities, and keeping this ratio constant promotes a cement of uniform setting and hardening qualities. The correcting basins will help keep the first ratio con- T III. WET PROCESS I57 stant, but the fixity of the second will depend entirely on the uniformity of the raw materials. It will be seen at once that in the wet process there are quite a number of steps over and above those required in the dry process, and that some power is also required for stirring the various slurry basins. The quantity of power is appreciable, being about O.O2 horsepower per barrel of cement produced per day, or about 60 horsepower for a 3,000-barrel plant, but it is certainly not suf- ficient to condemn the operation on the score of power, in view of the excellent opportunity which is afforded to secure uniform composition. To sum up the arguments as to the quality of the cement pro- duced by the wet process, it appears that it is easier to control the lime-silicate ratio by the wet process, but that this can be done perfectly satisfactorily also by the dry process if the mill is properly arranged for this. Grinding the Raw Materials The grinding of the raw materials in the wet process is usually carried out in one of the following combinations: I. Compeb Mills." 2. Kominuters and Tube Mills. 3. Ball Mills and Tube Mills. 4. Hercules Mills and Tube Mills. The water is added, if necessary, before the materials are fed into the grinders. If the grinding is in two stages, it is usual to place a small feed bin above the tube mill, in which the partly ground raw material is stored. The contents of this bin are kept continually stirred by means of a paddle agitator. The argument that wet material can be ground more easily than dry is probably well founded and what data the writer has been able to obtain (largely from metallurgical sources) leads him to believe that a wet tube mill will have greater output than one grinding dry. Most manufacturers are content to take this statement without investigating the actual saving which can be * See Chapter X for description of these mills. I58 PORTLAND CEMENT effected by the wet process over the dry, so that actual figures showing the saving of wet over dry grinding in the cement in- dustry are hard to get. It is also probable that while the output of the tube mill is greater with wet grinding than with dry, that the difference between wet and dry grinding in the ball mill is not marked. So far as the writer’s observations go, however, the power equipment installed per barrel of cement produced is fully as large in wet process as in dry process plants. Generally speaking, about 30 per cent of the total power re- quired to manufacture cement (or about 5 kilowatt-hours per barrel) is employed in the grinding of the raw materials. It will be seen, therefore, that in cement mill practice unless the relative saving in power by wet grinding is very marked, the actual dif- ference between the two processes in the power required for grinding might easily be accounted for elsewhere, such as in the agitation of the slurry, the grinding of the greater amount of coal required for burning, revolving the additional equipment for burning, handling the greater weight of raw material due to water, etc. - Wash Mills Wash mills are employed to some extent for triturating the clay with water so as to form a homogeneous slurry of the latter. The wash mill is employed because clay being sticky when fed into a crusher with limestone will often choke and gum the latter. It is, therefore, preferable to handle clay and limestone separately. As clay is already in a finely divided condition, no crushing, of course, is necessary and it is ready for the pulverizing machine. A few plants add the clay just as it comes from the clay pit ahead of the grinding machine. It is considered better practice now, however, to work this up into a slurry in a wash mill and then to feed this slurry into the pulverizing mill along with the limestone. The wash mill, Fig. 29, generally consists of a circular pan or tank made of concrete IO to 20 feet in diameter, in which re- volve a series of harrows or knives, which break up the clay THE WET PROCESS I59 Aeve/ Anºtarº yº Tºfaş. __*oexfºr Affair favºry—se –4 &tºur ºw -º: y arvel ºssar Dare vs - t *- * !. tº + § : - ... . º?. º Sweedar reaway 5**** º # *s He 'Q. Gorne Bearwo º ‘ºf g o!3 * , ºf Azers/awe & º tº c Wºwº & th lºº portravra's dº rºud - pº * - * * * * *** / #! ; * * sº 3tusºw iev's 4 z § :: \ 54.4/Arrºw is vººr º' --- } . . =====T-ETºjº-V------------ º --- a sº gºss-ºsmºs ºm-ºs ºsmº ºmºmºm. sº * = • * *: * - e :* *. ſº ,"." • J -: * & * * * . • * • * ..". * , tº º ºº: . . º nº º & }* * * - e º & , * 4. º * * gº * * * * * ... " . ſº ... • t º: e ºvrra was ºf ºscºpee d }- -. & * tº s • * * * • * . * * = e ... • - - * * - i. s & * . . ſ : * , º •".. & * * º * > * * & e e º w -'-'. * '. a •, e }r ~ tº ... • • *- * * * * * * * * . . m. * * s º $, ºr t *.*. *... • - S. .* ** * * * a. * * & $ , * * p. .* * * - * º • * 4: º $ tº s º ---ºvrºzzary pºscºw, * a .* § ...! *... " ; : sº * . e ~ • . ſº • 's N 2 * * , a - .*.*.* * * * a *, * - a . , ** * * * AP are ºf •- ..., was ºr * * [… *...* º * . • * * O * * * > * • ?-? - ºr Fºllº -- Aarºº Aravºa5. Fig. 32.-General arrangement of Dorr slurry mixer. upon swirling the contents of the tank. The apparatus consists of a hollow vertical shaft extending downward through the middle of the basin to almost the bottom of the latter. This shaft is supported by a rigid “A” frame to which are attached the two bearings in which the shaft revolves and at the top of which are located the bevel gears actuating the shaft. No step bearing is employed. To the lower end of the shaft, are fixed two radial THE WET PROCESS 167 arms with plow blades. The latter move the slurry towards the center of the basin. The shaft as stated is hollow and the slurry is made to flow up through this by means of an air lift. The slurry overflowing at the top of this hollow shaft, is caught by two radial launders or troughs which revolve with the shaft. These launders distribute the slurry uniformly over the surface of the basin . The hollow shaft is provided with auxiliary dis- charge openings so that the slurry is distributed at different Fig. 33.--Dorr slurry mixers–Oklahoma Portland Cement Co., Ada, Okla. elevations and circulation is maintained when the basin is only partly filled. The plow arms are also provided with air jets so as to provide vertical mixing throughout the basin. The mixer revolves at from one to three revolutions per minute according to the size of the basin; from which it is evident that mechanical agitation is not depended upon for the mixing. In- stead this is secured by the distribution of the slurry through the launders and with the help of the air jets in the radical arms I68 PORTLAND CEMENT at the bottom. The advantages claimed for the Dorr Mixer are thorough mixing, low power, low upkeep due to all bearings being out of the slurry, etc. The Dorr mixer requires about one-half horsepower per 1,000 cubic feet of basin capacity for revolving the mechanism and about the same amount for compressing the air. Both the quantity and pressure of the air depend on the intensity of agita- tion required, viscosity of the slurry, size of basin, etc. The air pressure depends on the depth of the basin but generally for a basin less than 20 feet deep is from IO to 25 pounds gauge pressure. The quantity of air required varies from 4 to IO cubic feet per minute per I,OOO cubic feet of basin capacity. As an example of an actual installation, in a basin 20 feet in diameter by I2 feet deep holding 3,770 cubic feet of slurry the Dorr Mixer required 17.3 cubic feet free air per minute at 17.5 pounds gauge pressure and 3. I horsepower to operate. Handling the Slurry For handling slurry four methods are in common use, (I) plunger pumps, (2) compressed air lifts, (3) centrifugal pumps, and (4) elevators and conveyors. Quite a number of plants employ for handling the slurry, bucket elevators and screw conveyors similar in every respect to those which are employed for handling fine dry materials. As far as the operation goes, this equipment is perfectly satisfac- tory. It is, however, much more expensive to install and takes up a great deal more room than do the pumps and air lifts. Screw conveyors are often placed in troughs to keep the slurry moving since the trough would otherwise have to be pitched at a considerable angle in order to avoid settling. When no elevating of the slurry has to be done and a short straight line conveyor can be employed this is good practice. Plunger pumps with ball valves are used to some extent for handling slurry, particularly in the older plants in this country and in Europe. Fig. 34 shows such a pump of American design, manufactured by the Bonnot Company. Its action is similar to - THE WET PROCESS 169 () - --- - - Sºº Fig. 34.—Ball valve slurry or marl pump. Fig. 35–Wilfley sand pump for pumping slurry. 170 PORTLAND CEMENT that of other plunger pumps and the operation of the valves will be evident from the cut. The plunger pumps are now generally being displaced by cen- trifugal pumps. The latter are very compact and may be driven by direct connection to a motor. The Wilfley Sand Pump, which has been extensively used for moving tailings and pulp in metal- lurgical plants, is now being much used in cement plants. This pump is shown in Fig. 35. The advantage of this pump is that no stuffing box is required as is the case with the ordinary cen- trifugal pump where such a device is necessary in order to pre- vent the material from leaking out where the shaft projects from the pump. The stuffing box causes wear on the shaft when gritty materials are handled. In the Wilfley pump, a centrifugal seal takes the place of the stuffing box. This seal consists of a revolving member called an “expeller” having paddles radiating from a recess in its center to its periphery and a stationary mem- ber which has a projecting groove. The revolving member is cast in integral with the runner and is set close to the stationary member which acts also as a side wearing plate. In action, the slurry is prevented from leaking out by the centrifugal action of the wings of the expeller, similar to that of an open runner, and any slippage by the side is caught by the projecting groove and delivered to the wings. A check off valve seals around the shaft while the pump is not in action. The Allis-Chalmers slurry pump is an air lift and is shown in Fig. 36. It is an adaption of the “blow case” used in chemical plants. It consists of two receiving or “blow-tanks” which are set side by side and into which the slurry flows by gravity. Each tank is equipped with a float which operates an air valve. The slurry entering the tank raises the float and when the tank is full this float opens the air valve allowing compressed air to flow into the tank. This in turn forces the slurry out of the tank and to whatever elevation is desired. This lift has the advantage of having no moving parts, but the disadvantage of taking up con- siderable floor space. The top of the blow tanks must also be below the level of the bottom of the slurry basins. The air jet lift has also been employed for lifting slurry. THE WET PROCESS I7I Fig. 36.—Allis-Chalmers air slurry pump. Weight of Slurry The weight of cement slurry varies considerably, depending principally on the amount of water it contains and also to a slight extent on the nature of the solid material itself. For estimating the capacity of tanks, the horsepower to move the slurry, etc., it may be taken as weighing approximately IO5 pounds per cubic foot, having an apparent specific gravity of I.7 and one cubic foot containing 65 pounds of dry raw material. Table XIV gives an idea of the variation in weight, etc., with varying percentages of water. The actual weight may be found in the laboratory by weighing a marked liter flask empty; and then filled to the mark first with the slurry and then with water, or visa versa. The weight of a cubic foot of slurry will then be— #. X 62.43 = W When F = weight of flask filled with slurry. S = weight of flask empty. C = weight of flask filled with water. W = weight of one cubic foot of slurry. I72 PORTLAND CEMENT Complete Grinding Plant Fig. 37 shows the raw mill of a modern wet process cement plant. This is equipped with ball and tube mills but only the tube iſiſ – *=== | | 33. N . : #. #| - | | - sº fº º: 5/urry 5forage /3a5/7 º #j| ºw /fay//// M/r//77 AoS/n Fig. 37.—Raw mill—Pyramid Portland Cement Co., Des Moines, Ia. mills and slurry tanks are shown. The installation of Compeb mills would be essentially as shown. TABLE XIV.-WEIGHT OF CEMENT SLURRY, WEIGHT OF SOLIDS PER CUBIC Foot, DENSITY, ETC. Sl y Water Solids Water per Solids per Weight Apparent jºi. per cent per cent cu. ft. slurry cu. ft slurry per cu. ft. density Cemle 11t By weight by weight I,bs. I,bs. I.bs. Water – I Cu. ft. 30 70 32.7 76.2 Io8.9 I.75 8.O 3I 69 33.3 74.3 IO7.6 I.72 8. I 32 68 34. I 72.4 IO6.5 I.7O 8.3 33 67 34.8 70.6 IO5.4 I.69 8.5 34 66 35.5 68.8 IO4.3 I.67 8.7 35 65 36. I 67.I IO3.2 I.65 8.9 36 64 36.8 65.4 IO2.2 I.64 9.2 37 63 37.4 63.8 IOI.2 I.63 9.4 38 62 38. I 62.2 IOO.3 I.62 9.7 39 ÖI 38.8 60.6 99.4 I.59 9.9 40 60 39.4 59.0 98.4 I.58 IO.2 CHAPTER IX CRUSHING MACHINERY Development of Grinding Machinery In the early days of the industry when the plants were small, manufacturing only a few thousand barrels a year each, both the raw rock and the clinker were ground with mill stones, just as corn is ground in the small water-power mills familiar to every one. The first advance upon this was to encase the stones, and as the American manufacturers began to work up a home market for their product and to increase their output to meet the demand, they also began to experiment with a view to securing more effi- cient pulverizers than the mill stones. As a result of their ex- periments, the Atlas Portland Cement Co. patented the Hunting- ton mill which they still use. In 1889 the American Cement Co. installed a Griffin mill in their plant at Egypt and this mill is still in use there, and in many other large plants throughout the country. Another system of grinding consisting of a ball mill for the coarse grinding and a tube mill for the final pulverization was introduced about this time by the Bonneville Cement Co. in their plant at Siegfried, Pa., and this combination also came into prominent use in the industry. Newer types of pulverizers are the Kominuter, The Fuller- Lehigh Pulverizer, the Raymond Roller Mill, the Bonnot Mill, the Kent or Maxecon Mills, the Sturtevant Ring Roll Pulverizer, the Bradley-Hercules Mill, the Allis-Chalmers Compeb Mill, etc. All of these mills have been extensively used in the cement in- dustry. The Fuller-Lehigh Mill and the Raymond Mill are used now chiefly for pulverizing coal, practically all cement plants em- ploying either one or the other mill. A few plants use the Bonnot Mill for this purpose. Ring Roll Mills are still used to some ex- tent for preparing for tube mills; the newer plants, however, are being chiefly equipped with (1) Hercules Mills followed by Tube Mills, (2) Kominuters followed by Tube Mills, or (3) Compeb I74 PORTLAND CEMIENT Mills alone. These combinations are suitable for grinding both the raw material and the clinker and to both wet and dry grinding. In the use of any of the above mills upon dry raw materials, it is necessary to break up the material to a size which will per- mit the material to be fed to the mills. In order to do this, as has been stated, crushers of the gyratory, jaw or roll-jaw type are usually employed, as the first stage in this preliminary reduction. The gyratory crusher was developed by the Gates Iron Works, Chicago, but is now made and sold by several firms. This type of crusher was used in cement mills almost exclusively until about 1914 when large size jaw crushers began to receive atten- tion. About the same time the Allis-Chalmers Co. brought out the Fairmount Crusher (Roll-jaw) and this proved satisfactory where the limestone was not too tough. The opportunity for the jaw and roll-jaw crushers was made by the rise in the wage paid labor and the introduction of steam shovels to take the place of hand loading in most quarries incident thereto. This change made it necessary to employ crushers which would handle large pieces of rock. For the same capacity, the jaw and roll-jaw crushers will take much larger stone than will the gyratory crushers; although in other respects probably not so desirable as the latter. At most mills, particularly where large size crushers are em- ployed for breaking down the rock as received from the quarry, it is necessary to follow the primary crusher by a secondary breaker. These latter are now generally of the “hammer mill” type. Small gyratory crushers and rolls are also used to a limited extent for this purpose. The large primary crushers generally reduce the limestone to 6 to 8 inches and under, while the second- ary crushers reduce this product to such size as can be handled by the granulators or pulverizer, usually to at least 2 inches and under. Clay is generally handled as received from the bank by wash mills, if the wet process is employed, or by edge runner mills if the dry process is used. Hammer mills are employed for shale. CRUSHING MACHINERY I75 Below will be found descriptions of various types of crushers, pulverizers, etc., used in cement mills for preparing the raw ma- terial for the kilns and for grinding clinker. The Raymond and Fuller-Lehigh Mills which are used chiefly for pulverizing coal are described in the section on fuel. Gyratory Crusher Fig. 38 shows a section of a gyratory crusher and Fig. 39 a view of this. Referring to the former illustration, it will be seen Ø 2. siu-º Ż Fig. 38.—Gyratory crusher. that the outer shell of this type of crusher resembles an hour- glass somewhat in shape. It is open at the top for receiving the 176 PORTLAND CEMENT stone and is provided with an inclined spout at its lower lobe for discharging the crushed rock. The main shaft, g, is suspended from a spider that spans the top of the opening and extends downward through the throat, h, to a step bearing, d, in the base. A conical shaped crushing head, c, is keyed to the shaft where this passes through the throat. The throat is lined with plates Fig. 39.-Large gyratory crusher-Allis-Chalmers Mfg. Co. of some hard tough metal such as chilled-iron, manganese steel, etc., and the crushing head also is made of such a material. The crushing is done in the annular space between the head and the throat plates. The lower end of the shaft passes through a sleeve CRUSH ING MACH IN ERY 177 which is bored off center one-half the required gyration, to form an eccentric, and this sleeve is driven by a pair of bevels, b, which in turn receive their power through the pulley to the right of the machine. The main shaft being centrally held in the spider at its upper end and slightly off center in the eccentric at its lower, the axis of the shaft describes a cone as it revolves causing the crushing head alternately to approach and recede from the throat plates. This action causes the breaking of the material, which as it is crushed drops further down into the throat and finally out of the machine by means of the discharge spout. The larg— est motion is, of course, at the bottom of the throat and the de- gree of motion here is the “throw” or “stroke” of the crusher. The spindle receives no direct rotating motion from the shaft and is held loosely in the eccentric. The number of revolutions of the eccentric and the number of strokes correspond. These vary with the make, size of the crusher, etc., but are seldom more than 250 revolutions per minute. The throw also varies but is generally only a fraction of an inch. The crushing is done in all parts of the throat and hence is continuous. For this reason the gyratory crusher is steady in the power required and has large capacity. On account of the sidewise rolling of the head upon the concaves it is also less liable to choke than the ordinary jaw crusher. The main shaft is adjustable and can be raised or lowered by means of the step bearing, d. By raising, the opening between the bottom of the throat and the crushing head is decreased in width and this in turn gives a smaller product, and vice versa by lowering, a larger product. This arrangement also allows wear in the crushing head and plates to be taken up. The gyratory crusher is made in sizes ranging from laboratory grinders to machines having a capacity of several thousand tons an hour. Table XV gives information about the capacities, weights, etc., of crushers of this type. The sizes now generally employed in cement mills range from the No. 9 to the No. 24. The former size is, however, somewhat Small for a modern cement mill. It has enough capacity for the average mill but the annular receiving opening is not wide enough to take in the 178 PORTLAND CEMENT large blocks of stone which a steam shovel will handle, making it necessary to blast or sledge these into smaller pieces in the quarry before sending them to the mill. Most of the newer mills are equipped with the Nos. 18, 21 or 24 crushers. A No. 18 crusher will handle blocks approximately 36 x 36 inches and the No. 24 blocks 48 x 48 inches. The No. 5 and 6 crushers set to give a product from 2 to 3 inches, are sometimes employed after the large crusher to crush the product of the latter small enough to be fed to Kominuters, Hercules Mills, etc., but hammer mills are now more often used for this purpose. TABLE XV.-SIZEs, CAPACITIES, WEIGHT.s, ETC., of GYRATORY CRUSHERs' Size of -Approx. capacity—s Horse Shovel dipper each feed Size of Tons power Shipping rated capac- Size of opening product per to weight ity in cu. crusher Inches Inches hour operate Pounds yds.” O 20 x 80 4 250 IOO-I5O 93,000 ) Not satisfac- 7% I4 x 55 2% 75 50-75 38,000 } tory for 6 I2 x 46 2% 5O 30–45 28,000 J shovel work I2 26 x Ico 6% 525 I25–2OO I53,OOO 2 I8 36 x IS6 8 I,056 I50-250 300,000 2% 2I 42 X I53 8% I,581 I75-275 360,000 3 24 48 x 166 9 I,890 2O0-350 500,000 4 Gates crushers are well adapted for free feeding or feeding directly from cars, as the rock can be fed into them from all directions. Fig. 18 shows a large gyratory installed in a cement plant. Jaw Crusher The Jaw or Blake crusher is shown in Fig. 40. It consists of a heavy frame usually of cast steel or semi-steel in which is suspended a movable jaw plate b. Opposite this movable plate is a fixed plate, a, and the crushing is done between these two jaws, a and b. The jaw b is given a reciprocating motion by means of an eccentrically operated vertical pitman, d, and two * Information from Catalogue of Traylor Engineering and Manufacturing Com- pany, Allentown, Pa. Crushers of different makes vary somewhat in size of opening, weights, etc. * A crusher of the size given will take the largest stone which will pass through a dipper of this capacity or smaller. CRUSHING MACHINERY I79 toggles, c and c. It will be seen by referring to Fig. 40 that as the shaft, f, revolves the pitman is alternately raised and lowered by the eccentric, e. This upward motion of the pitman, in turn, straightens out the toggles and moves the swing jaw nearer to the fixed jaw. The rod, g, pulls the swing jaw back against the toggles during the return stroke. Fig. 40.-Section of jaw crusher—Allis-Chalmers Mfg. Co. The angle between the jaws must be small enough to nip the rock but large enough to give capacity at the mouth without hav- ing excessively long jaws. This angle in large crushers is usually about 25° and the fixed jaw is often nearly perpendicular. The number of effective strokes is the same as the number of revo- lutions of the pulley, since no crushing is done on the return stroke. Half the time is occupied, therefore, in storing up energy in the fly wheels. The movement at the bottom of the jaws or throat is the “stroke” or “throw” of the crusher. This can be adjusted by means of different size toggle plates and sometimes by means of wedge plates against which the rear toggle presses The jaw plates are usually ribbed and are made of chilled iron or manganese steel. They are made renewable. The lubrication I8O PORTLAND CEMENT of this type of crusher is important and usually a forced feed and filtering system is employed. The Blake crusher will take a rock the full size of the receiv- ing opening and reduce the same to pieces not larger than the maximum opening at the throat. The size of the crusher is usually designated by the dimensions of the receiving opening. Blake crushers are well adapted to hard rock which breaks up into cubical pieces, but are less desirable for soft material and limestone which breaks in the form of slabs. The size jaw crushers usually employed in cement mills, weights, capacities, etc., are given below. TABLE XVI.—SIzE, WEIGHT, CAPACITY, ETC., of LARGE JAw CRUSHERS' 2—Approx. capacity—— Horse- Shipping Shovel dipper 2 Size ill Size product Tons per power to weight rated capacity inches Inches hour operate Pounds in cubic yards 36 x 42 6 I44 II5 II6,000 I}% 42 x 48 8 260 I5O I55,000 I3% to 2 48 x 60 IO 7I3 I8O 215,000 2% to 3% 56 x 72 IO 740 230 3IO,OOO 4 66 x 86 I2 I, IIO 3OO 460,000 5 Fairmount or Roll-Jazv Crusher The Fairmount crusher" is much used for crushing cement- rock and soft limestone. This crusher is illustrated in Fig. 4I. Referring to the illustration it will be seen that the crushing is done between a toothed roll, a, and a curved jaw or anvil, b. The latter is generally stationary, but can move backward under very heavy pressure as it is held in position by heavy steel tie rods, c, which pull against a powerful nest of heavy springs. This arrangement allows the jaw to take up or equalize the ex- * Information from Catalogue of Traylor Engineering and Manufacturing Com- pany, Allentown, Pa. * A crusher of the size given will take the largest stone which will pass through a dipper of this capacity or smaller. The first two crushers have a greater capacity than the shovels equipped with 1% to 2-yard dippers respectively. 1 Allis-Chalmers Mfg. Company., Milwaukee, Wis.; The Pennsylvania Crusher Company, Philadelphia, make a somewhat similar crusher. CRUSHING MACHINERY 181 cessive shocks and pressures met with in this type of crusher. The roll, a, is provided with teeth and is so located with relation to the jaw that the preliminary fracturing of the large pieces of rock fed to the crusher is effected by the sledging action of these Fig. 41.-Fairmount “roll-jaw” crusher, with hopper removed—Allis-Chalmers Manufacturing Co. teeth on the rock as it rests by gravity upon the roll. This action is intensified by having the teeth of different heights. Further crushing of the rock is accomplished by a direct nipping and crushing action between the roll and the jaw. The effect of the roll is to forcibly discharge the material when crushed and also to get rid rapidly of fines which may be fed to it along with boulders. For this reason the Fairmount crusher is particularly well adapted to crushing limestone containing clay or shale seams or other soft, sticky material. The jaw is lined with chilled iron ribbed plates. The teeth on the roll are removable and hence may be replaced when worn down or broken. 13 I82 PORTLAND CEMENT The Fairmount crusher is made in three sizes, 24 inches x 60 inches, 36 inches x 60 inches and 60 inches x 84 inches. Hammer Mill The hammer mill is made in a number of forms, each maker having his own type of mill and peculiarity of construction. In some, the hammers are fixed and in some hinged, while in one form rings take the place of hammers. The form shown in Fig. 42 is the Williams Mill," while Fig. 43 is the “Pennsylvania Super” Hammer Mill.” This is one of the best of this type of granulator. It consists of a number of hinged hammers, which revolve around a horizontal shaft called the “rotor.” These hammers crush the material and pass it out through a grid Screen as shown in the cut. There are usually from eight to ten rows of hammers and eight to twenty-seven hammers to the row. The regulation of the size of the product is by means of spacing between the bars of this grid. The hammer mill as now made is provided with an arrange- ment by which the grinding plates can be moved nearer the ham- mers, usually by means of a rack and pinion operated by a hand wheel on the outside, to take up the wear of the hammers. Other mills of this type are the “Jeffrey* Swing Hammer Pul- verizer,” and the “K. B. Mill.” In the latter, hinged bars take the place of hammers. Mills of this type have been employed to some extent in place of ball mills, particularly where these latter are designed to pre- pare for Fuller-Lehigh or Griffin Mills, as the installation is not only much cheaper of itself but considerable building and bin space is saved thereby. At a few cement plants, mills of the swing hammer type are also used in connection with some form of outside separator such as the Newaygo (see page 236) to prepare material for the tube mill. They compare favorably with Ball mills for this purpose in 1 Williams Patent Crusher and Pulverizer Company, St. Louis, Mo. * Pennsylvania Crusher Company, Philadelphia, Pa. * Jeffrey Manufacturing Company, Columbus, Ohio. * K. B. Pulverizer Corporation, New York, N. Y. CRUSHING MACHINERY Fig. 42.-Williams mill. Fig. 43.-Hammer mill–Pennsylvania Crusher Co. I84 PORTLAND CEMENT point of both power consumed and output but are not so effi- cient as the newer Hercules mill. Hammer mills are also used quite generally for the primary crushing of shale. This type of mill is well adapted to this. At a few plants, very large hammer mills have been employed in place of large crushers for primary crushing of limestone. The chief employment of large hammer mills is now to replace the small crushers (No. 5) when these latter are used after a large crusher. Hammer mills are now made with a capacity of from IOO-250 tons of limestone per hour, reducing this from pieces Io inches and under down to material passing a 2-inch screen. Such material is suitable without further reduction, to be fed to Hercules mills, Compeb mills or Kominuters. Hammer mills are made in a great range of size. Some of the large mills used in connection with the primary jaw or gyra- tory crushers having capacities comparable with these. As is the case with all crushers and grinders, the capacities vary not only with the size mill, but also with the hardness or brittleness of the material to be reduced and the size product desired. The following figures are by way of illustration only. When preparing for a tube mill the No. 3 Williams mill will grind from 8 to IO tons per hour to a fineness of 95 per cent passing the No. 20 sieve taking pieces I3/3 inches in size with an expenditure of from 45 to 55 horsepower and a repair cost of from 1% to 2 cents per ton (O.4 to O.6 cent per barrel of cement). When used for secondary crushing a No. 12 Pennsylvania “Super” Hammer mill will take the product of a Fairmount crusher consisting of pieces of rock IO inches and under and re- duce this to 2 inches and under at the rate of 250 tons per hour. This mill requires about 200 h.p. where operating at full capacity. The repairs on a hammer mill vary with the hardness of the material crushed, the amount of flint or silica in this, the size of the product, type of mill employed, care in operation, etc., but are usually from O.I.5 to 2.0 cents per ton of material reduced; the former figure representing repairs where the machine is used for secondary reduction (from IO-inch to 2-inch) and the latter CRUSHING MACHINERY 185 figure the repair cost when the hammer mill is used to prepare for the tube mill. Hammer mills are usually provided with what is known as a “tramp-iron” separator. This consists of a compartment into which large pieces of iron which find their way into the mill are thrown; otherwise the entrance of a coupling pin or spike into the mill would result in broken hammers, etc. Hammer mills may be driven in any appropriate way such as by a belt from a line shaft or motor. The most approved method, however, is by means of a motor of proper speed, direct connected to the shaft of the mill by a flexible coupling. When Hammer mills are employed to prepare material for a tube mill, they are usually fed from an overhead bin by means of some arrangement which will give a uniform feed. When used for secondary crushing they are often fed directly from the primary crusher. (See page I35.) Table XVII gives information about Pennsylvania Hammer Mills, and is taken from the catalogue of the manufacturers of these. An idea can be obtained from this as to the outputs, horse- power required, etc., of hammer mills of various sizes. TABLE XVII.-SIZE, CAPACITY, WEIGHT, ETC., OF PENNsyLVANIA HAMMER MILLs Capacity H. P. 2–––Hopper—— (approx.) (approx.), Weight C--Hammers-—- Speed S126." Length Width (a) (b) (approx.). Dia, circ. Rows No. (rpm) SX- 5 2'-3%" I'-6" 55- 7o 80-90 I2,500 42" 8 8o 800-50 SX- 6 '-9 ° 1'-6" 70-85 IOO-II5 I3,500 42” 8 IO4 800-50 SX- 7 3'-2%” I'-6" 85-IO5 I25-I45 I4,500 42 8 I28 800-50 SX- 8 3'-8 " I'-6" Ioo-I25 I50-175 I5,500 42 8 152 800-50 SX- 9 4'-1%” I'-6" II5-I45 175-200 16,500 42" 8 176 800-50 SX-12 3'-8%” I'-7" 150-190 225-250 36,500 58". Io 180 720-50 SX-13 4'-2 ” I'-7” 175–220 265-300 38,500 58" Io 2Io 720-50 SX-14 4'-7%” I’–7” 200-250 300-350 40,500 58" Io 24O 720-50 SX-15 5'-I " I'-7” 225–285 340-4CO 42,500 58" Io 270 720-50 (a) CAPACITIES-These will vary widely with the size and kind of feed, hardness, structure, moisture content and fineness of crushing. The capacity figures therefore show the minimum and maximum range. (b) HORSEPOWER—These approximate Horsepowers represent Motor sizes but they will change with the varying conditions. 186 PORTLAND CEMENT Edge Runner Mill The edge runner (Fig. 44) is made in two different types and under the names “Edge Runner Mills,” “Chaser Mills,” “Chillean Mill,” “Dry Pan” and “Wet Pan,” according as used for wet or Fig. 44.—Edge Runner Mill. dry grinding. It consists of a pan in which revolve one or more rollers. Either the pan itself or the rollers may be driven. In the one form, the pan is driven and the rollers are revolved by friction with the former. In another type, the pan remains stationary and the rolls are driven around. This latter type of mill, however, is much less employed than the former and usually only in cases where the nature of the material would allow slip- ping of the rollers as in grinding paints and colors in oil. Both the pan and runners are usually made of cast iron. The mill grinds by the weight of the rolls acting on the particles to be ground. Chilled iron or steel scrapers or plows keep the material to be ground under the rolls as the pan revolves. Where the material is to be ground to a definite size, the pan bottom is often fitted CRUSHING MACHINERY - 187 with steel or chilled iron grids through which the fully ground material passes while the unground is scraped back under the rollers by means of scrapers. Edge Runner mills are not employed to any extent in dry pro- cess plants, but are often used in wet process plants to crush shale and sometimes for the secondary crushing of limestone. They can be used to reduce shale from quarry size to Kominuter or Compeb mill feed. They consume a relatively large amount of power for the amount of crushing done and can generally, even in wet process plants, be replaced to advantage by more efficient equipment. Wet pans have the advantage that material to be crushed can be fed into them in large quantity at once, and hence Small cars of shale can be dumped directly into them. Rolls Crushing rolls which are quite popular in metallurgical work have never been employed to any extent in the cement industry. This is probably due to the fact that, when required to make too great a reduction, the rolls must be unusually large if they are to work efficiently. Thus a set of 72-inch diameter rolls should not be fed material larger than 2.9 inches plus the distance be- tween the roll faces (“spread” of the rolls). Assuming the rolls are to crush to 2-inch and under, it will be seen from this that the material fed to the rolls should not be greater than 4.9 inches. A much less costly hammer mill than the above set of rolls will take Io-inch material and reduce to 2 inches, which probably accounts for the almost universal employment of the latter in- stead of rolls for secondary crushing. Rolls also, in spite of their apparent simplicity, require more than ordinary attention to keep them in good working condition. They must be fed the material to be crushed very uniformly and over the whole sur- face of the roll, the roll faces wear unevenly, the bearings re- quire much lubrication and the springs frequent adjustment. Fig. 45 shows a set of crushing rolls, the rolls themselves being only indicated by the dotted circles. Referring to Fig. 45 which represents the machine without its dust covers and automatic feed: A represents the main frame, I88 - PORTLAND CEMENT having the journals for the stationary rolls cast on in one piece. B is the movable journal which is held in the center of the frame, © r (5) © * * - +- @ * * * * * --! jkE :---. © / - * O Nº/ *. /e t \; a\ \m. [D p ić. ſº | | | * ); ſº p N\ \S2 \ | \ Z § N --i-N-A-- & --->|-fº yº º ! @ v * t º Z & «º- tº Jºãºr A # (ºr tº • * * / g e- * * ſ A===Pºs =e --2------7 /-----, @ A. ; Sº/ | As gº is ! I {A, I Ä 1. Nº.2 : I cº * s * w * —c Fig. 45.—Set of crushing rolls. A, by means of a heavy steel shaft, I, which passes entirely through the frame. The swinging journals are held in place by the tension rods, C, to which are attached nests of powerful coiled springs, D, held in position by the washers M and K. The springs are stiff enough to resist the pressure imposed upon them by ordinary crushing without compression, and yield only under abnormal strains, due to the accidental passage through the rolls of foreign substances, too hard to crush, such as broken drill points, etc. The power is applied to the rolls by means of the pulleys, P. and P. Both rolls are direct driven. In some form of rolls gears are used, and one roll is driven from the other by means of these. These gears, however, are liable to wear out rapidly from the grit, etc., which always finds its way into them. Some- times only one roll is driven. The rolls usually revolve at a sur- face speed of from 600 to I,OOO feet per minute. Rolls are often supplied with automatic feeds to regulate the stream of material passing through them. They are also usually enclosed in a dust-proof casing. CRUSHING MACHINERY 189 The diameter of rolls required to make a given reduction is determined by the maximum size of feed which can be nipped by the rolls without slippage. This size is calculated by the formula X = O.O8 R -- T. Where X is the maximum size feed, R = radius of the roll in inches and T the spread of the roll. The capacity is found from the formula c_TX W X S gºmºsºmeº 1728 Where C = capacity of roll in cubic feet per minute (in the case of limestone I cubic foot = IOO pounds), T = spread, W = width of roll faces in inches and S = peripheral speed in inches per minute. The above gives the theoretical capacity but on account of irregularity in feed, etc., the result should be divided by 4 for the actual capacity. CHAPTER X GRENDING MACHINERY The Ball Mill The ball mill" is of European origin and was used for grinding Portland cement in Germany before its introduction into this Sº º' Wºº fºº := tºº & L. sº Wºº sº tº ſº." I ¥g % --- &.º. &A - §º e & - & ſº. =\sº & º º ſº Ż. ZZZZZZZZZ Ż Ż% %% %% -ºšć%% % % ŻZZAT %% %% 777. %2%%% %%% ºf &zº 2%. % %2% %%%%% ź%%%.3% %2%%%%%%%%2% %%%%%%%:/.2%%2% %2%%%% 3%%%%%% - 22 %%%%%%%%% %2%.4%%%%%%% %%%%%%%%%%22%2%22% %2%%%%%% ź%%%%%%% %%%%%%%%%%%%% %%%%%%% a Ż2ZZZZZZZZZZZZZZZZZZZZZZZZZ2222222 Z * %% %% Fig. 46.-Ball mill, section showing grinding plates and sieves. S. . . . . . - . . º Nº N §§§ §§ s' SS §§§ § § § *N | !. * F. L. Smidth & Company, New York, N. Y.; Allis-Chalmers Mfg. Company, Milwaukee, Wis. GRINDING MACHINERY I9 I country. It is used in connection with a pulverizing mill to pre- pare the material for the latter, the ball mill reducing it to a coarse grit and the pulverizer completing the operation. Ball mills have now been largely replaced in the newer plants by either É i := #3 Š C- Ž 2, 12%22 * :^ 2 2 A. z 2. § Zl'ſ 2× 2.2 - 2%22 ſº %2F%2% Sºº %; * 22222222222%22 iž º %rº Grrrºº 2 2-1 22, 24.4% Žii. 21.1% Ž ZZZZZ:2; lº 2. ? %2%tiº tºº?/2%;% % %:4% %24%;%iº Žziłż%% º %#%iº Žiž%#% Żºłżºłż ż % ºftiº %: %tº %tº ºłºżā% %;ºftº %iº?%5% % % %.1%#% 2% %tºº? ź2% %#%újià % %íž%É% 2/2Z.2%22% % %#%#% É *ść tº jºiáà ż żºłż żºłż ż Żºliº Zºº º: Ż22 2. % %3% Ż%22%22#2%%zž ###% Żºłż º %#ºã %% * à% ** º, º,” * * ºr 2 : zºº. 2: 24-7 - * * * 2 - * % *ś !?!?!?!?! #42% ºz %łłºż à% % %#% %; %3% % %% %31%% % ſ? % Ż % 3% ****{{< % *ś% %2%-44%.52%.22% ãºã% % ºftº %; Žiž2%% 2%2%% .22:17.24:21.2%%% Żºłżºłż%% #4% <º “ & * * ** t #s | th º 3- I -Is |\ | Grit º #4 Flour Fig. 75.—Pfeiffer air separator. The Gayco-Emerick separator" is similar in principle to the Pfeiffer separator, but differs from it somewhat in details of construction. 1 Rubert M. Gay Company, New York, N. Y. 24O PORTLAND CEMENT & Air separators, of both Pfeiffer and Emerick make were given quite an extensive trial in this country some years ago, both placed after the tube mill, and also after the ball mill. In the former case, the grit passed directly from the ball mills through the tube mills and from the latter to the separators. The fine material is sent from the separators to the stock house, and the coarse particles are returned to the tube mill. At the time the first edition of this book was published, American cement manufacturers generally were giving the air separator a trial, in most cases installing the Emerick separator after the tube mill. At that time, some very good reports as to efficiency of the combination were given out both by the separator makers and certain cement manufacturers. In general, how- ever, it may be said that air separators did not prove entirely satisfactory. While some few mills still use them, the majority of those who tried them have now given them up. They have been used to some extent in connection with the Kent mill, where as we have said, the need of an outside screen has made something of this sort necessary. Here they seem to have given as good satisfaction as the screen. In Germany the Pfeiffers are installing separators at a num- ber of works in connection with a short tube mill filled with steel balls. The product from the latter is fed to the separator which takes out the fine material and returns the coarse to the mill for further grinding. The separators are also used to re- ject the coarse material and give a very fine product. As has been said the use of separators to take out the fine par- ticles from the ball mill product and so relieve the tube mill of part of its work is quite general in Germany, but so far has not been tried to any extent in this country. A ball mill provided with 16-mesh screens of No. 3 wire will give a product con- taining between I 5 and 20 per cent of material passing a No. 2OO test screen. The Kominuter on the other hand gives a much larger percentage of fine material, as would be supposed since the material must travel from end to end of the drum before passing out, while in the ball mill it falls through the plates and GRIN DING MACHINERY 24I screens as Soon as ground. A test of the Kominuter product made by the writer gave 25 per cent passing through a No. 200 sieve and 40 per cent through a No. IOO sieve. In this case the screens were 16-mesh and of No. 23 wire. A finer mesh screen on either ball mill or Kominuter will, of course, give a product containing more fine material. This fine material from the Kominuter contains considerable flour as sand briquettes made of the material passing a No. 200 sieve gave 335 pounds for seven days and 447 pounds for twenty-eight days. The material pass- ing the No. IOO sieve gave 267 pounds for seven days and 32O pounds for twenty-eight days. A rather amusing discussion of the separator question ap- peared in one of the engineering magazines, some years ago, the writer of which took the ground that the separators destroy the uniformity of the product and that, for example in a clay-lime- stone mixture, the lighter particles of clay would be blown away from the heavier limestone. The author seems to have over- looked the fact that by pulverizing the limestone particles a little finer they too will be blown out by fans of the separator so that while it may be true that on starting up a new separator the first product will be slightly overclayed, the trouble will be adjusted by the return of the limestone to the grinder for finer pulveriz- ing, after which it will be blown out on its next passage through the separator together with the clay from the new lot of mix fed into the tube mill, the process being a continuous one. This same objection can be raised against ball mills, that the softer particles of clay or cement-rock will be pulverized sooner and drop through the screens of the ball mill before the limestone. In this case also this irregularity adjusts itself and in the same manner. My own personal experience with air separation at the plant of the Edison Portland Cement Co. convinced me that there is nothing against its use on the ground of lack of uni- formity in the product. In both the Fuller-Lehigh and Griffin mills the separation of the finer from the coarser particles is effected by air separation, as fans are used in these mills to blow the fine material through the Screen. 242 PORTLAND CEMENT Capacity of Various Grinders In the descriptions of the various grinding mills and crushers which have been given in the preceeding paragraphs, an effort has been made to show the approximate output of these various ma- chines. These figures have been compiled from results obtained in actual practice and the output of the various machines is the average for long periods of time, but in all cases represents operating time only. An allowance should be made for shut downs occasioned by the need of making repairs, etc. - The condition of the material fed to the machine is an im- portant item in determining the output of the crusher or grinding mill. Various raw materials differ among themselves very /OO JO 80 2O O /O 2O JO 4.O JO 60 2O A3/9/7/7ZZ, S A A' A' A/O (/AP Fig. 76.—Relation between output and fineness of product, 5% x 22 ft. tube mill. greatly as to their hardness and some clinker will grind much easier than others. The amount of moisture in the material also effects very greatly the output of a grinding mill and with GRIN DING MACHINERY 243 crushers the amounts of clay and moisture effect their capacity. With crushers, too, it should be remembered that they are seldom fed continuously, and in most instances, they receive their ma- terial at irregular intervals, as when a car is dumped, etc. The size of the material fed to the mill is also an important factor in determining the output of this—thus a tube mill fed with the product from a ball mill fitted with 14-mesh screens will not pulverize as much as it would if the ball mill had 16-mesh screens, etc. Limestone in the form of slabs will also crush more easily than will limestone in compact form. The fineness of the product is an important item in determining the output of a mill. Fig. 76 illustrates graphically the relation between the output and the fineness of the product ground in a tube mill. With the tube mill, another consideration is important, namely, the weight and nature of the grinding charge. The output will vary almost directly in proportion to the weight of this. Thus, referring to the Tables on page 209, a difference in the weights given in the last column will materially effect the quantity of the output and the horsepower necessary to operate and start the mills. CHAPTER XI BURNING-KILNS AND GENERAL DESCRIPTION OF THE PROCESS Shaft Kiln The first Portland cement made both in Europe and America was burned in upright or dome kilns, in which the raw material is moulded into bricks and charged alternately with layers of coke. The kiln is unloaded at the bottom and, after the clinker is drawn, it is carefully gone over by men or boys and the over- burned and underburned sorted out and rejected. The prop- erly burned clinker only is ground. These kilns are similar to those used for burning lime, and their form is shown in Fig. 77. From their shape they are also called “bottle” kilns. They § Øzzzzzzzzzzzzzas. º Fig. 77.—Dome kiln. are intermittent in action, that is they must be freshly charged for each burning. On this account there is considerable loss due to the necessity of heating up the kiln for each burning. Saylor burned his first Portland cement in these kilns and the first mills in the Lehigh Valley all used this form of kiln. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 245 In Europe where the bricks were made from the more or less plastic mixture of chalk and clay no difficulty was experienced in forming the bricks; in this country, however, the fine crystal- line cement-rock did not have sufficient binding power of itself to make bricks of the strength to withstand the weight of the charge above them in the kilns, and it was found necessary to in- corporate with it a small proportion of Portland cement, to give it binding power. At the American Cement Co.'s plant at Egypt, Fig. 78.—Johnston kiln. Pa., the fine powder was mixed with liquid hydrocarbons to form a stiff paste, which was moulded by compression into bricks. This process saved drying the bricks and promised well, when the in- troduction of water gas raised the price of coal tar, and neces- sitated the abandonment of the scheme.". The first efforts made to improve the “bottle” kiln were natu- rally to use the waste heat in the products of combustion coming off at the mouth of the kiln for drying the bricks. Fig. 78 shows the form of kiln invented in 1872, by Mr. I. C. Johnston, of Greenhithe, England, for this purpose. A is the kiln and B is the drying chamber. The kiln is charged with the bricks which have been dried by the heat of the previous burn. The wet bricks for the next charge are placed at the same time, in the tunnel-shaped * For an excellent description of the process first used in the Lehigh District the reader is referred to an article “Looking Back to the Days of the Mud Floor,” by Charles W. Erdell, in Concrete, Jan. and Feb., 1922, Cement Mill Section, also to “History of The Portland Cement Industry in the U. S.,” by Lesley, Lober and Bartlett. 17 246 PORTLAND CEMENT flue and the hot gases from the kiln pass over and around them, and dry them thoroughly. These kilns are, of course, more sat- isfactory than the ordinary “bottle” kiln, but they still waste much heat. The hot clinker, of course, carries off a great deal, and the cooling of the kiln itself causes additional waste. These kilns were installed in the original mill of the Western Portland Cement Co., Yankton, S. D. The time lost in drawing the clinker, charging the kiln and heating it up, as well as the heat losses, led to the design of con- tinuous kilns, in which the charging is carried on continuously at the top, and the clinker is drawn off from time to time at the bottom. Among the best known of these kilns are the Hoffmann ring kiln, the Schoefer and the Dietsch kilns, the latter two are modifications of the etagen-ofen or kiln of several stories. These kilns are economical of fuel, but require the material to be made into bricks for burning and the clinker to be sorted. The Hoffmann kiln is shown in Fig. 79. It consists of a ring of chambers, built around a large central chimney. Each cham- ber is connected with the chimney by a flue and has a door open- ing outwards. The chambers are also all connected with each other. The bricks are piled up in the chambers, just as they are in a brick kiln, so that the products of combustion can pass around them and between them. The oven is operated as follows: When a chamber is loaded, it is shut off from the suc- ceeding one, which is empty, by a sheet iron door, and connected with the preceding one. The flue leading into the chimney is also opened and the corresponding flue in the preceding cham- ber is closed. By this means, the waste heat from the compart- ment, whose contents is beng burnt, is passed forward, around the ring of compartments, to the one just charged, and thence through the flue and up the chimney. By this means the con- tents of the chambers are gradually heated up, the bricks are dried in the chambers near the flue and then become hotter and hotter as the chamber of combustion is brought nearer. The air for burning is passed through the chambers in which burning is completed and is thereby itself heated and the clinker cooled. It is usual to load one compartment each day, and of course, to BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 247 draw one. The fuel for burning is not loaded in with the bricks, but is fed in from openings at the top of the kiln during burning. The Hoffmann kiln is very economical of fuel, but requires much skilled labor if it is to operate successfully. The bricks have to be carefully piled and the charging requires skilled hands. This kiln was much in use in Germany, but so far as the writer – N s º º N § º tºº s Fig. 79.-Hoffmann ring kiln. knows, was never used in this country for burning Portland Cement. The Dietsch kiln is shown in Fig. 80. It was patented in 1884. It consists of a cooling chamber, H, a burning chamber, F, and a heating chamber, C. The kilns are usually built in pairs, back to 248 PORTLAND CEMENT back. The kiln is loaded through the door, A, and as clinker is drawn out at the bottom, the dry slurry drops down into the heat- ing chamber where it is gradually brought up to a high tempera- ture. From the heating chamber it is raked over into the com- bustion chamber, by introducing a tool in the door, E, and fuel s § % º % ,º# § º 2 | : ; § % s § % § § Fig. 80.-Dietsch kiln. for the burning is mixed with it through the same door. The burning is completed in F. The cold air for combustion is heated by passing through the red hot clinker in H, cooling the latter. Eyes are placed at the lower levels of the combustion chamber, through which bars may be inserted to detach the sintered mass should it hang up, due to overburning. Several Dietsch kilns were introduced into this country in the early days of the in- dustry, one being built for the Buckeye Cement Co., of Belle- fontaine, O. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 249 A modification of the Dietsch kiln perfected in Denmark and known as the Schoefer kiln, was introduced into several of the earlier cement mills and was once used, I believe, by the Glens Falls Portland Cement Co., Glens Falls, N. Y., exclusively, and | à | | º à | Y- ſ | % § º/ Yº, 2. SN % § Fig. 81.—Schoefer kiln. also by the Coplay Cement Co., at one of their mills, at Coplay, Pa., where eleven were once in use. The Schoefer kiln is shown in Fig. 81. It operates upon the same principle as the Dietsch kiln 25O PORTLAND CEMENT and consists of a long vertical flue, the upper part of which serves as a preheating chamber, the middle narrow part as a combustion chamber and the lower section to heat the air. With all these kilns the product has to be sorted and the underburned portions picked out and reburned. The clinker from them also often “dusts”—that is, falls to a powder on cool- ing. This fault is supposed to be caused by changes in the structure of the clinker brought about by too slow cooling of the latter. These shaft kilns require only about 45 pounds of coal per barrel, but the labor cost connected with them is two or three times as great as the fuel cost. The shaft kilns themselves cost in proportion to their output of clinker about twice as much as a rotary kiln. The Rotary Kiln The kilns above described are still used to some extent in Europe—particularly in the smaller and older works. In this country the cost of moulding the raw material into bricks was considerable, and the sorting of the clinker, made necessary by the uneven burning in these kilns, further increased the cost of manufacture. Abroad where labor is much cheaper than it is in this country, these operations could be carried on successfully, so that European cements could be brought to this country and sold in competition with American cements at a good profit. Their reputations were established and they could successfully hold their market against the home manufacturers, who could not afford to cut the price of their cement owing to the high cost of manufacturing due to the expensive labor item, so that all the early American manufacturers were seeking a cheaper method of burning, one that would do away with the employment of so much hand labor and allow them to compete successfully with their foreign rivals. This led them to experiment with the rotary kiln which had been invented in 1873 by F. Ransom, an English engi- neer, but which had never been successfully used in England. In this country the first plant to attempt its use was a small plant BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 251 in Oregon, in 1887, but the attempt proved a failure and the plant itself was shut down, owing to litigation among its stock- holders. About the same time the Atlas Portland Cement Co. began to experiment with Ransom's kiln, first at East Kingston, New York, on wet materials and later with success upon the cement- rock of the Lehigh District, at Northampton, Pa. At first, many difficulties were met with, and it was only after much experi- menting, that they succeeded in making it work Successfully. They found that owing to the shorter time during which the material underwent calcination, it was necessary to grind it much finer than had been necessary with the old bottle-shaped kilns. They also found it necessary to carry the lime a little higher, in their raw material than had been done before, and to moisten it slightly with water. In Ransom's original patent he proposed to heat the kiln by producer gas, but its development in this country was made possible, by the use of crude oil, as a successful method of burning powdered coal had not been perfected at that time. At first these kilns were only 40 feet long, but it was found more economical to lengthen them. Now from 125 to 250 feet is the usual length with 175 as the average at the newer plants. General Description of the Rotary Kiln The rotary kiln (Fig. 82) in its usual form consists of a cylin- der from six to twelve feet in diameter and from 60 to 250 feet long, made of sheet steel and lined with fire brick. This cylinder is supported at a very slight inclination (a few tenths of an inch to the foot) from the horizontal, on two or more steel tires or riding rings which circle the shell and which in turn rest on heavy friction rollers. The cylinder is driven at a speed of from one turn a minute to a turn in two minutes by a girth-gear, situated usually near its upper end and a train of gears. The power may be supplied from a motor or a line shaft, but usually from the former. The upper end of the kiln projects into a brick flue which is surmounted by a brick lined stack. Fig. 82.-Vulcan rotary kilns—Crescent Portland Cement Co. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 253 The material to be burned is fed into the kiln in any regular manner through an inclined cast iron pipe, or by means of a water jacketed horizontal screw conveyor. The feeding device is usually attached to the driving shaft of the kiln, so that when the kiln stops rotating the feed also stops. The material enter- ing the kiln works its way through this, due to the rotation of the cylinder and the inclination, the time required to pass through the apparatus depending on the speed of rotation and the incli- nation. The fully burned cement or “clinker” drops from the lower end of the kiln. The lower end of the kiln is closed by a fire brick hood. This is mounted on rollers so it can be moved away from the kiln when the brick lining of the latter needs to be repaired. The hood is provided with two openings, one for the entrance and support of the fuel burning apparatus and the other for observ- ing the operation, temperature, etc., of the kiln. The bottom of the hood is left partly open. Through this opening the clinker falls out and most of the air for combustion enters. The kiln is heated by a jet of burning fuel introduced at the lower end, the material travelling in the opposite direction from the flame and the product of combustion. The lower end of the kiln is thus also a combustion chamber. Powdered coal is the fuel chifly employed but, in localities where they are as econom- ical as coal, fuel oil and natural gas are used. The temperature of the hottest part of the kiln is about 2,600°F. It is rarely less than 2,400 °F. or more than 2,800° F. The coal consumption varies from 80 pounds to 150 pounds per barrel of clinker, de- pending on the length of the kiln, the heating value of the fuel, whether the dry or wet process is employed and various other manufacturing conditions. Having described the rotary kiln in a general way it may be well before going into the details of its construction and the various features of its operation to give in concise form the re- actions" to be performed by this piece of equipment. * In connection with the chemistry of cement burning the reader is referred to Chapter II on “The Chemical Composition of Cement,” p. 24, et seq. 254 PORTLAND CEMENT Reactions which Occur in the Kiln The reactions which occur in the burning of cement clinker have been quite carefully studied by Rankin' at the United States Geophysical Laboratory. On entering the kiln the mixture is first dried, next the carbonates are decomposed and the sulphur and organic matter burned away. When the hot mixture of lime, silica and alumina enters the clinkering zone, there are first produced those silicates and aluminates of lime which form most readily, in other words at lowest temperatures. These com- pounds are 5CaO.3A1,O, and 2Ca(O.SiO,. These are probably formed in the order given, since the aluminate melts at a lower temperature than the silicate. Neglecting unessential elements we then have in the mix. 5CaO.3A1,O, 2CaC).SiO, CaO The first two compounds next unite in part with the third, lime, to form the tricalcium silicate and the tricalcium aluminate. At the temperature obtained in the ordinary cement kiln, the compound 5CaO.3Al2O3 will completely change to the compound 3CaC.Al2O3. The compound 2CaC).SiO2, however, is not com- pletely converted to the compound 3CaC).SiO2, partly because there is not sufficient lime present to form the latter compound. Our present knowledge of the composition of Portland cement is not sufficient to let us say with certainty as to what propor- tion of the final clinker should be dicalcium silicate and tri- calcium silicate respectively. In most commercial cements, how- ever, the two silicates are present in about equal quantities. We, however, do know that free lime should not be present to any extent and that the reaction in the kiln should be carried to the point where practically all of the free calcium oxide has united with dicalcium silicate to form the tricalcium silicate. Whether it would be of advantage to carry a higher percentage of tri- calcium silicate is a point which must be proved. Originally it was supposed that the larger the amount of tricalcium silicate *Jour. Ind. and Eng. Chem., Vol. VII, page 446, et seq. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 255 present in cement the higher the quality of the latter. Recent investigations, however, attribute to the dicalcium silicate certain desirable qualities. To sum up there are two important series of chemical re- actions to be effected in the kiln : I. The decomposition of the carbonates of lime and magnesia into the oxides of these two metals. 2. The recombination of these oxides with silica and alumina to form the three essential compounds of Portland cement —tricalcium silicate, tricalcium aluminate and dicalcium silicate. To carry out the first series of reactions, namely the breaking up of the carbonates, it is necessary for heat to be supplied to the raw material at the rate of approximately 950 B. t. u. per pound of clinker formed." To carry out the second reaction, the forming of the silicates, however, it is only necessary to heat the materials entering the burning zone up to a temperature of approximately 2,500° and to maintain them at this temperature or at a slightly higher temperature until the three compounds are formed. During this time the materials themselves give off 200 B. t. u. per pound of clinker.” The Four Zones The kiln may be roughly divided into four zones according to the work done in each : In the first zone the mix is being heated to the temperature at which the carbonates decompose. In a wet process plant, the water is being evaporated also in this zone. Various secondary reactions occur here, such as the burning of the sulphur and the organic matter in the mix, both of which give off heat, and the liberation of the combined water and moisture in the raw ma- terials, which reactions take place at comparatively low temper- atureS. * See page 290. * See page 291. 256 PORTLAND CEMENT In the second zone the carbonates are decomposed. This occurs in that part of the kiln which is at a temperature of approximately 1,650° F. In the third zone the material has been freed from its carbon dioxide and is being heated to the temperature necessary for the formation of the aluminates and silicates of lime. In the fourth zone the cement clinker is formed—that is, the silicates and aluminates of lime. This zone is also the combustion chamber for the fuel. It must not be supposed that these zones in the kiln are sepa- rated by any well defined lines. They unquestionably overlap and some of each reaction takes place in the adjacent zones. Generally speaking, in a dry process kiln we may consider 25 per cent of the length of the kiln as used to heat the material up to the point at which the carbon dioxide is driven off; 50 per cent of the kiln is utilized largely to drive off carbon dioxide, while 25 per cent constitutes the clinkering zone. In a wet pro- cess kiln the first zone is a somewhat greater percentage of the length and succeeding zones somewhat smaller percentages of this. Mechanical Details of Construction" The kiln shell is made of open-hearth steel plates. These vary in thickness with the size of the kiln but range generally from one-half to three-fourths inch thick. With small kilns the sections of the shell are one sheet to the round but with large kilns 8 feet and over are two sheets to the round. This forms the strongest and most rigid construction obtainable and is superior to a shell made in sections of three or four long sheets to the section with only a few circumferential joints. All joints are butt type, edge of plate to edge, all edges Squared, and are made with butt-straps which are usually of a trifle heavier plate than the shell itself. These entirely encircle the kiln. Each butt-strap adds strength The longitudinal joints are not in continuous line but are stag- gered, that is on adjacent sections they are on opposite sides. * Much of this information was furnished by the late Mr. J. T. Jeter, Engineer of the Vulcan Iron Works, Wilkes-Barre, Pa. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 257 The riveting must be well done and the rivets fit the holes tightly and be securely driven. The thickness of the plate composing the shell and the thickness and width of the butt-straps must be proportional to the length and diameter of the shell together with the weight of the brick lining and the material being burned. In a short kiln (under 80 feet), the thickness of the plate is usually the same throughout the shell, but in long kilns, the thick- ness of the plate in those portions of the shell at either end which overhang the tires may diminish as it approaches the feed and discharge ends. The greatest bending strain comes directly un- der and midway between each tire. It is well to use in large kilns wider butt-straps here and two or three rows of rivets on each side of the joint. Other joints including longitudinal joints have generally two rows of rivets on each side of the joint. The shell usually has one or more angle iron rings riveted on the inside, one of which is near the discharge end to take up the thrust of the fire brick lining. Where Sil-o-cel is used between the brick and the shell it is also well to rivet an angle lengthwise through the entire length of the kiln. The discharge end of the kiln is usually provided with a cast iron brick retaining ring. This is made in segments and bolted on so the brick can be slipped in place endwise. A cast iron ring known as the “feed-head” is also fastened to the feed end. Most kiln manufacturers have their own ideas as to where the riding rings should be placed, but the following formula" will give the approximate position for almost any make of well de- signed kiln. First tire (from feed end) O.24 X Length Second tire (from feed end) O.84 × Length OT Upper Overhang O.24 X Length Middle Section O.60 × Length Lower Overhang O.I6 X Length Each tire is supported upon a set of four rollers, mounted in pairs on two cradles or rocker arms. These latter automat- 1 Vulcan Iron Works, Wilkes-Barre, Pa. 258 PORTLAND CEMENT ically adjust themselves in such a way that an equal amount of pressure is always imposed upon each rollor. The rollers are removable and can be easily replaced if broken. Fig. 83 shows the method of supporting. The cradles are provided with an adjustment and by cutting them so that one pair of rollers is at Fig. 83.-Method of supporting kiln—tire and bearings. Vulcan Iron Works. a slight angle to the tire the kiln may be made to run up or down on the rollers as desired. By proper adjustment the shell can be made to run true. In order to take up the lateral thrust of the kiln and keep it on its bearings, at least one set of thrust rollers is used. This consists of two horizontal rollers which bear one on each side of the tire. The roller shafts revolve in bearings located on the same base with the rocker arm and supporting rollers. The thrust rollers are placed at the tire nearest the girt-gear. The girt-gear or gear-ring is usually cast in two or more sec- tions in order to permit of replacements. In the case of large cement kilns, a cross-section of the gear is usually in “T” shape. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 259 The gear is bolted to a flange ring also of the “T” section but inverted which in turn is riveted to the shell. The latter is pro- vided with a reinforcing band at this point. The drive gear consists usually of a train of gears having a reduction ratio of from IOO to I to 220 to I, that is for one revo- lution of the kiln the driving shaft makes from IOO to 220 de- pending on the size of the kiln. The final reduction is through a pair of bevel gears, which places the drive shaft at right angles to the kiln. This shaft may be driven from a motor either by direct connection through a speed reducer and flexible couplings or by a belt or silent chain drive. The firing hood is made of angle iron and steel plate and is to be lined with fire brick. The hood is usually mounted on four wheels. These usually rest on rails set in the floor. This per- mits the hood to be rolled entirely away from the end of the kiln when it is desired to repair the lining of the latter, etc. Stack and Dust Chamber The upper end of the kiln extends into the “Dust Chamber.” (See Fig. 84). The latter may be made of brick properly stayed with channel iron buckstays and tie rods, or it may be made of reinforced concrete. If of the latter it should be lined with fire brick and it is well to use a layer of Sil-o-cel blocks or other heat insulator between the fire brick and the concrete. The dust chamber is usually provided with one or more doors through which the dust which collects in the chamber may be removed. These also act as dampers when they are opened. A screw con- veyor is usually run in front of the cleanout doors and the dust is conveyed to the feed boxes or slurry tanks by means of this and an elevator. Where waste heat boilers are used, a seal ring" is employed to prevent air from leaking in where the kiln projects into the dust chamber. Each kiln is usually provided with its own stack and this rests on the dust chamber. Occasionally one stack is used for a bat- 1 See Chapter XV, for description of such a seal. 260 PORTLAND CENIENT tery of kilns but this is not usual. Even where waste heat boilers are used, a stack is generally provided so that the kiln may be operated without the boiler should occasion arise. The stack 24, sezza 22es A*/ºr azºº Aºre ar/r4 Mºre Azra/e/.4%r-Jºz/4's 4× Azeeze'arao'Zºrea/e/e Aa2 carrºzzº res. 22-9.2% zºo-woº, 26.9% " Fig. 84.—Reinforced concrete stack chamber. Designed by author. is always lined with brick. Steel stacks are generally used but if properly designed and built concrete stacks are better as they do not have to be painted. The diameter of a stack for any kiln may be found from the formula." _ B × K T 16.65 W77 d = 13.54 1/ZE -- 4 When E = effective area in square feet, H = height of chimney in feet, B = barrels of cement burned per hour, K = 90 for dry process kilns and I30 for wet process kilns, and d = interior diameter in inches. In steel stacks, an allowance should be made for the fire brick lining, or in other words the stack should be d – 8 inches. 1 Derived from Kent’s formula. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 261 For example, an 8 x 125 foot dry process kiln will produce about 30 barrels per hour. If the stack is made 70 feet high, then 30 × 90 27OO I6.65 V70 139 Allowing 8 inches for brick lining, the stack should be 72 inches. I9.5 Length and Diameter The first rotary cement kilns to be generally employed were 6 feet diameter by 60 to 80 feet long. Thomas A. Edison was the first person in this country to attempt a kiln longer than 80 feet, those at his plant at Stewartsville being 150 feet long. These kilns were put in operation in the fall of Igo3 and proved entirely practical and effected the economy in fuel which Edison had prom- ised they would. His experiment was watched with great inter- est, and, as soon as the success of these longer kilns was known, several of the mills then under construction lengthened their kilns to 80 feet. This plan has since been tried by most of the older mills who extended their kilns to IOO or more feet. All of the mills built since this time have installed kilns longer than IOO feet, some of them being 250 feet long. Kilns are usually made of the same diameter throughout their length, although some of them have the clinkering zone bigger than the rest of the kiln. That is to say the feed end is made of smaller diameter than the discharge end. Sometimes kilns taper through Io to 20 feet at the feed end to a diameter some- what less than the rest of the kiln. The relation between length and diameter, on the one hand and capacity and coal consumption on the other, is pretty well understood and we have had an increase in the size of kilns dur- ing the last two decades with a view chiefly towards obtaining greater outputs per kiln. The greater the diameter of the kiln, the more coal we can burn in it and consequently the greater the output. The theory of the long kiln is that the greater the length of the kiln the more opportunity will be given to the ma- I8 262 PORTLAND CEMENT terials to absorb the heat from the products of combustion, and to a lesser degree, greater time will also be given to effect the combination of the oxides with the silica and alumina to form the calcium aluminates and silicates. The smaller the diameter of the kiln the more intimately are the gases brought in contact with the material both directly and through the medium of the hot walls of the kiln. If a kiln 60 feet in diameter is increased to IOO feet an immediate economy will be effected. If at the same time, however, the diameter of the kiln is also increased very little, if any, saving in fuel will be effected. In fact, if the diameter is increased too much an actual increase in the quantity of fuel required to burn a barrel of cement will be required. - Unfortunately there is a structural objection in making kilns of small diameter and great length and generally in order to ob- tain a kiln which is mechanically satisfactory it is necessary to increase the diameter to some extent as the length is increased. In comparing the performance of two kilns, it is well to con- sider the ratio between the area of the cross-section of the kiln, lining to lining, that is, in a kiln 8 feet in diameter by I25 feet long with a 6-inch lining the ratio between the length and the area as 125 is to 38.5 or 3.2 : I. This gives us a better method of comparing kilns than that ordinarily used. The size kilns most popular are as follows: TABLE XXVII.-SIZES OF ROTARY KILNS COMMONLY EMPLOYED IN CEMENT BURNING. Area of cross- section of burn- Ratio length ing zone, 6” brick to area. 6” Diam. Length lining brick lining 6 60 I9.64 3. I : I 7 IOO 28.27 3.5 : I 8 I25 38.49 3.2 : I 9 I5O 50.27 3.O. : I 9 I75 50.27 3.5 : I 9 2OO 50.27 4.O. : I IO I75 63.62 2.8: I IO 2OO 63.62 3.I . I IO 250 63.62 4.0 . I II 250 78.54 3.2 : I BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 263 By referring to this table it will be seen that considerable difference exists between the length: area ratio in kilns com- monly employed. The writer has observed that the fuel consump- tion of kilns, other things being equal, is in inverse order to this ratio. From this we would expect a kiln 7 x 100 feet to be con- siderably more economical of fuel than one 6 x 60 feet and this has been found to be the case. On the other hand, a kiln 9 x 150 feet will be no more economical of fuel than one 6 x 60 feet and experience shows this also to be true. Longer kilns are usually employed in wet process plants than in dry process plants. The reason for this is that in the former process the upper end of the kiln acts as a dryer. By making the kilns longer the drying can be effected more economically; the increased length allowing the heat in the gases to be utilized more completely in evaporating the water, due to the longer period of contact between the gases and the slurry. Since the chief reason for length in the kiln is to utilize more completely the heat in the gases it is probable that present prac- tice has seen the limit for kilns of the diameters now in use. This is due to the fact that the gases can now be successfully em- ployed for steam generation, and the waste heat boiler offers a more efficient method of utilizing the waste heat in the gases than does the lengthening of the kiln. Present practice would seem to indicate for the dry process a kiln with a length: area ratio of about 3: I, followed by a waste heat boiler. For the wet process a kiln with a slightly higher ratio might be used. Where power can be purchased cheaply or generated hydro- electrically and fuel is high, long kilns will no doubt be employed to advantage. - The length of a two support kiln can not be conveniently made greater than sixteen to eighteen times the diameter. A kiln with two supports is now advocated by most authorities as preferable to one with three or more. It is obviously less difficult to get and keep two supports in line than it is to get three or more. Considerable distortion of the kiln can (and does) occur with- out effecting the carrying mechanism when two supports are em- 264 PORTLAND CEMENT ployed. If there are more than two, however, any warping will result in a transfer of the load from all three supports to only two and indeed momentarily while this transfer is being made to only one. This condition tends to spring the shell and break the supports. Where greater length is desired, the shell can be made in two sections, connected together by a link and driven by the same motor, etc., the upper section usually revolving the lower. Each section is supported by two tires. Several such kilns are now in use. Feeding the Raw Material Into the Kiln Dry material is fed into the kiln by means of an inclined spout or a water-jacketed screw conveyor running from large bins, * º % º # % N º , iſ f % ºft % % % % %º $ffiº. % % / º % º % % % %i * r * sº Fig. 85.-Stock bins and water-jacketed conveyor for feeding raw material into kiln. w BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 265 which are situated usually over or just back of the flue, through the latter, far enough into the kiln to prevent the materials falling into the flue when the kiln revolves. The feeding device is usually attached to the driving gear of the kiln, so that when the latter stops the feed is shut off. Fig. 85 shows an arrangement designed by the Allis-Chalmers Co. for feeding the material into the kiln by means of a water- a º : #####AAAA*2+\ tº VW º ſº NY, º, iſ ſºwy 1/ * * . i ! *— Fig. 86.—Method of feeding raw material into the kiln by means of a spout. jacketed conveyor. This plan is now considered inferior to the method of spouting the material into the kiln. Fig. 86 shows the arrangement generally employed where the latter plan for in- troducing the material into the kiln is followed. It will be noticed that the bins are located above the kilns. This saves room. The long conveyor leading from the bins to the hopper spout insures a regular feed of material to the kiln. The stack is set to one side of the center line of the kiln which gives the dust a chance to settle. Another arrangement of the stack is shown in Fig. 84. The spout is of cast iron pipe. 266 PORTLAND CEMENT Slurry is usually fed in by means of what is known as a “Ferris Wheel” feeder. Referring to Fig. 87 it will be seen that this consists of a series of buckets, a, similar to those used on an elevator, fastened to a wheel, b, the wheel being rotated by a pair of gears, c, which in turn are driven from the kiln shaft or Fig. 87–"Ferris wheel” for feeding slurry to kiln—Allis-Chalmers Mfg. Co. by a variable speed motor. The slurry is kept at a constant level in the tank, d, by means of a pump and an overflow pipe return- ing to the kiln feed basin. Occasionally the slurry is kept in a kiln feed basin located above the feeder and is run from the BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 267 former into the latter by gravity. In this case, the level of slurry in the tank, d, is maintained by means of a float valve. The buckets, a, dipping in the tank, d, as the wheel revolves, fill with slurry and elevating this to the point where they are turned over, discharge the slurry into the hopper, e, which leads to the kiln through the pipe, f. The amount of slurry fed may be varied by altering the speed of rotation of the wheel, by removing some of the buckets or even by altering the angle at which these are placed on the wheel making them pick up less slurry as they leave the tank. Another form of feeder employed occasionally consists of a needle valve operated by a wire cable so that it can be operated from the front end of the kiln. Still another type of feeder con- sists of a spiral pipe somewhat similar to the sampler for cement described in the section of this book on cement testing.” In the writer’s opinion these feeders are not so satisfactory as the “Ferris Wheel” described previously. In both the wet and the dry process, what is required of the feeder is that it shall deliver the material to the kiln in a regular amount. The slurry feeders all do this very nicely. With the screw feeders, however, used for dry material, the rate of feed is often irregular and sometimes the kiln is flooded with a rush of material and at others the material arches in the bins over the screw feeder and the bin sides must be rapped to break these arches. Flooding usually occurs when the bins are nearly empty, while “arching” may be avoided by making the hopper bottoms of the bins with at least one straight side and better with three straight sides. The screw feeder should be as long as a con- venient location of the bins will allow. Kiln Lining The rotary kiln as has been said is lined with fire brick. This brick should be of the most refractory kind. I believe at one time a magnesia brick was used but now a good quality fire brick is considered as satisfactory and more economical than the ex- * See Chapter XVII. 268 - PORTLAND CEMENT pensive magnesia lining. A good fire clay brick should analyze within these limits: Pe1 cent Silica, SiO, 45.0 to 50.O Alumina, Al2O, 43.0 to 48.0 Iron, Fe2O3 Less than 3.0 Magnesia, MgO Less than 0.5 Lime, CaO Less than 0.5 It should also be free from iron and alkalies, since these cause fusibility. A fire brick lining should last, if carefully attended to, at least 9 to I2 months and sometimes they go even longer than this. At the end of this time the bricks are eaten away nearly to the iron shell and it becomes necessary to cut away the brick from the first 20 or 30 feet of the kiln and reline this portion. The upper part of the kiln lining, or that portion of it which merely comes in contact with the powdered raw material before sintering commences, usually lasts indefinitely. In kilns work- ing on wet materials it is sometimes the practice to leave the up- per 20 or 25 feet of the kiln unlined since this part of the kiln is kept fairly cool by the wet slurry. Sometimes channel irons or Z bars are fastened to the sides of the kiln to form shelves for drying the material. A bauxite or alumina brick, manufactured by the Laclede- Christy Clay Products Co., St. Louis, Mo., has been extensively used in the west and middle west for lining Portland cement kilns and it is, in that section at least, considered superior to the silica brick. In place of fire brick, a concrete or clinker brick made from Portland cement clinker and Portland cement is sometimes used. The clinker should be screened and that portion of it passing a one-fourth inch screen used. This is mixed with Portland cement in the proportions of thirty parts clinker to twelve parts cement and made into a medium wet concrete. This is then rammed into wooden forms of the proper size and shape and allowed to harden. The bricks are ready for use several days after making. One large mill in the Lehigh District used these bricks exclusively at one time for lining the clinkering zone of their kilns, and found them BURNING-KII. NS AND GENERAL DESCRIPTION OF PROCESS 269 very satisfactory. Under conditions in this region, however, they do not seem to be any cheaper than fire brick. They also do not stand up well where the kiln is not run continuously. The fire bricks used to line the lower end of the kiln are usually from 6 to 9 inches thick, and those for lining the upper end, from 4 to 6 inches. These bricks are keyed to fit the circle of the kiln. In the old upright kilns, it was the usual practice to coat the lining of the kiln with a “grout” of slurry, so that it was natural for something of the same sort to be tried with the rotary kiln. It was soon found that a certain amount of the raw material could be made to adhere to the fire brick lining of the kiln, thereby protecting the bricks from the scorifying action of the caustic clinker. It is now the practice to burn entirely on coated bricks. When this coating falls off, usually only in patches, the kiln is heated up above the normal temperature, raw material is scraped down over the bare spot and pounded into place with a heavy iron bar. Water is then usually run on the “patch” to harden it. In some mills salt is used on the bare spot, as it is supposed to make the patch hold better. The writer has never seen any ad- vantage in its use, however. The fire brick are held in the kiln by a heavy angle iron run- ning around both ends of the kiln. This also helps to stiffen the kiln shell. The ordinary kiln brick is 9 inches long at the end nearest the shell, and 4 inches wide or three circles of brick per linear foot of kiln. The number of brick required to line a kiln, etc., may be found from Table XXIII. No allowance has been made in this table for breakage and other loss. Mr. W. S. Landis, formerly of the metallurgical department of Lehigh University but now of the American Cyanamid Co., first called general attention to the large loss of heat due to radiation from the kiln shell and suggested placing a coating of some efficient non-conductor of heat between the shell and the fire brick. The writer many years ago tried placing asbestos board between the shell and brick. He found then that while 27O PORTLAND CEMENT radiation losses were reduced, the life of the lining was decreased, partly because the asbestos board flaked under the pressure of the brick and allowed the latter to loosen up, but more particu- larly because the asbestos confined the heat to the lining and caused the latter to burn out in the clinkering zone more quickly than it would if it was allowed to dissipate its heat by radiation. The radiation losses from a cement kiln shell is shown in Fig. 92,” page 3O4. In this diagram the vertical lines show the temperature of the shell and the horizontal lines the loss of heat in the British thermal units (B. t. u.) per hour per square foot of kiln surface. In making use of this data, the kiln is usually divided into ten or more sections and the temperature of each is taken and the surface of each calculated. The heat lost in each section is then the product of its surface area and the heat lost at the determined temperature per square foot as shown in Darling's table. The heat lost by radiation from the entire kiln is, of course, the sum of the heat lost by all the sections. When kilns are exposed to the weather as is now sometimes the prac- tice, the loss shown by Darling's curve should be multiplied by I.3 for wind and by I.7 for rain and wind. It is now considered good practice to place a layer of 3-inch Sil-o-cel blocks between the fire brick and the shell throughout the kiln with the exception of the twenty-five feet nearest the dis- charge end. If the Sil-o-cel is used here the lining is destroyed rapidly. Cooling of this portion of the lining by radiation ap- pears to be necessary if the ordinary kiln brick are to last. The Sil-o-cel are laid flat and great care must be used to get both the Sil-o-cel and the fire brick in tight. The Sil-o-cel lining probably reduces the radiation losses to from 25 to 50 per cent of what they would be without such heat insulation. It also in- creases the temperature of the waste gases from 200° to 300° F. above what they are without it. This is important where waste heat boilers are employed as it materially increases the amount of steam which can be obtained from the waste gases. The quantity of Sil-o-cel blocks required to line a kiln may be cal- culated from Table XXIII. * C. R. Darling, Engineering (London), March 14, 1919, p. 643. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 27I The lining must be carefully put in with tight joints. The best method is to lay a ring at a time, without mortar in the joints, wedging each ring securely. After the bricks are in place they are slushed over with a thin grout of cement and water. Continuous kiln operation, with constant load and temperature conditions, and material to be burned of uniform composition, tend to lengthen the life of the lining. Shut downs, variable feed, material first high in lime and then low, cause a loss of coating and consequently damage to the brick; as each time the coating falls it carries away with it some of the surface of the fire brick. TABLE XXIII-DIMENSIONS AND NUMBER OF STANDARD ROTARY KILN BLOCKS REQUIRED TO LINE ROTARY KILNS OF VARIOUS DIAMETERS S--is A 7 Dimensions of and number of blocks for Dimensions of 2––——kiln and diameter shown below———— standard blocks 6’ O’’ 6’ 6” 7 o’ 7' 6" 8’ O’’ o' o' Io’ O’’ Standard 6" Block A—Dimension in inches 6 B—Dimension in inches Q Q 9 9 Q Q Q C–Dimension in inches 7.5Co 7.625 7.719 7,813 7.875 8.000 8. I25 D–Dimension in inches 4 4 4 4 4 72 60 6 6 6 6 6 6 4 4 Diam. outside circle, ins. 78 84 QO 96 IOS I2O Diam. inside circle, ins. 66 72 78 84 96 IOS Standard 9” Block A—Dimension in inches B—Dimension in inches Q 9 9 C—Dimension in inches .938 7.063 7.188 7.313 7.500 7.656 D–Dimension in inches 4 9 9 9 Q Q 6 g tº º tº sº º 4 4 4 4 4 Diam. outside circle, ins. 72 78 84 QO 96 IoS I2O 60 72 27 3I 9 Q º 750 : Diam. inside circle, ins. 54 66 78 90 IO2 Numger of block to circle 25 29 33 38 42 Number of block to line One linear foot of kiln 75 8I 87 93 99 II4 I26 Number of block to line One linear foot of kiln where 3" Sil-o-cel block is used between kiln shell and fire brick 69 75 8I 87 93 IoS I2O Number of 4% x 9 x 3 in. Sił-o-cel blocks required for insulation per linear foot of kiln when laid flat 67 73 78 84 90 IO2 II4 272 PORTLAND CEMENT Speed of Rotation The kilns are rotated in different mills at different speeds, varying from one turn in one-half a minute to one turn in three. The average, however, is from a turn in a minute to one in two minutes. The speed varies somewhat with the angle at which the kiln is pitched, the greater the pitch the slower the speed, as the steeper the angle of the kiln the greater distance the material will travel with each revolution. Usually the speed can be regulated by some arrangement of an automatic speeder, such as the Reeves, the Mosser speeder or, where run from separate motors, by a controller. In some mills all the kilns are on one shaft and consequently of fixed speed. There are some points in favor of each. Where the speed can be regulated by the burner, he has better control of the burning, but there is sometimes a tendency on his part, where the foreman is lax, to cut down the speed and consequently the capacity of the kiln in order to make his own work easier. Where there is a likelihood of the mix not being regular, speeders should always be put in, as it is easier to control the burning of such material by the kiln speed than by the coal feed. With line shaft, the kilns are arranged with some sort of jaw clutch, so they can be cut out for patching, relining, etc. It is also necessary occasion- ally to shut them down for “heat” if the mixture burns hard, or the raw material is fed into the kiln irregularly, causing it to be- come overloaded. As we have said, the raw material fed into the kiln should be controlled by the speed of the latter and be shut off when the kiln stops. Most of the newer mills are installing individual motor drives for their kilns, employing for this purpose slow variable speed motors. The power requirements to operate kilns of various sizes is about as follows: 6 x 60 ft., I to 3 R. P. M., 5 to 7 H. P. 7 x 80 ft., I to 2 R. P. M., 8 to 12 H. P. 8 x 125 ft., 34 to 19% R. P. M., I5 to 20 H. P. 9 x 150 ft., 3% to 34 R. P. M., 22 to 30 H. P. Io x 170 ft., 94 to Ø R. P. M., 30 to 40 H. P. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 273 A great deal has been said about the proper speed for a kiln to revolve, no two authorities agreeing, and the writer has come to the conclusion from personal experience that this will depend largely upon the material, how it burns, etc. If the kiln is run at a high speed, the material travels through in a thin stream and remains in the kiln but a short time. On the other hand, it is being continually turned over and exposed to the hot kiln gases and kiln lining, so that while the time of heating is shorter the chances of absorbing heat are greater. Inclination of the Kilm The inclination of the kiln affects, of course, the rapidity with which the material travels through the former, other things be- ing equal. The speed with which the material travels is also affected by the rate at which the kiln is rotated. If two kilns were inclined, one say at an inclination of three-fourth of an inch to the foot and the other one-half of an inch to the foot, the ma- terial could be made to travel through both at practically the same rate of speed by revolving the latter much faster than the former. On the other hand in the case of the more level pitch the kiln would carry a much larger body of material and consequently the material would remain in the kiln for a longer time. This point is worth considering where trouble is experienced with the sound- ness of the cement, as by increasing the time in the kiln a more effective combination of the lime with the dicalcium silicate can be effected. The inclination of the kiln in practice usually gets less as the kiln increases in diameter. Kilns 6 and 7 feet in diameter are usually pitched at about three-fourth inch to the foot, 8-foot kilns at five-eighth inch to the foot and 9-foot kilns and larger at one- half inch to the foot. Length of the Clinkering Zone The length of the clinkering zone is usually from 15 to 20 feet. A ring usually forms at the upper (feed end) of this and below this ring the formation of the clinker takes place. The 274 PORTLAND CEMENT fire brick here are usually coated with from 3 to 5 inches of sintered material as this is the portion of the lining most sub- ject to destruction. It is in this section of the kiln that the tri- calcium silicate and aluminate are formed. The clinkering zone is also the combustion chamber. Here the fuel is burned, and the length of the clinkering zone is de- termined by the length of the flame. Theoretically the length of the clinkering zone is effected by the fineness of the coal or the efficiency with which oil is atomized, the thoroughness with which the air for combustion is mixed with the fuel, percentage of volatile matter in the coal, etc. Practically the length of the zone is a matter of draft. This is usually regulated by the doors at the base of the stack chamber; or if waste heat boilers are employed, the fan on the latter. If the doors at the base of the stack are opened, this acts as a damper and crowds the clinkering zone nearer to the front of the kiln. Slowing down the draft fan if this is employed has a similar effect. Capacity of Cement Kilns Most tables showing the capacities of cement kilns have been compiled from results obtained in practice with little or no at- tempt to reconcile the various figures so given. Manifestly the only way to determine the relative output of kilns is to compare them when working under exactly similar conditions. It is, of course, difficult to compare more than a few sizes of kilns in any one plant, and so it is necessary to collect data from many plants in order to cover the wide range in size of cement kilns. It is evident that burning conditions vary widely in different plants and hence this data to be satisfactory must be reconciled to some standard condition. The most convenient form in which to place the result of this study of kiln capacity so it can be used for reference is in the form of an algebraic formula, the solution of which will express the average approximate capacity of a cement kiln of a given size. In using any formula, it should be borne in mind that local conditions influence greatly the capacity BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 275 and that any figures obtained are general and may not apply closely to any given case. Various attempts have been made at different times to devise a formula for determining the capacity of the rotary cement kiln. Engineers of the Portland Cement Association use the follow- ing formula - c £4. 4 When P = the circumference taken inside the lining, L = length in feet and C = capacity in barrels per twenty-four hours. Eckel in his work' gives the following formula for dry process kilns. L © C = D2 × +, maximum Z. tº º C = D2 × I, , minimum When C = capacity in barrels per day, D = diameter in feet and L = length in feet. With this formula there is quite a di- vergence between the two extremes and the upper limit is far higher in the case of large kilns than any capacities actually met with in practice. The writer has kept careful notes on the performance of kilns in all parts of the country and after careful study of this data devised a formula which he and his associates have used for many years in their work. The figures obtained by it check quite closely with average practice except in the case of very large kilns, II and I2 feet in diameter. It is doubtful, however, if these large kilns have been pushed to their limit in cases which have come under the writer’s observation. The formula is purely em- pirical and is as follows: X = (34 L + I5) × 4 × 0.17. When C = Capacity in barrels per day of twenty-four hours, L = length of kiln in feet and A = area cross-section excluding Diameter — I 2 ) X 3.1416. + Limes, Cement and Plaster, by Edwin C. Eckel. lining or ( 276 PORTLAND CEMENT Table XXIV showing the capacity of rotary kilns has been cal- culated from this formula. All of the above formulas refer to dry process kilns. Wet process kilns have from 60 to 75 per cent of the capacity of dry process kilns. TABLE XXIV.-CAPACITIES OF ROTARY CEMENT KILNS Dry Process Length—feet —, Diam. &T 6o 8O IOO I IO I25 I5O 2OO 6’—O'' 2OO 250 3OO 325 360 * * 6'-6" 24O 3OO 360 390 440 525 - 7'-o" 28O 360 43O 47O 525 600 - 7–6" - 420 5OO 550 600 725 925 8'—O” - 490 575 625 7OO 825 I,075 8"–6” - 550 675 725 825 950 I,225 9'—o" - sm- 775 825 925 I, IOO I,400 Io'—o" - *m. 975 I,050 I, IZ5 I,375 I,775 Wet Process r— Length—feet Diam. 60 8O IOO I 25 ISO 2OO 250 6’—o" I-40 I75 2IO 25O -- - * 6’—6" I70 2 IO 250 3IO 370 --- -- 7’—o” 2OO 250 300 37O 420 --- *-* 7–6" --- 295 350 420 5IO - * 8’—O" -- - 400 490 58o 755 *mº 8’ 6” *ms. - - 58o 665 855 - 9'—o" --- ºmºmºmº - ºmº 770 980 I,22O Io'—o" - - - --- 96.O I,245 I,540 The capacity of a cement kiln is influenced by many factors among which are (I) the skill of the operator, (2) the fuel and method of burning, (3) the draft, (4) the chemical composition of the material, (5) the moisture in this, particularly in the case of slurry, (6) the fineness of the material, and (7) the degree of burning, etc. Fuel Requirements The fuel requirements of the rotary kiln vary among other things with (1) the moisture in the materials burned, (2) the chemical composition and fineness of the raw material, (3) the length and diameter of the kiln, (4) the skill of the operator, (5) the heating value of the fuel and its nature, (6) radiation losses BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 277 from shell, etc. In general it may be said that the fuel required will increase with the moisture in the slurry—dry materials re- quiring much less fuel than slurry. The fuel requirements also decrease with the length of the kiln provided the diameter remains the same. Conversely if the diameter increases and the length remains constant the more fuel is needed. Some materials re- quire more fuel than others, due to chemical characteristics. Material high in lime is harder to burn than material low in lime. The fuel requirements are in inverse proportion to the heating value of the fuel; 40 per cent more coal with a heating value of Io,000 B. t. u. per pound would be required than of one with a thermal value of I4,OOO B. t. u., etc. Table XXV gives the fuel consumption of various kilns. The figures are average results over a period of time. They include the coal used for heating the kiln after patching and the usual shut downs and delays met with in every mill. The figures in the tables are for coal contain- ing I4,OOO B. t. u. per pound and oil with I4O,OOO B. t. u. per gal- lon. TABLE XXV.--FUEL Consu MPTION IN CEMENT BURNING 2–––Dry process———, ,--Wet process, 35% water—— Coal per Oil per Coal per Oil per Kill! barrel, barrel, barrel, barrel, dimensions lbs. gals. lbs. gals. 6 x 60 IIO II.O I40 I4.0 6 x IOO 88 8.8 II8 II.8 7 x IOO 94 9.4 I24 I2.4 8 x 125 97 9.7 I27 I2.7 Q X I5O IOO IO.O I3O I3 O 9 x I75 04 9.4 I24 I2.4 9 x 200 88 8.8 II8 . II.8 IO x I75 I O2 IO.2 I32 I3.2 IO X 200 QQ 9.9 I29 I2.9 IO X 25O 88 8.8 II8 II.8 II X 250 IOO IO.O I30 I3.O Labor The operation of Portland cement burning is essentially a skilled process and a skilled workman is required to attend it. He must know just how the clinker should be burned and have a good eye for “heat,” so that he can tell when his kilns are hot enough 19 278 PORTLAND CEMENT to clinker the raw material properly. The placing of the patches and the coating of a freshly lined kiln also require some skill. To be economically run the kilns should be kept at as nearly a uni- form temperature as the irregularity of the feeding devise will permit. Kilns run spasmodically, first hot, then cold, require much coal, turn out poorly burned clinker, and require much patching. Since patching requires the stopping of the kiln the output is also cut down. The burner should also be a sufficiently good mechanic to look after the mechanical part of his kilns. One burner usually looks after two to four kilns. The operations of the interior of the kiln are watched through darkened glasses. No efforts have been made to use pyrometers since the temperature must change with the refractoriness of the material, etc., and the heat is en- tirely judged by the incandescence of the interior of the kiln and the clinker as observed through these glasses. The method of injecting the fuel into the kiln and the prepara- tion of the powdered coal are described in the next chapter. Degree of Burning Properly burned Portland cement clinker is greenish black in color, of a vitreous luster and usually when just cooled sparkles with little bright glistening specks. It forms in lumps from the size of a walnut down, with here and there a larger lump. Un- derburned clinker, whether this is due to a low temperature in the kilns or an overlimed mixture lacks the vitreous luster and the glistening specks. The failure to sparkle, however, is not nec- essarily characteristic of underburned clinker, though the sparkle itself is never seen in underburned clinker, as the rate of cooling etc., effects this somewhat. If much underburned, the clinker is brown, or has soft brown or yellow centers. Low limed clinker unless very carefully burned, usually has brown centers also, but is hard and glassy. The two should not be mistaken; the clinker with soft brown centers is underburned that with hard brown centers is underlimed. BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 279 Overburned clinker shows the same characteristic as under- limed, the hard brown centers. I have never seen that the quality of cement was injured any by overburning, unless the material was low in lime when the resulting cement was apt to be “quick-setting,” but the proper degree of sintering is far enough to carry the process and to burn any harder is not only a waste of coal for burning, but also for grinding since the hard brown slag like clinker is very hard to pulverize. Properly burned clinker should have a specific gravity of at least 3.15 and when rapidly pulverized and ignited show a loss of under I per cent; although neither of these tests is of any value in determining the thoroughness of burning, when applied to ground cement. CHAPTER XII BURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS Chemical Changes Undergone in Burning The chemical changes undergone during burning may be Summed up as follows: All of the water originally present whether free, hydroscopic or combined is driven off and the carbon and organic matter in the raw material are also burned away. The carbon dioxide, existing in the raw material in combination with the lime and magnesia as carbonate of these elements, is practically entirely expelled. Even the little which exists in freshly ground, well burned cement is probably most of it ab- sorbed from the air, since cement very rapidly absorbs carbon dioxide and water. The iron, the greater part of which is usually present in clay and cement-rock in the ferrous condition is almost completely oxidized. - The sulphur whether present in the raw material as sulphide, sulphate or in combination with organic matter is much of it ex- pelled and the remainder is usually all of it, except a mere trace, found present as calcium sulphate. This is to be expected since calcium sulphate gives off its sulphuric acid, when heated with silica. Indeed, I believe it has been proposed to make cement by heating together a mixture of clay and gypsum, the sulphuric anhydride driven off during the process being caught and con- densed with water and sold for sulphuric acid. It has also been supposed that the sulphur of the coal entered the clinker. This is erroneous, since the amount of gas slack necessary to burn IOO pounds of clinker will contain sufficient sulphur to make the clinker analyze at least I.5 per cent SOs if it were all absorbed, while as a matter of fact clinker seldom analyzes anywhere near this amount. The alkalies, potash and soda are partly expelled in the kiln. In experiments made by the writer, which will be detailed later, BURNING-KILNS AND GENERAL DESCRIPTION OF PROCESS 281 the losses of soda amounted to from 19 to 28 per cent, while those of potash ran from 46 to 52 per cent.” This loss of alkali is also shown by analysis of the deposit col- lecting on the walls of the kiln stack, a sample of which con- tained: Per cent Soda I.38 Potash 6.83 Influence of Coal Ash on Chemical Composition of Cement In a paper read by the author before the Association of Port- land Cement Manufacturers, the results of an experiment to de- termine the losses actually occurring in the rotary kiln were given. This experiment consisted in sampling carefully the raw material going into the kiln, the clinker coming out and the coal used for burning. Three separate tests were made and the re- sults compared. As the result of this experiment, it was found that the silica, ferric oxide and alumina are increased by ap- proximately one-half the coal ash. Undoubtedly, in the rotary kiln much of the ash is carried out with the gases by the strong draft of the kiln. This we would expect when we consider that the particles of ash are of the same volume as the particles of coal, and yet only one-tenth their weight, for when the coal burns it leaves its ash in the form of a skeleton. These particles of ash are already in motion and are in the full draft. The gases have a velocity of at least 2,OOO feet per minute, which is quite enough to carry the particles up the chimney. It seems probable in view of these facts that what ash does contaminate the clinker, comes from the impinging of the flame upon the material in the kiln. The ash strikes the clinker and its velocity is stopped by the im- pact and it either falls among the clinkers or it sticks to the red- hot, semi-pasty mass. It is probable that the coarser the coal the more ash will contaminate the clinker. It is an important point where this ash falls. If it falls before the raw material begins to ball up, 24 pounds extra limestone should be added to every 600 pounds of raw material to take care of the ash, as in this case, * See page 317. 282 PORTLAND CEMENT it would form Portland cement clinker. If, however, it falls on the clinker after it forms into balls, this quantity should be very much less, if any at all, as its action would then most likely be merely on the surface of the clinker to form a slag and not a true Portland cement clinker. The above changes are simply those which we can detect by comparative chemical analysis of the raw material and the clinker. None of them is sufficient of itself to form Portland cement. All the carbon dioxide can be driven off the raw material and still Portland cement clinker will not be the result. For this it is necessary that the lime combine with the silica and the alumina, and in order for this combination to take place it is necessary for the material to be heated to a considerably higher temperature than that necessary to drive off carbon dioxide. If a small sample of raw material is heated to a constant weight over an ordinary laboratory blast lamp, very little, if any, clinkering will take place, except, perhaps, on the under side of the sample next to the crucible, yet all the carbon dioxide will have been driven off. The various opinions as to the constitution of Portland cement clinker have been fully detailed in Chapter II on the chemical composition of Portland cement, and it is unnecessary here to repeat them. Wm. B. Newberry made an experiment of great interest as tending to throw some light on the question of what takes place during the passage of the raw material through the kiln. During a temporary shutdown of one of the rotaries at the Dexter Portland Cement Co., at Nazareth, Pa., the kiln was al- lowed to cool down without being emptied and samples of the charge were then taken from every four feet throughout the length of the kiln. After careful examination these samples were analyzed, the results showing the changes which take place in the composition at successive stages of the burning. The raw material used was cement-rock without the addition of any other material. The first sample was of unburned raw material taken at the point of entering the kiln and the last (No. 14) was the finished clinker 1 Cement and Engineering News, Vol. XII, No. 5. See also Soper, Amer. Soc. Mech. Engrs., 1910. BURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS 283 & within four feet of the discharge at the lower end. Fig. 88 shows graphically the chemical charges which occurred in this experiment. Dia. Sta.1 60 Ft. End Length of Kiln 70 5 0. 4 0 | Fig. 88.—Chemical changes in a 6 ft. by 60 ft. rotary kiln. The physical change from raw stone to clinker is shown by the characteristics of the different samples given below: “Nos. 1, 2 and 3, blue gray powder, changing to buff between 3 and 4. “Nos. 4, 5 and 6, yellowish buff powder, commencing in 6 to ball up into small lumps. “Nos. 7, 8, 9 and Io, yellow to brown balls like marbles; soft, easily crushed in the fingers, becoming darker and harder toward Io. “No. II, lumps quite hard and brown, traces of sintering on surface, softer inside. 284 PORTLAND CEMENT “No. 12, lumps brown and partly sintered, beginning to lose regular rounded forms hard. “No. 13, larger lumps, irregular and rough, almost black. Very notice- able difference between I2 and 13, latter is like brownish clinker and is burnt throughout. “No. 14, smaller and more rounded lumps, black, has all the appear- ance of finished clinker, in fact, no further change is seen as it leaves the rotary.” Relation Between Time, Temperature and Fineness In the formation of clinker, the materials are never actually melted and the combination is brought about by the intimate con- tact between surfaces. This is affected by three things, the amount of surface exposed, or in other words, the fineness of the raw materials, temperature to which the material is heated and the time during which it is maintained at this temperature. These three conditions are intimately associated as has been pointed out previously. With very finely ground material the combination will take place at a lower temperature or with less heating than where materials are coarsely ground. With materials of the same fineness the combination will take place more rapidly where the temperature is higher, conversely the time required to bring about the combination will be the longest where the temperature is lowest or the grinding insufficient. Attention has been called previously to the expression of this law in the form of a mathematical equation. In which D represents time, T temperature, F fineness and C a consonant, namely, clinker. If we increase any one of the three variables D, T and F it will decrease one or both of the other two, thus by increasing the time in the kiln we decrease the tempera- ture necessary to clinker or the fineness, while if we grind the materials more finely we decrease either the temperature or the length of time in the kiln and may thus increase the output of the kiln or decrease the fuel required per barrel. This equation does not take care of the chemical composition of the mix and is intended to express rather the physical than the chemical relations \ N \ scIENTIFIC CONSIDERATION OF THE PROCESS 285 BURNING in burning. It also must be understood that the materials must be heated to the temperature, at which clinker will form. It has been both practically and theoretically demonstrated that this condition does exist in cement burning. There is a very practical point in connection with the tempera- ture of the kiln which must be considered, and that is the ability of the lining to stand the temperature. As a matter of fact, the lining not only has to stand the º but also the chemical action which occurs between the line and the aluminates from which fire brick is made. This affinity is marked at high tem- peratures. This brings up the point of the possibility of using another lining for the kiln rather than the ordinary, high alumina clay brick. In the early days of the industry, the rotary kilns were lined with magnesia brick. This lining was succeeded by the present lining of high alumina clay brick. The question naturally presents itself as to whether any better results would be ob- tained by the use of other brick, such for example as carborun- dum brick. Great improvements have been made in the manu- facture of fire brick of a very high degree of refractoriness. It is possible that cement manufacturers may be overlooking some- thing and that better results might be obtained than is now pos- sible by the use of some of these materials. This is a point which, however, can only be determined by experimenting. Temperature of Burning The temperature of the clinkering zone of the cement kiln as determined by optical pyrometers is generally found to be be- tween 2,525° F. and 2,650° F. with about 2,600°F. as an aver- age. In looking over quite a wide range of temperature mea- surements made by the author and covering both wet and dry process kilns, various raw materials, and kilns of sizes ranging from 6 x 60 feet to 9 x 200 feet the actual temperatures of the clinkering zone when the kiln was operating normally and turning out a well burned product were found to range from 2,545 to 2,640 with 2,585 as the average. The size of the kiln made no 286 PORTLAND CEMENT difference in the temperature nor did the raw materials. Soper measured the temperature 7 x 100 feet by means of a Le Cha e process employed or various points in a kiln ier pyrometer by inserting S Discharge of Kiln End Temperatures of Gases Sta.3 Stå.2 Sta.I / o Aſ %,” 1090; .r 2496.9 1648 33-4 5040” 8344" 100 | Curve-2-#axiratim Temperatures of Materials Calculated from Gas Temperatures Note:- Temp's at Sta's B, 1, 12 Actually Observed Fig. 89.--Temperature of gases and Materials in a 7 ft. by Ioo ft. rotary kiln, wet process. the porcelain tubes containing the elements through holes pre- viously drilled through the kiln shell and fire brick lining. This 1 Paper read before Western Society of Engineers, Nov. 15, 1905. BURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS 287 kiln was working upon wet materials. Fig. 89 shows the tempera- ture of the gases at various points in the kiln as ascertained in this test. Campbelli made some interesting experiments on the relation between the chemical composition, temperature, time and fine- ness of the raw material on the burning of cement. He found that the lower the lime: silica ratio the more easily the material could be burned, that the time in the kiln affected the temperature necessary and that the finer the material was ground the lower the temperature necessary for properly burning. Campbell's ex- periments were made in a small laboratory kiln” and the tem- peratures he employed were somewhat higher than those met with in practice, but they served to confirm experimentally opinions previously held by cement manufacturers. While there is no definite information to that effect it is gen- erally accepted as a fact that the presence of alkalies lower the temperature at which clinkering takes place. In a small furnace which the writer had he could never quite get the temperature up to the point for a thorough burning of the Lehigh cement-rock limestone mixtures, but if the small cubes of powdered material were made up with water containing enough sodium carbon- ate to make the mixture analyze about I.5 per cent soda, the clinkering could easily be accomplished. Iron always plays an important part in aiding the clinkering. The white Portland cements at present on the market are all hard to burn. Fluorspar or calcium fluoride, Cafe, has also the effect of lowering the clinkering temperature and has been used, commercially, for that purpose, I believe. Thermo–Chemistry of Burning Referring to the two major operations performed in the kiln, namely (I) the decomposition of the carbonates of calcium and magnesium into the oxides of these metals, lime and magnesia, and (2) the recombination of these oxides with silica and alumina * J. Am. Chem. Soc., XXIV, p. 969, and XXV, p. 1 Io9. * J. A. m. Chem. Soc., XXIV, p. 248. 288 PORTLAND CEMENT to form the di- and tricalcium silicates, and tricalcium aluminate, we have two separate and distinct kinds of thermal reaction. The first reaction, the decomposition of the carbonates, is an en- dothermic reaction, that is, it requires heat to bring it about. The second reaction, the formation of the silicates is exothermic, or a heat producing reaction. Of the various secondary chemical changes which occur in the kiln, Some are exothermic and some are endothermic. The evaporation of the water whether this be free as in slurry or combined as in dried clay requires heat. The oxidation of the iron and the burning of the sulphur, carbon and other organic matter are exothermic or heat producing. If a quantity of cement raw material is placed in a crucible and a pyrometer is inserted well into this and then heat is applied to the crucible at a uniform rate, it will be found that the tempera- ture will rise quite rapidly up to about 1,650° F. When this point is reached, the temperature remains stationary for a little while and then begins to rise again. In other words, when we first apply heat to the crucible all of this is utilized to raise the tem- perature of the mix until that temperature (1,650°) is reached at which the carbonates begin to decompose. After this, for a while, all of the heat which is supplied to the material is utilized in decomposing the carbonates into lime and magnesia. When the decomposition is complete, the effect of the heat is again to raise the temperature of the material gradually until the point (approximately 2,435° F.) is reached, where the lime combines with the silica and alumina when the temperature will begin to increase very much more rapidly. This more rapid increase is due to the additional heat which is supplied by the second re- action or the forming of the silicates and aluminates of lime. The diagram given as Fig. 90 illustrates this. The quantity of heat generated by chemical reaction or re- quired to bring it about is usually expressed in terms of one of two units. These are the British thermal unit, usually abbrevi- ated to B. t. u. and the Calorie sometimes abbreviated to Cal. The British thermal unit is the heat required to raise the tempera- ture of one pound of pure water through I? F. at or near 39.1° F., the temperature of its maximum density. The calorie is the heat BURNING—scIENTIFIC considerATION OF THE PROCESS 289 necessary to raise the temperature of one kilogram of water from 4°C. to 5° C. A calorie is equivalent to 3.968 B. t. u., and a B. t. u. to O.252 calorie. The B. t. u., however, produced by the - oxidation or combustion of one pound of a substance is 9/5 of the number of calories which would be produced by one kilogram 2600 24OO 22Oo 2OOO |jl: i 2 © © O JC 2O Jº-> 462 So Cºo 7o &O 96 Moo TiNarº-Minuu-rass Fig. 9o.—Diagram showing time-temperature curve in clinkering cement raw materials. of the substance. Hence, to reduce calories per kilogram to B. t. u, per pound multiply by 9/5 (or 1.8) while to change B. t. u. per pound to calories per kilogram multiply by 5/9. The heat of the formation of a chemical compound is usually expressed in terms of the molecular weight of the substances combined and of the products formed. Thus the heat produced by the burning of carbon to carbon dioxide is 97,200 cal. which * The gram-calorie is expressed as the heat necessary to raise the temperature of 1 gram of water 1 ° C. Gram-calories per gram are of course equivalent to calories per kilogram, but the gram-calorie itself is equivalent to o, oo I calorie. 29O PORTLAND CEMENT means that when I2 kilograms of carbon are burned with 32 kilograms of oxygen forming 44 kilograms of carbon dioxide, 97,2OO cal. are produced. This is, of course, equivalent to 8, IOO cal. per kilogram of carbon burned or to 2,209 cal. per kilogram of carbon dioxide formed. The former figure is, of course, equi- valent to I4,580 B. t. u. per pound of carbon burned. Heat of Decomposition The heat necessary to decompose the carbonates has been de- termined with a fair degree of accuracy by Berthelot and others. Berthelot places the figure for the decomposition of calcium car- bonate into calcium oxide and carbon dioxide at 43,300 calS., Thomsen at 42,52O cals. and De Forcrand" at 43,300 cals. The latter figure is probably quite near the truth and is equivalent to 779 B. t. u. per pound of calcium carbonate decomposed or I,392 B. t. u. per pound of lime formed. De Forcrand” places the molecular heat of formation of magnesium oxide from the car- bonate at 28,900 cal. and Simek at 23,200. The former figure is generally accepted and this is equivalent to 619 B. t. u. per pound of magnesium carbonate decomposed or I,282 B. t. 11. per pound of magnesia formed. These reactions occur at a definite temperature for each pres- sure and will not occur until this temperature is reached. This temperature is known as the dissociation temperature. The figures most accepted are those of Mitchell” who placed the dis- sociation of calcium carbonate into lime and carbon dioxide at 896° C. at 760 millimeters pressure. This is equivalent to 1,645° F. at 29.92 inches barometric pressure. The same authority places the dissociation temperature of magnesium carbonate at 756° C. at 760 millimeters pressure. This is equivalent to 1,361° F. at 29.92 inches barometric pressure. The dissociation temperature decreases in both cases as the pressure decreases and visa versa increases with the pressure. * De Forcrand, Comptes Rendus, Vol. CXLVI, p. 51 1 (1908). * De Forcrand, Ibid. * Mitchell, J. Chem. Soc., Vol. CXXIII, p. 1055 (1923). BURNING—SCIENTIFIC considerATION OF THE PROCESS 29; The heat necessary to evaporate free water is 970.4 B. t. u. per pound of water and to drive off combined water I, IOO B. t. u. per pound. The Heat of Formation of Clinker The heat liberated by the formation of the clinker from the oxides is variously placed by authorities at from 180 to 828 B. t. u. per pound of clinker formed. The latter figure is much too high. Tschernobaeff made a direct measurement in 191 I of the heat formed by burning calcium carbonate and clay to clinker in a bomb calorimeter in the presence of charcoal as a heating agent. He placed the heat of formation at 240 B. t. u. per pound of clinker formed as the result of this. Mr. W. S. Landis also de- termined the heat of formation of clinker in a like manner. His determination gave 200 B. t. u. per pound of clinker formed. R. Nacken, in 1922, determined the heat formed by solution of the materials in hydrochloric and hydrofluoric acid and measuring the heat of solution and other thermal changes. He placed the heat of formation of clinker at 180 B. t. u. per pound. In 1914, O. Dormann calculated the heat of formation from the best avail- able data (Tschernobaeff's) on the heat of formation of the cal- cium silicates and aluminates. He gave the figure as 20I to 203 B. t. u. per pound. A somewhat later calculation by R. Coghlan employing methods similar to Dormann placed the figure at 178 B. t. u. per pound. Thus we have three figures obtained by ex- perimental methods and two by carefully made calculations from the best available data on the heat of formation of the calcium silicates and aluminates which range from 178 to 240 B. t. u. per pound of clinker formed. The author now employs Landis's figure, or 200 B. t. u. per pound of clinker formed. Various determinations of the specific heat of the materials employed in cement manufacture have been made—most of them are for low temperatures only, however. The most acceptable figures are Mean specific heat Cement clinker 2,000°–o° O.246 Calcium carbonate o'-300° O.22 292 PORTLAND CEMENT Magnesium carbonate 24°—IOO’ O.2O Clay 20°–98° O.22 The latter three figures are probably at least O.O2 to O.O5 too low between the temperature of the air and that of dissociation. The author has usually employed the figure o.25 as the mean specific heat of cement raw material between zero and dissociation temperature. Table XXVI gives in convenient form the heats of the various reactions in cement burning. TABLE XXVI.-HEAT OF VARIOUS REACTIONS IN CEMENT BURNING B tº u. I Lb. of carbon (C) burned to CO., gives off I4,540 I Lb. of sulphur (S) burned to SO2 gives off 4,050 I Lb. of hydrogen (H) burned to H2O gives off 54,500 I Lb. of calcium carbonate (CaCOs) decomposed into CaO and CO2 requires 779 I Lb. of magnesium carbonate (MgCOs) decomposed into MgO and CO2 requires 619 I Lb. of calcium oxide (CaO) formed from CaCOs requires I,392 I Lb. of magnesium oxide (MgO) formed from MgCO, requires I,282 I Lb. of clinker formed gives off 2OO I Lb. of raw material (free of CO2) burned to clinker gives off I27 I Lb. of combined water requires for its liberation I, IOO Heat Required to Burn Cement The actual heat required to burn cement is, of course, the balance between the endothermic and the exothermic reactions given previously. In other words: assuming a raw material of the following composition: Silica I4.O Alumina and ferric oxide 6.7 Calcium carbonate 74.8 Magnesium carbonate I.2 Combined water o.6 Miscellaneous 2.7 IOO.O One hundred pounds of the above raw material will produce about 64 pounds of clinker if burned with oil or I.55 pounds of raw material will be required for one pound of clinker. BURNING—SCIENTIFIC considerATION OF THE PROCESS 293 Neglecting minor reactions, the heat necessary to form clinker from the above raw material will then be found as follows: ENDOTHERMIC REACTIONs * B. t. 11. Heat required for decomposition of the carbonates (CaO, CO2) I.55 × 0.748 × 779 903 (MgO, CO2) I.55 × 0.012 × 619 I2 Total endothermic reactions 9I5 ExOTHERMIC REACTION Heat liberated by formation of clinker I X 200 2OO Total exothermic reaction 2OO BALANCE Endothermic reactions 9I5 Exothermic reactions 2OO Balance to be supplied by fuel 7I5 In a wet process plant, there must be supplied an additional amount of heat—enough to evaporate the water from the slurry. Assuming the slurry to contain 40 per cent water and I.55 pounds dry material required for I pound clinker the additional items are: ENDOTHERMIC REACTION Water — I.55 : * : : 60 : 40, w = I.O4. Evaporating I.04 lbs. of water at and from 212° F. — I.04 × 970 = 1,009 The above supposes the water evaporated to be cooled to the starting temperature but not condensed. We thus see that to produce cement from dry raw materials requires 715 B. t. u. per pound of cement and from slurry con- taining 40 per cent water, 1,724 B. t. u. The wet process increases the work to be done by the kiln by about 140 per cent. Assuming that there are 376 pounds of clinker in a barrel of cement, the heat theoretically required to burn the latter by the dry process is 715 × 376 or 268,840 B. t. u. This is equivalent to about 19 pounds of good bituminous coal (I4,OOO B. t. u. to the pound). The average amount of such fuel actually required in practice ranges from 80 to IOO pounds which makes the efficiency of the rotary kiln burning dry materials 20 to 25 per 2O 294 PORTLAND CEMENT cent. In the wet process the heat requirements are 648,224 B. t. u. per barrel, equivalent to 46 pounds coal, and the fuel actually used ranges from II5 to 140 pounds. The efficiency of the kiln burning wet is, therefore, from 34 to 41 per cent. This seems to bear out the contention that kilns burn slurry more efficiently than dry mix. The amount of heat theoretically required to evaporate the water in slurry ranges from 300,000 to 400,000 B. t. u, per barrel. This is equivalent to from 21 to 29 pounds of coal (14,000 B. t. u. per pound). This figure supposes water cooled but not con- densed. The figure 20 pounds of coal per barrel is an ideal one, and in order to realize it in practice we would have to recover all the heat not actually utilized in the chemical reaction. We would have to cut off all radiation from the kiln, and the clinker and the flue gases would have to leave the kiln at the temperature of the air. Of course, it is impossible to do this economically. There will always be some loss by radiation. We must also have sufficient difference between the temperature of the waste gases and the outside air to produce natural draft. Application of Heat In a cement kiln, our object is to apply heat in the fuel to de- compose the limestone. This is done by burning the fuel and passing the products of combustion over a body of the cement raw material. The fore part of the kiln acts as a combustion chamber. The transferring of heat takes place from the gases to the cement mix and to the walls of the kiln, the heat being transformed from the latter again to the mix so that the mix is heated in two ways—chiefly by the products of combustion di- rectly and to a less extent through the walls of the kiln. The first step in the burning of clinker is, of course, the source of heat. Pulverized coal or oil are used almost universally.” Fortunately in both these fuels we have material which is sus- 1 The various fuels employed and methods of preparation and use are described in detail in the next chapter. RURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS 295 ceptible to very nice regulation and which can be burned with practically the exact amount of air theoretically necessary for combustion. We do not, as is the case with grate and stoker fir- ing, have to consider the condition of the fuel body, etc., with reference to supplying the oxygen to burn the fuel. Nor do we have to consider carbon or unconsumed coal carried out by the ash. Analyses of kiln gases show that in the great majority of cases the coal is burned either with a slight deficiency (a reduc- ing flame) or with a very small excess of air (an oxidizing flame). In other words with practically the theoretical amount of oxygen necessary (a neutral flame). Fortunately in a cement kiln we do not as in metallurgical furnaces have to consider the chemical qualities of the flame, and so far as the essential chemical combinations and decompositions to be effected in this are concerned these take place equally well in a reducing or an oxidizing atmosphere, consequently our con- cern is chiefly towards burning the fuel efficiently and in such a manner that its heat energy may be most effectively utilized. The greatest factor in determining the temperature of the flame is the amount of air used for combustion, thus if we burn one pound of coal with just the quantity of air necessary for combustion, the gases produced would weigh about II pounds. If we use twice as much air as necessary the products will weigh 21 pounds. Manifestly if we transfer the heat of one pound of coal to II pounds of gas the temperature of the latter will be much higher than if we transfer the same quantity of heat to 21 pounds of gas. The temperature of the flame unquestionably has a great in- fluence on both the economy and the chemistry of cement burn- ing. Aside from the fact that with higher temperatures in the kiln less time is required for burning or a coarser raw material may be used, it is well known that the rate of heat transfer is proportional to the difference between the gases and the ma- terial to be heated, other conditions remaining constant; hence the higher the flame temperature the more rapidly the heat can be transferred to the mixture. 296 PORTLAND CEMENT There is another objection to excess air. Some heat is always carried away by the gases leaving the kiln. This heat is propor- tional to the quantity and temperature of the gases. Eleven pounds of gas leaving the kiln will carry off only about half the heat which will be carried off by 21 pounds. This applies whether we use waste heat boilers or not and the relative percentage of heat carried off by the gases will be the same whether they are at a low or high temperature—that is to say, at the same tempera- ture II pounds of gas will carry off only half as much heat as 21 pounds, whether the temperature of the exhaust gases be 400° |F. or 1,600° F. Air Required for Combustion The air required for combustion is found from the ultimate analysis of the fuel. In order to illustrate the method we will assume the burning is to be done with slack coal of the following composition. Water (IIo° C.) I.9 Carbon 74.9 Hydrogen 4.8 Oxygen 8.6 Nitrogen I.4 Sulphur O.7 Ash 7.7 IOO.O Neglecting the sulphur which is present in very small amount the combustible elements in IOO pounds of this coal are 74.9 pounds of carbon and 4.8 pounds of hydrogen. Of this hydro- gen, however, * pounds will be needed for the oxygen of the © 8.6 ) coal itself, leaving only (4.8 —-a- = 4.8 — I.I = 3.7) to re- quire outside oxygen; hence, to burn IOO pounds of this coal will require For carbon, I2 : 32 : : 74.9 : 4. A = 200 lbs. O For hydrogen, 2: I6: ; 3.7: ..r * = 30 lbs. O For IOO lbs. of coal 230 lbs. O BURNING—SCIENTIFIC considerATION OF THE PROCESS 297 Now air is 23. I per cent (by weight) oxygen, therefore, 230 pounds of oxygen is equivalent to 230 –– 23. I = 996 pounds air. This is, of course, equal to 9.96 pounds of air per pound of coal. By a similar calculation, it will be found that the air required to burn one pound of crude California oil (composition—carbon, 86 per cent; hydrogen, II per cent; nitrogen, 2 per cent; sulphur I per cent) amounts to I3.8 pounds; or for one gallon (8 pounds) of this oil IIO.4 pounds of air. Products of Combustion. The products of combustion may also be calculated from the ultimate analysis of the fuel. Thus, referring to the analysis of coal in the preceding section, the hydrogen in IOO pounds of coal will form 43 pounds of water (2 : 18:: 4.8: 4", a' = 43.2). Added to the latter quantity will be the moisture in the coal (I.Q per cent or a total of 45 pounds of water produced. The car- bon will form 275 pounds of carbon dioxide. (I2:44:: 74.9; ºr, a = 274.6). The sulphur will form I.4 pounds of sulphur di- oxide (32: 64:: O.7: *, + = I.4) We have determined in the preceding examples that 230 pounds of oxygen are needed for the combustion of IOO pounds of coal and that this is equivalent to 996 pounds of air. The nitrogen in the air will then be 996 — 230 or 766 pounds. This will be increased by the nitro- gen in the coal itself (1.4 per cent) to 767 pounds. The above quantities are the products of combustion from IOO pounds of coal The products from one pound will of course be: I,bs. Water O.45 Carbon dioxide 2.75 Sulphur dioxide O.OI Nitrogen 7.67 Total IO.88 As a check" on the above calculation, the total weight given above should equal the air required for combustion plus the com- * A method of calculating the quantity of waste gases from the analysis of the exit gas itself is given in the section on the waste heat boiler, Chapter XV. 298 PORTLAND CEMENT bustible part of the coal (IOO per cent of ash), or in this case, 996 -– (IOO — 7.7) = 1,088 pounds, for IOO pounds of coal. Assuming that I2O pounds of coal are required to burn a bar- rel of cement, the products of combustion would be per barrel of cement burned : I,bs. Water 54 Carbon dioxide 33O Sulphur dioxide I Nitrogen 920 I,305 By a similar process of calculation, it will be found that the products from the combustion of California crude oil (C, 86 per cent; H, II per cent; N, 2 per cent; S, I per cent) amount to : Per pound Per gal, I,bs Lbs. Carbon dioxide 3. I7 25.36 Water .96 7.68 Nitrogen IO.65 85.20 Sulphur dioxide .O2 .I6 Total I4.80 II8.4o Excess Air Used in Burning. The excess of air admitted to the kiln over and above that re- quired to consume the coal has been variously stated at from IOO to 150 per cent, above the theoretical quantity. From the re- sult of many analyses made by myself and assistants I am confi- dent that this does not represent normal conditions. If the sample is taken from the kiln stack a large quantity of air, which has leaked in through the annular opening between the kiln and the brick-work of the flue is sure to be present, and consequently make the excess air appear much greater than it really is. The gas samples should be taken from the inside of the mouth of the kiln so that there is no air mixed with it which does not pass through the kiln. Below are given some average analyses of waste gases from kilns working under various conditions. BURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS 299 I. Average of all samples taken when the kiln was working normally. No flame or black smoke issuing from the kiln stack but only a thin white or reddish vapor. Carbon dioxide 27.4 Carbon monoxide O.3 Oxygen 2.7 Nitrogen 69.6 IOO.O 2. Average of all samples taken when the kiln stacks were Smoking. Carbon dioxide I9.2 Carbon monoxide I.2 Oxygen 3.4 Nitrogen 76.2 IOO.O 3. Average of all samples taken when kiln stacks were flaming: Carbon dioxide I4.2 Carbon monoxide 5.8 Oxygen I. I Nitrogen 78.9 IOO.O The nitrogen in the gases represents the air admitted for com- bustion as practically all of it is from either the excess air or the air actually used to burn the coal. A small part of the nitrogen comes from the coal, however, but for practical calculations the nitrogen may be considered as all coming from the air. The ex- cess air is shown by the oxygen. If we calculate the nitrogen equivalent to this oxygen by multiplying the percentage of the latter by 3.78, the result will be the nitrogen carried in by the excess air and this nitrogen subtracted from the total percentage of nitrogen found by the analysis will give the nitrogen belong- ing to the air needed to support combustion, from which data the excess can be calculated. For example, to find excess air in Sample: 3OO PORTLAND CEMENT Analysis No. 1. Per cell t Total nitrogen 69.6 Nitrogen in excess air 2.7 × 3.78 IO.2 Nitrogen in necessary air 59.4 Ratio — 59.4 : 69.4 :: IOO : + 4 = II.7. Excess = 17 per cent of air necessary for combustion. The above calculation is not strictly accurate for a number of reasons, but for practical use it answers the purpose very well since we never know in mill practice under present conditions exactly how much coal we are burning, or how much carbon dioxide is being driven off at a given time from the raw material. Of the air admitted to the kiln for combustion, part is blown in with coal; the rest enters between the hood and the kiln and where the clinker drops out, and is drawn in by the draft of the kiln. Heat Carried Out by Waste Gases. The chief object in calculating the weight of the products of combustion is to determine the heat carried out of the kiln by these. If we multiply the quantity of each gas present in the exit gas by the mean thermal capacity of this gas and the tempera- ture, the product will be the heat carried out by this gas. Figure 9I gives the mean thermal capacities of the gases found in the exit gas from cement kilns. It will be noticed that this figure varies with the temperature. For example, let us suppose the exit gases are at I,2OO° F. above the atmospheric temperature, then the products of combustion in the preceding example carry off heat as follows: (The small amount of sulphur dioxide may be neglected). By water vapor 54 × 1,2CO X 0.54 F 34,992 B. t. u. By carbon dioxide 330 × 1,200 × 0.252 = 99,792 B. t. u. By nitrogen 920 × 1,200 × 0.26I = 288,144 B. t. u. Total 422,928 B. t. u. BURNING—SCIENTIFIC considerATION OF THE PROCESS 301 If I7 per cent excess air is employed in burning this would carry Off (9.96 × I2O) × O. 17 × 1,2OO X O.254 = 61,930 B. t. u. per barrel of cement. (2O. . Q 25 (2 -6 O 0 24. O 23 (25 O O 22 0 2/ 0.40 is O JOO /62/22 { /JOO 2OOO NS: S 202/ 423%t f & \) CŞ S Q) § S. SS § (20262 426230Š n § .A. WS § Q (20/9 2025s, * N & SS $º S$ 3. § *D ooze oozoº O JOO /OOO /500 2OOO 72/770ézzzzz/re Zezrees /F2/?re/7/7e/? Fig. 91.—Specific heat of gases at various temperatures. Upper curves give specific heat of the gases per pound per degree F. rise. Lower curves give specific heat per cubic foot per degree F. rise. In addition to the carbon dioxide and water formed by com- bustion of the fuel, there will also be the carbon dioxide and water driven off from the raw materials. The amount of this 302 PORTLAND CEMENT can, of course, be determined from an analysis of the latter Assuming that 900 pounds of slurry are required to produce a barrel of cement and that 33% per cent of this is water and 33% per cent of the dry material is carbon dioxide the amount of heat carried out by these two gases is as follows: The carbon dioxide from the raw material would carry off 200 × 1,200 × 0.252 = 60,480 B. t. u. -- Similarly the water vapor present in the exit gases would carry out 300 × 1,2OO X O.54 == 194,400 B. t. u. This is in ad- dition to the latent heat of evaporation. The total sensible heat in the exit gases from the kiln per barrel of cement would then be the sum of these four quantities or Heat in products of combustion 422,928 B. t. u. Heat in excess air 61,930 B. t. u. Heat in carbon dioxide from raw materials 60,480 B. t. u. Heat in water vapor from slurry 194,400 B. t. u. Total per barrel of cement 739,738 B. t. u. Heat Loss Due to Carbon Burned to Carbon Monoacide. If the gas contains carbon monoxide this carries out latent heat. That is heat which would be produced if the carbon mon- oxide was burned to carbon dioxide. One cubic foot of carbon monoxide will produce 334 B. t. u., one pound of carbon mon- Oxide 4,280 B. t. u. Gas analyses are usually expressed in per- centage by volume and our heat calculations have been by weight. Now one pound of carbon will produce an equal volume of either carbon dioxide or carbon monoxide, whichever happens to be formed, and from our previous calculations we know that of a total of 530 pounds of carbon dioxide 200 pounds or 38 per cent comes from the raw material and 330 pounds or 62 per cent from the fuel. Hence if our gas contains O.3 per cent carbon monoxide and 27.4 per cent carbon dioxide, of this total 27.7 × 0.62 = 17.2 per cent comes from the coal. Hence the relative amounts of car- bon burned to carbon monoxide and carbon dioxide respectively are as O.3 is to 17.2 or O.3 : 17.2:: I.7: 98.3. Of our carbon there- fore 98.3 per cent has been burned to carbon dioxide and 1.7 BURNING—scIENTIFIC considFRATION OF THE PROCESS 303 per cent to carbon monoxide. Now one pound of carbon burned to carbon monoxide will produce 4,374 B. t. u. and to carbon dioxide 14,580 B. t. u. For every pound of carbon burned to carbon monoxide there will be lost, therefore, Io,206 B. t. u. Now in I2O pounds of coal containing 74.9 per cent of carbon there will be 90 pounds of carbon. If I.7 per cent of this is burned to car- bon monoxide, the heat lost will be 90 × O.OI7 × Io,2O6 = I5,615 B. t. 11. per barrel of cement. Heat Lost by Radiation. Radiation losses are usually figured by dividing the kiln into a number of sections and determining the temperature at the middle of each section. The area of surface exposed in each sec- tion is then determined and from this the heat loss is calculated by multiplying this area by the heat radiation per square foot of surface at the ascertained temperature. Various investigators have measured the heat lost from a heated metal wall for various temperatures. Darling's figures" are now most accepted. Fig. 92 shows graphically the radiation losses per square foot of surface at various temperatures and is prepared from Darling's figures. Boeck's formula” is also often used. It is probable that the figures obtained in either case are only approximate, as the heat radiated varies greatly under different conditions, thus it has been found that the heat lost from a horizontal surface is 22 per cent greater than that from a vertical surface and hence the loss from a cylindrical surface would lie somewhere in between these two figures. The loss from a surface exposed to wind is 30 per cent greater and of one exposed to the wind and rain 70 per cent greater than from a surface exposed only to still air. The kiln is moving which increases the radiation loss somewhat beyond what would be obtained from a stationary surface. The measurement of the temperature of the kiln shell is by no means easy. The method usually employed is to insert thermom- ters into steel wells or thimbles welded to the kiln shell. The temperature of these is taken at frequent intervals or a regis- * C. R. Darling, Engineering (London) Mar. 14, 1919, p. 643. * Boeck, Jour. A m. Soc. Mech. Engrs., Aug., 1916. 3O4 PORTLAND CEMENT 2007 ÓOO 3O C2 JO240 0O SS 2 O O /OO O /OO67 2O700 J'6262O >262OO ºf 200 A 7. ZZ A-2/~ CŞy /* A-2/~/722//- Fig. 92.-Radiation losses from the kiln shell (Darlings). BURNING—ScIENTIFIC coxsDERATION OF THE PROCESS 305 tering instrument is used. The readings are usually averaged over the period of the test. The following example shows the heat losses from a rotary kiln, 8 feet diameter by 125 feet long, burning wet materials. The kiln was divided into three zones each 25 feet long at the feed end and into four zones each I2% feet long at the firing end. Thermometers were inserted in the center of each zone. That is the first themometer was inserted 5 feet from the firing end, the second I5 feet, etc. The average temperature at each station, the heat lost per square foot at this temperature, the area of surface of each zone and the total heat lost per section is shown in Table XXVII. The figures in Column 5 are in each instance the product of corresponding figures in Columns 3 and 4. The figures in Column 3 are taken from Fig. 92. The total heat lost per hour in this instance was 3,906,640 B. t. u. The output of the kiln during the test was 530 barrels per day or 22. I barrels per hour. The heat lost per barrel by ra- diation was, therefore, 176,771 B. t. u. The fuel required per barrel was I2O pounds of coal (I4,OOO B. t. u.) equivalent to 1,680,000 B. t. u. The heat by radiation in this instance there- fore was equivalent to Io.5 per cent of the fuel. TABLE XXVII.-HEAT LOST BY RADIATION FROM ROTARY KILN 8 FEET DIAMETER × 125 FEET LONG BURNING WET MATERIALs Average Heat lost per Area of Heat lost temperature sq ft. of zone ZOI) e per zone ZOne o F. per hour—B t, u. Sq. ft. B. t. u. I 330 I,300 3I-4 308,200 2 360 I,500 3I4 439,600 3 340 I,4OO 3I4 47I,OOO 4 320 I,260 3I4 395,640 5 3I5 I,250 628 785,000 6 3I3 I,250 628 785,000 7 300 I, ISO 628 722,2OO Total 3,906,640 Heat Balance. In calcºlating the efficiency, etc., of a rotary cement kiln, what is known as a heat balance is often made. That is the heat re- ceived from the combustion of the fuel, the formation of clinker 3O6 PORTLAND CEMENT etc., is compared with the heat expended in decomposing the carbonates of lime and magnesia—or lost in various ways. The two sums should, of course, balance. The chief items making up this heat balance are: Plus Items. I. Heat derived from the combustion of the fuel. 2. Heat liberated by the formation of the clinker. 3. Heat brought in by the air used for combustion. 4. Heat brought in by the fuel. 5. Heat brought in by the raw materials. Negative Items. 6. Heat utilized in decomposing carbonate of lime. 7. Heat utilized in decomposing carbonate of magnesia. 8. Heat utilized in evaporating water. 9. Heat carried out by the clinker. Io. Heat carried out by the stack-gases. II. Heat lost by incomplete combustion (C to CO). I2. Heat lost by radiation. The following examples will show how the various items are calculated and the balance is struck. I. The heat liberated by the fuel may be determined directly in a calorimeter or calculated from the analysis. For methods of determining this the reader is referred to any of the standard works on analytical chemistry or the chemistry of fuels". Let us suppose we find the coal has a fuel value of I4,OOO B. t. 11, per pound and that I2O pounds are required to burn a barrel of cement. Then the heat supplied by the fuel is 1,680,000 B. t. u, per barrel of clinker. 2. The method of calculating the heat of the formation of the clinker has been shown previously. If the calculation is on the “per barrel” basis it is, of course, 200 × 376 or 75,200 B. t. u. * Meade, “The Chemists' Pocket Manual;” Somermeier, “Coal; Its Composition, Analysis, Utilization and Valuation”; Stillman, “Engineering Chemistry”; Gill, “Gas and Fuel Analysis for Beginners,” etc. BURNING—SCIENTIFIC consider ATION OF THE PROCESS 307 3. In order to find the heat brought in by the air it is neces- sary to know (I) the weight of air required for combustion. (2) The temperature of this air. (3) The excess air employed and (4) The specific heat of air. The method of determining excess air has already been ex- plained. If this is found to be 17 per cent of that theoretically necessary, the total amount of air used to burn one pound of coal would be 9.96 × I. I7 = II.65 pounds. If we burn I2O pounds of coal per barrel, the air employed for this is I,398 pounds. Again suppose the temperature of the air is at 92° F. and we have decided to make 32° F. our base. The mean thermal capacity of air (32° — 90°F.) is O.242. The heat brought in by the air is then 60 × 0.242 × 1,398 or 20,299 B. t. u. per barrel. 4. The sensible heat brought in by the fuel is always small. Assume the coal to be at 92° F. and its specific heat O.24, the heat brought in is then I2O (92 – 32) X O.24 = I,728 B. t. u. per barrel. 5. The heat brought in by the raw material is, of course, the sum of that brought in by the solid matter and the water. Let us assume 900 pounds of slurry containing 33% per cent of water at a temperature of 97° F. are used per barrel. Then the slurry will contain 300 pounds of water and 600 pounds of Solids and the heat brought in will be In solids, 600 X (97 – 32) × 0.22 = 9,580 B. t. u. In water, 300 × (97 – 32) X I.OO = I9,500 B. t. u. Total heat brought in by the slurry 28,080 B. t. u. 6. The heat utilized in decomposing carbonate of lime is cal- culated as previously explained. If the raw material contains 41 per cent lime, then the heat required will be 600 × 0.4I X I,392 = 342,432 B. t. u. 7. Similarly if the raw material contains 2 per cent magne- sium carbonate the heat required to decompose this will be 600 X O.O2 × 1,282 = I5,384 B. t. u. 3O8 PORTLAND CEMENT 8. The heat utilized in evaporating water will be first the heat necessary to raise the temperature of the water from 32° to 212° F. and then the latent heat of evaporation, or To raise temperature one pound water from 32 to 212° F (212 — 32) × I I80 B. t. u. Latent heat of evaporation 97o B. t. u. Total heat per pound of water I, I5o B. t. u. Heat for 300 pounds of water 345,000 B. t. u. 9. The heat carried out by the clinker is found by multiply- ing the mean specific heat of the clinker by its temperature. The specific heat of clinker is O.246 and let us suppose its tempera- ture to be 2,032°F. The heat lost is then, 376 × (2,032 – 32) X O.O246 = 184,992 B. t. u. IO. Let us assume the conditions given on page 300. The heat carried out by the waste gases will then be 739,738 B. t. u. per barrel as calculated previously. II. The method of calculating the loss of heat due to incom- plete combustion of carbon has been previously explained. If the conditions are as stated in this example the heat lost due to this cause is I5,615 B. t. u. per barrel as calculated there. I2. The method of calculating the heat lost due to radiation has been explained previously and in the example given was found to be 176,771 B. t. u. per barrel. The heat balance would then assume this form. Plus items B. t. u. B. t. u. I. Heat from fuel I,680,000 2. Heat from formation of clinker 75,2OO 3. Heat brought in by air 20,299 4. Heat brought in by fuel I,728 5. Heat brought in by raw materials 28,080 Miscellaneous and unaccounted for I4,625 I,819,932 Negative items 6. Heat for decomposing CaCOs 342,432 7. Heat for decomposing MgCOs I5,384 8. Heat for evaporating water 345,000 9. Heat lost in clinker I84,992 Io. Heat lost in stack gases 739,738 II. Heat lost by incomplete combustion I5,615 I2. Heat lost by radiation I76,771 I,819,932 BURNING—SCIENTIFIC Conside RATION OF THE PROCESS 309 From the above and similar tests it is found that the heat dis- tribution in burning cement is about as follows: Dry process Wet process Per Cellt Per cent For chemical reactions in burning 2O I6 For evaporating water - I9 Carried out by clinker I3 II Carried out by stack gases 55 44 Lost by radiation I2 IO IOO IOO Dust Losses The dust losses from the rotary kiln amount to from 3 to 6 per cent of the raw material. This dust consists of coal ashes, unburned raw material, partially calcined material and certain volatile products which are driven out of the clinker and which condense either in the upper part of the kiln, in the stack or when the open air is reached (either in their original form or in new combinations) such as potash, Soda and sulphate of calcium, etc. The analyses given below will give an idea of the compo- sition of the dust. These samples were collected by electrical pre- cipitation. CoMPOSITION OF CEMENT KILN STACK DUST. Kiln fired Kiln fired with coal with oil Calcium carbonate 25.56 3I.4O Calcium sulphate 7.82 6.3.I Calcium oxide 18.69 I9.03 Magnesium oxide I.5O o,60 Potassium oxide—water soluble 9.58 I4. I5 Potassium oxide—insoluble 3.72 I.26 Sodium oxide—water soluble I.O7 8.37 Sodium oxide—insoluble 0.95 In O116. Silica I6.80° 8.4I Iron oxide and alumina 9.06 7.02 Undetermined 3.45 5.25 IOO.OO IOO.OO The dust losses depend to some extent on the plant but it is safe to say that even under the most favorable conditions where dust precipitation apparatus is not used the loss amounts to 4 or 5 per cent on an average. 2 I 3IO PORTLAND CEMENT It has been frequently stated that the dust from the kiln stacks of the wet process is neglible and this is held as a strong argu- ment in favor of the wet process. The writer's study of the dust from the kiln stacks in connection with the recovery of potash, however, has led him to believe that the dust from the wet pro- cess kilns is nearly, if not actually, as great as that from the dry process. J. G. Dean in an article in Chemical and Metallurgical Engi- neering, describing the process of recovering potash which was employed at Victorville, Cal., stated that the amount of dust collected in their dry dust flue amounted to 3 per cent of the total dry material entering the kiln and admitted this was only a por- tion of the dust lost because when they put in their potash system they obtained a large additional amount in the spray chamber and condenser. Results there indicated that the dust lost must have amounted to about 5 per cent of the raw material. This agrees quite closely with the dust losses of the dry process. While the claim of less dust is generally made for the wet process, there does not seem to be available the results of any dust determination in support of this theory. Obviously it would be a comparatively easy matter to determine the dust losses by means of dust filters. The writer cannot find any evidence that it takes less raw ma- terial to make a barrel of cement by the wet process than by the dry. The dust losses at the average dry process plant are about 5 per cent of the raw material, or about 30 pounds per barrel of cement. Obviously if the wet process saved this loss, it should certainly be indicated by the smaller quantity of raw material required to produce a barrel of cement. Should the wet process produce less stack dust than the dry So long as the raw materials are damp no dust would theoretically be produced, but, manifestly, the raw materials do not remain damp until they clinker. On the other hand, they are probably for the greater portion of their time in the kiln in a condition where they will dust fully as freely as with the dry process. In some chemical work undertaken by the writer in which the effort BURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS 3 II was made to dry a very fine marl, it was found that in spite of the fact that the latter was fed into the kiln containing 60 per cent moisture, the dust losses were so great that the process could not be employed. Examination of any sample of stack dust will show this to contain some material which has been calcined (not necessarily clinkered), Some uncalcined material and some coal ash. Gener- ally speaking, fully half and often as much as 80 per cent of the dust is material which has been fully calcined to lime (or to the extent where the limestone has been freed from carbon dioxide). It would certainly seem evident that this portion of the dust had been picked up by the rapidly moving gases after the material reached the zone where the carbon dioxide was liberated and, of course, Some distance beyond the point where wet materials would have become dry. If the slurry when it dried out, took the form of small nodules free from dust and baked sufficiently hard to prevent dusting by attrition, then there would be some reason for assuming that the wet process would not produce dust. As a matter of fact, as anyone can prove by entering a wet process kiln which has been shut down, the material dries in the form of soft nodules and dust. The nodules can be easily pulverized by rubbing between the fingers or by rolling over one another. When burned to the point where calcium oxide is formed they usually break down still further. Certainly the slight difference in appearance of the material, after this has reached that part of the kiln where carbon dioxide is being liberated, fails to warrant the statement, that one will be carried out by the gases and the other not. Experiments made at various times show that in the dry pro- cess about half of the coal ash enters the cement and half is blown out of the kiln. The coal ash thus contributes something to the dust, usually to the amount of about 5 to 7 pounds of dust per barrel of clinker. The supposition that the dust will be caught and precipitated by the vapor given off by the mix in drying is, of course, un- founded. The temperature of the exit gases from even a wet 3I2 PORTLAND CEMENT kiln is far above the condensation point of steam. At such a temperature, steam is a perfect gas having the properties of any other gas and its addition to the products of combustion and the carbon dioxide might even increase the dust carrying properties of the waste gases by increasing their volume and consequently their velocity. The idea may hold that the wet material itself will catch and retain the dust. This can occur only to a very limited extent. The slurry so long as it is damp will no doubt collect any dust which impinges on it, but the amount of dust which actually strikes the wet material is, of course, but a small part of the dust in the gases. Any one who has tried to wash kiln gases with water sprays will realize how thoroughly this spraying must be done in order to collect even any considerable portion of the dust. In view of both practical data and theoretical consideration, therefore, the statement that the “wet process elim nates dust” is not warranted. Dust Collection Two methods of dust collection from the kiln are in use (I) the Cottrell or Electrical Method, and (2) Washing the gases with water. The Cottrell or electrical method of collecting dust was first proposed many years ago by Sir Oliver Lodge, the distinguished English physicist. No successful apparatus, however, was de- vised until Dr. Cottrell, then of the University of California, undertook to apply this principle to the precipitation of fume from smelter gases and a little later on to the precipitation of the dust from cement kiln gases. The latter undertaking was first brought to a successful conclusion at the plant of the Riverside Portland Cement Co. Various types of apparatus for carrying out the process have been tried at different times. The first large installation at River- side consisted of horizontal or plate treaters, but all of the later installations at cement plants employ the vertical or pipe treater. This latter consists essentially of an iron wire passing through BURNING—SCIENTIFIC considerATION OF THE PROCESS 313 the center of a sheet iron pipe. These two form the electrodes and are operated by a direct current of 45,000 to 80,000 volts. The gases pass up through the tube. There is a silent discharge of electricity passing from the wire to the tube and this effects the precipitation of the dust, the larger portion of which collects on the surface of the tube. Oly?/ef Sfack 2% Damper ſmsuſafor Bushing E ºre Electrode.9/or. /*sulator * K-ºs, .." ‘Wire £/ectrodes || || ;|| //7sa/afed || || || | #||||}|| Pºpe A/ectrodes : || || | 4' Grounded |||}||}|| ,” d t ; ſ 4,” | g t ſ ! |+| | || || || | º 4. g ſ º | | | | | | | | | | | !||}||||}|ſa/ef }||}||||}| of Gases iſosu/afor Bushing We/ghfs Hopper gº Cooregor g (9) Fig. 93.—Diagram illustrating typical Cottrell dust precipitator. Dr. Cottrell thus explains this action: “If a needle-point con- nected to one side of a high potential direct-current line be brought opposite to a point connected to the other side of the line, the space between them and any insulated body becomes 3I4 PORTLAND CEMENT highly charged with electricity of the same sign as the needle, whether positive or negative; and such body if free to move will be attracted to the plate of opposite sign.” In the tube treater the wire represents the needle and the surface of the tube the plate. As installed in the cement industry, the apparatus or “treater,” consists of a large number of such tubes which are connected above and below with flues. The gases enter the bottom flue and pass up through the tubes of the upper flue, or vice versa as occa- sion warrants. At frequent intervals, the current is interrupted Fig. 94.—Cattrell precipitator and flue connecting this with the kilns— Clinchfield Portland Cement Co., Kingsport, Tenn. and the dust is rapped from the surface of the tubes by means of a system of hammers. The wires are also provided with a knocking arrangement by means of which any dust which col- lects on them is shaken off. The dust falls into hoppers situated below the flue and from this it is drawn out as desired by means of slides and gates. A fan is generally employed to draw the gases through the treater and produce the draft in the kiln. A treater is usually divided into a number of units so that the oper- ation of the system is not interfered with when the dust is shaken down or when repairs are made. Refer to Figures 93 and 94. BURNING SCIENTIFIC CONSIDERATION OF THE PROCESS 315 Collection by Washing the Gases with Water The collection of dust by means of water sprays was one of the earliest methods and such methods of gas washing have been extensively employed in metallurgical and chemical industries. The cleaning of blast furnace gases by the use of water sprays is quite general in the iron industry, and in many chemical pro- cesses gases are passed through chambers in which sprays are located to free them from dust and impurities. A number of early experimenters undertook to wash the dust out of the rotary kiln gases with water but for the most part employed too little water and passed the gases through the appa- ratus at too high a velocity for good results, so that all efforts were a failure until the successful installation of such a process, designed along sound engineering lines, at the plant of the Cali- fornia Portland Cement Co., at Colton, Cal. This installation differs from most of the recent water spray systems, however, in that the wet scrubbers are preceded by a large dry settling chamber in which the major portion of the dust is precipitated, while in the newer wet collection systems only a scrubber is used. The first successful system installed in the cement industry was put in operation in 1911 and was the invention of T. J. Fleming, secretary and general manager of the California Port- land Cement Co." The installation at Colton treats gases from rotary kilns using the dry process and from the dryers—all employing oil for fuel. The draft of the kilns and dryers is produced by fans sucking at the end of separate flues. (See Fig. 95). There is a fan, motor and flue for each kiln, but the gases from a number of kilns and the dryer are passed into one treater. The fans are operated by variable speed motors so that the draft of the kilns can be increased or diminished to suit conditions. The treater itself consists of a large rectangular chamber built of steel and reinforced concrete and divided into two sections, one a dry * W. C. Hanna, Concrete Mill Section, Vol. XII, p. 33, also Trans. Amer. Inst. Chem. Engrs., Vol. VIII, p. 65. T. J. Flemming, Engineering Record, Vol. I, XIX, p. 649. 316 PORTLAND CEMENT 'ſe) ºu oļļ00 ‘‘OQ Quotuo) puell.I.O.J. eļu uogų įv.)—uuaļsÁs uoſ ſooſ ſoo nsup ºu ſuuuuo II—“G 6 -81） uo;, o^313 ſouoſ ! Des} sºwº-//o6o/////uæ2 oy y6ood №.3,*#: d/ºººººººººººººººș. . . . ） *（f£?. ¿:&&#. ----- - -_ſ|）- - - - ~- - - - ！→ sýð~ ~ ~ ~\~ ș%ø 3. R. º. §** « .. º,*-···---···:·º·:·º·：ſe• ·, …“? * ...sº º, ș ? * * ¿&& . \，\！·&\;&&* * :$'）;· ·:ğ •*;*ae} ~~: sº% • ';'| ſſſſs |-.*.**…g- •}）（）; }e 4 *§, && ！$，? »...:…， ¿ »? ！ |©sÁowoſº Jºſe/M • • №ºs！)， \, * * *^， /==ŒKoluogº |Ț6nO2'/Jēj0M • *• • • •== < *s** • •=• • • •=. --★ → • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ** = =， ！= ！！ ！！ ！=** • • • • • • • • •*• • •=， ！= = = ~ ~ • • • • • • • • • • • • • • •=. • • • • • • • • • • /3c/c/?/ ywo/ 6///es. AC/opa/o369. Avõu/~）; BURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS 3I 7 chamber 155 feet long, IOO feet wide and 31 feet high and the other a wet chamber 60 feet long and IOO feet wide. The fans discharge the gases from the kilns into the dry dust settling chamber in which the velocity of the gases is reduced about 90 to 95 per cent, resulting in a large amount of dust being deposited here. The extremely fine dust which does not settle in the dry chamber and the gases are then passed over to the washing chamber where the gases are forced up and down sev- eral times by means of a system of baffle-walls, causing them to follow a serpentine course. The wet chamber is provided with water sprays so as to thoroughly wash the gas. The dust settling in the dry chamber is carried out of the latter by means of screw conveyors running underneath this and the dust settling in the wet chamber is, of course, washed out of the latter by means of the water. The water carrying the dust in suspension and forming a very thin slurry flows from the washing chambers into conical bot- tomed settling tanks, where the dust is allowed to settle out, and the Solution is circulated through the sprays until of the desired strength after which the potash is separated out by evaporation. Other systems for precipitating dust were chiefly connected with the recovery of potash. Such systems were installed in the plants of the Santa Cruz Portland Cement Co.," The South- western Portland Cement Co.,” the Pacific Portland Cement Co., Ogden Portland Cement Co., the Utah Portland Cement Co.,” and the Atlas Portland Cement Co., at Hudson, N. Y. Potash from the Cement Industry” Reference has been made to the experiments by the writer and Dr. Hillebrand showing the volitilization of potash in the cement kiln. Mr. Clifford Richardson” read a paper at the 1904 * C. Krarup, Chem. and Metl. Eng., Vol. XXV, p. 3 16. *iº * J. G. Dean, Chem. and Metl. Eng., Vol. XIX, p. 439. * R. K. Meade, Rock Products, July 17 and 31, Aug. 14 and 28, 1918. * Those who are interested in this subject are referred to a series of articles by the author in Rock Products, July 17 and 31, August 14 and 28, 1918. * Richardson, Trans. Am. Soc. Test. Matls., Vol. IV, p. 465. 318 PORTLAND CEMENT meeting of the American Society for Testing Materials in which he proposed to the cement industry that they collect the potash lost, by means of a water spray and stated that Dr. Hillebrand had applied for a patent upon such a process. However, no patent was ever granted. The matter was discussed informally but it was generally conceded at that time that the cost of col- lecting this dust with the apparatus then known of, namely water sprays, would far exceed its value, if indeed it could be col- lected at all. The question of collecting potash from the cement industry, re- ceived no further consideration until imports of potash from Germany were discontinued by the World war in 1914. Due to agitation against the dust, two plants in Southern California had made provision to collect this and with the dust they also collected considerable potash mixed with the latter. The plant of the Riverside Portland Cement Co., employed the Cottrell System" of dust collection, while the plant of the Cali- fornia Portland Cement Co. employed a system” devised by Mr. T. J. Fleming. In order to obtain a material richer in potash, all of this dust was fed to a supplementary kiln and was burned to cement in that kiln. From this kiln, dust was obtained running in excess of 30 per cent K.O, but it was found that most of the potash in the dust fed into the kilns did not volatilize but remained with the clinker, due no doubt to the fact that the potash was present in the dust as sulphate, When the fertilizer companies began to purchase low grade material for potash, one of the first substances which attracted their attention was the crust which collects on the inside walls of the stacks of the rotary kiln and which falls down at intervals into the dust chamber, its high potash content having been pointed out by the writer in a paper read before the Cement Manufac- turers and also in former editions of this book. They persuaded a number of the cement manufacturers to save this crust which * See page 312. * See page 315. BURNING—SCIENTIFIC CONSIDERATION OF THE PROCESS 319 they purchased at prices ranging from $1.50 per unit in the early days of the war to $3.00 per unit later on. This dust averages 6 to 8 per cent (or units) of water soluble potash. The Security Cement & Lime Company, Security, Md., were among the cement companies who sold their flue dust. Later on in 1916 they installed the Cottrell system and from that time until the close of the war collected from $800 to $1,000 worth of potash daily. Numerous other plants installed collectors but only a few of them made any money. Water Soluble Potash One very peculiar situation presented itself when the collector at Security was placed in operation, which has not been fore- seen. At the plant of the Riverside Portland Cement Company, practically all of the potash in the dust was in the water soluble condition. At Security, it was found that only a little more than half of the total potash in the dust was water soluble and that while the dust contained from 12 to 15 per cent total potash it contained only about 6 to 7% per cent of water soluble potash. The only explanation which could be offered to account for the difference in the state of the potash at the two plants was that at Security the cement was burned with pulverized coal and at Riverside with oil. It appears, therefore, that chemical combi- nation takes place between the ash and the potash both of which are in a state of extreme mechanical subdivision.* It was found, however, that all of the potash in the dust may be dissolved by prolonging the digestion with the hot water or by digesting under high pressure. It is also readily soluble in acid. In making mixed fertilizers with this dust it was found that a considerable portion of this potash was rendered soluble when the dust was mixed with acid phosphate. It has, of course, been known that chlorides will increase the volatilization of potash. The plan which proved most success- ful was to introduce a small amount of salt with the raw material and also with the pulverized coal. By doing this the liberation 1 Potler and Cheesman, J. Ind. and Eng. Chem., Vol. X, p. Io9. 32O PORTLAND CEMENT of potash was materially increased and the recombination of the potash prevented due to the Saturation of the ash by the soda in the salt. Huber and Reath (U. S. Pat. Nos. 1,194,344 and 1,219,- 315) proposed to use calcium fluoride in place of salt. They claimed that where the potash is leached from the dust the fluoride is entirely recovered by the treaters so that only a very small quantity of this mineral is needed, the original charge passing around in a cycle as it were. The soda as well as the potash is volatilized to some extent so that the dust will contain some water soluble soda. Usually the proportions are about I of soda to 3 or 4 of potash. As practically all the potash in kiln dust can be slowly ex- tracted with water it is highly probable that all of the potash in this material is available for plant food. In addition to the potash, this material is rich in lime so that we have in this one material two very valuable fertilizer ingredients, lime and potash. Potash Salts from Dust The Riverside Portland Cement Co., the Security Cement & Lime Co., the Santa Cruz Cement Co., and the Southwestern Portland Cement Co. all made potash salt of more or less purity during the last year of the war. The process at Riverside is typical and was as follows: The dust was deposited from the treaters into cylindrical tanks filled to a depth of about 6 feet with water heated by means of live steam to a temperature of 85°C. The tanks were provided with agitators and the mass was continually stirred. After the dust was charged into the water the temperature of this latter rapidly rose to the boiling point due to the hydration of the quick lime contained in the dust. The whole operation of extracting the water soluble potash from the dust was accomplished in about fifty minutes. From the tanks the slurry was run by gravity to an Oliver filter press, its temperature being maintained at 85° C. by steam coils and the separation of the solids from the solution being affected by the filter press. The solution was stored in shallow concrete tanks which served as an evaporating pond where under the influence of the very dry climate of BURNING—SCIENTIFIC considERATION OF THE PROCESS 321 Southern California, considerable evaporation took place. When the liquid attained a specific gravity of about I. I it was pumped to evaporating pans. As the solution became concentrated the salt dropped to the bottom. It was then raked out on to drain boards where it was allowed to remain some minutes and then deposited in a hopper where the draining continued for several hours. From this hopper it was passed through a rotary dryer and thence through a Williams mill which reduced it to the de- sired fineness for the market. The loss of potash during burning in any cement plant may be proved and the quantity easily determined. To do this an average sample of the raw material should be taken before it enters the kiln and a sample of the clinker collected at the same time. It is hardly necessary to say that these samples should be representative and the kilns must be operating under normal con- ditions. The samples of clinker and raw material should then be analyzed to determine the percentage of potash contained in these." Since there are approximately 600 pounds of raw material re- quired to make a barrel of cement, if we multiply the percentage of potash in the raw material by 6, we will obtain the total quantity of potash in pounds entering the kiln in the raw mater- ials necessary to produce one barrel of clinker. There are ap- proximately 380 pounds of clinker required per barrel of cement; hence, if we multiply the percentage of potash in the clinker by 3.8 we will obtain the quantity of potash in pounds leaving the kiln per barrel of clinker. The difference will be the amount of potash in pounds liberated and volatilized per barrel of cement. For example, suppose the raw materials contain O.95 per cent potash and the clinker O.80 per cent potash then : I,bs. Potash in raw material to burn I bbl. of clinker = 6 X O.95 = 5.70 Potash in I bbl. of clinker = 3.8 × 0.8 = 3.04 Potash volatilized per bbl. of cement = 266 This is equivalent to 2.66 X I.58 or 4.20 lbs. of muriate (KCl). * See Chapter XVI. 322 PORTLAND CEMENT The U. S. Bureau of Soils (Bulletin No. 572) found that the potash in the raw mix as fed into the kilns at different cement plants ranges from O.20 per cent potash at the plant of the Uni- versal Portland Cement Co., Duluth, Minn., to 1.16 per cent potash at the plant of the Three Forks Cement Co., Trident, Mont. The former plant uses a slag-limestone mix. The aver- age loss as shown by the Bureau's figures is I.93 pounds of pot- ash per barrel of cement, or eliminating the plants using slag and limestone as raw materials, 2.09 pounds. The writer made some experiments on the possibility of mak- ing Portland cement using feldspar (a mineral containing from 8 to 17 per cent potash) in place of clay and adding iron ore to supply the deficiency of iron oxide. The cement obtained from this mixture was normal in chemical composition and physical properties and from 6 to 7 pounds of potash was liberated per barrel of clinker burned. The production of potash salt or even the potash bearing dust has been discontinued by most cement manufacturers, and if practiced at all now is in connection with dust recovery systems where the prevention of a nuisance is the object sought and not pecuniary gain from the sale of potash. CHAPTER XIII BURNING (CONTINUED)—FUEL AND PREPARATION OF SAME As has been said, the principal fuels used for burning cement are pulverized coal, oil and natural gas. It will be conceded by all that the wonderful growth of the American cement industry was made possible by the rotary kiln and that the success of the latter in turn has been due largely to the use of pulverized coal. The rotary kiln is peculiarly adapted to American conditions— large output, expensive labor and cheap fuel. As originally in- troduced in the cement industry in the early nineties, it was heated by fuel oil and unquestionably its early development was hastened by the use of this fuel because of the simplicity of its application and the ease with which an oil flame can be regulated. About 1895, however, the price of oil having risen appreciably, cement manufacturers sought a cheaper fuel. Experiments were made with pulverized coal which proved so successful that in a few years this fuel was adopted by all cement manufacturers, except those located in natural gas belts or where fuel oil was cheaper. Pulverized coal has no advantages over fuel oil or natural gas aside from the fact that it is cheaper in most localities. Un- questionably natural gas is the most perfect fuel because air itself is a gas and two gases can be thoroughly mixed so that each particle of one comes in contact with the other. Liquid fuels do not burn well except from a wick or when atomized or sprayed. In the latter condition, a mist is formed which approaches a gas in the mobility of its particles. The composition of both natural gas and oil is such that no contamination of the cement results as is the case with coal. Oil, therefore, was at one time very gen- erally used for burning white Portland cement in order that no iron oxide might be introduced into the latter. The only element in oil and natural gas which might possibly prove objectionable is the sulphur. Oil sometimes contains considerable of this element, but this does not enter the cement at the high temperatures of the rotary kiln. The choice of fuel for the kiln, therefore, is purely 324 PORTLAND CEMENT a matter of cost. Fig. 96 shows diagrammatically the relative cost of various fuels and by reference to this it will be seen which fuel is most economical. In comparing various fuels the cost of handling and use must be considered and in this table due con- sideration has been given to this. To use the chart in comparing two fuels; if oil or natural gas is used, refer to the bottom of the chart and run up the nearest vertical line until the curve representing this fuel is reached, then AAP/ce O/ CO44. A £/º 7-o/Y (2Ooo zas) #2 4. & /O /2 Fig. 96.-Relation between cost of fuels, efficiency, and cost of preparation being considered. K. § Q Q § S. S U. S $ Ö 2 <3 4. 5" 6 CA O/S C2/Z – CA/y/S /*AA’ 6/9/467/Y 3 /C2 /* /& 2 o 22 24, 26 Azar/c4r oar/yazz/ea/ 645 – ce/yz's aerºr Zoao C4'ſ 7 Note: Natural gas, efficiency, 90 per cent; cost of preparation, $o.o.o. Fuel oil, efficiency, 90 per cent; cost of preparation, % cent per gallon. Grate firing, efficiency, 65 per cent; labor, 75 cents per ton. Producer gas, efficiency, 80 per cent; cost of preparation, $1.50 per ton. Pulverized coal, efficiency, 90 per cent; cost of prepara- tion, $1 per ton. BURNING—FUEL AND PREPARATION OF SAME 325 along the nearest horizontal line until the curve representing pul- verized coal is reached, and then up the nearest vertical line to the upper margin where the corresponding price of coal will be found. If it is desired to start with pulverized coal, reverse the process and start at the upper margin, etc. For example, to find what price coal used in the powdered condition is equivalent to oil at three and one-half cents per gallon, we find this to be $6.OO per ton. The dotted line abcd indicates the course to be followed to reach this conclusion. Cost of Pulveriging Coal With efficient apparatus the cost of preparing pulverized coal is about that shown in Table XXVIII. TABLE XXVIII.-Cost OF PULVERIZING CoAL, CENTRAL PLANT SYSTEM /- -, Quantity to be pulverized in 8 hrs. in tons Item of expense 50 - IOO I5o 250 Dryer fuel $,087 $.087 $.087 $.087 Labor .300 .200 .I.60 . I2O. Repairs, supplies, etc. O.73 .073 .073 .073 Power . I 50 . I5O . I5O . I 50 Milling cost per ton .6OO .5IO .470 .43O Interest and depreciation .500 .300 .250 . I7O Total cost per ton $1. IOO $0.81o $o.720 $0.6co *The above costs are based on dryer coal at $6 per ton and 8 per cent moisture in undried coal, labor at 50 cents per hour and power at one cent per kw-hr. Interest and depreciation are figured at 15 per cent of cost of plant and 3oo days’ operation, 8 hours per day. Composition of Coal for Cement Burning Formerly it was believed that the only coals suitable for burn- ing in the pulverized condition were those high in volatile matter such as bituminous coal and lignite. This supposition was based on the fact that such coals ignite more readily than do the low volatile coals. This belief was no doubt also due to some ex- tent to the fact that coals rich in volatile matter (the so-called soft coals) are much more easily pulverized than are the anthra- cite coals, the latter being difficult to pulverize. It also happens that up until the time of the World War, slack coal or “screen- ings” could be obtained much more cheaply than could run-of- mine and lump coal. This slack is usually high in volatile matter, 326 PORTLAND CEMENT and possibly for this reason was considered most desirable. As a matter of fact, the employment of high volatile coal was in- fluenced largely by the low price at which this fuel could be ob- tained and the ease with which it could be pulverized. It is quite probable that the prices being equal, high volatile coal is to be preferred because the rapidity with which it ignites would seem to make fine grinding less necessary; its soft structure also makes pulverizing comparatively easy. The temperature of the flame obtained from powdered coal, however, is so high, ranging as it does from 2,500 to 4,000° F., that practically all grades of coal can be burned under suitable conditions. Given a number of coals to select from the question would be one of economy—that is to say, the cost of the coal delivered, the ex- pense of its preparation and its thermal value, rather than its chemical composition. The coal now most generally employed for burning is gas slack and should fill the specifications below: Per Cent Volatile and combustible matter 30–45 Fixed carbon 49-60 Ash, as low as can be obtained cheaply and not over 25 In the Lehigh district good gas coal can be obtained with less than 12 per cent ash. In other sections, however, poorer coal has often to be bought. The ash, when under the limit specified, of course merely takes away from the fuel value of the coal. Above this limit it is hard to burn satisfactorily. Sulphur has no effect on the burning, except in large quantities. Iron pyrites are hard, and consequently may not pulverize. When coal containing much of this is used the pyrites may remain in coarse crystals after grinding, which are not blown in the kiln and burned, but fall from the nozzle of the burner among the clinkers and remaining unoxidized, are ground with the clinker, causing the resulting cement to develop brown stains. Practically none of the sulphur of the coal enters the cement, except as above. BURNING—FUEL AND PREPARATION OF SAME 327 TABLE XXIX. —ANALYSEs of CoALs USED FOR BURNING CEMENT Volatile combustible Moisture matter Fixed carbon Ash From Per Cent Per cent Per cent Per Cent Wellston, Ohio 2.94 41.96 42.82 I2.27 Connellsville, Pa. I.38 35.04 56.03 6.27 Fairmont, W. Va. 2. I5 34.20 57.49 6. I6 Alabama 7.50 30.70 53.80 8.00 Hocking Valley O.82 33.76 61.57 3.85 Illinois 6.59 34.97 48.85 8.00 Poor quality Penn'a. 2. IO 29.63 51.28 I6.99 Poor quality Penn'a. 2.32 27.08 47.34 23.26 Preparation of the Pulverized Coal As to the preparation of the powdered coal itself, this will de- pend to Some extent on the system which is used for burning. In general, two systems are employed—in one of which the coal is pulverized in a central plant and conveyed either mechanically or with air to the point of use (“Central Station System”). This system is employed by practically all cement manufacturers using coal for burning. In the other system, the pulverizer is located adjacent to the furnace and the coal is blown into the latter by a current of air which passes through the pulverizer. This sys- tem known as the “Unit System” is employed at only a few mills. Where the coal is pulverized in a central plant, it is conveyed into bins at the kilns and is fed from these bins as desired and blown into the kilns with air. In this system, the central plant usually consists of some form of coal crusher in order that run- of-mine and large size coal may be handled, a dryer and one or more pulverizers. The details of this equipment are given below. Coal Crushers In the older plants, the coal was usually crushed between rolls or in a small “pot-crusher.” This latter resembles most an ordinary hand coffee mill in which the grinding is done between corrugated surfaces. It is suitable for small installations only and is generally considered inferior to the special forms of coal crusher now on the market. Where a pair of rolls is used these are usually provided with heavy spikes or teeth. These two-roll or “Cornish” rolls as they are sometimes called are still much used in coal breakers where crushing of the coal finer than two and 328 PORTLAND CEMENT one-half inch lumps is not necessary, but are not adapted to finer work. As I have said, both of these forms of crusher are now largely superseded by special coal crushers of the “Single-Roll” type. These latter (Fig. 97) consist of a cast-iron frame on which is mounted a crushing roll which revolves against a concave breaker plate. The roll is usually provided with teeth. The breaker plate is hinged at its upper end and is provided with arrange- ments for adjusting the clearance between the roll and the plate. The size of the product is regulated by this opening. The roll is Fig. 97.-Single roll coal crusher–Pennsylvania Crusher Co. usually driven by means of a countershaft mounted on the frame through a pair of gears. The coal is broken between the roll and the plate. These machines are adapted to handle large lumps of coal and very wet material and will reduce the product to one inch and under. The fineness to which the coal should be crushed will depend on the size and type of pulverizer used, but one inch lumps are sufficiently small for any pulverizer used in a cement mill. The following are the usual sizes and capacities of single roll crushers when taking Ohio and Illinois coal and reducing to one inch lumps and under. When operating on Pocahontas and other BURNING—FUEL AND PREPARATION OF SAME 329 soft bituminous coal the capacity is about double that given in the table. The capacity is also increased if a coarser product is desired. TABLE XXX.-CAPACITY OF SINGLE-ROLL CoAL CRUSHERS Size crusher Approx. /- Capacity in tons per hour——--> Opening—inches H. P. I In... material I}. In. 111aterial I8 x 18 I5 20 3O 24 X 24 30 5O 7O 3O x 30 40 75 IOO 36 x 36 60 II5 I50 Drying the Coal In order to get the greatest efficiency out of the pulverizing machinery, it is necessary to dry the coal so that it does not con- tain more than I per cent moisture. Still better results will be obtained if the moisture is reduced to about one-half per cent. For cement burning, where the stack gases leave the furnace at a high temperature, there is no economy in grinding coal without drying, and often there is some objection in such practice. For example, if the gases leave the furnace at a temperature of 2,500° F., every pound of steam carries out 2,600 B. t. u., while at 400° F. the average temperature of dryer waste gases, the steam only carries off 1,300 B. t. u, or about half as much. It is only fair to say, however, that with coal containing IO per cent moisture, this would only represent a loss of about I per cent of the heating value of the coal; so that this objection is theoretical rather than practical. The drying temperature should not be allowed to exceed 212° F., by any considerable degree as otherwise some of the volatile matter of the coal will be lost. If kept around this temperature, there is no danger of driving it off. Several forms of dryer are now used for drying coal. The simplest of these is a properly designed direct-heat dryer. Other forms in common use are the Ruggles-Coles dryer and the Mat- cham or Fuller-Lehigh dryer. 33O PORTLAND CEMIENT Fuller-Lehigh Dryer The Matcham dryer was developed in the Lehigh District of Pennsylvania and is used quite extensively in the cement industry. It was the design of the late Mr. Charles A. Matcham, of Allen- town, Pa. This dryer with some modifications and improvements is now on the market under the name of the Fuller-Lehigh Dryer." * Fuller-Lehigh Company, Fullerton, Pa. In this latest form it consists of an inclined cylinder mounted on steel tires which revolve on rollers. The cylinder is turned by means of a girt-gear and pinion at an approximate speed of one to four revolutions a minute. The inclination of the cylinder is approximately five-eighths of an inch to the foot and it revolves partly in the brick housing which contains the furnace. The hot gases pass up around the cylinder and thence through a short flue to the discharge hood and from this up through the cylinder. Draft is provided either by means of a stack or an exhauster fan. The latter is to be preferred. (See Fig. 98). Fig. 98.-Matcham coal dryer. The coal is fed in at the upper end of the cylinder and owing to the inclination of the shell, the material is gradually moved for- ward as the cylinder revolves until finally it reaches the lower end of the cylinder where it drops out into a hopper and from this latter it is usually spouted to the boot of an elevator. Z-bars or other forms of lifters are bolted to the inside of the shell and as BURNING—FUEL AND PREPARATION OF SAME 33I the cylinder revolves these lift the coal and drop it in a steady cascade through the hot gases from the combustion chamber, which are passing through the cylinder. This exposes a large surface of coal to the drying action of the gases and tends toward efficient drying. This dryer is made in various sizes. These are given in Table XXXI together with the power required to operate and the capa- city based on coal having less than Io per cent extraneous mois- ture, as stated by the manufacturer. TABLE XXXI.-CAPACITIEs of FULLER-LEHIGH DRYERS 2– º Size ~, Capacity Power to Diam. Length per hour operate Ft., in. Ft. Tons H. P. 3-O 20 2 5 3-0 30 4 8 3-6 30 6 IO 4-6 30 8 I2 4-6 42 IO I5 5-6 42 I4 I7 6-0 42 2O 2O 6-6 42 25 24 Ruggles-Coles Dryer" The Ruggles-Coles (Class A) Dryer consists of two concentric cylinders which are fastened together and revolve on steel tires supported by rollers. The dryer is revolved as in the case of the Matcham Dryer by means of a girt-gear and pinion. The inner cylinder extends beyond the outer one at the head end and is connected with a brick furnace by a flue lined with fire brick. The coal is fed into the head end of the dryer between the two cylinders and is caught up by flights on the inside of the larger shell and dropped on the hot inner shell. As the machine con- tinues to revolve, the coal in turn drops from the inner shell to the bottom of the larger one, is carried up by the flights and again dropped on the hot inner shell, etc., and gradually works its way through the cylinder due to the inclination of the latter. (See Fig. 99). The hot products of combustion pass from the furnace down through the inner cylinder and then back between the shells. 1 The Hardinge Co., New York, N. Y. 332 PORTLAND CEMENT Draft is induced through the cylinders by means of an exhaust fan. The drying is effected by means of the hot inner shell and the current of hot gases to which the material is subjected. Fully Fig. 99.—Ruggles-Coles dryer. dried coal is discharged through the center of the rear end by means of a special arrangement of lifting plates. This dryer also is made in a number of sizes which are indicated below. TABLE XXXII.-SIZE, CAPACITY, ETC., RUGGLEs-CoLEs DRYERs Dia1n eter Length outer cylinder outer cylinder Capacity in Power NO. I n . Ft. tons per hr. to operate A-I 36 I6 2 6 A-2 48 2O 4 IO A-4 54 26 5% I 2 A-8 60 3O 8% I6 A-IO 7o 35 I3% 2O A-12 8O 45 I8% 33 A-I4 90 55 24 45 Both the Fuller-Lehigh and Ruggles-Coles Dryers are what are known as “Indirect Fired Dryers”—that is, the gases from the furnace do not come directly in contact with the material to be dried but are first allowed to cool somewhat so that when they come in contact with the coal being dried, there is no danger of the latter being ignited or even suffering the loss of any of its volatile content. BURNING—FUEL AND PREPARATION OF SAME 333 Direct Fired Coal Dryer By so placing the combustion chamber that there is no pos- sibility of any flame coming in direct contact with the coal being dried, it is possible to use direct-fired dryers for drying coal and many of these are now so used. In order to accomplish this re- sult, it is only necessary to set the grate at a sufficient distance from the end of the cylinder to have the gases of combustion cool below the point at which the coal ignites. This is accom- plished by placing a brick chamber between the fire box and the cylinder. The cooling of the gases is also facilitated by leav- ing openings in the chamber between the grate and the end of the cylinder so that air can be mixed with the products of combus- tion and further cool these. It is desirable in the case of these dryers to install a pyrometer where the gases enter the cylinder in order that the temperatures may be controlled. This pyrometer should be attached to an automatic governor by means of which air is added to the fur- nace gases to cool these as needed. While the entrance of the air cools the combustion gases, it does not necessarily detract any from the efficiency of the dryer, because hot air itself is an ex- cellent medium for drying. Everyone is familiar with the rapidity with which a substance may be dried if it is placed in a current of warm air. This is due to the capacity of air for taking up mois- ture and this capacity to take up moisture increases with the temperature of the air. For instance, IOO cubic feet of air at 60° F. will absorb approximately O.O82 pound of water. If we heat the temperature of this air, however, to IOO’ F. it will increase to IO8 cubic feet and will absorb O.305 pound or about four times as much. This difference becomes much more marked when we heat the air to higher temperatures. This action increases very markedly the efficiency of both the direct and indirect types of dryer. A fan is desirable to furnish draft in the case of any dryer because of the larger volume of air which may be em- ployed thereby. The capacity of a direct-heat dryer is greater than that of an indirect dryer of the same size. Table XXXIII gives the aver- 334 PORTLAND CEMENT age figures for direct-fired dryers of various sizes when drying coal containing IO per cent moisture. TABLE XXXIII.-CAPACITY AND SIZE OF DIRECT FIRED CoAL DRYERS Size —w Diam. Length Capacity in H. P. to operate Ft. Ft., in. tons per hour with stack draft 4-O 40 7-8 7% 4-6 45 IO-I2 IO 5-0 5O I2-I4 I5 6-0 60 I7-2O 2O In the cement industry it is usual to discharge the gases from the coal dryer directly into the air by means of a stack or fan. The more modern practice, however, is to discharge the gases into a cyclone collector and from this into the air. The cyclone collector is, of course, designed to catch the fine particles of coal which are carried out by the gases and so reduce the dust loss from the dryer. - It is possible to fire any of the three types of dryer mentioned by means of pulverized coal. The powdered coal must be burned in a Dutch oven of appropriate design and care, of course, must be exercised that the flame does not extend so far beyond the nozzle of the burner that it will reach and ignite the coal being dried. The dryers are usually fed from an overhead bin by means of some mechanical device such as a reciprocating feeder or a re- volving table. The former is the more usual method. The feed is attached to the driving mechanism of the dryer so that when the dryer ceases to revolve the feed stops. Pulveriging the Coal Four types of pulverizers are now in general use for pulveriz- ing coal, while several more are in use at a few plants only. In the early days of the cement industry, the Griffin Mill was quite generally used for pulverizing coal, but while still used to some extent in this industry, it is not, So far as we know, being in- stalled in any new plants. The types of pulverizer now most commonly used are the Fuller-Lehigh and Raymond Mills. A BURNING—FUEL AND PREPARATION OF SAME 335 few plants employ tube-mills and one or two, Bonnot Mills. Fuller, Raymond, Bonnot and Griffin Mills are self-sufficient units, but the tube mill requires that the coal shall be prepared for it by Some other grinder which will reduce the coal to approx- imately IO- to 16-mesh material. All these mills are described in Chapter X. The tube mill is not so well adapted to pulverizing coal as the first mills referred to. The principal objection raised to the high speed mills has always been one of repairs, as it is generally con- ceded that they are so far as power goes, more economical grinders than the tube mill. Coal, however, is soft and easily ground if properly dried and the repairs in the case of ordinary bituminous coal free from pyrite are low, so that the objection raised to the high speed mill for grinding clinker will not hold here. In addition to the advantage of being a self-sufficient unit, the high speed mills require less floor space and do away with the extra elevator and bin necessary for the two-stage reduction. The tube mill requires that the coal fed to it shall be ground so that all of it will pass a Io- to 16-mesh screen. This latter operation is usually conducted in a ball mill, a kominuter, or more frequently in some form of hammer or cage mill such as the Pennsylvania, Williams or Jeffrey hammer mills or the Stead- man Cage Disintegrator. The good points of the tube mill are its simplicity and the fact that repairs were exceptionally low. Its bad features are high power consumption per ton of output, large floor area required by the installation and the disadvantage of TABLE XXXIV.-CAPACITIES OF TUBE MILLs GRINDING COAL Mill charged Mill charged with steel balls 2–– with pebbles —N r- and pebbles— –y 2–—Size Weight of *Output in Weight of Weight +Output in Diam. Length charge of tons per Steel of tons per Ft., in. Ft. pebbles—1bs. hour H. P.++ ball$ pebbles hour H. P.++ 5 22 2O,OOO 5 8O 9,000 I5,000 8 IOO 5-6 22 24,000 6% IOO II,000 18,000 IO I2O 6 22 29,000 8 I25 I3,OOO 22,000 I3 I50 *Mill to receive a feed all of which will pass a 16-mesh screen. ** About 150 per cent of this power is required for starting. This does not in- clude power required to prepare feed for the tube mill which will add about 35 per cent to above figures. 336 PORTLAND CEMENT the two-stage process, necessitating as it does an extra mill, bin and elevator. The output and horsepower required to drive tube mills, when grinding bituminous coal of average hardness to a fineness of 95 per cent passing the IOO-mesh sieve is given in Table XXXIV. General Coal Plant Arrangement Run-of-mine and even screened coal often contains scrap iron such as parts of mine machinery and cars, bolts, nuts, etc. These are apt if they enter the pulverizer to cause break-downs or at least excessive wear to the latter. It is now, therefore, general practice to protect the pulverizer by the employment of a mag- netic separator at some point before this. The form of separator generally used consists of a magnetic head pulley over which the conveyor belt passes. This serves to divert the iron from the coal discharge and so free the latter from the former. It is now quite general to include automatic recording scales at some convenient point before the dryer. These are usually placed at either the discharge of the elevator which carries the coal up into the dryer feed bin or else between the bin and the dryer. The coal as it drops from the dryer is usually led by a hopper and spout into the boot of a bucket elevator and carried up into a bin which feeds the pulverizers. In the early days of the cement industry several bad fires and explosions occurred in connection with the pulverizing of coal. As the result of this the danger of an explosion was at one time often raised as an objection to the use of powdered coal. This latter danger, however, was always very largely exaggerated and it has now been many years since an explosion occurred in the coal pulverizing department of a cement plant. Powdered coal suspended in air is a very explosive substance and indeed the energy of a pound of coal in this condition is greater than that of a pound of gunpowder. At the same time, however, powdered coal in a mass, that is, when it is in a pile or a bin, burns very slowly and with absolutely no explosive effects. BURNING--FUEL AND PREPARATION OF SAME 337 The idea, therefore, in preventing coal mill explosions is not to allow the coal dust to be stirred up and mixed with air. The department of the plant in which the coal is ground should always be well ventilated so that no gas can accumulate. This can be accomplished by the use of a monitor running the full length of the roof and having louvers so that any gases which may be generated from the coal will rise to the roof and so escape In place of the monitor, any of the accepted forms of roof ven- tilator can be used. Reinforced concrete offers a splendid ma- terial for the construction of fuel-mill buildings as the walls are straight and there are no projections to catch dust. In order that any fires which start in the coal pulverizing de- partment may not be communicated to other parts of the mill, this building should be fireproof and located with at least an alley be- tween it and the other parts of the mill. Stairways, bins, plat- forms, conveyor troughs, elevator casings, etc., should be made of sheet steel. Platforms and steps should be constructed of perforated sheet steel, or better still Irving's Subway Grating, or Some similar form of bar grating may be used to advantage, as less dust collects on them in consequence. The electrical wiring of the mill should be carefully installed and the lights placed to best advantage. The latter should be of the incandescent type. Arc lights are not permissible. Most fires in coal mills result from attempts being made to repair elevators and mills by the light of the ordinary workman's torch. The hammering shakes the dust from its lodging place and the naked flame ignites the mixture of dust and air. No naked lights should be allowed at any time in the coal pulverizing building and warn- ings against the uses of torches, etc., should be displayed prom- inently here and large signs to the same effect should be placed upon the doors. This rule should be rigidly enforced with the penalty for breaking it of dismissal. Conveying the Coal With all of the types of pulverizer which have been described, the powdered coal is conveyed from these to a large bin or num- 338 PORTLAND CEMENT erous small ones located adjacent to the kilns. Until very re- cently, the practice in the cement industry has been to convey the coal to the point of use by means of a screw conveyor and bucket elevator. This could be easily done because with the exception of a very few plants where the raw material dryers were also heated with pulverized coal, this latter had to be conveyed only to the kilns. This permitted the fuel pulverizing building to be located adjacent to the kiln building and one straight screw con- veyor carried the powdered coal to the kiln bins. In some in- stances the coal mill and kiln building adjoined each other. It was generally considered better practice, however, to have at least an alleyway between the kiln building and the coal mill. At a few plants, screw conveyors of several hundred feet were required to carry the coal to the kiln building but at most plants a conveyor half this length was sufficient. The more recent installations for handling coal in the cement industry employ the Fuller-Kinyon system. A “blow-tank” sys- tem is often employed for conveying powdered coal in metal- lurgical plants but this latter method has never found use in the cement industry. Fuller-Kinyon Pump The Fuller-Kinyon system consists of four elements: I. A power-driven pump, the function of which is to start the mass in motion. 2. A source of compressed air supply. A pipe line through which the material flows. 4. Diverting valves which permit the flow of material to be discharged through any one of a number of branch lines leading into the kiln service bins. 3. The pump (Fig. IOO) embodies a specially designed worm or screw revolving in a closed chamber or working barrel. The screw is mounted on an extension shaft which passes through end packing boxes in the casing and is supported on outboard bearings. This arrangement prevents contact between the bear- ing metal and the pulverized material. The screw is usually BURNING—FUEL AND PREPARATION OF SAME 339 driven by a direct-connected motor. A separate motor-driven air compressor is provided to furnish the necessary air for aerat- ing the coal. However, where an air compressor is already in- stalled in the plant, this unit is depended upon for the air supply. Fig. 100.-Fuller-Kinyon coal pump. Pulverized coal is fed from the storage bins or from the Fuller mills direct into the pump hopper by gravity and is carried by the screw to the discharge end. The design of the worm is such that the material is compressed as it moves forward so that at the end of the worm it is dense enough to act as a seal or check against the compressed air and prevent the latter from blowing back into the feed bin. At the discharge end of the screw, the mass is aerated by a small amount of compressed air at moderate pressure. The pres- sure and amount of air are regulated and depend upon the dis- tance, height, etc., to which the material must be conveyed. This aeration changes the nature of the material from a compact mass to a semi-fluid, in which state it is carried to its destination. The amount of air used is so small that no cyclone separator or dust collector is required at the point of delivery. An extra air line, 34O PORTLAND CEMENT by-passing the pump, is supplied so that the pipe line may be cleared of material whenever the pump has been stopped. The pump, consisting of a 6-inch worm, is capable of handling upward of 50 tons of pulverized coal per hour, and easily handles material a distance of over 1,500 feet. The power is approx- imately the same as would be required for screw conveyors and elevators doing the same work. The air pressure required var- ies from about I5 pounds per square inch for short distances to about 45 pounds for longer distances. The air volume varies from 6 to 8 cubic inches free air per cubic foot of pulverized coal handled. Distribution Line The conveying line is usually built of ordinary black or gal- vanized iron pipe properly jointed to eliminate recesses in which particles might lodge. The diameter depends upon the quantity of coal to be transported, but ordinarily varies from 3 inches to 5 inches. The pipe line may be carried in the most convenient manner such as on Overhead supports, laid underground, or placed on the surface to follow the natural slope of the land. Bends, elevations and depressions do not decrease the satisfac- tory operation of this system, although no doubt as with liquids they increase the frictional resistance to the flow of the coal and hence increase the power or air required. Distributing valves are placed in the main line at points where the main flow is to be diverted to one or more branch lines. In the Fuller-Kinyon system, these are of the disc, multiple dis- charge type and are electro-pneumatically controlled from a con- venient point. Their action is positive, preventing the flow past the ports which are in closed circuit and at the same time allow unobstructed passage through the open main. The individual kiln bins may be equipped with indicators showing the condition of the contents of the bin. In the Fuller- Kinyon system, there are high and low point indicators, which automatically and instantly reflect the condition of the bins on the switchboard located at any convenient point in the coal prep- BURNING—FUEL AND PREPARATION OF SAME 34I aration plant. Thus the operator under this system has constant intimate knowledge of the fuel supply in all the bins throughout the plant, and by means of the electro-pneumatic valves he can' instantly direct the flow of material from the main line to any individual point without leaving the coal house. Equipment Employed for Heating the Kiln with Powdered Coal The apparatus originally developed in the cement industry is shown in Fig. IOI. This arrangement is more or less typical of Fig. Ior.—Method of burning powdered coal. (B. F. Sturtevant Co.) modern powdered coal installations also. It consists of a bin in which the pulverized coal is stored, a worm feeder from which it is delivered into an injector through which air is forced by a pressure blower. The injector may be of cast iron, but it was quite common in the cement industry to have them made of gal- 23 342 PORTLAND CEMENT vanized iron by a local tinsmith. The blast pipe leading to the kiln is often also of galvanized iron, in which event it terminates in a nozzle of wrought iron which projects for a foot or more through the hood into the kiln. Lap-welded steel or wrought iron pipe, however, makes a much neater and more permanent job than galvanized iron. The worm is operated by means of some form of variable speed control. (See also Fig. IO4). The feed bin does not differ materially from other bins except that it should have a hopper bottom and the sides of the latter should be steep. It is always best to have one side perpendicular as shown in the drawing and still better results will be obtained if three sides are perpendicular, as this gives less hold to the toe of the arch. The bin should, of course, be dust-proof. It should be made of steel plate and supported on a light frame of structural steel made without cross-pieces. Steel tanks are sometimes used but are less desirable than the hoppered bottomed square bins. Round bins with cone-shaped hoppers are also used but the square bins of the type described are to be preferred to these also. As pulverized coal is perfectly dry, no corrosion will occur in these bins from the sulphur in the coal, as happens when steel bins and bunkers are employed in connection with stokers. Air for Carrying Coal It will be recalled that theoretically approximately IO pounds of air are required to burn a pound of coal. This weight of air occupies under ordinary temperature and pressure a volume of 125 cubic feet, while one pound of coal neglecting voids has a volume of less than O.OI2 of a cubic foot. It will be seen, there- fore, that if this volume of coal is blown into a furnace with at least 25 per cent of the air necessary for combustion (or 34 cubic feet) that the volumes of coal and air will bear respectively the relation of I to 2,833. There is, of course, no objection to increasing the air to the full amount required by theory, and indeed this is often done, when the volumes will be as I to II,332. It will be seen, there- fore, that provided the coal is dry and the particles are not clotted BURNING—FUEL AND PREPARATION OF SAME 343 together by moisture, etc., there is ample opportunity for the coal particles to be surrounded with sufficient air to at least cause their ignition. In cement burning, instantaneous combustion is not only unnecessary but, in fact, is not desired, the only requisite for economy and the desired effect being that the particle of fuel shall be completely consumed in the forepart of the kiln. In the early days of powdered coal, it was the practice with high pressure air (60 pounds or more) to employ about IO per cent and with low pressure air (6 ounces or more) as little as 25 per cent of the air necessary for complete combustion. Now, how- ever, it is becoming more and more the practice to mix with the coal in the burner a comparatively large percentage of the air nec- essary for combustion. Manifestly as we approach this condi- tion more rapid combustion will occur. In some of the earlier installations in the cement industry com- pressed air was used, while at a few installations a steam jet was employed. The general practice now, however, is to use an ordinary centrifugal fan or pressure blower and operate this under a pressure of from 4 to Io ounces, which gives sufficient velocity to the air in the blast pipe to carry the coal into the furnace. These fans if properly designed and run at the speed required for this pressure give a regular and constant supply of air under uniform pressure. They are simple in construction and easily kept in repair. They consequently meet all require- ments as to air supply. Worm Feeder for Coal The problem of supplying a regular stream of coal to the kiln, however, is by no means so simple. Practically all equipment now employed makes use of a worm or helical conveyor feeder and the amount of coal delivered is regulated by the size and speed of the screw or worm. There are objections to this form of feeder but no better device has been offered. The amount of coal which will be fed out of a bin by a given worm revolving at a given speed under uniform conditions is definite and fixed. Unfortunately, however, these worm feeders do not work under constant conditions. The chief variable in- 344 PORTLAND CEMENT fluencing the rate of feed is the quantity of coal in the bin, so that unless the coal is of the same depth in the bin at all times, the quantity of coal delivered by the worm at a given speed is apt to vary. In practice, however, this feature is not so serious as it sounds because as the quantity of coal in the bin increases or decreases, the attendant has merely to vary the speed of the worm at in- tervals in order to keep the coal supply constant. The real trouble is to provide against sudden rushes of coal or a marked diminu- tion of the quantity delivered. Both troubles usually result from the “arching” over of the coal in the hopper part of the bin so that the coal does not flow regularly into the burner. The sudden breaking of the arch due to the weight of the coal above it, or, as often happens, the effort of the kiln attendant to break the arch by hammering on the sides of the bin, will cause a sudden rush of coal into the feeder and consequently into the kiln. This difficulty can be eliminated to some extent by proper construction of the feed bins and de- sign of the feeder. The worm feed is usually bolted directly to the bottom of the bin. Steel sliding plates or gates are placed between the bin and the feeder so that the coal can be entirely cut off from the latter. This allows repairs, etc., to be made to the worm without empty- ing the bin. The worm consists of a helical screw which revolves in a tubular housing. This screw is made of either thin steel plate or cast iron. If the former, it is usually made with flights half the pitch of the standard screw conveyor, as this gives a more regular feed and also a greater obstruction to the flow of the coal, which under certain conditions will flow around the shaft of the screw just as would a liquid. It will be noted that the worm and tube extend beyond the bottom of the bin. This is done in order to prevent the coal from flushing or flooding the burner. The tubular housing fits close to the worm for the same reason. BURNING--—FUEL AND PREPARATION OF SAME 345 TABLE XXXV.-CAPACITY OF WORM CoAL FEEDERS MADE FROM STANDARD HELICOID Conveyors. WEIGHT OF PULVERIZED COAL TAKEN As 40 POUNDS TO CUBIc Foot. Pounds of Diam. of Pitch Diam. Thickness Pounds of coal coal per hour conveyor of flights of shaft of flights per revolution at 50 r. p. m. In. IIl. I11. In. I,bs. I,bs. 3 3% Iºſis O. I406 0.30 OOO 4 4% I''/16 o.1875 O.96 2,880 5 6 2/18 O.250 I.99 5,97O 6 6% 2/16 O.25O 3.4I IO,230 The worm revolves in a casing which is usually made in several parts and according to the ideas of the maker. The writer makes the hopper part below the bin of plate metal and the tubular part extending beyond the bin of steel or cast iron flanged tubing. The chief points to be taken care of in the design of the casing are: (I) To have the tube fit the worm snugly, but at the same time the two should not actually rub: (2) To so arrange the parts that the worm can be drawn out easily for repairs to the flights, etc. : (3) To give a rigid support for the end bearing so that the shaft will be kept properly centered, and (4) To make all connections dust-proof. The amount of coal fed out of the bin by the worm will depend on the size of the worm and of the pipe on which it is mounted, the pitch of its flights and the speed at which it revolves. As I have said, helicoid conveyors used for this purpose are often made one-half of the standard pitch and the sizes generally employed range from 3 to 6 inches conveyors. The capacity of such con- veyors is given in Table XXXV. If the pitch is half the standard figures, the feeder will deliver only one-half the coal shown in this table, etc. Liberal allowance should be made from these figures in actual work. Equipment for Reducing and Varying Feed The shaft of the worm is usually keyed to the larger one of a pair of bevel gears and the worm is so driven. Another good arrangement is the friction disc and wheel described below. Sometime a worm gear is used and occasionally a gear and pinion. 346 PORTLAND CEMENT The simplest and also the crudest method of varying the speed of the worm is by means of a pair of stepped pulleys connected by a belt such as is employed for altering the speed of machine tools, etc. The objection to such a method is that the fuel con- trol is by steps and intermediate points between those given by the various steps are not possible; whereas kilns are often sus- ceptible to very slight changes of fuel and one step on the pulley might give too hot a kiln and the next below, one which is too cold. The step pulleys are not now used to any extent and have been superseded by some of the patented forms of speed control such as the Reeves, the Mosser or that made by Moore & White. An- other form of speed control which gives good satisfaction is that of the disc and friction pulley. osci Mozzzz /eeae, AN 'X& AN ^ =2~Rºkº Z N 2. ee/ Z NZT Y NZ NZ AZZee/ Fig. 1 oz.-Disc and wheel worm feeder for pulverized coal. BURNING—FUEL AND PREPARATION OF SAME 347 This latter is more or less of a “homemade” affair and will be described first. It is shown in detail in Fig. IO2. It consists of a friction disc which is revolved by means of a friction pulley. The disc is keyed to the worm shaft and the pulley to a counter- shaft driven at constant speed. The surface of the pulley is often covered with rawhide to give greater friction. This pulley is arranged so as to slide back and forth along the shaft, being moved by a screw rotated by a hand or chain wheel, which screw in turn moves a nut connected by a link to a collar on the friction wheel. Manifestly as the wheel is brought nearer to the center of the disc, the latter revolves more rapidly, etc. The pressure between the wheel and disc is kept constant by means of a spring which acts on the worm shaft. The Reeves, the Mosser and the Moore & White speed con- trols are all on the market and may be obtained from the makers. When the coal feed is driven from a line shaft, they may be em- ployed to advantage although the friction disc and wheel is simpler and in the writer's opinion is more satisfactory as the belts of the speed controls give trouble. When motor drives can be employed nothing will answer better, however, than to employ a variable speed motor. When these latter are used the plan is to drive the shaft of the feeder by means of either a worm and gear or else to employ some form of spur- gear or worm-gear speed reducer between the motor and the shaft. It is needless to say that gears encased and running in oil are to be preferred to those without casings. A neat arrange- ment consists of a variable speed motor connected to the feed screw by means of a reliable worm-gear reducer. The horsepower required to operate the feed is merely nominal. The small sizes can be driven by a I or 2 horsepower motor and the largest by a 3 horsepower one. Burners The coal usually drops from the feeder into what is known as the “burner” or injector. This in its simplest form is shown in Fig. IO3 and consists of a short cone within a tube. The coal is 348 PORTLAND CEMENT usually fed into the injector at a point just behind the small end of the cone. The air enters the larger end of the cone and issues in the form of a jet from the smaller end. The sudden expansion * CZ//~ --> Cocº & —- ) * - - —- aſ 2׺kº- fo A//zz ——- Fig. Io9. of the air as it leaves the jet causes a partial vacuum in the space behind it, with the result that air is sucked into the tube through any openings placed behind the apex of the cone. Usu- ally only a part of the air is blown through the nozzle of the inner cone, the balance is sucked in with the coal. This secondary GAA/º APA2/YAS" Tº || Jaazy - t gº AEA.A.S 7" & MZ /. Ary/26" cel, G.47 AT SA. A 6'4/A OAT ºr/6 64. AE. Oz. 7 S 7 O D O/ASTA® Aw'ZA'A'z. Aſ AZO, ZO/S 7" cº, --> --- - - - - r | t t ſ ! º | | cºs 34% I | t ; Y. Z2A; 7/9/Z. O/F //XMATC7 O/k’ | 1 ſº Nº. Fig. Ioa.—Burner and injector made of standard pipe fittings. BURNING——FUEL AND PREPARATION OF SAME 349 air can be very readily controlled by means of a shutter or reg- ister. The best place to admit this secondary air is where the coal drops down, as this allows the air to mix with the coal and help carry it into the injector. An arrangement of feeder, injector and fan employed by the writer for rotary kiln heating is shown in Fig. IO4. It is made of standard pipe fittings and parts. The worm is a piece of half pitch screw conveyor and the extension of this beyond the bin is encased in a piece of ordinary wrought iron pipe. The bearings are made of cast iron and bolted on the pipe flanges. The worm is driven by a variable speed motor through an encased worm gear. When a motor can not be conveniently used, the disc and wheel arrangement previously described is used. The injector is made of standard pipe fittings and consists of a cross-tee which the air cone fits as indicated. The upper branch of the cross receives a nipple which connects with the coal feed. The branch below this receives a pipe which rests on the floor and serves to help support the burner, while the fourth branch connects with the furnace. Air is admitted above the coal feed. If more air is de- sired it may be admitted back of the air cone. Steam and High Pressure Air Burners Occasionally injectors are operated by means of steam or compressed air and Fig. IO5 shows an injector suitable for this purpose. (An injector similar to those shown in Figs. IO3 and IO4 except that a steam pipe takes the place of the cone described above may also be employed). C |- %f=# #4, # ź 2N £4%=º, sº--------- ====----- + -— TT *-*---------_ *N*====== I - - * Ø2 i:=== -Fºssº SS -is &S*4 a *22222zz: .* z:#Eis iss v. sº-F#44 “r- * Fig. IoS.—High pressure coal burner. 35O PORTLAND CEMENT The high pressure burner shown consists of a series of cones placed one within the other. The orifice of each cone being some- what larger than the preceding one. High pressure air or steam at 60 to 80 pounds is led into the first cone at HPA. As it ex- pands it sucks a portion of air through the openings AA. As it leaves the first cone it expands again sucking a further portion of the air through the openings BB. As it leaves the second cone and enters the third one, it expands a third time sucking a third portion of the air through the opening CC. Coal is fed through the openings D1, D2 and D3, from a worm feeder above similar to that employed for the low pressure burner. In this burner the great difficulty is, of course, to so proportion the coal that each opening will deliver some to the burner. The difficulty of doing this will be appreciated. It is much more expensive to operate a burner with high pressure air than with air from a blower so that these high pressure burners are not now used to any great extent. Where steam is employed a large volume of air is sucked into the burner and this air is really the carrying medium for the coal, Charles A. Matcham, manager of the Lehigh Portland Cement Company in 1908 took out a patent on a method of introducing pulverized coal into the cement kiln by means of the draft of the latter. His “natural-draft” system consists in feeding the coal from a bin by means of a worm in a thin sheet across a slit in the hood or end housing of the kiln. Air sucked in by the draft of the kiln through this slit picks up the coal here and carries it into the kiln. No fans or blowers are required and the necessary draft is secured by means of a stack of the proper height. This system was never used to any extent in the cement industry. Another burner which was developed for cement is that de- vised by W. R. Dunn, superintendent of the Vulcanite Portland Cement Company. This burner is intended to give a more inti- mate mixture of air and coal than is secured by the ordinary feeders. In order to secure this result, instead of dropping through one opening in the bottom of the conveyor trough, the coal falls through a number of such openings, while air is sucked BURNING—FUEL AND PREPARATION OF SAME 35I in above and passing down through these openings mixes with the fuel. Practically all of the firms making a specialty of pulverized coal installations have developed burners. Most of these are modifi- cations of the standard cone and worm with some additional features designed to regulate the air supply or to give better mix- ing of the air and coal. Unit System and Aero Pulveriger The Unit system, in which the coal is pulverized and blown into the furnace by one machine, has been employed to a very limited extent in the cement industry, The general impression seems to be that the system is inefficient as regards power and re- pairs and does not grind the coal fine enough. This is not borne out by the writer’s experience. So far as power consumption and repairs go an installation of Aero Pulverizers will operate as economically as will a central station plant, when power required to transport and blow the coal into the furnace is also considered in connection with the latter. These pulverizers will also grind coal sufficiently fine for cement burning, where a fineness of 90 per cent passing the No. FOO mesh sieve is sufficient, and no economy can be shown by pulveriizing any finer than this. The unit pulverizers require no dryer unless the coal is very wet. They show better efficiency as regards power if fed with dried coal, however. The best known unit pulverizer is the Aero. This consists of three or more communicating chambers, (Fig. IO6), each slightly larger in diameter than the preceding one. A series of paddles mounted on discs, which are in turn keyed to a central, horizontal shaft, revolve in each chamber. An addi- tional chamber at the end of the pulverizer nearest the furnace contains a fan the function of which is to blow finely pulverized coal and air through a pipe to the furnace. The communicating chamber provides the air separation within the unit and an ade- quate control of the fineness. The coal is fed into the pulverizer by means of an automatic feed. Some air is also admitted with the coal through inlets in 352 PORTLAND CEMENT the feeding device. An additional supply of air can be admitted at a point just preceding the fan chamber and the regulation of the air supply used for combustion is usually effected at this - | - Fig. ros.-Aero pulverizer with cover lifted. point. The pulverizer runs at a constant speed and the supply of coal burned in the furnace is regulated at the feed mechanism of the pulverizer. - One of the outstanding advantages of the aero-pulverizer is the uniform mixture of air and coal obtained in the fan chamber. The thoroughness of this mixture determines more than any other factor the ability to burn coal efficiently, whether coarse or fine. Fuel engineers now generally agree that a uniform mixture of air and coal is fully as important as fineness of the latter and re- peated tests which have been made by the Bureau of Standards and other users of pulverized coal indicate that when the mixture of coal and air is complete and the furnace of proper design, moderately coarse coal is burned as efficiently as the fine product. BURNING—FUEL AND PREPARATION OF SAME 353 Owing to the fact that the operation of the furnace is dependent on the pulverizer being in operating condition, it is highly desir- able that repairs can be quickly made. The parts most subject to wear are the paddles and liners. The latter have a compara- tively long life and the replacements most often necessary are the paddles, hence it is well to provide close at hand an extra rotor with paddles attached, so that repairs can be rapidly effected. The time required to make the change from the old to the new rotor need then not exceed 20 minutes. These pulverizers are made in a number of sizes ranging in capacity from 600 pounds of coal per hour to 5,000 pounds. The horsepower required varies from Io horsepower for the smaller size to 60 horsepower for the one of largest capacity. Table XXXVI gives the makers' figures as to size, capacity and normal power consumption of the various sizes of this mill. TABLE XXXVI.—CAPACITY AND Power CoNSUMPTION OF AERO CoAL PULVERIZERs. Normal power Size Capacity consumption A 600 IO B I,OOO I4. D I,800 25 E. 3,000 40 G 5,000 60 The most recent installation of Aero pulverizers in a cement mill is in connection with the new plant of the National Cement Com- pany, Montreal, Fig. IO7. In this plant, there are three kilns, 9 feet by 160 feet, dry process. Each kiln has its own aero pulver- izer, the Size G being used. This size is good for 5,000 pounds of coal per hour. In order to faciliate repairs, an I-beam passes over the mills so that the rotors and liners can be easily replaced, a spare rotor and paddles being kept on hand for this purpose. A fourth aero with its motor is also mounted on a truck. This truck moves on a track behind the row of regular pulverizers. In case of accident to one of the latter or its motor, the spare pulverizer is moved into position and connected up with the kiln. This can be done in a few minutes thus avoiding any shutdown. 354 PORTLAND CEMENT Fig. 107.—Arrangement for heating kilns with aero pulverizers— National Cement Co., Montreal, Que.. BURNING—FUEL AND PREPARATION OF SAME 355 The aero can be best driven by means of direct connection through a flexible coupling to a motor of the proper Speed. Storage of Coal. Cement plants are required to keep on hand a considerable amount of coal in order to have a steady supply independent of car shortages, transportation tie-ups, strikes at the coal mines, etc. Slack coal is also somewhat cheaper during the summer months than in the winter and many consumers purchase and store a large part of their yearly requirements in the former season. Coal is generally handled in the newer cement works by a locomotive crane equipped with a clam shell bucket. In the older plants, a trestle with or without underground conveyors is sometimes employed. There is some risk of fire in storing coal in open piles. O. A. Done, writing in Engineering News, gives the follow- ing hints on the prevention of Spontaneous ignition in coal piles. The amount of moisture in a bituminous coal is a measure of the risk of spontaneous combustion when the fuel is stored. Bituminous coal should not contain more than 4.75 per cent water. Coal bins should be of steel or iron protected by con- crete and should be roofed over. Free air passages should be provided around the walls and beneath the bins to keep the pile cool, and the depth of the coal should never exceed 12 feet. It is useless to provide air passages in the body of the pile as these only tend to promote oxidation. Hence cracks, etc., in the walls of the fuel bin increase the risk. - Oil Oil is employed where it can be obtained more cheaply than coal. This is an excellent fuel easily employed and free from ash. Oil is burned by spraying it into the kiln with air or steam. The apparatus employed generally consists of an atomizer or burner where the oil and air are mixed, a pump for supplying the burner with oil and a source of air. The burner is merely an adaptation of the common atomizer of the drug store and is shown in its 356 PORTLAND CEMENT simplest form in Fig. 108. The burner shown here is designed for use with compressed air and consists of internal pipe through which the oil passes, an external pipe through which the air is forced. The air and oil meet at the orifice of the pipe and ------ *_-T Fig. 108-Oil burner. leave the latter in a mist or spray which in turn is mixed with more air in the kiln. Where the oil is very viscid it is necessary to heat it in order to make it flow easily so that it can be atomized. Steam coils - - - º Fig. 109–System for burning oil–Great Western Portland Cement Co., Mildred, Kans, (Kilns and blowers driven by Wagner Electric Co. motors.) BURNING—FUEL AND PREPARATION OF SAME 357 are often placed around the exit pipe in the storage tank when the oil is so viscid that it will not flow out of this. With most oil, however, such a coil would only be used in cold weather. It is the general practice to heat the oil before it goes to the burner, however, and this is usually done by means of regular oil heaters similar to feed water heaters in which the heating is done by the exhaust steam from the pumps or else by live steam. Oc- casionally the heat of the clinker is made to do this work by placing a coil of the oil supply pipe at Some point where the heat radiated from this can reach it. At one of the western plants a coil of pipe was placed in the hood and the oil so heated just before it reached the kiln. Fig. Io9 shows an installation of oil burners on a kiln. It will be noted that a number of burners are employed. This is the general practice—to use a number of small burners rather than one large one. Burning with Natural and Producer Gas Natural gas has been successfully used for the heating of the kiln, both in the Kansas field and at Wampum, Pa. At the plant of the Iola Portland Cement Company, Iola, Kansas, the gas was also used in gas engines to generate power for grinding, etc. Producer gas has been tried but the writer knows of but one plant where it was used for any great length of time, that was at a small plant in Canada. In conversation, the man- ager of this plant informed the author that they considered it as cheap as powdered coal, but saw no particular advantage in its use. The question has been raised at numerous times as to whether sufficient heat could be developed by its use to secure the proper temperature in the kiln for burning, and numerous cal- culations have been given to prove that without regeneration producer gas could not be used for burning Portland Cement. The fact that it has been used at several plants should effectually set at rest this contention. The temperature required for cement 24 358 PORTLAND CEMENT burning has been placed too high, however, and the gas con- sidered as cold in most of these calculations, whereas it is usually introduced hot from the producer into the kiln. The Diamond Portland Cement Company, Middle Branch, O., at one time had a Swindell gas producer in operation heating one of their kilns, but have now discontinued its use. Fig. IIo. shows the installation of the producer at this plant. The gas producer was built I5 feet in front of the kiln, which was 6 feet in diameter and 60 feet long. The coal, which was of inferior º *NS$ # ºk. Niº 33 - 2. - X- zzº 2×3% tº-2 rº2 E.-K. iß iii. º: sº 3. # Fig. I Io.—Swindell gas producer and rotary kiln. quality and cost only $1.50 per ton was introduced into the producer by means of sliding hoppers. Steam and air were introduced under and through the inclined grates by means of blowers. The air used for combustion was preheated by pass- ing up through iron tubes built in the walls of the producer. BURNING—FUEL AND PREPARATION OF SAME 359 The air and gas were led to the kiln by separate flues as shown in the plan. The labor required to operate the producers amounted to about 3% cents per barrel of cement including the wages of the burners, the coal consumption amounted to I30 pounds per barrel and the output to 240 barrels per day. In order to properly clinker the materials, it was found necessary to add soda ash to the mix to lower the clinkering temperature to a point which the producer gas could reach. This installation of producers was here found unsatisfactory and was finally re- placed by coal burning and pulverizing apparatus. Mr. H. F. Spackman, in a paper read at a meeting of the Cement Manufacturer’s Association, stated that in a plant de- signed by his company, producers were tried in connection with powdered coal on two rotary kilns, 60 feet long by 5 feet in diameter, burning slurry containing 60 per cent water. Actual figures in this plant obtained on a two or three months' run, were I25 barrels of cement per day, with a coal consumption of I35 pounds of coal per barrel, while the kilns working on powdered coal required on an average for a seven months’ run I 38 pounds of coal per barrel. To greatly overbalance this 3 pounds sav- ing in coal, however, was the fact that six men each shift of twenty-four hours were required to work the producers and that as gas slack could not be employed a coal costing 50 cents a ton more had to be substituted. All attempts to burn cement by producer gas were confined to a period about fifteen years ago and the writer knows of no plants which are at the present time employing it. Powdered coal has the disadvantage over gas firing in that the inherent losses of the gas producer are overcome. These losses are by no means small. It is estimated that the average loss of heat in the gasification of fuel, due to complete combustion to carbon dioxide, heat radia- tion, etc., is seldom less than 20 per cent. If to this is added the loss due to the carbon which the ash carries away with it and the coal consumed in the boiler for the production of the steam 360 PORTLAND CEMENT required for the gas producer, it is safe to say that the loss may generally be considered as 30 per cent of the thermal value of the coal. Furthermore, with gas firing the ashes have to be handled and disposed of while with pulverized coal the ash is blown away or enters the clinker. No advantage can be claimed for gas firing which can not also be claimed for coal except the doubtful one of the contamination of the cement by the ash. As was shown in a preceding section, about half the coal ash goes up the chimney and it is very doubtful if what falls down into the mix does not form hydraulic compounds with the lime of the latter. It is certain that it does combine with the lime as is shown by the fact that practically all cement is soluble in dilute acid, while coal ash is insoluble. If, therefore, the ash did not combine, a residue of at least one-half per cent would be left when cement is treated with dilute acid. Another advantage claimed for producer gas is the ease with which the flame can be regulated. Analyses of the flue gases of the kiln show combustion to be complete with about 20 per cent excess air which is as good as could be expected with pro- ducer gas. Furthermore, pulverized coal is of almost constant composition throughout long periods while the composition of gas varies with the operation of the producers, etc. Coal can be pulverized for less than it can be gasified, the labor of handling the producers alone amounting to more than it costs to pulverize coal. The cost of pulverizing coal rarely amounts to more than 3 cents per barrel of cement burned and often falls below this. Natural gas is found in too few localities to make it gener- ally applicable to cement burning, and, even when found, the supply is limited and may give out after a few years. Below are analyses of the gas at Iola, Kansas, and at Independence, Kansas, at both of which places Portland cement mills used nat- BURNING—FUEL AND PREPARATION OF SAME 361 ural gas not only for heating the kilns but also for generating power. ANALYSIs of NATURAL GAs USED FOR BURNING PoRTLAND CEMENT IN KANSAs (BAILEY). Iola Independence Hydrogen O.OO O.OO Oxygen O.45 trace Nitrogen 7.76 3.28 Carbon monoxide I.23 O.33 Carbon dioxide O.90 O.44 Ethylene series O.OO O.97 Marsh gas 89.66 95.28 CHAPTER XIV C00LING AND GRINDING THE CLINKER, STORING AND PACKING THE CEMENT, ETC. Cooling the Clinker The clinker leaves the kiln at a temperature of about 2,100° F. It is, of course, entirely too hot to grind and must be cooled. It has generally been found preferable to do this mechanically in- stead of letting the clinker lie in heaps and cool of itself. In Some mills this has been done in the open air, in others in rotary coolers, while a few of the older mills still use the upright cooler shown in Fig. III. This consists of an upright steel cylinder about 8 feet in diameter and 35 feet high provided as shown with baffle plates and shelves. As the clinker falls over these it meets a current of air blown in through a perforated pipe running up through the center of the cylinder and is thus cooled. There is usually one cooler to each pair of 60-foot kilns or to one 7 by IOO-foot kiln. Larger coolers are also employed for bigger kilns. The clinker is led from the kilns by chutes to a bucket elevator which carries it to the top of the cooler. The clinker is usually drawn from the bottom of the cooler on to belt conveyors, or else into barrows and carried to an elevator, wheh carries it up to the bins above the ball mills or rolls, whichever are used to grind the clinker. Usually water is added to the clinker in a steady stream as it falls into the elevator pit. This helps to cool the clinker, makes it more brittle and easier to grind and saves the elevator from handling such very hot material. There is probably no action toward curing of the cement or hydration of the free lime, since any of the latter present is usually locked up in the interior of the clinker. The writer has frequently cooled clinker suddently by plunging it, red hot from the mouth of the kilns, into water. The only perceptible effect is to bleach the color from dark greenish black to nearly white. If this clinker is dried and ground, it will be COOLING AND GRINDING THE CLIN KER 363 found to have pretty much the same properties as clinker caught at the same time and allowed to cool slowly in air. The writer has never observed that unsound cement could be made sound by this process. It does take up some water (probably on the - - --- *:::- ={- ---4------> Fig. I I I.—Upright clinker cooler (Mosser & Son). outside of the lumps only, however), as a loss on ignition test will show. Such clinker is easily ground and the resulting cement trowels nicely. 364 PORTLAND CEMENT The more modern mills employ a rotary cooler (see Fig. 112) which consists of a steel shell similar to that of the kiln and mounted on carrying rollers just as the kiln is carried. Usually this is lined with cast iron plates which are bolted in, so that they can be easily removed. Occasionally, however, the coolers are lined with fire brick or vitrified brick. One cooler is generally employed for each kiln, the cooler being located below the kiln to Fig. 112.-Rotary cooler–Great Western Portland Cement Co., Mildred, Kans, (Driven by Wagner Electric Co. motors.) permit of the discharge of the hot clinker directly from the kiln into the cooler by means of a chute. The air for cooling is drawn in by the draft of the kiln, and, as the air passes from the cooler to the kiln, such coolers act as preheaters for the air entering the kiln. As every pound of clinker carries out of the kiln between 4oo and 500 B. t. u., it will be seen that this practice should save some coal. COOLING AND GRINDING THE CLIN KER 365 The cast iron lining plates are often made T-shaped so that when they are inverted and bolted in the kiln they will form shelves running lengthwise with the latter. These shelves act as carriers, lifting the hot clinker and dropping it through the current of air. Sometimes the coolers are lined at the feed end only, the balance of the shell being unlined but usually pro- vided with angle irons or Z-bars fastened to the inside of the shell to serve as lifters. Water is sometimes fed in at the upper end of the cooler to help cool the clinker. At the discharge end of some of these coolers, for about 3 feet, the shell is perforated with holes from 194 to 2 inches in diameter, while at the end itself is a large angle iron with the flange turned in so as to hold inside of the coolers any large lumps of clinker which do not pass through the holes, making a rotary screen out of the lower end of the cooler. The large lumps may be broken up by an attendant with a bar or hammer, or else several large balls may be placed in the cooler and allowed to roll around in the latter, thus serving to break up the large pieces of clinker. This form of screen cooler, we believe, was first introduced at the plant of the Louisville Portland Cement Company, Speeds, Indiana but it has since been adopted at a number of mills. Occasionally rotary coolers are mounted separately from the kilns so that the air from the former does not pass into the latter. This is usually done where the lay of the land will not allow excavating for the coolers. When so located the clinker is carried from the kilns to the cooler by means of a bucket elevator and the air for cooling may be either drawn through the coolers by means of a stack at the upper end or else blown in by a fan. The question of the thermal advantage gained by allow- ing the air employed for combustion to enter the kiln has received considerable attention by cement mill engineers and there seems to be some uncertainty in the minds of these as to the benefits to be derived from the practice. Theoretically a barrel of clinker (380 pounds) leaving the kiln at 2,OOO° F. above atmospheric temperature should carry out with it, 380 × 2,OOO X O.246 = 186,960 B. t. u. This is equivalent to about 13.4 pounds of coal. 366 PORTLAND CEMENT If all of this heat could be applied to the work to be done, the use of the cooler would save this amount of fuel. Unfortunately, only 20 to 35 per cent of the thermal value of the fuel is utilized in burning the cement, the balance is wasted in various ways as explained in Chapter XII. Some of the heat carried out of the kiln by the clinker is not transferred to the air entering the kiln but instead is lost by radiation from the cooler shell. In the case of a metal-lined cooler from 30 to 40 per cent of the heat of the clinker is so lost. Of the 150,000 to 200,000 B. t. u. carried out of the kiln by the clinker, therefore, only 90,000 to 140,000 B. t. u. is employed in heating the air entering the kiln. Assuming IOO pounds of coal (I4,OOO B. t. u.) are required to burn a barrel of cement, or the equivalent of 1,400,000 B. t. u., of which only about 28O,OOO B. t. u. or 20 per cent are employed in doing work, it will be seen that by adding 90,000 to 140,000 B. t. u. we have increased the thermal input of the kiln by from 6% to IO per cent or to 1,540,000 B. t. u. per barrel. This should burn, therefore, from 6% to IO per cent more cement from the same fuel. When tests have been conducted with rotary coolers and the preheated air used the coolers have generally effected a saving of from 5 to 7 pounds of coal per barrel of cement burned. The capacity of a rotary cooler will depend much on the in- stallation, particularly as regards the flow of air through it and the lifting of the material. Efforts should be made to arrange the cooler so that practically all the air needed for combustion, aside from that used for blowing the coal should pass through it. Under such conditions the capacity of various sizes of rotary coolers is as follows: TABLE XXXVII.-CAPACITY OF AND Power REQUIRED TO OPERATE ROTARY COOLERs Capacity per day Size Bbls. H. P 5 ft. diam. x 50 ft. long 425 7%-Io 6 ft. diam. x 60 ft. long 8CO IO-I5 7 ft. diam. x 70 ft. long I,350 I5-2O 8 ft. diam. x 80 ft. long - 2,000 25-35 COOLING AND GRINDING THE CLIN KER 367 The capacity of the cooler can be materially increased if water is employed at the feed end. When the air from the cooler enters the kiln, however, there is an objection to the steam which tends, if present in too great quantity, to cool the kiln. The clinker usually drops from the coolers on to belt or pan conveyors; which carry it to the clinker grinding department or else into storage. Utilisation of Heat in Clinker for Other Purposes than Preheating Air for Kiln One of the New York state mills, at one time, used a cooler which consisted of a water-jacketed revolving cylinder, the water entering and leaving the jacket through pipes leading from a specially designed feeder placed in the center of the discharge end of the cooler. The water after leaving the cooler was used in the boilers, the cooler simply acting as a feed-water heater. These coolers are said to have worked well, and to have cooled the clinked perfectly. The employment of the heat in the clinker in this manner does not seem to promise much in view of the fact that there is usually about the power plant itself sufficient waste heat in the ex- haust steam from pumps, etc., or in the stack gases to take care of the boiler feed water. The heating of this latter in a feed water heater or an economizer of the Green type is manifestly a much simpler undertaking than in a rotary cooler and the ap- paratus itself is less complicated and apt to get out of order. There is also the objection to connecting together two such dis- similar operations as cooling clinker and heating feed water. At one or two mills, the hot air from the cooler is passed through a rotary dryer and used to dry the coal. There is no objection to this practice except that the coal dryer is often so placed that a long flue would be necessary to connect the cooler with the dryer. From the score of both efficiency and safety in coal drying the practice is admirable, as the air from the cooler is always much below the temperature at which coal ignites and the large volume of warm air is a most effective dry- 368 PORTLAND CEMENT ing medium. The drying of coal seldom requires more than 30 pounds of coal for firing the dryer per ton of coal dried or about I}% to 2 pounds of coal per barrel of cement. The utilization of the heat in the clinker in this manner, therefore, would not seem to be as desirable as in the kiln where a saving of from 5 to 7 pounds of coal should be effected. It would, however, at many plants be an easy matter to employ the air from one or two coolers as might be required for drying the coal and the air from the balance of the coolers in the kilns. In this way, the entire quantity of heat in the clinker could be utilized. To those who are inter- ested in such a system the Randolph Dryer" should appeal, as this is especial designed to make use of warm air of low temperature, such as boiler stack gases, in drying coal. Storing and Seasoning Clinker Cooling clinker in pits has been tried at a number of places, but does not seem to have worked very well anywhere. Some few mills convey their clinker red hot out into the fields and allow it to cool naturally. This is usually done at plants employing some form of crane for the handling and storage of clinker. The usual practice at such plants is to drop the hot clinker from the kiln into some form of pan or chain drag conveyor and con- vey the material outside the building, depositing it upon a pile or into a pit. Water is usually added at this point, although it is sometimes sprinkled on the clinker as the latter leaves the kiln or moves along on the conveyor. The crane handles the clinker from the pile or pit and carries it out into the storage, spreading it in layers so as to allow it to cool. This action is materially assisted by sprinkling the pile with water from a hose. Until quite recently it was very generally believed that seasoned clinker, provided it is dry, grinds much more easily than clinker fresh from the kilns, the slaking of the free line no doubt serving to help break down the structure of the material. In order to take advantage of this fact, mills which cool their clinker by means of one of the mechanical devices described above have installed systems for seasoning their clinker. By cooling the clinker first * Fuller-Lehigh Company, Fullerton, Pa. COOLING AND GRINDING THE CLINKER 369 it is much easier handled as belt conveyors can be used to re- place the more troublesome pan and apron conveyors necessary for the hot material, and also if rotary coolers are used the heat in the clinker may be utilized to heat the air entering the kiln, whereby fuel will be saved. The arrangements provided for the seasoning of the clinker are, of course, intended to pile this economically and in large quantity and then to reclaim as much of the pile as possible automatically and with a minimum of labor. The first systems employed consisted of pan or belt conveyors, but all of the recent clinker handling systems make use of some form of crane and grab bucket, using the latter both for conveying the clinker into stor- age and for reclaiming it when it is ready to grind. One of the first mechanical systems for seasoning clinker was worked out by Mr. Owen Hess and the author for the Dexter Fig. 113–Clinker storage—Dexter Portland Cement Co., Nazareth, Pa. Portland Cement Company, at Nazareth, Pa. (Fig. 113). This storage consists of a pan conveyor which is supported on a 370 PORTLAND CEMENT steel trestle and protected by a roof. The conveyor may be dis- charged at fixed points. The clinker is carried out and deposited underneath this conveyor in a long pile. It is allowed to remain here two or three weeks, when it is drawn out by means of spouts on to belts in two underground tunnels, which run length- wise under the clinker piles. No roof is placed over the clinker and any rain which falls upon it helps to season it. Owing to the fact that in very rainy weather this clinker when drawn from the pile is wet, it was deemed advisable to install a dryer just before the grinding mills, but this dryer was only used occasion- ally when the clinker was very wet and finally was removed altogether. The capacity of the storage is about 72,000 barrels of clinker. The clinker is drawn out of one end of the pile while it is being dropped into the other. Traveling Crane for Handling Clinker The most popular system for handling clinker is unquestionably the overhead electric traveling crane and grab bucket (Fig. 114). Fig. 114.—Clinker handling bridge crane, 80 ft. span, at the Bath Portland Cement Co., Shepard Electric Crane and Hoist Co., maker. This will handle hot or cold clinker and may be made to cover practically any desired area. The traveling crane consists of a COOLING AND GRINDING THE CLIN KER 37I bridge composed of two parallel I-beams or plate girders which travels on two parallel rails supported at an elevation from the ground. The rails may be supported by an “A”-frame or in any appropriate manner. When the clinker storage is in the form of a bin, the rails may be supported on the side walls of the bin. The bridge is propelled by means of a motor located at some convenient place on it which is controlled from the operators cage. This motor actuates through gearing a shaft parallel with the bridge, which in turn revolves the wheels on trucks at the two ends of the beam. There operates back and forth on the bridge a trolley upon which are located three drums which in turn lower, open, close and raise the grab bucket. The trolley and drums are operated by suitable motors, controlled from the oper- ators cage, usually located at one end of and below the bridge. With this crane it is possible to deposit and reclaim clinker at any point over which the bridge moves. The dimensions of the crane, of course, depend entirely on the size and shape of the clinker storage and the amount of clinker to be handled. The buckets usually hold from 2 to 5 cubic yards of clinker. The bridge beams is generally from 60 to I2O feet long. A 5-ton crane will handle a 2-cubic yard bucket and a IO-ton crane a 4-cubic yard bucket. The clinker storage of the new National Cement Company’s plant at Montreal-East, Quebec, is a good example of such a stor- age. This storage takes clinker direct from kilns and has a 5-ton bridge crane" of IOO-foot span equipped with a 2-cubic yard bucket. The storage itself is 255 feet long. The area covered is 25,500 square feet. The supporting track is 45 feet from the ground and the capacity of the storage 225,000 barrels of clinker. The bridge itself has a maximum travel of 3OO feet per minute, the trolley travels at a speed of I25 feet per minute and the hoisting at IOO feet per minute. It will handle 3,000 barrels of cement daily in and out of storage. 1 Shepherd Electric Crane and Hoist Company, Montour Falls, N. V. 372 PORTLAND CEMENT Revolving Cranes for Handling Clinker At the plant of the Bessemer Limestone and Cement Company a stationary crane is employed (Fig. 115). This crane was made by the American-Terry Derrick Company, and is known as a full circle crane. It is mounted on a concrete foundation 25 feet Fig. 115–Full circle crane–Bessemer Limestone and Cement Co., American Terry Derrick Co., maker. high and located in the center of the storage pile. As its name implies the boom which is too feet long moves over the entire radius of the pile and handles a 3-cubic yard clam shell bucket. The main hoists are equipped with too horsepower motors and the swinging hoists with 30 horsepower motors. This storage has a capacity of 150,000 barrels. Figure 116 shows the form of crane employed by the Pacific Portland Cement Company. This crane also swings in a circle over a circular pile. The effective radius of the crane is 80 feet while the distance from the bottom boom to the guy cap is 50 feet. cooling AND GRINDING THE CLINKER 373 Fig. 116–Clinker storage and crane–Pacific Portland Cement Co., American Hoist and Derrick Co., makers. The crane is supported by six 1-inch steel guy ropes each 240 feet long. The entire machine is operated by one 35 horsepower motor operating at 90o revolutions per minute. The crane is equipped with a 40-cubic foot Brownhoist clam shell bucket. _-_-_- l _-_- Fig. 117–Clinker storage—Riverside Portland Cement Co., Brown Hoisting Machine Co., makers. Still a fourth type of clinker handling crane is shown in Fig. 117. This shows the clinker storage of the Riverside Portland Cement Company, Riverside, Cal. The double contilever full 25 374 PORTLAND CEMENT circle rotating crane employed here has an effective radius of IIO feet. It is mounted on a hollow reinforced concrete tower, 55 feet high and 34 feet in diameter. Entrance to the tower and crane is through a tunnel under the clinker pile. The clinker is handled by means of two 60 cubic foot buckets—one on each arm. The effective height of the storage is 50 feet and this gives a storage of about one-half million barrels, allowing for reduc- tion of the pile by buildings, etc., which cut into the storage. The bucket hoisting and closing motors are each 25 horsepower, the trolley travel motors I5 horsepower and the motor for the rotat- ing mechanism 50 horsepower. At the above plant, the twelve rotary kilns dump into a McCas- lin conveyor, which in turn conveys the clinker into storage, discharging it at a height of 35 feet at a point passed over by the extreme ends of the crane arms. The clinker is removed from this discharge pile and deposited in any desired space within the swing of the crane by the buckets. Reclaiming is effected by taking it from the desired part of the storage and dumping it over a reclaiming tunnel. The latter extends under and partly through the storage and is provided with spouts and a 24-inch belt con- veyor which carries the clinker to the finishing mill. One op- erator can handle both buckets and distribute 6,000 barrels in storage and reclaim a like amount daily. Properties of Seasoned Clinker As has been intimated damp clinker is difficult to grind. Dryers are not, however, placed after the storage as a general rule. Sometimes a roof is placed over the storage but more often the pile is simply exposed to the rain and Snow. In which case, during wet weather only fresh clinker is ground, allowing the pile to dry itself by the absorption of the water by the lime of the clinker or by evaporation during clear weather. With the crane, the clinker may be dried when it is not actually raining or snowing by mixing damp clinker with hot clinker. At some mills, it is, therefore, the practice to spread a layer of hot clinker on the floor of a part of the storage and then a layer of damp clinker COOLING AND GRINDING THE CLIN KER 375 on top of this and then when the latter is dry and the former is cooled, the mixture is ground. At the plant of the National Cement Company, previously mentioned, the drying of the seasoned clinker is effected by mixing some hot clinker with this and passing the two through a rotary dryer. No fire box is to be used for the latter and the heat in the fresh clinker is utilized in evaporating the moisture in the seasoned material. Clinker which has been seasoned has absorbed more or less water and carbon dioxide, the quantity usually amounting to from 2 to 4 per cent, depending on the length of time of exposure and atmospheric conditions during this period. The effect of this seasoning is to improve the soundness and trowelling proper- ties of the cement. Seasoning always, however, lowers the spe- cific gravity and often the one and seven day tests of the cement made therefrom. Generally speaking, it has been found most desirable to grind a mixture of fresh and seasoned clinker rather than seasoned clinker alone. The seasoned clinker, while unquestionably softer, gives off much steam in the mills and the presence of the fresh clinker counteracts this by absorbing this steam. This, of Course, in turn results in hydration of the free lime in the fresh clinker and hence to some extent rapidly seasons the latter. Adding the Retarder. Before being ground, it is usual to mix with the clinker the gypsum necessary to retard the setting time of the cement (see Chapter XXI). The gypsum is usually received at the plant in the form of small lumps, crushed to pass a one-inch ring screen. In most plants the retarder is added by hand although at a few, automatic scales are used. The latter have not always proved successful, the usual trouble being the small amount of gypsum (2-3 per cent) added to the clinker and the difficulty of getting automatic scales which will handle a few pounds of such lumpy material simultaneously with several hundred pounds of clinker. At the older plants where the clinker is wheeled from the coolers to the grinding department the gypsum is usually added 376 PORTLAND CEMENT to the barrow and the amount added is determined by volume and not by weight. A shallow box holding the desired amount of gypsum is used and this is filled with gypsum and struck off level with the top. This answers the purpose very well and serves to control the gypsum in the cement within narrow limits. When belts are used to convey the clinker, these usually dump into a hopper scale. This latter may be either automatic or hand controlled. An attendant adds the gypsum, by means of a box which holds the correct weight of gypsum for One dump of the scales. The scales if automatic are usually pro- vided with counters or if operated by hand the attendant keeps tally on a board so that an account of the amount of clinker ground may be kept. At one time plaster of Paris was employed to slow the setting time of cement but since the writer pointed out in the first edi- tion of this work that gypsum was fully as efficient a retarder as plaster of Paris and as it costs much less, the former has al- most entirely taken the place of the latter. At one time also, Nova Scotia gypsum was almost universally used as it contains a higher percentage of sulphuric anhydride than the native gyp- sums. Now the cheaper American mineral has replaced the im- ported one to a great extent. In purchasing gypsum, the manu- facturer purchases sulphur trioxide (SOs) and the considera- tion with him is usually how much of this he will get for his money. Grinding the Clinker. The clinker is ground by any one of the following systems: SYSTEMS USED FOR GRINDING THE CLINKER. A. Tube Mill preceded by (a) Hercules Mill, (b) Ball Mill with screens, (c) Kominuter with screens, (d) Single roll Griffin Mill, (e) three-roll Griffin Mill, (f) Kent Mill, (g) Sturtevant Mill, (h) Huntington Mill, or (i) Fuller Mill. B. Compeb Mill alone. COOLING AND GRINDING THE CLIN KER 377 C. Griffin Mill preceded by (a) ball mill provided with per- forated plates and without screens, (b) Set of crushing rolls, or (c) pot crusher. (Often followed by tube mill, see A.) D. Fuller Mill preceded by (a) ball mill provided with per- forated plates but without screens, or (b) set of crushing rolls. (Often followed by a tube mill, see A.) E Kent Mill and (a) screen separator (b) air separator. (Generally followed by tube mill, see A.) F. Sturtevant Mill and Newaygo separator (Generally fol- lowed by tube mill, see A.) G. Huntington Mill preceded by rolls. (Now generally fol- lowed by tube mill, see A.) Of these systems the last three so far have found only a lim- ited use. The Huntington Mill both alone and followed by the tube mill is used only by the Atlas Portland Cement Company. It is usual for the clinker to be ground by the same type of machinery as is used to grind the raw material. The principal reason for this is that only one set of repair parts have to be car- ried in stock. A number of mills, however, use ball and tube mills to grind the raw materials and Griffin Mills to grind the clinker, the idea of these manufacturers being that the former is the better of the two for soft or wet materials, and the latter the more suited to the hard clinker. The tube mill is also popularly supposed to be a better mixer than other mills but this is not borne out by practice, and the general experience has been that the mill which will grind the raw materials finest will in all cases give the best cement. No mill holds enough material to obtain a uniform mix where this is not secured before the materials reach the mill. The tube mill and Compeb mill are better suited to wet grinding than other mills, and hence are often used in wet pro- cess plants for grinding the raw materials even where other mills are employed for clinker. All of the above mills have been described in Chapter X. Factors Influencing Grinding of Clinker. It is now well understood that the percentage of moisture, the 378 PORTLAND CEMENT temperature, chemical composition, degree of burning, amount of seasoning, and to some extent the size of the clinker, all influence the operation of grinding cement. The influence of moisture and seasoning has already been noted. Hot clinker grinds much harder than cold clinker and for this reason all clinker should be cold when fed to the mills. The heat resulting from the friction obtained in grinding is itself sufficient to raise the temperature of the cement to 200° to 350° F. If we start with hot clinker, therefore, the temperature finally obtained in the mill is almost sure to be excessive. The loss of output in a mill grinding very hot clinker may be as much as 40 to 50 per cent of one grinding cold clinker, while the power per barrel of cement ground may increase 80 to IOO per cent. It will be quite evident that the degree of burning must have marked influence on the grinding of cement since by hard burn- ing we may obtain a clinker which is completely vitrified and in consequence of this both hard and heavy. The softer the burn- ing, therefore, the easier the grinding. For this reason it is usual to burn only to the degree of vitrification necessary to produce sound cement. It will generally be found preferable where this can not be obtained by a reasonable amount of vitrification to grind the raw materials finer in order to secure this end rather than to burn harder. The chemical composition of the clinker has a marked influ- ence on the ease with which it can be ground. Clinker low in iron oxide grinds much easier than clinker high in iron oxide. An increase in the percentage of lime on the other hand makes clinker easier to grind. The writer has frequently stated this, but quite recently Mr. Wm. P. Gano, Chief Chemist, Penn- sylvania Cement Company, undertook an extensive series of tests which proved the writer's contention. Gano found for example that, with clinker having a lime ratio" of I.97 a certain tube mill would give 51 barrels per hour; the same mill when grinding clinker having a lime-ratio of 2. IO had a capacity of 68 barrels per hour while with a clinker having a ratio of 2.22 the mill ground 79 barrels. It will be seen, therefore, that the higher the * See page 76. COOLING AND GRINDING THE CLINKER 379 lime in the cement can be carried, the easier the grinding. Since the power to operate the mill in each case was the same, the power requirements were: For the clinker with 1.97 lime ratio 5.1 kw-hr. For the clinker with 2. Io lime ratio 3.85 kw-hr. For the clinker with 2.22 lime ratio 3.23 kw-hr. A lime ratio of 2.22 is probably rather high and in this case it might be that much if not all of the power saved on the clinker side would be made up for in increased power necessary for grinding the raw materials fine enough to make a sound cement with such a high ratio. At the same time, a ratio of 2. Io is good practice and it will be noted in Gano's figures that 30 per cent more power was required to grind the clinker with a ratio of 1.97 than to grind one with the higher ratio (2. Io). In addition to the saving of power the repairs are, of course, less and there is a saving in interest, etc., on the smaller amount ofgrinding equip- ment necessary, when a fairly high ratio is employed. Conveying Clinker and Cement. The hot clinker, when it is desired to handle this, can best be conveyed by means of pan conveyors, bucket carriers or drag chains. The latter are now considered best. Occasionally drag conveyors are made by fastening a 6- to IO-inch piece of angle iron on to ordinary conveyor chain and allowing these to drag the hot clinker along. The most recent development, however, is an adaptation of the ordinary sawdust or wide link chain, only made much heavier and of special metal designed to withstand heat and abrasion. These operate in a trough the bottom of which is lined with white iron and the material is carried on the upper or lower run of the chain. They are suitable for carrying material on the level or up a slight inclination, say I5 or 20° from the horizontal. Cold clinker in any form may be elevated by means of any of the standard forms of bucket elevators or conveyed horizontally or up a slight incline on belt conveyors. Fully ground cement is generally conveyed laterally by means of screw conveyors and 38O PORTLAND CEMENT the product of the granulating mills (16- to 20-mesh) may be handled in the same way. Inclined belts are sometimes used to both convey and elevate cement. The Fuller-Kinyon system described for handling pulverized coal is now being used at a number of plants for handling cement This system requires somewhat more power to operate than do elevators, belt and screw conveyors, but its evident advantages such as absence from dust, maintenance and attention required for long lines of screw conveyors, flexibility as regards arrange- ment, ease of extension to any length desired and in any direc- tion and saving in space required give it the preference over other forms of conveyor yet devised for moving ground cement. Nearly all of the most recently built mills are employing this system for conveying cement from the mill into the stock house bins. One new mill is employing for placing cement from the stock house bins into the packing bins a portable Fuller-Kinyon pump. The latter is mounted on a truck operating on a track under the bins, connection is made with the bin and with the pipe line leading to the packing bin by means of removable con- nections. For this purpose the pump is mounted on a car which in turn runs on a track under the silos as shown in Fig. 121. (Refer to page 384). Referring to this a is the pump and b the motor driv- ing this. The pump is placed directly under the bin opening, c, and connection made with the latter by means of clamps and a gasket, d, and with the pipe line,e, through the hinged connecting pipe, g, by the same means. The cement is fed out of the bin by an auto- matic feeder, h, which is driven from the pump shaft. The air gauges i are mounted on the car and connection is made with the air line by air hose. The car is kept in place under the bin by suitable track clamps, k. One objection to the use of this system here is that two or more pumps are usually required and more room is needed beneath the silos. Stock Houses. From the grinding mill the finished cement goes to the stock house. In the early days of the industry this usually consisted COOLING AND GRINDING THE CLIN KER 381 of a long low frame building divided into bins by means of wooden partitions, so that each day's grinding could be kept sep- arate. These bins usually held from I,000 to 5,000 barrels and were arranged either on each side of a central aisle or else with an aisle on each side. The parts of the bins facing the aisles were stopped up by means of boards which might be easily re- moved, and below the floor of the aisles, ran screw conveyors to the packing room, which was usually one end or a large room in the middle of the stock house. The screw conveyors were cov- ered with boards, except in front of the bins where gratings 3 or 4 feet in length were placed. The cement was usually brought in from the grinding mills by an overhead screw conveyor, from the trough of which spouts ran to the middle of the bins. The openings in the trough leading into the spouts were closed by iron slides or gates so that the cement might be run into any bin de- sired at any time. When it was desired to open a bin the bottom plank was removed from the front of the bin and the cement was allowed to run into the screw conveyor, through the grating. When it ceased to run of itself, a scraper, which consisted of a flat iron plate, about 6 inches by 18 inches, from the middle of which a long handle projected was introduced and all of the cement which could be pulled through the opening conveniently was drawn into the conveyor, after which the remainder of the boards were taken down, and the rest of the cement was drawn into the conveyor, either with the scraper or wheeled by barrows to the grating. This form of stock house was occasionally equipped with cross conveyors which ran across the bins and consequently at right angles to the main conveyors and which emptied into the main conveyors. To do away with the manual labor required by such a method of opening a bin, stock houses provided with tunnels running under the bins are used. The conveyors are located in the tunnel and the bins are fixed with sloping floors and spouts which de- liver into the conveyor. Fig. I 18 shows a type of stock house which was installed with various modifications by many of the 382 PORTLAND CEMENT mills built between 1900 and 1910. It will be seen that the con- veyors are in concrete passage-ways and that most of the con- tents of the bin can be run out by gravity. Nº. ºx^* - º SS Fig. I 18.-Stock house with rectangular bins and tunnels. Silo Stock Houses. The only type of stock house which is now built is is the silo or tank type of stock house, such as is shown in Fig. I 19. Such a stock house as its name implies consists simply of a row of reinforced concrete tanks or silos. These are usually made from 25 to 40 feet in diameter and 60 to 80 feet high, each silo will then hold from 7,500 to 25,000 barrels. In addition to the circular bins there are also star-shaped bins which occur between each four tanks. In other words in a silo stock house consisting of eight silos arranged in two rows of four silos each, there will be three star-shaped bins and for each pair of tanks added there will be an additional star-shaped bin. Cool, ING AND GRINDING THE CLINKER 383 These stock houses are now made monolithic and with sliding forms, the concrete being poured continuously. They are usually waterproofed by adding a small percentage of hydrated lime to the concrete mixture. The silos are provided with a concrete Fig. 119.-Silo bins and pack house, National Cement Co., Montreal, Que. slab roof sloped only enough to secure draining off of rain water. This slab is covered with a tar and gravel or other bituminous composition roofing. The pent house on top is usually made of concrete also. The most important feature of the design of a silo stock house, aside from the structural features are the methods of carrying the cement into and out of the bins. In the former case the use of the Fuller-Kinyon system greatly facilitates the placing of the cement into the bins. When this is not employed the cement is usually distributed by means of screw conveyors with gates in the trough. 384 PORTLAND CEMENT The ports in the bottom of the bins should be so arranged and spaced that the bins will be as completely emptied as possible. Two methods are commonly employed–one (usual in stock ~~~~ : - ------------------- - - - - -------- - - ------------------ Fig. 120–Silo stock house with sloping bottom. Designed by Richard K. Meade & Co. houses of the writer's design) in which a tunnel is run under the bin and the bin bottoms are sloped so as to discharge into this. (See Fig. 120). This arrangement not only allows very complete emptying of the bins, but in it the load of cement in the bins is carried directly on the ground and no heavy foundations are re- Fig. 121.-Fuller-Kinyon portable pump for emptying stock house bins— Fuller-Lehigh Co., Fullerton, Pa. COOLING AND GRINDING THE CLIN KER 385 quired. In the other system, the bottom of the bin is 6 to 8 feet above the ground level and consists of a heavy slab of reinforced concrete resting on short concrete columns and side walls. As the entire load of the contents of the bins, press on these col- umns they must rest on very solid and even foundation. The flat bottoms also do not allow the bins to be emptied so com- pletely as the sloping bottom. On the other hand, this form of stock house allows ample room under the bins and working con- ditions here are better. The type of bin shown in Fig. I2O is the cheaper of the two. Table XXXVIII gives the capacities of silos and interspaced bins of varying diameters. TABLE XXXVIII.—CAPACITY OF SILO BINS PER LINEAR FOOT OF HEIGHT *Capacity of star- *Capacity of silo Floor area of shaped bin perft. Internal Floor area bin per foot of star-shaped bin of height in diameter of of silo in 11eight in barrels between each four bbls. Of silo in feet square feet of cement (3761bs.) silos in sq. ft. Cern ent 25 490.9 I2I.5 I34 33.2 26 530.9 I31.4 I45 - 35.9 27 572.6 I4I.7 I56 38.6 28 615.8 I52.4 I68 4I.6 29 660.5 I63.4 I8O 44.6 30 706.9 I75.O I93 47.7 3I 754.8 I86.8 2O6 5.I.O 32 804.3 I99. I 22O 54.5 33 855.3 2II.7 234 57.9 34 907.9 224.7 249 6I.6 35 962. I 238. I 263 65. I 36 IOI7.9 252.O 278 68.8 37 IO75.2 266. I 294 72.8 38 II34. I 280.7 3IO 76.8 39 II94.6 295.7 326 80.8 4O I256.6 3II.O 343 85.o *Weight of cement in bins 93 pounds per cubic foot or 4.04 cubic feet per barrel of cement. . Pack House. The pack house is usually located at one end of the stock house with railroad sidings on each side. In it are located the auto- matic machines for packing the cement. These are usually set in a row with a belt conveyor running in front of and below them. The bags when full are dropped from the sackers on to 386 - PORTLAND CEMENT this belt and conveyed to the door of the railroad car. Here they discharge on to an incline table and a laborer drops them from the latter on to a truck. The sacks are usually piled four to six high on the latter. When the truck is full it is wheeled to the proper point in the car and the sacks tilted off so they remain piled one on top of the other. Sometimes arrangements are made for taking care of and storing return bags in the pack house, but most mills now have a separate building located adjacent to the stock house for this purpose. Bags are usually sorted and counted as received and then cleaned. The cleaning may be done in a batch by a clean- ing wheel. The latter consists of a wheel 8 to Io feet in diameter by 4 to 6 feet wide made of structural steel and covered with coarse mesh wire cloth. This wheel revolves slowly in a dust- tight metal casing. The bags are placed in the wheel and as the ſatter revolves they tumble around and this action beats the dust out of them. Continuous cleaners which are really nothing but very light rotary inclined screens provided with tumblers and completely housed in a dustproof casing are also used. With these the bags are fed in at one end and work their way through. The clean bags fall from the lower end on to a flat belt conveyor which moves very slowly and attendants on each side of the belt pick out the torn and foreign bags as they pass by. The only other equipment in this department consists of sew- ing machines for repairing bags and whatever is necessary for tying the bags. They are usually tied as received and stored in this shape in order to be ready when wanted. Bags are usually stored in a fireproof building but, of course, the bags themselves are inflammable. In order to minimize fire risk the Security Cement & Lime Company, Hagerstown, Md., employ a compartment storage in which the bags are stored in rooms separated by fireproof partitions, each room is 18 feet by Io feet and holds 40,000 bags. This is done in order to minimize fire by confining one should it occur to a very small part of the entire stock of bags. Ample bag storage should be provided in a modern mill since the bags come back during the winter in COOLING AND GRIN DING THE CLIN KER 387 northern latitudes in large quantities and are then constantly ac- cumulating. The Space required to store bags is about 45 cubic feet per I,000 bags piled and tied. If untied and laid flat one on top the other in bales, less room is required for storage. When two tracks are not enough for packing, small pack houses are sometimes set to one side of the main pack house and separated from each other by tracks so that a car can be loaded on each side. Two sackers are usually located in each house. The cement and bags are brought in overhead by means of a gal- lery connecting this auxiliary pack house with the main pack and stock house. Packing. Cement is packed in wooden barrels holding 380 pounds or into paper or cloth bags holding 94 pounds net by means of packers. The cement is packed as shipped and the bags or bar- rels are trucked directly to the cars. For this reason the packing room should be so arranged that the cars to be loaded can be brought alongside of the room and a shed roof should be run out over the cars so the loading will not be interrupted by rainy weather. Since some seasons of the year are much busier than others, the packing house should be able to load and ship at least twice as much cement as the mill can make in a day. The floor of the packing room should be on a level with the floor of the cars to be loaded. Cloth bags are used much more for packing cement than anything else. In the case of cloth bags the consumer is charged with the value of the bag, IO cents, and credited by IO cents when the bag is re- turned. The bags are all marked with the label of the brand and So each manufacturer knows his own bags. Barrels and paper bags are sold to the customer and are not returnable. Methods employed for bagging the cement were at first of the crudest kind. Formerly machines similar to flour packers were used. The Bates valve bags and machine for filling these are now almost universally employed in America for sacking cement. The system does away with many of the defects of the 388 PORTLAND CEMENT old methods of packing, including short and overweight, bags coming untied in transit, slowness of packing, need for skilled labor, etc. t `----... CZošecº º- — — — — — — — — — — — — — — — — — — — — — — — — — * * ~ * * * * * | \ | \ | | w j Fig. 122.-Bates valve bag. The Bates system primarily depends upon a novel bag, of which the fundamental feature is a valve in one corner. This valve projects into the bag as is shown in Fig. I22. It is made by folding over one corner of the bag and sewing across the dotted line shown in the figure. When pressure is applied to the valve, as when the cement comes against it, the valve closes. With this bag, the operation of filling which ordinarily con- sists of putting the material in the bag and then tying it, is re- versed and instead, the bag is first tied and then filled, the filling being done through the valve by means of a special bagging machine which will be described a little further on. When paper sacks are used, these are closed at both ends in the bag factory, where the valve is also placed in the bag by folding and pasting. The cloth bags are tied by means of a wire tie which is twisted on to the bag by a special tool. To fill the bag the operator has only to slip the tube of the bagging machine through the self-closing valve of the finished bag (Figs. I23 and 124). This he can do with a quick one-hand motion. A lever is then opened which permits the material to flow COOLING AND GRINDING THE CLINKER 389 into the bag. The material flows into the bag in a thin stream about one inch in diameter, and consequently there is no danger of tearing or ripping the bag. When the exact quantity of cement has been fed into the sack, the weight of the bag and contents offsets a counterpoise at the opposite end of an evenly balanced beam. The bag, of course, begins to fall and simultaneously with this, Fig. 123.--Bates valve bag packer. the flow of material is shut off. The bag has only to move one- eighth of an inch for this to take place. It is consequently pos- sible to make a very nice adjustment of the weight by this means. When the bag has been filled, it is left hanging suspended by the valve spout in a position breast high to a man. From this point it is easily tilted down to the truck by means of a lever and arm. A three-tube bagging machine will pack about 1,000 to 1,500 barrels per day of ten hours. Two men are required to operate the machine and place the bag on the trucks. 25 390 PORTLAND CEMENT One of the greatest advantages of the valve bag is the ease with which samples may be drawn from a shipment of cement. For this purpose a small round brass tube, I’’ x 18”, with both ends open and one end bevelled is simply thrust into the bag through the valve of the latter and the cement which it retains O Fig. 124.—Cross section of the Bates packer, showing the course of material feeding through the machine into a valve bag. is withdrawn for sampling. The excellency of this device and the speed with which the sampling can be done, makes it possible to sample a large number of bags in the time formerly occupied in cutting and tying one or two. - COOLING AND GRINDING THE CLIN KER 39 I Some cement mills have a cooper shop connected with the mill. Some of these shops are equipped with barrel making machinery, and at others all the work is done by hand. At the present time, however, barrels are but seldom used except for export and water shipments. Even for the latter, double duck bags are replacing barrels and most of the cement shipped from this country for the Panama Canal was so packed. A new development in the package line is the Bates “multi-wall” bag. This is made of five or six layers of strong water-proof paper and the joints are sewn not pasted as is usual with paper bags. This makes a strong serviceable package. These bags are of course not returnable, but as there is always a considerable loss in handling cotton sacks, the cement packed in these bags probably costs the user no more than when packed in returnable cotton bags. CHAPTER xv. POWER EQUIPMENT, GENERAL ARRANGEMENT OF PLANT, COSTS OF MANUFACTURE, ETC. In the early days of the industry, all of the machinery in the cement plant with the exception possibly of a few units at some distance from the rest of the plant was driven with line shaft- ing, the latter being Operated by cross-compound, condensing, engines, usually of the Corliss type. To-day, practically all American cement plants are electrically driven, the steam tur- bine being the most popular prime mover. There are many points in favor of the electrical transmission of power." (I) The direct connected turbine and generator is a much more efficient producer of power than the reciprocating engine. (2) The loss of power due to leakage from trans- mission lines is not as great as that due to friction in a long line shaft. (3) Electrical transmission allows a better arrangement of the buildings and machinery both with a view to future ex- tensions and as regards the handling of the materials to be ground or burned. (4) Where each machine is run by a sep- arate motor, the plant is not affected by the shutting down of any particular machine and the operation is smoother and more continuous and the speed of the driven machine more uniform. (5) Power can be purchased. Shaft Driven Mills. In the older mills as we have said, the machinery was usually driven by shafting. Short powerful shafts were used which were driven directly from the engine by belting or rope drives. The power was then transmitted from these shafts to the crush- ers and grinding mills by belts. Often the use of one or more jack shafts was necessary. Long chain and belt drives were often required to reach the elevator head shafts and the conveyors in the roofs of the building. * See also “Electric Drive for Economic Operation of Cement Mills,” by J. G. Porter, Trans. A. S. M. E., 1914. POWER EQUIPMENT, ETC 393 As a general thing, the mills grinding the raw material were operated from one engine, while those grinding clinker were driven by another. This was considered better practice than to use one large engine for both departments. It was also the gen- eral plan to run the kilns by a separate engine in order to make the operation of the latter independent of the rest of the plant and hence more continuous. Electric Drives. It was soon evident that certain departments of the mill could be operated better by electric motors than by a small engine, and it became the general practice, even where the raw and clinker mills were driven through shafting by powerful engines, to in- stall an engine and generator to produce electric power and to employ motors to drive the kilns, pack house and often the crush- ing plant and other departments of the mill where a small amount of power was used. One of the defects of mills actuated by horizontal pulleys, such as the Fuller-Lehigh Mill and the Griffin Mill, consisted in the necessitary of driving them by a quarter twist belt. With the introduction of the motor drive, mills of this character were driven by vertical motors. The writer believes that the Tidewater Portland Cement Com- pany, Union Bridge, Md., with whose construction he was con- nected as consulting engineer, was one of the first plants in which the individual motor drive was employed. In this plant, not only the kilns, crushers and grinding machinery were driven by individual motors, but also the conveyors, elevators, etc., were so operated. Each conveyor and elevator had its own individual motor, doing away with practically all shafting in this mill. This is now the general practice in cement plants, and in a modern mill all of the machinery, with the possible exception of the primary crusher, is driven by a direct connected motor of the proper size and speed. Usually a flexible coupling connects the motor and the machine. A magnetic coupling is often em- ployed between the tube-mill and motor. In cases where the 394 PORTLAND CEMIENT machinery is very slow moving, back-geared motors are often used. A somewhat better plan, however, is to employ between the motor and the machine one of the so-called “speed reducers.” These may be either of the spur-gear or of the worm-gear type. With the development of the central station and of the hydro- electric generation of power, it has become quite common prac- tice in the cement industry to purchase power. This is done almost universally in sections of the country where cheap hydro-electric power is available. Such a situation exists on the Pacific Coast, in the South Atlantic and Gulf States and in Canada. At the new plants of the Universal Portland Cement Com- pany; a subsidiary of the United States Steel Corporation, the waste gases from the blast furnaces are used to generate the power needed for the cement mill. The gas engines are located at the furnaces and are direct connected to generators. Power is transmitted some distance in each case to the cement plant. One or two plants where oil is cheap have used engines of the Diesel type for generating power. At some of the plants in Kansas, gas engines were installed making use of natural gas for power. I believe, however, that this fuel has now be- come too expensive to be used by any cement plant. Boiler Plant. Up to about ten years ago, it was almost the universal prac- tice in the cement industry to generate steam by hand or stoker fired-boilers and pulverized coal was never used successfully here for the generation of power, in spite of the fact that within the last few years this form of boiler firing has become very popular with large users of power. The improvement along this line in the cement industry in the last few years has consisted in the installation of the waste heat boiler which uti- lizes the waste heat in the kiln gases and of which more will be said later. Practically all of the older cement plants made use of water tube boilers, generally of the horizontal type. A few plants POWER EQUIPMENT, ETC 395 had vertical boilers. Probably the larger percentage of boilers were hand fired. A few plants used stokers. None used pul- verized coal. Power Required. The actual power which will be required by any cement plant will depend to some extent on circumstances. With modern installations, however, the variation between different plants is not great. Where installations are faulty or the machinery has not been well chosen, the power required may be excessive, but the only variable which would affect the operation of a well designed plant would be the hardness of the raw mater- ials, making more power necessary for preparing these for the kilns. As a general rule, it may be said that there will be required to operate the machinery from I.O to 1.5 horsepower installed for each barrel per day capacity of the mill. In other words, to operate a mill making 3,000 barrels of cement daily there will be required generators having a capacity of from 3,000 to 4,500 horsepower or 2,250 to 3,375 kilowatts. Figured on the barrel basis, between 15 and 20 kw-hr. are required per barrel of cement produced, with an average of about . I6 kw-hr per barrel at plants properly laid out, with well chosen machinery and raw materials of average hardness. This power is proportioned about as shown below. DISTRIBUTION OF Power IN CEMENT MANUFACTURE UNDER AVERAGE CONDITIONS ‘. Kw-hr. - Per cent Crushing and drying I. I 6.9 Raw mill 5.8 36.2 Kiln room 0.8 5.O Coal mill I.O 6.2 Clinker mill 6.3 39.4 Miscellaneous I.O. 6.3 I6.o IOO.O It will be noted from the above that about 40 per cent of the power is required to crush and pulverize the raw materials, a 396 PORTLAND CEMENT like amount to pulverize the clinker and the balance to operate the kilns, pulverize the coal, etc. |Waste Heat Boilers. The attempt to utilize the heat of the kiln gases under boilers was first made, I believe, at the plant of the Nazareth Cement Company, Nazareth, Pa., in 1897 by Dr. Irving A. Bachman. Dr. Bachman placed the boiler immediately over the rear kiln housing so that the dust laden gases entered the first pass of the boiler directly after leaving the kiln. No intervening flue was employed to collect even a portion of the dust. Natural draft was used to carry the gases through the boiler. It was found impossible under these conditions to keep the boiler clean and the dust accumulated so rapidly that continuous op- eration of the kiln was impossible. After encountering these difficulties, the plan was abandoned and the boilers were taken away. The late Professor R. C. Carpenter, of Cornell University, installed waste heat boilers to receive the exit gases from the rotary kilns in the plant of the Cayuga Lake Cement Company. The installation here was somewhat better than that at Naza- reth, but much was still to be desired in the way of facilities for keeping the boiler clean. In this plant, one boiler of the Wickes vertical water tube type, of 3,000 square feet of heat- ing surface was installed for each two kilns (6 feet by 60 feet) of the plant. When these boilers were clean they gave very satisfactory results. When operated on kiln gases alone these boilers pro- duced about 250 boiler horsepower. The same general difficul- ties, however, were encountered at Cayuga Lake as at Naza- reth. The company, in spite of these, struggled for quite a long period to handle the dust before finally abandoning the waste heat boilers. A similar installation by Professor Car- penter at the plant of the Kosmos Portland Cement Company near Louisville, Ky., had pretty much the same history. POWER EQUIPMENT, ETC 397 The efforts to use waste heat boilers were abandoned after these attempts for some years. The late Mr. Spencer B. Newberry, of the Sandusky Cement Company, however, profit- ing by the experiences of the early attempts, placed his boilers at a greater distance from the kiln with a substantial flue con- structed between the kilns and the boilers. As the importance of this began to be realized, other engineers experimenting with the use of the waste gases for steam generation provided additional facilities for taking care of the dust and for keeping the boilers clean. It was also found advisable to employ in- duced draft rather than stacks. Among the plants which installed successful waste heat boil- ers prior to IQI 5, when the subject received the almost univer- sal attention of cement manufacturers, may be mentioned the Louisville Cement Company, the Sandusky Portland Cement Company and the Burt Portland Cement Company. With these installations about half of the steam required to operate the plant was obtained. The boilers were also generally so in- stalled that they could be fired by hand when the kilns were not operating, or a greater quantity of steam was desired than the kiln gases could produce. Air Leakage and Draft. While these installations were faulty they turned the atten- tion of the cement mill engineers to the possibilities of the waste heat boiler. It was soon realized that in the early in- stallations due consideration had not been given to air leakage. Little or no importance was attached to the lowering of the temperature of the kiln gases by the infiltration of cold air at the feed end of the kiln. This condition occurred both in the boiler setting itself and at the opening between the kiln and the flue. In the modern installations, air seals are placed on the upper end of the kiln shell to exclude the cold air at this point. All clean-out doors on the dust chamber flues and at the bot- tom of each pass in the boilers are tightly fitted and in many places the joints are luted with clay which is renewed each time the doors are opened and closed. Great care is also used 398 PORTLAND CEMENT in the construction of the boiler settings themselves in order to make them air-tight. In some places, the flues are housed in a steel jacket as brickwork is much more porous than steel and consequently allows air to penetrate through it. The feature in the modern design, however, which probably did most to make the waste heat boiler practical was the in- crease of the intensity of and the regulation and control of the draft. It has long been known that the rate at which heat is transferred from the gas to the water in the boiler tube in- creases as the velocity of the gas increases, thus if the velocity of the gas should be increased three times, the heating surface could be reduced by half. In all of the recent waste heat boiler installations, the gases have been passed through the boilers at a fairly high velocity, a draft at the exit of the boiler of from 6 to Io inches of water being employed. It was also found advisable to lengthen the gas passages as this facilitates the transfer of heat. This was accomplished by an arrangement of baffle walls in standard boilers. Heat in the Gases. The amount of heat in the waste gases from the kilns de- pends largely on how the kilns are operated. Prior to the ad- vent of the waste heat boiler, kilns were always operated with a view to the economical use of the fuel for burning cement. Where boilers are installed, however, kilns are often operated with a view to furnishing steam enough to operate the plant, with the result that where inefficient engines were employed the amount of coal burned per barrel of cement exceeded con- siderably the normal requirements for cement burning only— the manufacturer figuring that any coal lost in cement burning would be utilized in producing steam. Under normal condi- tions the gases leave the kiln at about 1,500° F. and there are about 12,OOO cubic feet of gas per barrel of cement. The mean specific heat of the gases at the above temperature is O.O.22 per cubic foot per degree rise. Assuming the tempera- POWER EQUIPMENT, ETC 399 ture of the gases can be reduced to 400° F. in a proper recov- ery system, the heat utilized in raising steam would then be 290,400 B. t. u. The heat necessary to generate I pound of Steam at 200 pounds per Square inch gauge pressure and IOO pounds superheat from feed water at 2009 F. is I og I B. t. u. It will be seen, therefore, that the heat in the gases is equiva- lent to 266 pounds of steam at the above pressure and temper- ature. In a modern turbo-generator set, the requirements are about 17% pounds of steam per kilowatt-hour at the switchboard, if So utilized, therefore, the above quantity of steam will pro- duce I5.2 kw-hr. or practically the full requirements of a mod- ern plant. In actual practice, the amount of heat recovered would be reduced somewhat by the air leakage through the boiler setting and increased by the combustion in the boiler of the carbon mon- oxide in the gases. The kiln can always be so operated as to give a larger volume of gas and gas both of higher temperature and greater content of carbon monoxide, so that where steam turbines are employed the waste heat boilers can be made to furnish all the steam required in the plant. By operating the kilns under reducing conditions, that is with a deficiency of air, the waste gases can be made to contain a large percentage of carbon monoxide. By admitting addi- tional air to the gases just before or as the latter enter the boiler, the carbon monoxide is burned to carbon dioxide and the latent heat of combustion of this is added to the sensible heat in the gases. Where more steam is required for power, therefore, than would be produced by the kilns when operated normally, it is generally the practice to operate the latter so as to give a gas containing from 3 to 5 per cent carbon monoxide, the additional steam being produced by this so-called “secondary combustion.” 4OO PORTL AND CEMENT Table XXXIX illustrates the performance of waste heat boiler installations at various American cement plants and also gives data as to the nature of equipment employed and operating conditions. Quantity of Gas and Heat in This. The heat available in the stack gases may be calculated from their temperature and analysis. It is in the case of each gas found, the product of the quantity X temperature drop X specific heat. The quantity of gas can be measured directly by means of a pitot tube or calculated from the carbon dioxide found by analysis of the gas. The latter is the simpler method and is as follows. Twelve pounds of carbon burned to carbon dioxide will unite with 32 pounds of oxygen and produce 44 pounds of carbon dioxide. Hence one pound of carbon will produce 3.67 pounds of carbon dioxide. One pound of carbon dioxide occupies 8.152 cubic feet at standard temperature and pressure. Hence 3.67 pounds will occupy 29.92 cubic feet. This is equivalent to the volume of carbon dioxide produced by the burning of one pound of carbon, therefore, one pound of coal containing 74.9 per cent carbon will produce 22.4 cubic feet of carbon dioxide. Similarly it will be found that one pound of carbon will pro- duce 29.8 cubic feet of carbon monoxide or about the same quantity of either carbon monoxide or carbon dioxide. From the above, it will be seen that for each pound of coal burned in the kiln there will be produced 22.4 cubic feet of carbon dioxide (or carbon monoxide). This volume of carbon di- oxide is further increased by that driven off from the raw materials during burning. The amount of the latter can, of course, be determined by analysis of the raw materials and the clinker, or assumed at 200 pounds per barrel. On the latter basis, the carbon dioxide driven off from the raw materials will occupy 2OO X 8. I52 = I,630 cubic feet at standard temperature and pressure. If we assume IOO pounds of coal are required to burn a barrel of cement, then the total carbon dioxide produced per barrel of cement is I,630 —H (22.4 × IOO) = 3,870 cubic feet. POWER EQUIPMENT, ETC 4OI Let us assume Analysis No. I on page 299 as that of the gas, then it will be seen that the latter contains 27.4 per cent carbon dioxide and O.3 per cent carbon monoxide or a com- bined percentage of 27.7. To find the volume of gas leaving the kilns, therefore, it is only necessary to divide 3,870 by O.277. This gives the total volume of gas or I3,971 cubic feet per barrel of cement produced (measured at standard tempera- ture and pressure). To find the heat carried out by this volume of gas we could multiply the above quantity by the percentage of each gas pres- ent for the volume of gas and then the latter volume by the mean thermal capacity of the gas and temperature rise above normal. It is simpler, however, to find the mean specific heat for the mixture of gases and then multiply the total volume of gas by this and the temperature rise. For example, refer- ring to Fig. 91, it will be seen that the mean thermal capacities of one cubic foot of air, nitrogen and oxygen are the same and since these gases (neglecting water for the present) form prac- tically all of that portion of the gas which is not carbon dioxide, we can determine the mean thermal capacity of the exit gases of the kiln by multiplying the percentage of carbon dioxide by the thermal capacity of this gas and adding to this the result obtained by multiplying the difference between one and the per- centage (expressed decimally) of carbon dioxide (which mani- festly represents the percentage of air, oxygen and nitrogen in the exit gases) by the mean thermal capacities of the latter gases. In our case, the mean thermal capacity of carbon dioxide at 1,2OO° F. is found to be O.3I4 and of air, nitrogen and oxygen O.OI99. The mean thermal capacity of the exit gases is, therefore, O.274 × O.O3I4 + O.726 X O.OI99 = O.O22O5. This latter is the mean thermal capacity of the gas per de- gree rise between O and 1,200° F. One cubic foot of gas at I,2OO° F. will, therefore, carry out (1,200 — 32) × O.O2205 = 24.65 B. t. u. and I3,971 cubic feet, 13,971 X 24.65 = 344,385 B. t. u. 4O2 PORTLAND CEMENT In the wet process the exit gases also carry out the water evaporated from the slurry. Some water is also formed by the burning of the hydrogen in the fuel. This water is not shown by an ordinary gas analysis. The water in the slurry is, of course, 300 pounds. Coal contains, say, 4.8 per cent of hydrogen. This will, of course, produce 2: 18:: O.O48: 4, 4 = O.432 pound of water. The quantity of coal to burn a barrel of cement will therefore produce O.432 × I2O or 51.84 pounds. The total quantity of water in the exit gases is therefore 300 + 51.84 = 351.84 or say 352 pounds per barrel of cement burned. The mean thermal capacity of steam between 212° F. and 1,200° F. is O.54. The water, therefore, carries out 352 × 0.54 × (1,2OO – 212) = 187,799 B. t. 11. per barrel of cement burned. The latent heat due to carbon incompletely burned, (that is burned to carbon monoxide) is, of course, the heat which would be generated by the burning of the carbon monoxide in the kiln gases. One cubic foot of carbon monoxide burned to carbon dioxide will produce 43 B. t. u. We have pre- viously calculated the total amount of gas at I.3,971 cubic feet per barrel. This contains O.3 per cent carbon monoxide or I3,971 × O.Oo3 = 41.8 cubic feet. The heat liberated due to combustion is of the carbon monoxide, therefore, 41.8 × 43 = 1,787 B. t. u. per barrel of cement. The Boiler. The waste heat boiler as installed at the present time consists of a standard horizontal water tube boiler. Fig. 125 shows the method of installing the boiler and of making the connection with the kiln, etc. In a dry process cement plant where the gases are at approximately 1,500° F., ten square feet of heating surface are employed for each boiler horse- power. Sometimes the boilers are equipped with superheaters. Originally one boiler was employed for each kiln. This is con- sidered disadvantageous, however, and now only a few large boil- ers are employed even where there are quite a number of kilns. By having fewer and larger boilers efficiency is increased and floor Power EQUIPMENT, ETC 403 space is decreased. The number of openings permitting air leak- age is also cut down and there are fewer units to look after and clean. The boilers should be set fairly close to the kiln. There should, however, be installed between the boilers and the kiln a Fig. 125–Waste heat boiler installation–Edge Moor Iron Co., Edge Moor, Del. large flue in order that some of the dust may settle. This flue is usually provided with a hopper bottom and openings through which the dust may be drawn into a conveyor located alongside of the flue. Boilers are usually provided with four passes. The tubes are usually kept clean by blowing them off at least once a day with a steam or air jet. Openings are provided for this purpose in the sides of the boiler. Air Seal and Dampers. The waste heat boiler owing to its recent adaptation to the cement industry has generally been installed in plants which have been previously designed for hand fired boilers and for kilns which were intended to discharge their gases directly in- to the atmosphere through individual steel stacks. These stacks have generally been left in place and the only change 4O4. PORTLAND CEMENT which has been made in the kiln itself is to provide an air seal between the kiln and the stack housing. - Fig. I26 shows a form of seal which has been quite gen- erally used in the cement industry. It will be noted that this consists of a plate “A” rivetted to the kiln. There is keyed to this plate a cast iron ring “B.” This is free to move hori- # /º/, 3/e/ 222222* NS –2– 2 2S : Counſer We/g/77. - - - - - - - - - ---------4- - Operažzz e | Z//7e 5fac/. //or” Fig. 127.-Damper for kiln stacks, waste heat boiler installation. POWER EQUIPMENT, ETC 405 zontally up and down on the kiln but is caused to revolve with the kiln by the keys. Any expansion or contraction in the kiln is taken care of by the sliding of the ring over the plate. This ring in turn revolves in a close fitting groove made by two angle irons which are fastened to a round box arrange- ment on the stack chamber. The kiln stack is generally provided with a damper. This should effectively close the stack so that no cold air can leak in at this point. Fig. I27 shows an acceptable form of damper. Still another damper is usually placed between the kiln and the boiler so that when the kiln is not in operation the port con- necting the kiln with the boiler can be closed. It is advisable to make the outer casing of the flue either of reinforced con- crete or of steel. The steel jacket as has been previously noted is impervious to air, particularly if the joints in this flue are welded instead of riveted. From the main flue the gas is distributed to the boilers through short connecting flues. The boilers them- selves are usually set quite high so as to allow a large chamber underneath the tubes in which the dust may settle. Clean-out doors are provided at the bottom of this space so that dust can be removed at intervals. Economizer, Fan, Etc. The boilers are now quite generally followed by economizers in which the feed water for the boiler is heated. The gases leave the boiler at a temperature of from 475 to 600° and they are further reduced in the economizer to about 300 to 350° F. The economizer is set immediately after the boiler and is fol- lowed by the draft fan. Owing to their higher velocities, economizers on waste heat boilers have a greater capacity than in ordinary power plant work and should have about 33% per cent of the heating sur- face of the boiler to which they are connected. Economizers should have steel plate sides packed with asbestos or other heat insulator to conserve heat, cut down air leakage, etc. An 27 - TABLE XXXIX. —DATA ON WASTE HEAT BOILER OPERATION Plant Process Type of boiler Number of boilers Number and size of kilns connected to boiler Clinker per hour—bbls. Square ff. heating surface each boiler Square ft. heating surface superheater Economizer heating surface, sq. ft. Draft at feed end of kiln, ins: water Draft at fan inlet, ins. water Temperature of gas leaving kiln “ F. Temperature of gas leaving boiler or economizer * F. Fuel—kind Fuel—heating value, B. t. u. per lb., B. t. u. Coal required per barrel of clinker Carbon dioxide in gas leaving kiln Carbon dioxide in gas leaving fan Steam produced under operating conditions, lbs. per hour Steam produced under operating conditions, lbs. per barrel Steam produced under operating conditions, lbs. per lb. of coal burned Boiler horsepower developed Steam pressure of boilers—lbs. per sq. in. Temperature of steam at boilers, * F. —*— Dry Edgemoor 2 6–7x IOO II5 7,493 747 2,OIO O.3 3.9 I,450 336 Bit. coal I3,OOO 89.09 28.8 I4.9 25,744 3IO 3.48 833 I58 430 B C E. F Dry Dry Wet Dry B. & W. Sterling Edgemoor Edgemoor 2 7 2. 3 2—IOxI50 2–7xIOO 7–8xIoo 2–IoxI5o 6–6%xIOO 2–8x125 I5O Io.7 87.7 II2 I5,3OO 3,450 6,384 7,493 691 None *mº 400 None None 2, I42 2,0IO . O.25 O.O7 O. I2 O.45 5.00 No fan 4.30 6.80 I,300 I,350 I, IOO I,300 430 6OO 390 436 Bit. coal Bit. coal Bit. coal Bit. coal I3,000 I3,000 12,78o I3,500 IO3 I09 I27.2 95 20.5 24. I 27.5 26.5 I8.0 * 18.7 I4.0 53,760 25,320 35,000 7O, II3 3OI 34O 4II 457 3.8o 3. I2 3.22 4.81 1,680 I,350 I, I60 2,030 I55 I5O I75 I7O 43O 366 5IO 390 —º- Dry Edgemoor 2 5–8x125 I40 Io,662 2,300 0.40 4.50 I,3OO 3IO Oil I9,000 8.90 gal. 24.0 70,000 500 2,230 185 480 POWER EQUIPMENT, ETC 4O7 efficient economizer will show a saving of from 8 to Io per cent. The draft fan should be a heavy duty fan. The bear- ings are made extra large and are generally water cooled. The blades are so shaped that dust will not accumulate on them. The wheel and rotor are made heavy so that accumulation of dust will not affect smooth running. A draft at the fan inlet of from 6 to 8 inches of water is usu- ally employed. With 6-inch draft the loss of pressure is about as follows: In S. In the kiln O.5 In the flues O.5 In the boiler 4.O In the economizer I.O The fans are driven by either small steam turbines or by electrical motors. The motors are generally considered the better arrangement as they operate independently of the steam pressure in the boiler. With the turbine, when the steam pres- sure in the boiler is low, the speed of the turbine, and conse- quently the speed of the fan is reduced correspondingly and this happens to be the very time that full draft is needed. The motor on the other hand is independent of conditions in the boiler. When the temperature of the available feed water is low it is more economical to employ turbines and exhaust these to a feed water heater, but when the feed water can be heated to a temperature of about 200° F. by other equipment, the electric motor is preferable. Auxiliary Departments The auxiliary departments of the cement plant consist of a building or buildings in which are housed the mill office, lab- oratory, machine-shop, store-house, electrician’s shop, carpen- ter’s shop, blacksmith's shop, oil supply, lavatories and wash room, first-aid station and dispensary, etc.; and where elec- trical power is purchased, a transformer-house. Often, all of these departments are housed in one long building, but gener- 408 PORTLAND CEMENT ally two or more buildings are employed particularly if the plant is large. The mill office and laboratory are quite often housed in the same building and if much clerical work is done at the mill this should not be too near the plant on account of the dust. The various shops are generally housed in one build- ing and this often contains the store-house also. Oil and grease are usually stored in a separate building. The shops are best located convenient to the grinding mills as these need repairing most. The equipment of the laboratories is quite fully discussed in the next chapters of this book. The space necessary depends entirely on the size of the plant. The chemical laboratory for a 3,OOO-barrel plant will require about 400 to 600 square feet which should be divided into at least two rooms, a large labora- tory proper and a small office and balance-room combined. The physical laboratory may consist of one large room of about 350 square feet. There should also be a small room or a large closet connected with the laboratories for supplies. The mill office will depend entirely on what clerical work is done at the mill. When this is limited to keeping account of pay- rolls, supplies, mill correspondence, cost of manufacture, etc., one large general office and a smaller one for the mill superin- tendent will answer. If the purchasing agent is located at the mill he should, of course, have his own office. Most mills now have a room set aside for a first-aid station. This is equipped with the appliances and supplies ordinarily found in the offices of a physician and is usually furnished and stocked under the advice of the latter. The inside of this room should be painted white and the floor be of tile or hard wood. Where dispensary service for the employes is maintained two small rooms are generally found advisable—one for a waiting room and one for a consulting room. Machine-Shop. The machine-shop should, where possible, be located adjacent to the grinding departments of the mill as the heaviest repairs POWER EQUIPMENT, ETC 4O9 are connected with these. Even the smallest cement mill will need a fairly well equipped shop. The equipment of this will in- clude such tools as a small and a large lathe, drill-press, planer, shaper, milling-machine, hack-saw, pipe and bolt-threader, em- ery-wheel, grindstone and acetylene outfit. There will, of course, be benches and a full supply of bench tools. It is advisable to place a small hand operated overhead travel- ing crane in the machine shop and also a track on which to bring in parts should run lengthwise through the shop. Where the crane is not employed an I-beam and overhead trolley block should be installed. The blacksmith's shop should have a forge, an anvil and the usual forge tools. Often a small trip-hammer is installed and mechanical tools for sharpening and shaping rock-drills are very useful and pay for themselves very soon. The blacksmith's shop is often housed in one end of the machine shop. When the quarry is at Some distance from the mill another shop is placed here for taking care of the sharpening, etc., of the drills. The store-house is, as its name indicates, the room in which the repair parts and mill supplies, except gypsum and oil, are kept. It consists simply of a large room provided with racks and bins for the smaller parts, the larger parts being kept on the floor. The electrician's shop is usually adjacent to the machine shop or store-house. Here are kept a few spare motors and motor parts and here repairs to motors are made. The electrician is generally provided with a full set of test instruments, etc. Lamps and other electrical supplies are often kept here rather than in the store-house. All repair parts, supplies and machine shop labor expended in making repairs are kept account of and are charged against the department in which the latter occur. Where power is purchased, a transformer-house has to be pro- vided. In this are housed the transformers and the switchboard. The transformer building should be located as near the grinding 4IO PORTLAND CEMENT mills and crushing department as possible since approximately two-thirds of the power is used here. The oil house is provided with tanks, filters, etc., and should be near enough to the store-house to allow one man to attend to both but separated from it in order to lessen fire danger. Arrangement of Plant. Before the advent of the individual motor drive it was neces- sary to so arrange the mill as to best distribute the power. Now when electric drives are employed, the various departments of the mill may be grouped in almost any desired manner. The general idea now among cement engineers is to so arrange the mill as to facilitate elevating and conveying of the materials. Following out this idea, the various departments are usually grouped so that the materials move naturally from one step to Fig. 128-Bird’s-eye view National Cement Co., Montreal, Que., Richard K. Meade & Co., Engineers. Explanation: A, Quarry; B, Crushing plant; C, Rock dryers; D, Rock storage; E, Bradley-Hercules mill room; F, Tube-mill room; G, Synchronous motor room; H, Blending silos and kilns; L, Coal pulverizing room (Aero pulverizers); K, Coal dryer; J. Coal crushers and unloading department; M. Clinker Storage; N, Clinker dryer; o, Gypsum storage; P, Cement storage; Q, Pack-house; R. Bag storage; S, Machine- shop, stores, office, laboratory, etc. POWER EQUIPMENT, ETC 4II the next. The relation of the railroad sidings and quarries also has an important bearing on the arrangement of the mill. The use of the Fuller-Kinyon pump, however, allows the coal mill and the stock house to be placed at almost any desired angle to and at Some distance from the rest of the plant and hence allows more flexibility in the layout. Figs. I28 and 129 give an idea as to the layout of a modern cement plant. The former illustrates the arrangement of the tracks and equipment in a dry process plant while the latter shows a wet process plant. Table XL gives the equipment employed in a number of Amer- ican Portland cement plants. This information is taken from pub- lished descriptions of these plants and may not represent present conditions exactly at any plant. The descriptions, however, show quite clearly what equipment is necessary for plants of the size indicated and taken in connection with the preceding chapters should enable the reader to form a good idea of a modern cement plant. TABLE XL.—MECHANICAI. EOUIPMENT OF SOME MoDERN PORTLAND CEMENT PLANTs. Allentown Portland Cement Co. Materials—Cement-rock and limestone. Dry process. Fuel—coal. Capacity—2,800 barrels daily. Location—Evansville, Pa. Quarry Equipment. Deep well drilling machine. End dump cars, capacity 75 cubic feet. I Marion shovel—65 tons. I Atlantic shovel—65 tons. I Thew shovel for stripping. Electric hoists, incline and automatic car dumping arrangement. Stone House. I No. Io McCully crusher. 3 No. 6% Lehigh crushers. I Motor, 250 H. P. used to drive crushers. 4 Waste heat dryers, 7' × 50'. I Motor, 5o H. P. for driving all above. Stone storage, capacity 5,000 tons. I Volume mixing apparatus. Raw Mill. 2 No. 8 Krupp ball mills, without screens, each driven by a 50 H. P. ImOtor. * 25.2° Stock Air 7.///76 2. A/ºrs S. "Caff Woſer //a/{e feed & Gas O/C/5 Aower Surry ſanks Jam/.5 3/F, D/A J.5/r Alga JW/fches ZA 23 Sørry 7,7745 * * = as sº as as ºmºm a- - ºr = < * ~ * = = 2, … = - - - - - -, * = = = * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * = - - - - off/ 30"Wafer () schorne Fig. 129-a.—Plan and elevation—Manitowoc Portland Cement Co., Manitowoc, Wis., raw mill, slurry tanks, power house, waste heat boilers, and feed end of kilns. 5 of Upper/ſun & Peck Conveyor [] //mne/ */6O'/ſ/75 [] […] E. C] [] Conveyors 7:22' C/nker Mofor- N * w * Carrier 5forage || 5/65 Cemenſ Cony fo Fig. 129-b-Plan and elevation—Manitowoc Portland Cement Co., Manitowoc, Wis., discharge end of kilns, coolers, finishing mill, stock house, and pack house. j 4I4 PORTLAND CEMENT II Fuller-Lehigh mills, 42", each driven by a 75 H. P. vertical motor. Kiln Room. 4 Rotary kilns (Wetherill), 8 × 120', each driven by a 30 H. P. variable speed motor. 4 Rotary coolers, 5' X 50', all driven from a line shaft by one 50 H. P. motor. Clinker storage consisting of steel trestle above and tunnel below, with belts for conveying. Capacity 90,000 barrels. Finishing Mill. I No. 8 Krupp ball mill, without screens, driven by 50 H. P. motor. 5 Fuller-Lehigh mills, 42", each driven by a 75 H. P. vertical motor. 3 Fuller mills, 54", driven by individual vertical motors. 2 Fuller mills, 57", driven by individual vertical motors. Stock house with a capacity of I2O,000 barrels. 4 Bates automatic valve bag packers. Fuel Mill. I Set rolls, driven by 4o H. P. motor. 2 Matcham coal dryers, driven by 30 H. P. motor. 3 Fuller-Lehigh mills, 42", 75 H. P. motor for each. Fuller-Kinyon System for handling pulverized coal. Coal storage for handling coal as unloaded. Pozver Plant. 3 Wetherill cross-compound condensing engines, direct connected to (Westinghouse) A-C. generators, 937 kv-a. each. I Relay unit. I Motor generator set for exciting. I Engine-driven generator for exciting. 5 Rust vertical tubular boilers, 4o H. P. each. 5 Sets Lehigh stokers. I Traveling crane, Io tons. Mesta barometric condenser, pumps, etc. All machinery is motor-driven and most of it by individual motors Buildings are of steel and plastered expanded metal. Dixie Portland Cement Co.” Materials—Limestone and shale. Wet process. Fuel—coal. Capacity—6,000 barrels daily. Location—Copenhagen, Tenn. Quarry Equipment. 4 Well drilling machines. 3 Porter steam locomotives. Steam shovels for loadng. Side dump all steel quarry cars. Electric hoisting engine. 1 Rock Products, Oct. Io, 1924, 27. POWER EQUIPMENT, ETC 4I5 Belt conveyor (2,200 feet) from shale pit to mill. Stone House. I No. 42 McCully crusher, driven by its own electric motor (for lime- Stone), followed by, I Revolving screen, 2" openings, followed by I Worthington 72" diam. X 30” face rolls. Raw material storage, 80 × 240', equipped with Shepard traveling Crane, Capacity 30,000 tons. 4 Williams hammer mills (for shale). 2 Shale storage tanks, capacity 300 tons each. Razv Mill. 2 N § I06 Smidth kominuters, driven by 300 H. P. motors, followed V, 2 Smidth Trix screens followed by, 2 Smidth 7" X 27' tube mills, driven by 500 H. P. motors. I Blending tank, 3,200 barrels capacity. 8 Slurry storage tanks, 900 barrels capacity each. Kiln Room. IU Rotary kilns, S' × 125', each driven by a 30 H. P. motor. 5 Revolving coolers. - Finishing Mill. 20 Griffin mills, 30”. 2 Tube mills, 7" X 27'. Stock house with a capacity of 300,000 barrels. 7 Automatic weighing and sacking machines. Fuel Mill. I Coal crusher. 2 Rotary coal dryers. 5 Fuller-Lehigh mills, 42". Pozver Plant. There are two power plants, one driving the raw mill and one for the clinker mill, in each of which are I Direct-current generator, 400 kw. 3 B. & W. water tube boilers, 7oo H. P. each. 3 Westinghouse turbo generators, 1,200 kw. each. I Reinforced concrete chimney, I50 feet high. Buildings are of reinforced concrete or of steel and plastered expanded metal. Roofs are of corrugated iron. This represents a mill built some years ago and rebuilt and enlarged recently. Security Cement & Lime Co." Materials—limestone-shale and boiler ashes (cinders). Dry process. Fuel—coal. Capacity—5,000 barrels daily. Location—Security, Md. * Concrete, August, 1923, p. 21, Cement Mill Edition. Rock Products, Nov. 15, 1924, p. 35. 4I6 PORTLAND CEMENT Quarry Equipment (located one-fourth mile from mill). 2 Sanderson cyclone steam well drills. I Loomis clipper electric well drill. I Marion steam shovel, Model 70, 4-cubic yard dipper I Marion steam shovel, Model 65, 2%-cubic yard dipper. I Marion electric shovel, Model 70, crawler tread. I Thew traction steam shovel, A-1, 34-cubic yard dipper. I Vulcan saddle tank locomotive, 26 tons. Side dump, IO ton, quarry cars. Crushing Plant (located at quarry). I Flory 48" drum electric hoist for hauling up incline. I Mundy hoist for dumping. I Allis-Chalmers 54" × 60" jaw crusher driven by 200 H. P. motor. I Allis-Chalmers screen 60" × 25', for commercial stone. 2 McCully gyratory crushers, No. 7%. Raw Material storage, concrete, 50' wide X 230' long × 35" high, ca- pacity I2,000 tons. Material delivered in and out of storage by belt conveyors. I Steel loading hopper, IOO tons capacity. Stone transported to mill by 50-ton standard gauge hoppered car. I Vulcan locomotive, 26 tons. Raw Mill. I Receiving hopper, I25 tons capacity. 3 Crushed stone tanks, capacity 927 tons combined. I Pennsylvania hammer mill, size SXP-8, for stone. I Jeffrey hammer mill, Type B, for cinders. 3 Vulcan dryers, 5'6" × 50'. 2 Storage tanks, 1,300 tons capacity combined. I Schaffer poidometer. 17 Fuller-Lehigh mills. (8 mills are driven by two 300 H. P. syn- chronous speed motors through line shafting; 5 mills are driven by 75 H. P. individual vertical motors; 4 mills driven in pairs by two 150 H. P. motors). Kiln Department. 5 Rotary kilns, Io' to 8" X 125'. Clinker storage, 55,000 barrels capacity, equipped with Niles crane. Fuel Mill. I Cummer dryer, 48" X 36". 3 Fuller-Lehigh mills, 42", driven by individual 75 H. P. vertical In OtorS. POWER EQUIPMENT, ETC 417 Finishing Mill. Io Giant Griffin mills. 4 Krupp tube mills. 6' X 16". (Two 300 H. P. Synchronous motors each drive 5 Griffin mills and One tube mill through line shafting; 5 Griffin mills are driven by in- dividual 75 H. P. vertical motors; and 2 tube mills have 250 H. P. individual motors). Stock House. 8 Reinforced concrete silos, 30' diameter × 70' high, capacity Iooooo barrels. I Wooden Stock house, IOO,000 barrels, capacity. 5 Bates packers. Power purchased. This represents a mill built some fifteen years ago and greatly enlarged and remodeled in recent years. National Cement Co. Material—cement rock. Dry process. Fuel—coal. Capacity–3,300 barrels daily. Location—Montreal-East, Quebec, Canada. Crushing Department. I Flory single-drum car hoist, 54" × 36", operated by 350 H. P. ImOtOr. I Pennsylvania single-roll crusher, class M, 36" × 60", driven by 200 H. P. motor. I Pennsylvania hammer mill, Super G-12, direct connected to 3oo H. P. motor. - I Overhead traveling hoist, Io ton. 2 Dryers, 6 × 70', each driven by 15 H. P. motor. I Aero pulverizer for coal for heating dryers, D-1, driven by 40 H. P. motor. Stone storage, 44' × 150'. Capacity 6,000 tons. Material handled in and out by belt conveyors. Raw and Clinker Mill. 4 Bradley-Hercules mills, direct connected to 300 H. P. motors. 4 Canadian-Vickers tube mills, 7" X 26', direct connected to G. E. super-synchronous, 500 H. P. motors Any unit can be employed for either raw material or clinker. Fuller-Kinyon System used for handling ground raw material and Cement. Kiln Department. 6 Reinforced concrete blending silos, I5' diameter × 43' high. 3 Vulcan kilns, 9 × 160', each driven by 50 H. P. motor. 3 Aero pulverizers, G-1, direct connected to IOO H. P. motors. I Spare aero pulverizer as above mounted on truck. 418 PORTLAND CEMENT I Coal dryer, 6 × 60', driven by 15 H. P. motor. I Pennsylvania single-roll coal crusher, 24" × 24" driven by 25 H. P. ImOtOr. Drag line scraper for handling coal in and out of storage. No coolers. Clinker storage, IOO' X 250', capacity 200,000 barrels clinker, equipped with Shepherd 5-ton crane and 2-yard basket. I Clinker dryer, 6' X 70'. Wet seasoned clinker to be dried by mixing with hot fresh clinker. I Gypsum silo, I5' diameter × 52' high. Stock House. Io Reinforced concrete silos 30' diameter X 65' high, 126,000 barrels capacity. 3 Bates packers direct connected to 15 H. P. motors. Power is purchased but provision has been made for waste heat boiler plant if desired. Large motors employ 2,200 volts, small motors 550 volts. Buildings are of structural steel. Pyramid Portland Cement Co.' Materials—limestone and clay. Wet process. Fuel—coal. Capacity—2,500 barrels daily. Location—Valley Junction, Iowa. Quarry Equipment—Quarry located at Gilmore City, Ioo miles from mill. 2 Cyclone well drills. I Bucyrus steam shovel, Ioo tons, 3%-cubic yard dipper. Standard gondola cars for transporting stone to mill. Crushing Plant (at mill). I Clyde double-drum electric car hoist. I Chicago rotary car dumper, operated by Io H. P. motor. I McCully gyratory crusher, No. 18. I Dixie hammer mill, No. 9, (crusher and mill driven by 300 H. P. motor). I Revolving stone screen, 5' X 30' (this is used to produce com- mercial stone of which plant sells some). I Raw material, gypsum, coal and clinker storage, 78' wide X 400' long, equipped with Milwaukee 8-ton traveling crane with 3-yard clam shell bucket. Capacity of storage 15,000 tons of stone, 5,000 tons shale and Ioo,000 barrels clinker. Material reclaimed on belt conveyor. Raw Mill. 2 Kominuters, driven by 150 H. P. motors. 2 Trix screens, driven by Io H. P. motors. 2 Smidth tube mills, 7' × 22', driven by 400 H. P. motor through Lenix drive. * Rock Products, October 20, 1923, p. 45. POWER EQUIPMENT, ETC 4I9 3 Correcting basins, 600 barrels capacity each, agitators driven by 5 H. P. motors. I Mixing basin, 2,000 barrels capacity, mechanical agitators driven by I5 H. P. motor. 3 Smidth plunger pumps for handling slurry. Kiln Department. 3 Kiln feed basins, capacity 2,700 barrels, mechanical agitators driven by I5 H. P. motors. 2 Rotary kilns, II'3" to Io' × 240', reinforced concrete stacks 216' high. 2 Rotary coolers, 7" X 70" equipped with fans. Clinker storage as noted. Fuel Mill. I Dixie crusher. I Cummer coal dryer, 6' × 50'. 3 Raymond roller mills. Finishing Mill. 3 Kominuters. 2 Smidth tube mills, 7' × 22'. Stock House. 6 Reinforced concrete silos, 32' diameter × 80' high, capacity IIo,000 barrels. 2 Bates packers. Power is purchased. Signal Mountain Portland Cement Co." Materials—Limestone and clay. Wet process. Fuel—coal. Capacity—2,500 barrels daily. Location—Signal Mountain, Tenn. Quarry Equipment (Quarry located one-third mile west of plant). 2 Sanderson cyclone well drills, No. 14. I Air compressor driven by I25 H. P. motor. I Bucyrus steam shovel, No. 85-C, 3%-yard dipper. Io Western side dump, air operated cars, 16 yards capacity. I Baldwin locomotive, 50 tons. Crushing Department. I Allis-Chalmers gyratory crusher, No. 21, driven by 200 H. P. motor. 2 Williams Hammer mills, No. W-2, driven by 150 H. P. motors. Storage 80' X 350' capacity, I5,000 tons of stone and 5,000 tons of clay equipped with traveling crane. - Raw Mill. I Wash—mill for clay, 26 diameter; agitator driven by 75 H. P. motor. 2 Allis-Chalmers compeb mills, 7" X 22', driven by 500 H. P. syn- * Concrete, January, 1924, p. 1, Cement Mill Edition. 42O PORTLAND CEMENT chronous motor through magnetic clutch. 4 Steel blending tanks, each 290 yards capacity, air agitation. I Air compressor, driven by Ico H. P. motor. 3 Centrifugal pumps, rubber-lined, 4", driven by 40 H. P. motors. Kiln Department. 2 Kiln feed tanks, each 600 cubic yards capacity, air agitation. 2 Rotary kilns, II' X 175', each driven by 75 H. P. variable speed motor. 2 A. B. C fans, No. 9, each driven by 25 H. P. motor. Fuel Mill. I Webster single roll crusher, 30" × 3o". I Rotary dryer, 8' X 55'. 2 Fuller mills, 46", driven by Ioo H. P. motors. Coal conveyed to kilns by Fuller-Kinyon system. Finishing Mill. 2 Allis-Chalmers compeb mills, 7" X 26', driven as above. Stock House. 6 Reinforced concrete silos, 35’ diameter X 85’ high, capacity 90,000 barrels. 2 Bates packers. Buildings are of structural steel, with concrete floors and concrete roof tile. Electrical power is purchased but provision has been made for a waste heat boiler plant at any time. Oklahoma Cement Co.” Raw Materials—Limestone and shale. Wet process. Fuel—natural gas. Capacity—4,500 barrels daily. Location—Ada, Okla. Quarry Equipment—Quarry located about six miles from mill. Keystone well drills. 2 Marion steam shovels, No. 80, 3-yard dipper. Io Woodfort Engineering Company electric-driven, Io-ton side dump cars, each operated by 35 H. P. motors—switches are controlled from crusher building. Shale Pit. 2 Steam shovels, No. 60-E, 2%-yard dippers. Side dump gondola cars are used for shale. Crushing Plant. I Traylor jaw crusher, 36" × 72". 1 Scalping screen, 64" × 18'6". I Mammoth Jumbo Williams mill, No. 9. 1 Concrete, September, 1920, Cement Mill Edition. POWER EQUIPMENT, ETC 42I 2 Double-jacketed revolving screens, 84" × 26'. (About 1,500 tons of stone is sold daily. - Stone House. Material delivered to plant by rail. Stone storage, 80' wide X 300' long × 70' high, half for each material. Materials enter by overhead tracks. Material reclaimed by I5-ton, 4- cubic yard crane. One 20' bay in middle used as proportioning department, Schaffer poid- ometers used for proportioning. I Double roll shale disintegrator, 36" × 36". Raw Mill. 3 Allis-Chalmers compeb mills, 7" X 26', driven by 450 H. P. syn- chronous motors through 54" magnetic clutch. 3 Correcting basins, each 20' diameter X 14' high, Dorr agitators. 2 Mixing basins, each 34' diameter X I4, Dorr agitators. 2 Slurry storage basins, 34' diameter X 22' high, Dorr agitators. Kiln Room. 3 Four-tire, rotary kilns, Io' × 240', equipped with concrete, stacks 9 × 270', driven by IOO H. P. variable speed motors. 3 Fans, capacity 9,000 cubic feet minimum at 6-ounce pressure. Natural gas used as fuel—two 17" Kirkwood burners for each kiln. 3 Rotary coolers, 8 × 80'. Io Reinforced concrete silos, 26' diameter X 85’ high, for clinker storage, capacity I35,000 barrels. Finishing Mill. 3 Compeb mills, 7" X 26', driven as above. 3 Emerick separators, I4 diameter. Stock House. Io Reinforced concrete silos, 26' × 85’ capacity, 125,000 barrels. 4 Bates packers. Power is purchased, 480 volts is employed in mill. Buildings are of re- inforced concrete. Petoskey Portland Cement Co. Materials—Limestone and shale. Wet process. Fuel—coal. Capacity—2,000 barrels daily. Location—Petoskey, Mich. Quarry Equipment. Well Drills. I Steam shovel, 70 tons for limestone. I Steam shovel, 45 tons for stripping. Side dump cars, Io tons. Steam locomotive. 422 PORTLAND CEMENT Stone House. I Gyratory crusher, No. 12. 4 Rotary screens, 5' X 14'. 3 Gyratory crushers, No. 5. (About 1,000 tons of stone are sold daily for commercial purposes). Razvy Mill. 2 Allis-Chalmers compeb mills, 7" X 22', each driven by 400 H. P. synchronous motors through magnetic clutches. 4 Slurry tanks, each 20' diameter X 40' high, air agitation. Slurry handled by compressed air and blow tank. Kiln Room. 2 Allis-Chalmers kilns, Io' X 150'. 2 Kiln feed tanks, 20' X 20'. 2 Coolers, 6 × 60'. No clinker storage. Clinker conveyed direct to mills by Peck carrier. Fuel Mill. I Indirect fired coal dryer, 6' × 60'. 3 Fuller mills, 42". Coal conveyed by elevator and conveyors. Finishing Mill. 2 Compeb mills, 7" X 22', driven as noted above. Stock House. 6 Reinforced concrete silos, 30' diameter X 70' high, capacity about IOO,000 barrels. Bates valve baggers. Power Plant. 2 Edgemoor boilers, four-pass, 638 H. P., equipped with superheater, waste heat. 2 Green economizers. 2 Buffalo exhausters, 580 R. P. M., driven by 75 H. P., variable speed ImOtOrS. I Boiler, 313 H. P., spare. 2 Allis-Chalmers turbo-generators, 1,000 kV-a. each. 2 Jet condensers. I Exciter set, steam-driven, 30 kw. I Exciter set, motor-driven, 30 kw. 2 Air compressors, motor-driven, capacity each 300 cubic feet min- imum. Large motors employ 2,300 volt, 60-cycle, 3-phase current, small motors 480 volts. Crusher building is of reinforced concrete, balance of plant of steel. POWER EQUIPMENT, ETC 423 International Cement Co., Birmingham Plant' Materials—Limestone and shale. Dry process. Fuel—coal. Capacity—4,700 barrels daily. Location—North Birmingham, Ala. Quarry Equipment. 2 Cyclone electric well drills. Eastern Car Company V-shaped, Io-ton side dump cars. 2 Marion, Model 37, electric shovels, full revolving, caterpillar tread. I General Electric storage battery locomotive, 8-ton. * I Devenport steam locomotive, 15-ton. I Single drum Flory hoist, driven by Ioo H. P. motor. I Single drum hoist for dumping cars, driven by 15 H. P. motor. Stone House. I Superior gyratory crusher, 3o" driven by 15o H. P. motor. I Pennsylvania hammer mill, Model Ajax, No. 8, driven by 200 H. P. motor. Stone storage, 82' wide X 195' long, with one large bin for stone and three small bins for shale. Material handled by Champion, 8-ton, crane and 3-yard Blaw-Knox clam shell bucket. 2 Bins, I5' X I5' X 15', one each for stone and shale, equipped with Schaffer poidometers for proportioning these. 2 Vulcan rotary dryers, 7" X 70", fired by pulverized coal. Raw and Clinker Mill (Combined. Any unit may be employed for either raw material or clinker). 4 Bradley-Hercules mills, each driven by 300 H. P. slip ring motor. 4 Traylor tube mills, 7" X 26', each driven by 500 H. P. synchronous motor through Cutler hammer 60” magnetic clutch. I Traylor rolls, I6" × 24", for clinker. 5 Reinforced concrete blending silos, 17' diameter × 64’ high, capacity I,600 barrels each. I Gypsum silo, 20' diameter × 42' high. Kiln Room. 3 Vulcan kilns, Io' X 150', individual motors, reinforced concrete stacks 96" × Io3'. Clinker storage, 82' wide X 195' long, equipped with I Champion 8– ton crane and Blaw-Knox 3-yard clam shell bucket. This is a con- tinuation of the stone storage and equipment duplicates latter. Fuel Mill. I Orton & Steinbrenner Locomotive crane, 18 tons. I Fuller-Lehigh dryer, 66" × 42', pulverized coal fired. * Rock Products, August 25, 1923, p. 21. Concrete, October, 1924, p. 60, Cement Mill Edition. 424 PORTLAND CEMENT 3 Fuller-Lehigh mills, gear-driven, 42". Fuller-Kinyon System for distributing pulverized coal. Stock and Pack House. 12 Reinforced concrete silos, 32' diameter × 84' high, in two rows, capacity 200,000. 3 Bates packers. No power plant. Power purchased. 2,300 volts employed for large motors and 440 volts for smaller motors. Buildings are of steel frame, covered with Gunite (stucco) side walls and reinforced concrete tile roof. Kansas Portland Cement Co.” Raw materials—Limestone and shale. Wet process. Fuel—coal. Capacity—3,000 barrels daily. Location—Bonner Springs, Kansas. Crushing Plant. I Fairmount roll crusher, 36". I Pennsylvania hammer mill. Stone storage, equipped with Milwaukee 8-ton overhead traveling crane. A belt in a tunnel beneath the storage also helps reclaim. Raw Mill. 2 Smidth kominuters, No. 85, driven by I25 H. P. motor. 2 Smidth Trix screens. 2 Smidth tube mills, No. 18, driven by 250 H. P., G. E. Super- synchronous motors. 3 Correcting basins with mechanical agitation. Elevators and screw conveyors handle slurry. Kiln Room. 3 Kiln feed basins with mechanical agitation. 3 Rotary kilns, 9' to 8 × 220' driven by 50 H. P. motors, concrete chimneys. 3 Coolers, 8'6" × 78'. Finishing Mill. 7 Giant Griffin mills, driven by 75 H. P. vertical motors. 2 Allis-Chalmers tube mills, No. 722, driven by 400 H. P. G. E. super- synchronous motors. Cement handled by Fuller-Kinyon system. Fuel Mill. I Jeffrey single-roll coal crusher. 2 Ruggles-Coles coal dryers driven by 20 H. P. motors. 4 Fuller-Lehigh mills. 1 Rock Products, June 13, 1925, p. 49. POWER EQUIPMENT, ETC 425 Stock House. 6 Reinforced concrete silos, 32' diameter X 80' high, capacity IIo, Ioo barrels. 4 Bates valve packers. Power is purchased. Cost of Plant. The cost of building a modern cement plant will naturally de- pend on many variables—chief of which are the cost of con- struction in the locality in which the mill is built, the equipment selected, type of the buildings employed, storage provided for raw materials and cement, whether power is made or purchased, etc. At this writing, the mill itself will cost, exclusive of power plant, about $1.75 to $2.00 per barrel of annual output (daily ca- pacity multiplied by 300). A power plant equipped with waste heat boilers and turbo-generators will add from 50 to 75 cents to this figure. Most going cement plants, however, taking into con- sideration the value of their raw material deposits, quarry equip- ment, railroad sidings, locomotives and locomotive cranes, stocks of cement, fuel and supplies on hand, as well as the mill proper, will appraise from $3.OO to $5.00 per barrel of annual output. In providing for the building of a new mill, where securities must be sold, allowance should be made for brokerage. Work- ing capital should also be provided. Various authorities will have their own ideas as to the amount of the latter, but in gen- eral 50 cents per barrel of annual output would be a safe and conservative figure. The elements entering into the cost of manufacturing a barrel of cement are as follows: I Raw Material. (a) Limestone. (b) Shale, clay, etc. 2 Labor. (a) Operating. (b) Repairs. 3 Supplies. (a) Fuel for burning. 426 PORTLAND CEMENT (b) Fuel for power or electric-power. (c) Fuel for drying. (d) Gypsum. (e) Repair parts. (f) Lubricants. (g) Dynamite. (h) Miscellaneous. 4 Administrative. (a) Mill-office and administration. (b) Laboratory. 5 Fixed Charges. (a) Depreciation and obsolescence of mill buildings and machinery. (b) Depletion of raw materials used. (c) Insurance and taxes. (d) Contingencies and reserve. Cost of Raw Materials. The cost of quarrying the raw materials varies greatly in dif- ferent localities. It depends on the hardness of the raw material, the overburden to be removed, the water to be handled and method of doing this, the width, thickness, pitch, etc. of the stone deposit, whether hand or shovel loading is employed, the cost of labor and supplies, etc. The relative amount of material and stripping is the first consideration and naturally it is cheaper to quarry where the latter is relatively small compared with the former. Drilling will cost from 50 to 80 cents per foot for deep well drill work and I foot of drilling is equivalent to 20-30 tons of rock or about 2.5 to 4 cents per ton of rock blasted. Dyna- mite in the east ranges from 5 to 8 cents per ton of rock blasted. Hand loading at present costs about I4 to 18 cents per ton. Shovel loading from 6 to IO cents per ton. Miscellaneous quarry charges amount to about 5 to IO cents per ton. The following is probably an average figure for quarrying cement rock. POWER EQUIPMENT, ETC 427 Drilling and blasting labor 5.0 cts. per ton Loading (steam shovel) 7.0 cts. per ton Explosives 7.O cts. per ton Miscellaneous supplies and repairs 4.5 ctS. per ton Stripping and miscellaneous IO.5 cts. per ton Total cost per ton 34.O CtS. per ton This is equivalent to about II cents per barrel of cement. Labor. The cost of labor varies greatly in different sections of the country. The cost of unskilled labor can of course be estimated fairly well by any one familiar with local conditions. In general, it may be said that a 2,500 to 3,000 barrel mill will require one employee at the mill (quarry not included) for every I5 to 25 barrels of cement produced per day, or from I} to 2% barrels per man hour. Of the skilled laborers, there will be needed a quarry foreman, drillers, millers, burners, engineers, firemen, packers, mill foremen, machinists on repair work, blacksmiths, etc. Of these the millers, burners, packers, mill foremen and some of the machinists must be experienced in cement mill work, and consequently a new mill, located in a new section must im– port these men from one of the old established centers of the in- dustry, and, in order to induce these men to leave their homes, must pay them much higher wages than the older mills do. In the east the usual charge for all mill labor (skilled about 50 to 75 cents per hour, unskilled, 35 to 40 cents) is between I2 and 20 cents per barrel. The list below gives an idea of the force necessary to operate a modern cement mill with a capacity of from 2,500 to 3,000 barrels per day and equipped with all labor saving machinery. In this instance power is purchased and the mill is located in a section where labor is cheap. LABOR FOR A 3,000-BARREL PER DAY CEMENT MILL Quarry (8 hours). Well drilling by contract, shovel loading. I Quarry foreman @ $150 month $6.00 per day 2 Shovel engineers (a) $175 month I4.00 2 Firemen (a) $125 month IO.OO 6 Pitmen (a) 35¢ I6.8O 428 PORTLAND CEMENT 2 Trackmen (a) 35% 2 Jack drillers (a) 35¢ 2 Powdermen (a) 40% 4 Miscellaneous (a) 35% I Water boy I Locomotive engineer I Fireman 2 Brakemen Total quarry labor Cost per ton (a) I,000 tons daily Cost per barrel at 3.2 barrels to ton Crusher Bldg. (Io hours). I Hoist man @ 40% I Crusher man @ 30¢ I Hammer mill man @ 4cº I Assistant (a) 30% I Oiler (a) 35% Dryers (Io hours). I Dryer man @ 40% I Bin tender (a) 30% I Oiler and sweeper (a) 35% Stone Storage (Io hours). 3 Belt tenders (@ 30% Mill Room (2 Io-hour shifts). I General foreman @ $175 2 Millers (a) 45% 2 Oilers and bin tenders (a) 30¢ 2 Assistant millers (a) 35% Kiln Building (2 I2-hour shifts). 3 Burners (a) 50% 2 Oilers and sweepers (a) 3Cé 2 Bin tenders (a) 30¢ Clinker Storage (2 Io-hour shifts). 2 Crane men (a) 50¢ 2 Gypsum men (a) 50% 5.60 6.40 6.40 II.2O 2.50 $5.00 3.20 5.60 *mº-mº $3.20 2.40 3.20 2.40 2.80 $4.00 3.CO 3.50 $6.00 9.00 6.oo 7.OO $12.00 7.2O 7.2O $12.00 4.80 $78.90 I3.80 $92.70 9.3 Cents 2.9 centS $14.00 $10.50 9.00 28.00 26.40 I6.80 POWER EQUIPMENT ETC. 429 Fuel Mill (8 hours). I Miller (a) 456: I Fireman @ 30¢ I Laborer (a) 30¢ (4 hours) Machine Shop (Io hours). 2 Machinists (a) 75¢ 2 Helpers (a) 35¢ I Blacksmith (a) 604 I Helper (a) 35% I Repairman quarry cars @ 60¢ 1 Helper (a) 35% Store House. I Head storekeeper I Assistant Electrical Shop. I Chief electrician I Assistant electrician 4 Helpers Repair Gang. 6 Repairmen (a) 40% I Master mechanic $3.60 2.40 I.2O $15.00 7.OO 6.00 3.50 6.00 3.50 $5.00 3.50 $6.00 5.60 I6.00 $19.20 8.00 - $7.20 4I.OO $8.5o 27.60 27.20 Yard Gang. I Craneman 6 Laborers I Team and driver I Truck driver Miscellaneous Crafts. I Carpenter I Helper I Welder I Helper I Babbitting and sheet iron worker I Helper Laboratory. 2 Assistant chemists I Physical tester 2 Sample boys $6.00 I4.40 5.OO 4.CO $4.00 3.00 6.00 3.OO 4.00 3.00 $12.00 6.00 29.40 23.00 24.OO 43O PORTL AND CEMENT Plant Administration. 3 General foreman $20.00 I Timekeeper 4.OO I Shipping clerk 5.00 I Stenographer 4.00 I Switchboard girl 3.00 I Office boy 2.40 $38.40 Total $33I.Io Miscellaneous labor not distributed 20.35 $351.45 Cost per barrel in bins based on 2,892 barrels average daily production I2. I5 Cents Add for packing and sack cleaning by contract 4.OO cents Labor pack house I.O2 CentS Total cost per barrel f. o. b. cars I7.17 cents Supplies and Fuel. The cost of the supplies, coal, gypsum and limestone or clay, if these have to be purchased, can, of course, be calculated fairly closely. Under favorable conditions, such as soft raw material and a well installed power generation and transmission system, the power necessary to manufacture a barrel of cement can be made with 35 pounds of good coal. Even hard raw materials should not increase this to more than 40 pounds. Low grade fuel, poor engines and boilers and faulty power transmission, however, may easily raise this much higher. Where waste heat boilers are employed and a modern turbo- generator set is installed practically all the power necessary to operate the plant can be obtained from the waste gases of the kilns. Power obtained from waste heat boilers costs about o.6 to O.8 cents per kw-hr. covering interest on investment, operating and maintenance charges. Where power is purchased, the amount of this necessarily will range between 14 and 18 kw-hr. (with an average of 16 kw-hr per barrel of cement produced for modern equipment). That is to say a 3,000-barrel per day cement mill will manufacture 90,000 barrels per month and use I,440,000 kw-hr. in so doing. POWER EQUIPMENT ETC. 43 I For the amount of coal used to burn see the chapter on burn- ing. In general, a barrel of cement can be burned by the dry pro- cess in long kilns with about IOO pounds of good coal (14,000 B. t. u. per pound) or IO gallons of crude oil. A barrel of ce- ment can be burned by the wet process with about 120 pounds of good coal or I2 gallons of oil. Where the coal is of poorer quality than is indicated above proper allowance, on a B..t. u. basis, should be made. Each barrel of Portland cement has added to it from 8 to 12 pounds of gypsum. The latter is the limit placed by the standard specifications and about IO pounds is the usual amount required. If plaster of Paris is used in place of gypsum, practically the same amount is required and its cost delivered is usually about twice as great. In the eastern part of the United States, gypsum can generally be obtained f. o. b. the mill at from $5 to $8 per ton. The cost of lubricants varies greatly, but under good manage- ment and careful attention to avoid waste, can be reduced to from I.O to I.7 cents per barrel. The repair parts form one of the heaviest of the supply items of a cement mill and this item of expense depends, of course, largely on the type of machinery installed to do the grinding. The care with which the machinery is used also has a large in- fluence on this item. Repair parts may cost anywhere from 6 to IO cents a barrel, even with good management. The miscellaneous supplies usually foot up to about 2 to 4 cents a barrel. Theoretically, the container in which cement is shipped is supposed to pay for itself and is not included in the cost of mill supplies. The labor of packing and of checking, sorting, cleaning and repairing bags has been indicated under labor. Administrative Expenses, Depreciation, Etc. The administrative expenses vary greatly with the size of the mill and the calibre of the men employed. With a small mill em- ploying a first-class manager and chemist and good assistants, 432 PORTLAND CEMENT this may figure as high as I5 cents a barrel, while a large mill may reduce this easily to 5 to 8 cents a barrel. Of the fixed charges, taxes and insurance usually amount to I to 2 cents a barrel. The depreciation of mill buildings and ma- chinery is usually figured at 5 per cent of their cost erected, and the interest on bonds, etc., can, of course, be calculated with cer- tainty. To calculate the value of the raw materials used, it is necessary to know the amount of these available, when the calcu- lation becomes merely one for arithmetic. The cost of manufacturing Portland cement may, therefore, be said to depend on (I) the location of the mill and the ease with which it can obtain its supplies, (2) the cost of labor, fuel, power and gypsum, (3) the efficiency of the machinery installed, (4) the extent, suitability and softness of the raw materials, and (5) the management of the mill and the purchasing of its supplies. Present Cost of Manufacture. At the present time the cost of manufacturing cement at a plant located in the central or eastern part of the United States will range somewhat as follows: Cost of raw materials IO to I5 cents Mill labor Repair 5 to 8 cents Operating I2 to 25 cents Supplies Fuel 3O to 45 cents Gypsum 3 to 4 cents Lubricants I to 2 CentS Repair parts 6 to IO cents Miscellaneous 2 to 4 cents Power (when purchased) I6 to 24 cents Mill administration 3 to 5 cents Cost f. o. b. bins $0.88 to $1.52 Packing, loading and sack expenses .06 .08 Cost f. o. b. cars $o.94 to $1.60 The above is, of course, a bare manufacturing cost. To it must be added administrative salaries and expense of the general office and sales force, depreciation and depletion, insurance, taxes and interest charges, reserves, losses, etc. These items will greatly increase the above figure. ANALYTICAL METHODS CHAPTER XVI THE ANALYSIS OF CEMENT Preparation of the Sample! * See also Chapter XIX on “The inspection of cement.” The sample is usually received at the chemical laboratory in a paper or cloth bag or in a tin box or can. Here the sample is well mixed by passing several times through a coarse sieve, and by rolling back and forth on a sheet of paper, or better still, one of oil cloth. When thoroughly well mixed it is spread out in a thin layer on the paper, or oil cloth, and divided into 20 to 30 little Squares with the point of a spatula or trowel. A small quantity (about I or 2 grams) of cement is now taken from each one of these Squares with the trowel or spatula point and these small samples are mixed and 5 to Io grams of the mixture pre- pared as described in the next paragraph for the chemical analy- sis. The main portion of the cement is then replaced in the bag or bucket and used for the physical tests. In order that the solvents used to decompose the cement for analysis may do their work, the portion weighed out must con- tain no coarse pieces of clinker. To guard against this, pass the Smaller Sample through a No. IOO-mesh test sieve, grinding any residue caught upon the sieve in an agate mortar until it, too, passes. From the size and shape of the ordinary agate mortar and pestle the operation of grinding is very fatiguing. It may be much facilitated, however, by cutting a hole, of such size and shape as to hold the mortar firmly, in the middle of a block of hard wood, a foot or so square. The pestle is then fixed in a piece of round brass tubing of sufficient bore, or else in a round hard wood handle. Several mechanical grinders are on the mar- ket, descriptions of which may be found in the trade catalogues of most of the prominent dealers in chemical apparatus. 434 PORTLAND CEMENT After being ground the sample for chemical analysis should be placed in a small (one or two ounce) wide mouth bottle and tightly corked. If for immediate use a sample or coin envelope may be substituted for the bottle. The bottles are cheap enough, however, and, as cement rapidly absorbs water and carbon diox- ide from the air, it is a good rule to use them altogether. Standard Specifications for Chemical Properties of Cement. The following limits shall not be exceeded: Loss on ignition, per cent 4.OO Insoluble residue, per cent o.85 Sulphuric anhydride (SO3), per cent 2.OO Magnesia (MgO), per cent 5.00 Standard Methods for Chemical Analysis The standard specifications and tests for Portland cement give the following directions for determining loss on ignition, in- soluble residue, sulphuric anhydride and magnesia. There are no standard methods for determining the other constituents in Cement. Loss on Ignition One gram of cement shall be heated in a weighed covered platinum crucible, of 20 to 25-cc. capacity, as follows, using either method (a) or (b) as ordered: (a) The crucible shall be placed in a hole in an asbestos board, clamped horizontally so that about three-fifths of the crucible projects below, and blasted at a full red heat for fifteen minutes with an inclined flame; the loss in weight shall be checked by a second blasting for five minutes. Care shall be taken to wipe off particles of asbestos that may adhere to the crucible when withdrawn from the hole in the board. Greater neatness and shortening of the time of heating are secured by making a hole to fit the crucible in a circular disk of sheet platinum and placing this disk over a somewhat larger hole in an asbestos board. - (b) The crucible shall be placed in a muffle at any tempera- ture between 900 and I,000° C. for fifteen minutes and the loss in weight shall be checked by a second heating for five minutes. 1 Tentative American Standards, A. S. T. M., CG-21. ANALYTICAL METHODS 435 A permissible variation of O.25 will be allowed, and all results in excess of the specified limit but within this permissible varia- tion shall be reported as 4 per cent. Insoluble Residue To a I-gram sample of cement shall be added Io ce. of water and 5 cc. of concentrated hydrochloric acid; the liquid shall be warmed until effervescence ceases. The solution shall be diluted to 50 cc. and digested on a steam-bath or hot-plate until it is evident that decomposition of the cement is complete. The residue shall be filtered, washed with cold water and the filter paper and contents digested in about 30 cc. of a 5 per cent solution of Sodium carbonate, the liquid being held at a temperature just short of boiling for fifteen minutes. The remaining residue shall be filtered, washed with cold water, then with a few drops of hot hydrochloric acid, I-9, and finally with hot water, and then ignited at a red heat and weighed as the insoluble residue. A permissible variation of O.I5 will be allowed, and all results in excess of the specified limit but within this permissible varia- tion shall be reported as O.85 per cent. Sulphuric Anhydride One gram of the cement shall be dissolved in 5 cc. of concen- trated hydrochloric acid diluted with 5 cc. of water, with gentle warming; when solution is complete 40 cc. of water shall be added, the solution filtered and the residue washed thoroughly with water. The solution shall be diluted to 250 cc., heated to boiling and Io ce. of a hot Io per cent solution of barium chloride shall be added slowly, drop by drop, from a pipette and the boil- ing continued until the precipitate is well formed. The solution shall be digested on the steam-bath until the precipitate has settled. The precipitate shall be filtered, washed and the paper and contents placed in a weighed platinum crucible and the paper slowly charred and consumed without flaming. The barium sul- phate shall then be ignited and weighed. The weight obtained multiplied by 34.3 gives the percentage of sulphuric anhydride. The acid filtrate obtained in the determination of the insoluble 436 PORTLAND CEMENT residue may be used for the estimation of sulphuric anhydride in- stead of using a separate sample. A permissible variation of O.I.O will be allowed, and all results in excess of the specified limit but within this permissible vari- ation shall be reported as 2 per cent. Magnesia To o.5 gram of the cement in an evaporating dish shall be added Io ce. of water to prevent lumping and then Io ce. Of concen- trated hydrochloric acid. The liquid shall be gently heated and agitated until attack is complete. The solution shall then be evaporated to complete dryness on a steam or water-bath. To hasten dehydration the residue may be heated to I50 or even 2OO° C. for one-half to one hour. The residue shall be treated with Io ce. of concentrated hydrochloric acid diluted with an equal amount of water. The dish shall be covered and the solu- tion digested for ten minutes on a steam-bath or water-bath. The diluted solution shall be filtered and the separated silica washed thoroughly with water. Five cubic centimeters of con- centrated hydrochloric acid and sufficient bromine water to pre- cipitate any manganese which may be present, shall be added to the filtrate (about 250 cc.). This shall be made alkaline with ammonium hydroxide, boiled until there is but a faint odor of ammonia, and the precipitated iron and aluminum hydroxides, after settling shall be washed with hot water, once by decanta- tion and slightly on the filter. Setting aside the filtrate, the precipitate shall be transferred by a jet of hot water to the pre- cipitating vessel and dissolved in IO ce. of hot hydrochloric acid. The paper shall be extracted with acid, the solution and wash- ings being added to the main solution. The aluminum and iron shall then be reprecipitated at boiling heat by ammonium hydrox- ide and bromine water in a volume of about IOO ce. and the second precipitate shall be collected and washed on the filter used in the first instance if this is still intact. To the combined fil- trates from the hydroxides of iron and aluminum, reduced in volume if need be, I ce. of ammonium hydroxide shall be added, the solution brought to boiling, 25 cc. of a Saturated solution of ANALYTICAL METHODS 437 boiling ammonium oxalate added, and the boiling continued un- til the precipitated calcium oxalate has assumed a well-defined granular form. The precipitate after one hour shall be filtered and washed, then with the filter shall be placed wet in a platinum crucible, and the paper burned off over a small flame of a Bunsen burner; after ignition it shall be redissolved in hydrochloric acid and the solution diluted to IOO ce. Ammonia shall be added in slight excess and the liquid boiled. The lime shall then be re- precipitated by ammonium oxalate, allowed to stand until settled, filtered and washed. The combined filtrates from the calcium precipitates shall be acidified with hydrochloric acid, concen- trated on the steam bath to about 150 cc. and made slightly , alkaline with ammonium hydroxide, boiled and filtered (to re- move a little aluminum and iron and perhaps calcium). When cool, IO co. of Saturated solution of sodium-ammonium-hydrogen phosphate shall be added with constant stirring. When the crys- talline ammonium-magnesium orthophosphate has formed, am- monia shall be added in moderate excess. The solution shall be set aside for several hours in a cool place, filtered and washed with water containing 2.5 per cent of NH4. The precipitate shall be dissolved in a small quantity of hot hydrochloric acid, the solution diluted to about IOO co., I ce. of a saturated Solu- tion of sodium-ammonium-hydrogen phosphate added, and am- monia drop by drop, with constant stirring, until the precipi- tate is again formed as described and the ammonia is in moderate excess. The precipitate shall then be allowed to stand about two hours, filtered and washed as before. The paper and con- tents shall be placed in a weighed platinum crucible, the paper slowly charred, and the resulting carbon carefully burned off. The precipitate shall then be ignited to constant weight over a Meker burner, or a blast not strong enough to soften or melt the pyrophosphate. The weight of magnesium pyrophosphate obtained multiplied by 72.5 gives the percentage of magnesia. The precipitate so obtained always contains some calcium and usually small quantities of iron, aluminum, and manganese as phosphates. 29 438 PORTLAND CEMENT A permissible variation of O.4 will be allowed, and all results in excess of the specified limit but within this permissible vari- ation shall be reported as 5 per cent. DETERMINATION OF SILICA, FERRIC OXIDE AND ALUMINA, LIME AND MAGNESIA Method Proposed by the Committee on Uniformity in the Analy- sis of Materials of the Portland Cement Industry of the New York Section of the Society of Chemical Industry" Solution One-half gram of the finely powdered substance is to be weighed out and, if a limestone or unburned mixture, strongly ignited in a covered platinum crucible over a strong blast for fifteen minutes, or longer if the blast is not powerful, enough to effect complete conversion to a cement in this time. It is then transferred to an evaporating dish, preferably of platinum for the sake of celerity in evaporation, moistened with enough water to prevent lumping, and 5 to IO ce. Of strong HCl added and digested with the aid of gentle heat and agitation until solution is com- plete. Solution may be aided by light pressure with the flattened end of a glass rod.” The solution is then evaporated to dryness, as far as this may be possible on the bath. Silica The residue without further heating is treated at first with 5 to IO ce. of strong HCl which is then diluted to half strength or less, or upon the residue may be poured at once a larger volume of acid of half strength. The dish is then covered and digestion allowed to go on for ten minutes on the bath, after which the solu- 1 This committee consisted of Messrs. Clifford Richardson, Spencer B. Newberry and H. A. Schaffer. Their various reports were published in Journal of the Society of Chemical Industry, XXI, 12, 830 and 1216, Journal American Chemical Society, XXV, 1180, and XXVI, 995; and Cement and Engineering News, XVI, 37. * If anything remains undecomposed it should be separated, fused with a little Na,CO, dissolved and added to the original solution. Of course, a small amount of separated non-gelatinous silica is not to be mistaken for undecomposed matter. ANALYTICAL METHODS 439 tion is filtered and the separated silica washed thoroughly with water. The filtrate is again evaporated to dryness, the residue without further heating, taken up with acid and water and the small amount of silica it contains separated on another filter- paper. The papers containing the residue are transferred wet to a weighed platinum crucible, dried, ignited, first over a Bunsen burner until the carbon of the filter is completely consumed, and finally over the blast for fifteen minutes and checked by a further blasting for ten minutes or to constant weight. The silica, if great accuracy is desired, is treated in the crucible with about Io co. of HF1 and four drops of H2SO, and evaporated over a low flame to complete dryness. The small residue is finally blasted, for a minute or two, cooled and weighed. The difference be- tween this weight and the weight previously obtained gives the amount of silica." Iron Oxide and Alumina The filtrate, about 250 cc., from the second evaporation for SiO2, is made alkaline with NH, OH after adding HCl, if need be, to insure a total of IO to I5 cc. strong acid, and boiled to ex- pel excess of NHa, or until there is but a faint odor of it, and the precipitated iron and aluminum hydrates, after settling, are washed once by decantation and slightly on the filter. Setting aside the filtrate, the precipitate is dissolved in hot dilute HCl, the solution passing into the beaker in which the precipitation was made. The aluminum and iron are then reprecipitated by NH, OH, boiled and the second precipitate collected and washed on the same filter used in the first instance. The filter-paper, with the precipitate, is then placed in a weighed platinum cruci- ble, the paper burned off and the precipitate ignited and finally blasted five minutes, with care to prevent reduction, cooled and weighted as Al,O, + Fe,0s.” * For ordinary control work in the plant laboratory this correction may, perhaps, be neglected; the double evaporation never. * This precipitate contains TiO2, P.O.s, Mn,0,. 44O PORTLAND CEMENT Lime To the combined filtrate from the A1,O, + Fe,C), precipitate a few drops of NH, OH are added, and the solution brought to boiling. To the boiling solution 20 cc. of a saturated solution of ammonium oxalate are added, and the boiling continued until the precipitated CaC2O, assumes a well-defined granular form. It is then allowed to stand for twenty minutes, or until the precipi- tate has settled, and then filtered and washed. The precipitate and filter are placed wet in a platinum crucible, and the paper burned off over a small flame of a Bunsen burner. It is then ignited, redissolved in HCl, and the solution made up to IOO ce. with water. Ammonia is added in slight excess, and the liquid is boiled. If a small amount of Al2O, separates this is filtered out, weighed, and the amount added to that found in the first deter- mination, when greater accuracy is desired. The lime is then re- precipitated by ammonium oxalate, allowed to stand until settled, filtered, and washed," weighed as oxide by ignition and blasting in a covered crucible to constant weight, or determined with dilute Standard permanganate.” Magnesia The combined filtrates from the calcium precipitates are acid- ified with HCl and concentrated on the steam-bath to about 150 cc., IO co. of saturated solution of Na (NH,) HPO, are added, and the solution boiled for several minutes. It is then removed from the flame and cooled by placing the beaker in ice-water. After cooling, NH, OH is added drop by drop with constant stir- ring until the crystalline ammonium-magnesium ortho-phosphate begins to form, and then in moderate excess, the stirring being continued for several minutes. It is then set aside for several hours in a cool atmosphere and filtered. The precipitate is re- dissolved in hot dilute HCl, the solution made up to about IOO cc., I co. of a saturated solution of Na (NH4)HPO, added, and ammonia drop by drop, with constant stirring until the precipitate * The volume of wash water should not be too large; vide Hillebrand. * The accuracy of this method admits of criticism, but its convenience and rapidity demand its insertion. AN ALYTICAL METHODS 44 I is again formed as described and the ammonia is in moderate ex- cess. It is then allowed to stand for about two hours when it is filtered on a paper or a Gooch crucible, ignited, cooled and weighed as Mg., P.O. Method Proposed by the Committee on the Uniform Analysis of Cement and Cement Materials of the Lehigh Walley Section of the American Chemical Society" Silica Weigh out O.5 gram into a wide platinum dish of about 50-cc. capacity; add a very little water and break up lumps with a glass rod; add 5 cc. hydrochloric acid (I : I) and evaporate to dryness at a moderate heat, continuing to heat the mass—not above 200° C.—until all odor of acid is gone. Do not hurry this baking or skimp the time. The whole success of the analysis depends on thoroughness at this point. Cool; add 20 cc. hydrochloric acid (I : I); cover and boil gently for ten mintes; add 30 cc. water, raise to boiling, and filter off the silica; wash with hot water four or five times; put in crucible, ignite (using blast for ten minutes), and weigh as SiO2. Iron and Alumina Make filtrate alkaline with ammonia, taking care to add only slight excess; add a few drops of bromine water and boil till odor of ammonia is faint. Filter off the hydroxides of iron and aluminum, washing once on the filter. Dissolve the precipitate with hot dilute nitric acid, reprecipitate with ammonia; boil five minutes; filter and wash the iron and alumina with hot water once; place in crucible, ignite carefully, using blast for five min- utes, and weigh combined iron and aluminum oxides. *This committee was appointed at a meeting of the Lehigh Valley Section of the American Chemical Society, held November 18, 1903, and consisted of Messrs. Wm. B. Newberry, Richard K. Meade and Ernest B. McCready. Their report was pub- lished in Cement and Engineering News, August, 1904, and embodies the methods most acceptable to the chemists actively employed in the cement industry as ascer- tained by correspondence with these chemists themselves. 442 PORTLAND CEMENT Lime Make the filtrate from the hydroxides alkaline with ammonia; boil; add 20 cc. boiling saturated solution ammonium oxalate; continue boiling for five minutes; let settle and filter. Wash the calcium oxalate thoroughly with hot water using not more than I25 cc., and transfer it to the beaker in which it was precipitated, spreading the paper against the side and washing down the pre- cipitate first with hot water and then with dilute sulphuric acid (I : 4); remove paper; add 50 cc. water, IO ce. concentrated Sul- phuric acid, heat to incipient boiling and titrate with perman- ganate," calculating the CaO. Magnesia If the filtrate from the calcium oxalate exceeds 250 cc., acidify, evaporate to that volume; cool, and when cold add I5 cc. strong ammonia and with stirring I5 cc. Stock solution of sodium hy- drophosphate. Allow to stand in the cold six hours or prefer- ably over night; filter; wash the magnesium phosphate with di- lute ammonia (I : 4 + IOO gms. ammonium nitrate per liter) put in crucible, ignite at low heat and weigh the magnesium pyro- phosphate. NOTES Of the above schemes, the first is undoubtedly the more accurate of the two. It does not seem practicable, however, to use it in the every- day routine work of the mill laboratory. It also requires a high de- gree of manipulative skill to carry out the additional steps in its per- formance. When very accurate determinations are required, it will un- doubtedly give better results than the second scheme, provided the analysis is skillfully executed. On the other hand, under the conditions usually met with in the laboratories of cement manufacturers and large users, where rapidity, coupled with a moderate degree of accuracy is required, and where one man is required to run a number of analyses per day, the second scheme will unquestionably give more satisfaction, if properly carried out. A combination of the two schemes which will usually be found as far as the general run of analysts would care to go towards using the first scheme, consists in determining silica as directed by the first scheme, without, however, purifying the silica with * See “Volumetric Determination of Lime,” page 451. ANALYTICAL METHODS 443 hydrochloric and hydrofluoric acids, and then the other elements by the second scheme. This adds to the accuracy of the latter and is not so tedious as the first. A good well-made Portland cement is practically entirely soluble in hydrochloric acid. Fusion, therefore, with sodium or potassium carbo- nate is rarely necessary. It is also objectionable, for when calcium and magnesium are precipitated, as oxalate and phosphate respectively, from Solutions containing much sodium or potassium salts, the precipitates are almost Sure to be contaminated with alkaline salts. Even much washing fails to remove the impurity from the precipitate. When, therefore, the sample of cement has been fused directly with from 3 to 5 grams of sodium carbonate, there is sure to be this danger that the lime and magnesia precipitates will carry down some sodium salts, from which subsequent washing will fail to free them. In accurate work this error can be eliminated by reprecipitation. If instead of fusing the sam- ple directly with five to ten times its weight of sodium carbonate, the impure silica, separated by treatment with hydrochloric acid, is fused with an equal bulk of sodium carbonate, the quantity of sodium salts introduced into the solution will be reduced to one-fourth, usually be- tween I.O and I.5 grams of sodium chloride. Should the cement prove to leave a considerable residue of silicious matter on dissolving in acid, the best plan will be to weigh out a new sample and pursue the following method suggested by Dr. Porter W. Shimer, Easton, Pa.; Weigh V4 gram of the finely ground dried cement into a platinum crucible and mix intimately, by stirring with a glass rod, with O.5 gram of pure dry sodium carbonate. Brush off the rod into the cruci- ble with a camel's hair brush. Cover the crucible and place over a low flame. Gradually raise the flame until the crucible is red hot and con- tinue the heating for five minutes longer; then place over a blast lamp and heat five minutes more. While still hot, plunge the bottom of the crucible half the way up into cold water. This will loosen the mass. Drop the mass into a casserole or dish and cover the latter with a watch-glass. Pour into the crucible a portion of a mixture of 30 cc. of hot water and Io co. of dilute hydrochloric acid. Heat on a hot plate, and then pour into the dish or casserole. Clean out the crucible with a rubber-tipped rod, using the rest of the acid and water. The quantity of sodium salts introduced into the solution from 0.5 gram of carbonate is so small that possible contamination of the lime and mag- nesia precipitates is done away with. On heating cement and sodium carbonate together in this proportion no fusion takes place, only a sin- tering. 444 PORTLAND CEMENT The above method of procedure will be found useful also in analysis of Rosendale or Natural cement, hydraulic limes, slag cement, puzzolana and the so-called “Iron-cements.” The amount of residue left on solution with acid is considered to be a test of the thoroughness with which the cement has been made. Peck- ham uses a IO per cent solution of hydrochloric acid and 5 grams of cement just as received, making the solution slowly and with care. Blount dissolves the cement in strong hydrochloric acid, evaporates the solution to dryness, but not intentionally baking the evaporated material, re- dissolves in hydrochloric acid, filters, washes, dissolves the precipitated silica with sodium carbonate solution and collects, ignites and weighs the final insoluble residue. In carrying out this test, the standard method should be followed carefully as variations in the method of manipulation will give different results. The quantity of silica which will be left on treating cement with acid will depend not only upon the chemical composition of the cement, but also upon the fineness to which the sample is ground, strength of acid, etc., coarsely ground material giving much more residue than finely ground. Cement passing a 50-mesh sieve, but retained by a 100, will give much more silica than that passing a 100-mesh, but retained on a 200-mesh, yet neither has binding properties in the ordinary sense of the word, so that the contention made that the silica which does not dissolve even though it may come from good properly burned material, still comes from inert particles, and is therefore not in a form of active combination, is not logical because by grinding these inert particles a little finer we can con- siderably reduce the silica left without increasing any of their hydraulic value. Many silicates are also soluble in acid, which have no hydraulic properties, such as slags, so that all the silica which goes into solution is not necessarily combined in such a way as to form hydraulic com- pounds. The test does not seem to the writer to be of much practical value. Of course, when the residue of uncombined silica is large, it shows something is wrong with the cement, but this fact is usually revealed much more satisfactorily by the tests for soundness which property is dependent on the proper combination of the silica with the lime. A marl containing a per cent or so of silica in the form of quartz grains would probably give a cement containing from 94 to I per cent of in- soluble or uncombined silica, yet if this quartz had been taken into con- sideration in proportioning the raw materials, this cement might easily be better than one which gives no free or uncombined silica, because the latter might be unsound. Also, as we have said before, all the silica, which is reported as combined is not necessarily so combined as to form Portland cement. ANALYTICAL METHODS 445 At the mill itself, there is little knowledge to be gained by the test, as the soundness test, coupled with the usual determinations, will tell whether the fault is due to careless manufacture or improper proportioning of the raw materials. Alex. Cameron,” in 1894, pointed out the fact that no matter how many evaporations were made in determining silica, accurate results could not be obtained unless a filtration intervened between each one. This paper seems to have escaped the notice of most chemists and was only brought to their knowledge by Dr. W. F. Hillebrand," in 1901, in a paper read at a meeting of The American Chemical Society, in Phila- delphia, in December of that year, in which he gave the results of his own experiments along that line. It was in accordance with his sug- gestion that the committee of the New York Section of the Society of Chemical Industry advised the double evaporation with intervening filtra- tion, which they inserted in their scheme. There is no question but that Dr. Hillebrand is right and that this procedure is necessary in very accurate work. In the analysis of Portland cement, a residue of silica, amounting to from two to four milligrams, can usually be ob- tained by evaporation of the filtrate from the first silica precipitate to dryness, still the extra step is tedious, and adds considerably to the time necessary for making an analysis. It is also true, however, that there is considerable iron and alumina carried down with the silica, and that these two errors will balance each other to a great extent, so that the amount of silica reported is seldom more than one or two-tenths of a per cent low. Below are some figures upon this. d) . I tº { ~ (ſ) 35 a. 3 g tº . E < 5's tº * v E 8 .3 t it res. E ~5 S 3 o “o. #3 * 3 # =#. º 5 * ** O º: : O * ºt sº * Cement No. <3 – 3 pa- O'5, # aš; ſt 5 - 3 ‘7.3 . § * = Q. #2 .E <- “- c. •- . E. is: ºn + : sº º † J o P, -: - C !-- © $– sº tº dº e ºf gº; C O C O O - cºf 5.o 6 * * v=1 !- ° 5- E.: 3 g : 3 = ex; + {-, * & cº; 3. rº ºu Sº : -; sº ſº SU - i. E.8 !-4 - v=º wº S _- _ _ _ <- ſ H | V Fig. 150.-Marl sampler. cup. In removing this sampler from the tank care must be used not to lower it at all. If this is done, the valves of course, open and the sample previously taken is lost, and in its place will be a new sample from the point of lowering. Fig. I 50 shows a marl sampler of the above order described in The Cement Record. It is made of tin and the top is held in place by a bayonet catch. Flap valves are fastened to the top and bottom by hinges, the former opens outward and the latter inward. It is used as described above. Mr. Homer C. Lask, of the Omega Portland Cement Co., also makes use of a bucket with a valve in Sampling marl. His appa- ratus consists of a heavy iron bucket, 3 inches in diameter and THE AN AI.YSIS OF CEMENT MIXTURES, SLURRY, ETC. 50I 9 or IO inches long. It has a valve in the bottom, which opens as the bucket sinks through the marl, but closes as soon as it is started in the opposite direction. A sample can thus be taken at any depth desired. The sampler is attached to a rope and sinks into the marl by its own weight. It is withdrawn by means of a small windlass. From three to five samples are taken from a tank, the different samples mixed together, and the whole taken as the tank sample. The slurry is sampled, automatically, as it leaves the tube mill by an ingenious device. The tube mills at this plant have a cen- tral discharge and on the inner surface of the discharge conduit is attached a stout cup, of about I cubic inch capacity, with its open end towards the stream of slurry as the mill makes its revo- lution. The cup fills as it passes through the stream of slurry and discharges as it is carried over the top. A portion of the dis- charge is allowed to fall into a small trough, down which it flows into a bucket. This bucket holds about four pints and the sam- pler is so gauged that the former will fill in about an hour. Samples of slurry and marl may also be taken by agitating the vat or tank thoroughly and then taking two or three small sam- ples from the elevator or pump discharge, and mixing and grind- ing the sample obtained. In order to correct the composition of slurry found to be under or overclayed, it is necessary to know not only how much carbonate of lime it contains, but also how much water. To de- termine the latter the usual rule is to evaporate a weighed por- tion of the slurry to dryness and determine the loss in weight. This evaporation can be carried on most rapidly and also safest on an electric hot-plate or oven, the temperature of which can be regulated. A “radiator” may also be used consisting of a round sheet iron box, with an open top and bottom flanged on. It is made of any convenient dimensions and usually with its diameter at the top a little larger than at the bottom. Convenient dimensions are 6 inches deep, 5% inches diameter at the top and 4% inches diameter at the bottom. The radiator will then set in the ring of a 5-inch tripod. The substance to be evaporated is held on a triangle support, midway between the top and bot- 33 502 PORTLAND CEMENT tom of the box and made of heavy copper or iron wire. Fig. I5I shows the apparatus, which is to be heated by a burner. Practically the same results can be arrived at by using a round sheet iron cylinder, 6 inches high and 5 inches in diameter with a DISH TRIANCLE —CYLINI) ER Fig. I 51.-Radiator for drying slurry samples. support 3 inches from the bottom, and setting over the hottest part of the hot-plate. An ordinary porcelain dish may be made use of to hold the sample but a flat dish of tin or aluminum or even a flat sheet of thin sheet iron or aluminum with a corner turned up to serve as a handle will serve the purpose better. Not only because greater surface is exposed but also because metal is a better conductor of heat than porcelain. As a quick test to determine when all the water is driven off, hold a cold watch- glass over the dish and observe if any moisture collects on it. If I6.88 cc. of slurry are taken for evaporation each O.OI gram of dried residue will represent the number of pounds of dried slurry in a cubic yard of the wet slurry. This amount may be measured by means of a small pipette made to hold exactly this amount to the mark. In use the pipette must be washed out with a jet of water from a wash-bottle. Or 6.25 cc. may be taken when O. I gram will represent pounds per cubic foot, etc. When organic matter is present this also acts as a disturbing element in determining the correctness of the composition of the slurry. If constant, allowance can usually be made for it, but when variable the best plan is either to burn this off or else run the mix by a ratio of lime to insoluble." Mr. A. Lundteigen recommended weighing the dried sample into a small iron tray, which is suspended in a larger one and * See Chapter IV. THE ANALYSIS OF CEMENT MIXTURES, SLURRY, ETC. 503 this in its turn is covered and put over a good Bunsen burner for twenty minutes. In this way over three-quarters of the organic matter is driven off without decomposing the carbonate. This also puts the sample in such a condition that it will sink in a solution of hydrochloric acid, and be quickly dissolved. With- out this baking process the marl used by one company will float on top of the acid and even shaking and boiling will dissolve it only with difficulty. The baked sample, however, is very hygro- scopic and takes up moisture rapidly from the air, so it must be weighed quickly. RAPID METHODS FOR CHECKING THE PERCENTAGE OF CALCIUM CARBONATE IN CEMENT MIXTURES By Standard Acid and Alkali Phenolphthalein Dissolve I gram of phenolphthalein in IOO ce. Of alcohol (50 per cent). Keep in a small bottle provided with a perforated - - -* F- – S--→ Fig. 152.—Phenolphthalein dropper. stopper through which passes a small pipette, made from a piece of 5-inch narrow bore glass tubing by drawing out one end to a fine opening, and blowing a bulb in the other, Fig. I52. One drop of this solution is sufficient for a determination. 504 PORTLAND CEMENT Standard Alkali In order to prepare standard alkali of exactly */, N strength it is necessary to first prepare a standard solution of some acid, preferably of sulphuric, because of the ease with which this can be standardized by precipitation with barium chloride. To pre- pare this standard acid, measure out with a burette II.2 cc. of concentrated sulphuric acid (1.84 sp. gr.) and dilute to one liter. Shake well and measure into each of two small beakers IO ce. of this sulphuric acid and dilute to IOO ce. Add a few drops of hydrochloric acid, heat to boiling, and precipitate the sulphuric acid with barium chloride. Let the precipitate stand over night, then filter through a double filter (or preferably the Shimer fil- ter"), wash with hot water, ignite and weigh. Calculate the quan- tity of this acid equivalent to IO ce. of */s N sulphuric acid in the following manner. Ten cc. of */s N sulphuric acid should give o,467 gram of BaSO4. If the average weight of both pre- cipitates is a gram, then letting a represent the number of cubic centimeters containing O.467 gram of BaSO,. 4.67 a. * O.467 : a a : Io or a = .6 iº g g Hence tº: cc. of our standard acid will be equivalent to IO co. of */, N acid. This should be marked on the bottle and the solu- tion put away in a dark cool place for use at any future time. To prepare the standard alkali, dissolve 175 grams of caustic soda in eight liters of distilled water in a two-gallon bottle (which usually holds nine liters) and mix well by shaking. Now measure into each of two beakers the quantity of our standard sulphuric acid equivalent to IO ce. Of normal acid, and after adding a drop of phenolphthalein solution, run in the sodium hydroxide solution from a burette until the solution turns purple red. The two titra- tions should check exactly. If not, repeat until they do. Now dilute the caustic soda solution so that it is exactly */, normal. * See page 472. THE ANALYSIS OF CEMENT MIXTURES, SLURRY, ETC. 505 The number of cubic centimeters of water necessary to add to the caustic soda solution may be found by the formula IO ( à T ) × c when b = cc. soda required to neutralize the equivalent of Io co. of */s N acid and C = quantity of caustic Soda solution still left in the bottle. Example of the preparation of the standard */s N alkali. Weight of Ist BaSO, precipitate . . . . . . . . . . . . . . . . . . . O.4975 Weight of 2d BaSO, precipitate . . . . . . . . . . . . . . . . . . . . o.4987 Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O.4981 Therefore #= 9.38 cc. of the acid, are equivalent to Io ce. of */s N acid. Now 9.38 cc. of the above acid require 8.7 cc. of caustic soda, as de- termined by duplicate titrations. As we have used 20 cc. of our caustic soda we will have in the bottle 8,000 — 20 = 7,980 cc. and hence we must add to this (;- 1) 7,980 or 1,189 cc. Since our bottle will only hold nine liters it will probably be better to draw off exactly one liter when the amount to be added to the remainder will be ;- ..) 6,980 or 1,040 cc. We therefore measure out this quantity of water and add it to the con- tents of the bottle. The standard caustic soda solution should now be checked against the acid and, if not of correct strength, water must be added, as indi- cated, until it is exactly */s N strength. One ce. of this solution is equivalent to exactly o.o.20 gram of CaCO3, or 2 per cent where a I-gram sample is used. A two-gallon bottle of standard alkali will make at least 2,000 determinations so it pays to make it of correct strength and save calculations. Standard Acid Take the specific gravity of a bottle of hydrochloric acid, using a hydrometer for the purpose. Refer to the table of specific gravities of hydrochloric acid given below and calculate from this the quantity of acid necessary to contain 97 grams of HC1. Measure this quantity of the acid into a liter flask and dilute to the mark, pour into an eight-liter bottle and add seven liters of water, measuring with the flask. Mix the contents of the bottle 506 PORTLAND CEMENT well by shaking. Ten cc. of this solution should be equivalent to from 8. I to 8.5 cc. of the */s N alkali when checked by adding a drop of phenolphthalein solution and running in the alkali to a purple red color. If its value does not lie between these figures add acid or water to make it of this strength. TABLE XLIII.-SPECIFIC GRAVITIES OF HYDROCHLORIC ACID Sp. gr. at Degrees Degrees Per cent Grams of HCl Correction of 15° C. Baume Twadd’1 of HC1 in I liter the sp. gr. *— for + 19 C. I.OO5 O.7 I I. I2 II.32 o.OOO6 J.OIO I.4 2 2. I2 2I.43 o.OOO6 I.O.I.5 2. I 3 3. I2 31.67 o.OOO6 I.O2O 2.7 4 4. II 4I.99 o.OOO6 I.O25 3.4 5 5. II 52.4I O.OOO6 I.O.30 4. I 6 6. II 62.93 o.OOO6 I.O.35 4.7 7 7.IO 73.55 o.OOO6 I.O4O 5.4 8 8.IO 84.27 O.OOO6 I.045 6.o 9 9. IO 95.09 o.OOO6 I.O5O 6.7 IO IO.09 IO6.ol o.OOO6 I.O55 7.4 II II.OO II.7.O2 o.OOO6 I.060 8.0 I2 I2.09 I28.14 O.OOO6 I.O65 8.7 I3 I3.08 I39.36 o.OOO6 I.O7O 9.4 I4 I4.08 I50.68 o.OOO6 I.O75 IO.O I5 I5.08 I62. Io o.OOO6 I.08O IO.6 I6 I6.07 I73.63 o.OOO6 I.085 II.2 I7 I7.07 I85.24 0.0006 I.O90 II.9 I8 18.07 I96.96 O.OOO6 I.O.95 I2.4 IQ I9.O7 208.78 O.OOO6 I. IOO I3.O 2O . 20.06 220.7O O.OOO6 I.IO5 I3.6 2I 2I.06 232.68 O.OOO6 I. I IO I4.2 22 22.06 244.80 O.OOO6 I. II5 I4.9 23 23.05 257.02 o.OOO6 I. I2O I5.4 24 24.05 269.34 o.OOO6 I. I25 I6.0 25 25.05 281.76 O.OOO6 I.I.3O I6.5 26 26.04 294.28 o.OOO6 I.I.35 I7. I 2 27.04 306.90 o.OOO6 I. I.40 17.7 28 28.04 3I9.62 o.OOO6 I. I.45 I8.3 29 29.03 332.44 O.OOO6 I. I50 I8. 30 30.03 345.36 o.OOO6 I. I55 I9.3 3I 3I.03 358.34 o.OOO6 I. I60 19.8 32 • 32.02 37I.44 o.OOO6 I. I65 20.3 33 33.02 384.64 O.OOO6 I. I70 20.9 34 34.02 397.94 o.OOO6 I. I75 2I.4 35 35.0I 4II.34 O.OOO6 I.180 22.O 36 36.OI 424.84 o.OOO6 I.185 22.5 37 37.OI 438.44 O.COO6 I.I.90 23.0 38 38.01 452. I4 o.OOO6 I.I.95 23.5 39 39.00 466.00 O.OOO6 I.2OO 24.O 40 40.00 479.84 o.OOO6 THE ANALYSIS OF CEMENT MIXTURES, SLURRY, Etc. 507 Example of the preparation of the standard acid. On testing a bottle of hydrochloric acid its specific gravity is found to be I.I.95° C. at 23° C. Correcting this to 15° C. we have 1.95 –– (23 – 15) × 0.00006 = I.1998, or practically I.20 sp. gr. at 15° C. Hy- drochloric acid of I.20 sp. gr. contains 479.84 grams of HC1 per liter or 0.480 gram per cubic centimeter. Therefore sº or 202 cc. will con- O.4öO tain 97 grams of HCl, hence we measure out this quantity of acid and dilute to eight liters. Standard Sample A standard Sample of the raw material is necessary to stand- ardize the acid and alkali for actual use. This sample should be ground in the same manner as the daily run of samples to be checked by the acid and alkali. It should all pass a Too-mesh sieve and be freed from hygroscopic moisture, by drying for some hours, at I IO* C. Three of four pounds of this sample should be prepared and kept in air-tight jars or bottles. A small sample (one or two ounces) of this should be placed in a two-ounce bot- tle and stoppered with a rubber cork when not in use. This small sample can then be redried for an hour at IOO9-IIo° C. and used for standardizing, avoiding the frequent opening and mixing of the contents of the large jars or bottles. After drying, the standard sample should be carefully analyzed. It should contain approximately the quantity of carbonate of lime which it is desired to have in the mix, and the amount of magnesia should also be normal. When the magnesia varies at different times fresh standard samples should be prepared to con- tain these varying percentages of magnesia; otherwise the lime will be reported too high. Standardizing the Acid Weigh I gram of the standard sample into a 600 cc. Erlen- meyer flask and run in from a pipette 50 cc. of standard acid. Close the flask with a rubber stopper, having inserted through it a long glass tube 30 inches long and about 3%-inch internal diameter. Heat the flask on a wire gauze over a burner as shown in Fig. I53 until steam just begins to escape from the upper end of the tube. The heating should be so regulated, that the opera- tion requires very nearly two minutes, from the time the heat is 508 PORTLAND CEMENT. applied, until steam issues from the tube. Remove the flask from the heat, as soon as the steam escapes from the tube, and rinse the tube into the flask, in the following manner. Rest the flask, still stoppered, on the table and grasp the tube between the thumb and forefinger of the left hand. Direct a stream of cold water, from a wash-bottle in the right hand, down the tube, hold J.*Ayaar/- Fig. I 53.−Apparatus for determining calcium carbonate with acid and alkali. ing the latter inclined at an angle 45°, and rolling the flask from side to side on the table, in sweeps of 2 or 3 feet, by twirl- ing the tube between the finger and thumb. Unstopper the flask and rinse off the sides and bottom of the stopper, into the flask, and wash down the sides of the latter. Add a drop or two of phenolphthalein and run in the standard alkali, from a burette, until the color changes to purple red. This color is often ob- scured until the organic matter settles, so it is necessary to hold the flask to the light and observe the change by glancing across the surface. A little practice will easily enable the operator to carry on the titration with accuracy and precision. If the standard sample contains I, per cent carbonate of lime and d co. of alkali are required to produce the purple red color, THE ANALYSIS OF CEMENT MIXTURES, SLURRY, ETC. 509 then to find the carbonate of lime in other samples it is only nec- essary to subtract the number of cubic centimeters of alkali re- quired in their case from d, multiply the difference by 2 and add to L for the percentage of carbonate of lime in them; or if the number of ce. is greater than d, subtract d from this number, mul- tiply by 2 and subtract from L for the carbonate of lime. In order to avoid all calculations prepare a table giving the various percentages of carbonate of lime corresponding to differ- ent quantities of alkali. Example of Such a Table : Suppose the standard sample contains 75.0 per cent carbonate of lime and 4.6 cc. of standard alkali are re- quired to produce a purple red color. Then since each ce. Of alkali is equivalent to O.O2 gram or 2 per cent of carbonate of lime 4.5 cc. alkali would represent 75.2 per cent carbonate of lime and 4.4 cc. alkali would be equivalent to 75.4 per cent carbonate of lime. Similarly 4.7 cc. alkali are equal to 74.8 per cent carbonate of lime. So we see the lime progresses by O.2 per cent for each decrease of O.I ce. alkali and we can quickly write the following table: CC. Per Cent CC. Per cent CC. Per cent alkali CaCO3 alkali CaCO3 alkali CaCO3 3.8 76.6 4.5 75.O 5.2 73.8 3.85 76.5 4.55 75. I 5.25 73.7 3.9 76.4 4.6 75.O 5.3 73.6 3.95 76.3 4.65 74.9 5.35 73.5 4.O 76.2 4.7 74.8 5.4 73.4 4.05 76. I 4.75 74.7 5.45 73.3 4. I 75.O 4.8 74.6 5.5 73.2 4. I5 75.9 4.85 74.5 5.55 73. I 4.2 75.8 4.9 74.4 5.6 73.O 4.25 75.7 4.95 74.3 5.65 72.9 4.3 75.6 5.0 74.2 5.7 72.8 4.35 75.5 5.O 74. I 5.75 72.7 4.4 75.4 5. I 74.O 5.8 72.6 4.45 75.3 5. I5 72.9 5.85 72.5 Determination Weigh I gram of the sample, which has been ground to pass a IOO-mesh sieve, into the flask, add 50 cc. of the standard acid and proceed as directed under standardizing the acid. The percent- age of carbonate of lime may be found from the number of ce. of alkali used either from the preceding table or by the formula Where L and d have the same values as in the paragraph on 5IO PORTLAND CEMENT “Standardizing the Acid” and S represents the number of cubic centimeters required for the sample whose composition is de- sired. If 4.25 cc. of alkali are required then the sample contains 75 -- (4.6 — 4.25) × 2 = 75.7 per cent carbonate of lime. NOTES The process depends upon the decomposition of calcium carbonate by a measured quantity of standard alkali in excess of that required by theory and then determining the excess acid by titration with standard alkali. CaSO, + 2HC1 = CaCl2 + H2O + CO2. HCl -- NaOH = NaCl –– H.O. Hence, I cc. of */s normal acid will decompose ooz gram of CaCOs and I ce. of */s normal acid will neutralize as much acid as O.02 gram of CaCO3. Phenolphthalein is a very delicate indicator. It is, however, very sus- ceptible to carbon dioxide and the solution must be freed from the latter by boiling whenever this indicator is used. It is also useless in the presence of free ammonia or its compounds. The addition of a few drops of the indicator to an acid or neutral solution shows no color, but the faintest excess of caustic alkali gives a sudden change to purple red. Methyl orange may be used in place of phenolphthalein. While not so delicate it possesses certain advantages over the latter. It can be used in the cold with carbonates, and its delicacy is not impaired by the presence of ammonia or its salts. A convenient strength for the methyl orange indicator is o. I gram of the salt to IOO co. of water. One drop of this solution is sufficient for Ioo co. of any colorless solution. Alkaline liquids are faintly yellow with methyl orange and acid ones are pink. Of the two indicators, however, phenolphthalein is much to be pre- ferred for this work, as the carbon dioxide has all been boiled off the acid and provided the alkali is properly kept, the amount in this is constant and hence exercises the same influence all the time. Standard */; N caustic soda may be prepared, however, free from carbon dioxide, by the following method: Take about twice the quan- tity of caustic soda required for the standard solution, dissolve in water and add 25 grams of freshly slaked lime made into a milky paste with water. Boil for ten or fifteen minutes and, when cool enough to avoid cracking the latter, pour into a five-pint bottle. Add water enough to nearly fill the bottle, stopper, shake and let stand over night to settle. In the morning, siphon off the clear liquid and make up to five or six liters. Run against the standard sulphuric acid solution and dilute with freshly boiled distilled water as directed above for the preparation of */, N alkali. THE ANALYSIS OF CEMENT MIXTURES, SLURRY, ETC. 5 II As a preliminary standard for the preparation of the */s N alkali, hydrochloric acid may be used instead of sulphuric acid. It is more troublesome to standardize, however. Prepare the */s normal hydro- chloric acid as directed in the scheme and standardize gravimetrically as follows: To any convenient quality of the acid to be standardized, add solu- tion of silver nitrate in slight excess, and 2 cc. pure nitric acid (sp. gr. I.2). Heat to boiling-point, and keep at this temperature for some minutes without allowing violent ebullition, and with constant stirring, until the precipitate assumes the granular form. Allow to cool some- what and then filter through asbestos. Wash the precipitate by de- cantation, with 200 cc. of very hot water, to which has been added 8 cc. of nitric acid and 2 cc. of dilute solution of silver nitrate contain- ing I gram of the salt in Ioo co. of water. The washing by decantation is performed by adding the hot mixture in small quantities at a time, beating up the precipitate well with a thin glass rod after each addi- tion. The pump is kept in action all the time; but to keep out dust during the washing, the cover is only removed from the crucible when the fluid is to be added. Put the vessels containing the precipitate aside, return the washings once through the asbestos so as to obtain them quite clear, remove from the receiver, and set aside to recover the silver. Rinse the receiver and complete the washing of the precipitate with about 200 cc. of cold water. Half of this is used to wash by decantation and the remainder to transfer the precipitate to the crucible with the aid of a trimmed feather. Finish washing in the crucible, the lumps of silver chloride being broken down with a glass rod. Remove the second filtrate from the receiver and pass about 20 cc. of alcohol (98 per cent) through the precipitate. Dry at from 140° to 150°. Exposure for half an hour is found more than sufficient at this temperature, to dry the precipitate thoroughly. The weight of silver chloride multiplied by O.25424 gives the hydrochloric acid in the volume taken. Instead of */s normal caustic soda the corresponding */; normal caustic potash may be used. To prepare, substitute 220 grams of KOH for I75 grams of NaOH, and proceed as directed in the scheme. The standard hydrochloric acid used in the determination itself is not exactly “ſs normal; in fact, is much weaker than this. It is made so in order to avoid waste of the alkali. If made */s normal strength, it would require about 12.5 cc. of alkali to titrate back. A smaller pipette might be used or the acid measured with a burette. The automatic pipettes are usually made in sizes, 25 cc., 50 cc., etc., and are so con- venient for measuring the acid that, as there is nothing to be gained by making the acid “ſs normal strength, it will be found more convenient to make it of the strength indicated in the scheme, and use a 50 cc. automatic pipette. 5I2 PORTLAND CEMENT In some laboratories, the acid and alkali are both made of "/s N strength and a half gram sample is used for the determination. There appears to be nothing gained by this and something may be lost as the stronger acid is a better solvent for the sample. The bottle of strong hydrochloric acid, used to make the standard acid, should be marked with the number of cubic centimeters required to make eight liters of standard acid and put away for use in making up the next lot of acid. In preparing a second lot of acid it will save calculation and the preparation of a new table, if the acid is made up to the same strength as before. To do this make a little weaker than the figures call for and JA/C/ == C - Fig. 154.—Stand for acid and alkali bottles and pipettes. 1– ascertain its strength by a trial determination on the standard sample, then, if too much carbonate of lime is found, add acid cautiously until THE ANALYSIS OF CEMENT MIXTURES, SLURRY, ETC. 5I3 the value of a determination made with the standard sample shows the proper percentage of lime. Standard nitric acid may be used in place of the standard hydrochloric acid. It keeps better and is not quite so volatile, but, on the other hand, is not so good a solvent. On the cement-rock mixtures of the Lehigh District hydrochloric acid works best, but nitric acid is used in the lab- oratories of several wet process mills in the west. The nitric acid is prepared exactly as is the hydrochloric acid, using such a quantity of strong acid, however, as will contain I67 grams of HNO3. Fig. I54 shows a convenient way of arranging the bottles, burette and pipette for the acid and alkali. Its construction is so evident from the drawing that a description seems unnecessary. Both the burette and pipette are of the Eimer and Amend automatic zero pattern. Fig. I55 shows the pipette in detail. R-rº---- -N \ ^N, Nº. s" se_-Mºº- Fig. 155.-Automatic pipette. The object of the long glass tube is that of a condenser to catch any volatilized acid. This may be replaced by a Leibig’s return condenser cooled by water or by a tube full of glass beads, which are wet before the determination with cold distilled water. 5I4 PORTLAND CEMENT A water cooled condenser which is used in the laboratory of the Cowell Portland Cement Co., Cowell, Cal., is shown in Fig. I56. It is made of ordinary iron pipe. The condensers, a, a, a, a, contain each a glass tube, b, b, b, b, held in place by rubber stoppers. Over the ends of these tubes are slipped rubber stoppers which fit the flasks, c, c, c, c. Fig. I 56.-Condenser for acid and alkali method. Water enters at d, and flows in the direction of the arrows, being led from one condenser to the next through the side pipes, f, f, f, and finally out at c. The flow of water is controlled by the valve, d. The glass tube, i, is attached to a reservoir of distilled water and the tubes are washed into the flasks by means of the small jets, h, h, h, h. This THE ANALYSIs OF CEMENT MIXTURES, SLURRY, ETC. 515 apparatus will be found very convenient where many determinations are made. If the flasks show a tendency to slip off a small tin collar cut to fit half way around the neck of the flask as shown in k, and attached to the tube a by a rubber band will serve to keep them on. Mr. F. H. Ronk, Chemist, Union Portland Cement Co., in a communi- cation to the author states that he dispenses with the long glass tube and other forms of condenser entirely and obtains just as good results by merely boiling the sample for a few minutes in an open Erlenmeyer flask on the hot-plate. The author has also tried this method and found it satisfactory. A perpetual table for use with any strength acid and alkali may be made as follows: The number of cubic centimeters and twentieths cubic centimeter of alkali from 3 to 8 are written on a piece of stiff paper and pasted fast to a soft pine board. The percentages and tenths of carbonate of lime from 70 to 78 are next written on a piece of card- board and this is merely fastened to the board with thumb tacks so that the number of cubic centimeters of acid required by the standard sam- ple coincide with the percentage of lime it contains. For instance, in the example given 75 per cent lime are made to coincide with 4.6 cc. of alkali. The board is then to be hung up on the wall behind the alkali burette, etc. By Measuring the Volume of C0, Evolved At one time, checks upon the composition were made to some extent in this country by means of calcimeters. These all de- termine the calcium carbonate indirectly by measuring the vol- ume of carbon dioxide given off. These calcimeters are still used extensively in Europe but in this country have been entirely superseded by the simpler and fully as reliable acid and alkali method. The older form of this apparatus was that of Scheibler but with this apparatus tables were necessary in order to correct the volume of gas for various temperatures and pressures. After Lunge invented the compensating tube various improved calci- meters were devised making use of this and doing away with the calculations and tables required by the Scheibler apparatus. It seems probable, however, that none of these calcimeters will find extensive use in this country and most German chemists who have come to American mills have discarded them for the simpler acid and alkali method. Those who are interested in this method of determining lime are referred to the former edi- tions of this book for a description of Scheibler's apparatus and 516 PORTLAND CEMENT to Butler’s “Portland Cement” and Gatehouse’s “Handbook for Cement Work's Chemists” for descriptions of other improved forms used in English and German mills. Marshall’s calcimeter is described in Sutton's Volumetric Analysis. By Permanganate Weigh O.5 gram of the sample into a platinum crucible and mix intimately, by stirring with a glass rod, with 94 gram of finely powdered dry sodium carbonate. Brush off the rod into the cru- cible with a camel's-hair brush. Cover the crucible and place over a low flame. Gradually raise the temperature until the cru- cible is red-hot. Then after a minute or two remove to the blast- lamp and ignite for five minutes. Cool the crucible by plunging its bottom in cold water and place in a 400 cc. beaker. Cover with a watch-glass and add 40 cc. of (I : 4) hydrochloric acid (or 20 cc. of water and 20 cc. of hydrochloric acid, (I : I). Heat on a hot- plate until solution is complete. Lift out the crucible with a glass rod, bent in a crook at one end, and rinse it off into the beaker. Heat the contents of the beaker to boiling, add ammonia until alkaline, and then IO ce. of a IO per cent Solution of oxalic acid, and proceed as directed on page 456. This method will be found very useful in checking the acid and alkali determinations. DETERMINATION OF SILICATES In order to better control the mixture of raw materials it is often of advantage to determine the insoluble matter or silicates. This practice differs considerably at different works, but the fol- lowing will illustrate the general run of methods. By Solution and Precipitation Weigh O.5 gram of the sample into a porcelain dish or casserole, add IO ce. of dilute (I : I) hydrochloric acid and a few drops of nitric acid, and evaporate to dryness, as rapidly as possible, with- out spattering. Bake at about 120° C. until all odor of acid has disappeared from the contents of the dish. Cool the latter, add Io co. of dilute (I : I) hydrochloric acid and cover with a watch- glass. Heat for a few minutes and add 50 cc. of hot water. Boil THE ANALYSIS OF CEMENT MIXTURES, SLURRY, ETC. 517 a few minutes and add ammonia in faint excess. Boil a little longer, allow to settle and filter. Wash with hot water a few times, ignite and weigh. The residue is called “the silicates” and should, provided the mix is of proper composition, bear a certain ratio to the percentage of carbonate of lime. This ratio varies at different mills, but the figure is usually around I : 3.6. By Solution Weight O.5 gram of the mixture into a beaker and boil with Io per cent hydrochloric acid for five minutes. Filter off the “in- soluble matter,” wash, ignite and weigh. This method is in use in the laboratories of the Sandusky Portland Cement Co., and the mix is so proportioned as to give a certain ratio between this “in- soluble matter” and the lime. This ratio varies at the two mills of the company. At the Sandusky mill the ratio is 3.9 and at the Syracuse mill it is 4.2, the higher ratio being due to the more silicious clay at the latter point. COMPLETE ANALYSIS OF CEMENT MIXTURE OR SLURRY Method of the Committee on Uniformity in Analysis of Materials for the Portland Cement Industry of the New York Sec- tion of the Society of Chemical Industry One-half gram of the finely powdered substance is weighed out and strongly ignited for fifteen minutes, or longer if the blast is not powerful enough to effect complete conversion to cement in this time. It is then transferred to an evaporating dish, preferably of platinum for the sake of celerity in evaporation, and the analysis completed as directed on page 438 by moistening with water and digesting with hydrochloric acid, etc. The above method is tedious and so cumbersome and long as to preclude its use in cement mill laboratories, where samples of the mix are analyzed daily, except for the preparation of standard samples. Even these should be analyzed also by the method in daily use in the laboratory in order to get all the work on the same relative basis and the longer and more accurate results should only be used to check the shorter mill scheme, and to make 34 518 PORTLAND CEMENT sure that the results of the latter are not too wide of the truth. The results which should actually be used as the values for the carbonate of lime, etc., in the samples should be those obtained by the regular mill scheme. If this is not done, acid and alkali will give one set of results and a complete analyses another, etc. The scheme given below is modeled after those generally in use in cement mill laboratories and combines a fair degree of ac- curacy with rapidity and convenience of execution. Method of the Committee on the Analysis of Portland Cement and Cement Materials of the Lehigh Walley Section of the American Chemical Society Weigh O.5 gram of the finely ground Sample into a small plati- num crucible and mix intimately, by stirring with a glass rod, with O.5 gram of pure dry finely powdered sodium carbonate containing 2 per cent potassium nitrate. Brush off the rod into the crucible with a camel's-hair brush. Cover the crucible and place over a low flame. Gradually raise the latter, until the crucible is red-hot, and continue heating, in the full flame of the Bunsen burner, for five minutes longer; then place over a blast- lamp and heat for five minutes more. Cool and place the cru- cible on its side in a porcelain casserole or dish, or preferably a platinum dish, and dissolve the mass in IO ce. Of water and Io co. of hydrochloric acid. Heat until solution is complete, keeping the dish covered to avoid loss by effervescence. When everything, except a little gelatinous silica, which usually sep- arates out, is in solution, remove the crucible and clean off into the dish with a rubber-tipped rod. Evaporate to dryness at a moderate heat, continuing to heat the mass—not above 200° C.— until all odor of acid is gone. Do not hurry this baking or skimp the time. The whole success of the analysis depends on thoroughness at this point. Cool; add 20 cc. hydrochloric acid (I : I ); cover, and boil gently for ten minutes; add 30 cc. water raise to boiling, and filter off the silica; wash with hot water four or five times; put in crucible, ignite (using blast for ten minutes), and weight as SiO2. THE ANALYSIS OF CEMENT MIXTURES, SLURRY, ETC. 519 Iron and Alumina Make filtrate alkaline with ammonia, taking care to add only slight excess and boil until Odor of ammonia is faint. Filter off the hydroxides of iron and aluminum, washing once on the filter. Dissolve the precipitate with hot dilute nitric acid, precipitate with ammonia; boil five minutes; filter and wash the iron and alumina with hot water once; place in crucible, ignite carefully, using blast for five minutes, and weigh combined iron and alu- minum oxides. Iron If it is desired to separate the two oxides add 4 grams acid potassium sulphate to the crucible and fuse at a very low heat until oxides are wholly dissolved—twenty minutes at least; cool; place crucible and cover in small beaker with 50 cc. water; add I5 cc. dilute sulphuric acid (I : 4); cover and digest at nearly boil- ing until melt is dissolved; remove crucible and cover rinsing them carefully. Cool the solution and add Io grams powdered C. P. zinc, No. 20. Let stand one hour, decant the liquid into a larger beaker, washing the zinc twice by decantation, and titrate at once with permanganate. Calculate the Fe,C), and determine the Al,Os by difference. Test Zn, etc., by a blank and deduct. Iron may also be determined by using a separate sample, ignit- ing with half its weight sodium carbonate, dissolving the mass in hydrochloric acid and titrating with stannous chloride as directed on page 463 or the iron may be precipitated with ammonia redissolved in sulphuric acid, and the iron determined by reduction with zinc and titration with permanganate. (See page 457). Lime Make the filtrate from the hydroxides alkaline with ammonia; boil; add 20 cc. boiling saturated solution ammonium oxalate; continue boiling for five minutes; let settle and filter. Wash the calcium oxalate thoroughly with hot water, using not more than I25 cc., and transfer it to the beaker in which it was precipitated, spreading the paper against the side and washing down the pre- cipitate first with hot water and then with dilute sulphuric acid 52O PORT LAND CEMENT (I : 4); remove paper; add 50 cc. water, IO ce. concentrated sul- phuric acid, heat to incipient boiling and titrate with perman- ganate, calculating the CaO. Magnesia If the filtrate from the calcium oxalate exceeds 250 cc.; acidify, evaporate to that volume; cool, and when cold add 15 cc. strong ammonia and with stirring I5 cc. stock solution of sodium hy- drophosphate. Allow to stand in the cold six hours or preferably over night; filter; wash the magnesium phosphate with dilute am- monia (I : 4) plus IOO grams ammonium nitrate per liter; put in crucible, ignite at low heat and weigh the magnesium pyrophos- phate. Other Constituents For the determination of sulphur, carbon dioxide, hygroscopic and combined water, and alkalies, refer to the methods given under cement. The fusion method is to be used for determining sulphur which is usually present as sulphide (iron pyrites) or in combination with organic matter in mixtures of marl and clay. Calcium sulphate may be determined by simple solution in hydro- chloric acid as in cement. CHAPTER XVIII THE ANALYSIS OF THE RAW MATERLALS METHODS FOR LIMESTONE, CEMENT-ROCK AND MARL By Ignition of the Sample with Sodium Carbonate Silica Weigh O.5 gram of finely ground dried sample into a platinum crucible and mix intimately with O.5 gram of pure dry sodium carbonate containing 2 per cent potassium nitrate by stirring with a glass rod. Place the crucible over a low flame and gradually raise this latter until the crucible is red-hot. Continue heating for five minutes, then substitute a blast-lamp for the Bunsen burner and heat for five minutes longer. Place the crucible in a dish or casserole, add 40 cc. of water and Io ce. of hydrochloric acid, and digest until all the mass is dissolved out of the crucible. Clean off the crucible inside and outside, add a few drops of nitric acid to the solution and evaporate it to dryness. Heat the residue in an air bath or electric oven at I Io9 C. for one hour, cool, add 15 cc. of dilute hydrochloric acid, cover with a watch- glass and digest for a few minutes on a hot-plate. Dilute with 50 cc. of hot water, heat nearly to boiling, and filter. Wash the residue well with hot water. Dry, ignite, and weigh as silica, SiO,. If the limestone is high in silica a trace will be found in the fil- trate from the silica as precipitated above. If great accuracy is desired, after evaporation to dryness, dissolve the mass in the dish in hydrochloric acid and water as usual without heating it to IIo° C. for one hour and filter and wash. Evaporate the filtrate to dryness, and again dissolve in water and hydrochloric acid, fil- ter, and wash. Ignite the two precipitates together and weigh as SiO,. Ferric Oride and Alumina Heat the filtrate to boiling, add ammonia in slight but distinct excess, boil for five minutes and filter. Wash the precipitate * The author employs this method for the analysis of composition and slurry. 522 PORTLAND CEMENT twice with hot water. Remove the filtrate from under the funnel and in its place stand the beaker in which the precipitation was made. Dissolve the precipitate in dilute nitric acid and wash the filter-paper free from iron with cold water. Heat the solution to boiling and precipitate the iron and alumina with ammonia as before. Filter, allowing the filtrate to run into that from the first precipitation, wash once with hot water, dry and ignite. Weigh and report as ferric oxide and alumina. If the percentage of ferric oxide and alumina are desired sepa- rately, proceed as directed in A, B, C, or D. A. Ignite I gram of the sample with 94 gram of sodium carbonate as directed under silica. Dissolve the sintered mass in dilute hydrochloric acid. Heat to boiling, reduce with stannous chloride and titrate with standard bichromate as directed on page 463. B. Fuse the precipitate of ferric oxide and alumina, after weighing, with a little sodium carbonate, dissolve in a little water to which a few cubic centimeters of hydrochloric acid have been added, and drop into the solution a few small crystals of citric acid. Add ammonia until the solution smells slightly of the re- agent, and then an excess of ammonium sulphide. Allow the black precipitate to settle, filter, wash a few times, dissolve in hy- drochloric acid, add a little bromine water, boil awhile and add ammonia in slight but distinct excess. Filter, wash well with hot water, ignite and weigh as Fe2O3. Deduct this weight from that of the total ferric oxide and alumina, for the weight of alumina, Al2O3: C. Fuse the precipitate of ferric oxide and alumina, after weighing, with caustic potash in a silver crucible or dish, Treat the fusion with water, boil, filter, and wash. Dry, ignite, and weigh the residue as ferric oxide, Fe,Oa. Deduct this weight from that of the ferric oxide and alumina, for the weight of alumina, Al2O3: D. Dissolve the residue, after fusion with sodium carbonate, in a little dilute hydrochloric acid and determine the ferric oxide volumetrically by the method given on page 463. THE ANALYSIS OF THE RAW MATER LALS 5 2 3 Lime Heat the filtrate from the iron and alumina, which should measure between 30O and 500 cc., to boiling and add 25 cc. of a saturated Solution of ammonium oxalate. Stir and boil for a few minutes and allow the precipitate one hour in which to settle. Filter and wash well with hot water. After washing, treat the precipitate as directed below in A or B. A. Punch a hole in the filter-paper and wash the precipitate into the beaker in which the precipitation was formed. Wash the paper with dilute sulphuric acid from a wash-bottle and then with hot water. Dilute the solution to 300 or 400 cc., heat to 60° or 70° C., and after adding IO ce. of dilute sulphuric acid titrate with permanganate. Calculate the per cent of lime, CaO, or calcium carbonate, CaCO3, in the limestone, as directed under “Volu- metric Determination of Calcium,” page 455. B. Dry the precipitate by heating over a low flame, in weighed platinum crucible, ignite until all carbonaceous matter is de- stroyed and ignite for fifteen minutes over a blast-lamp. Cool and weigh. Again ignite for five minutes over a blast-lamp and weigh. If this weight agrees to within O.OOO2 gram of the former one it may be taken as the weight of the calcium oxide, CaO. If it does not agree, ignite again and repeat, if necessary, until the weight is constant. Magnesia To the filtrate from the calcium oxalate add sufficient hydro- chloric acid to make it slightly acid, and 30 cc. of sodium phos- phate solution. Concentrate to about 200 cc. by evaporation. Set the solution in a vessel of cold water and when cooled to the tem- perature of the latter add ammonia, drop by drop, from a burette, with constant stirring until slightly ammoniacal and the precipi- tate begins to form. Stop adding ammonia and stir for five min- utes, add one-tenth the volume of the liquid of strong ammonia and continue the stirring for three minutes more. Allow the solu- tion to stand in a cool place over night, filter, wash well with a mixture of I,000 cc. water, 500 cc. ammonia (sp. gr. O.96), and I 50 grams ammonium nitrate. Dry, ignite, and weigh as mag- 524 PORTLAND CEMENT nesium pyrophosphate, Mg, P.O. Multiply this by O.36219 for its equivalent of magnesia, MgO, or by O.75744 for magnesium carbonate, MgCOs. By Solution in Hydrochloric Acid In soluble Silicious Matter Weigh os gram of the finely ground dried sample into a porcelain dish or casserole, cover with a watch-glass and add 30 cc. of water and Io co. Of concentrated hydrochloric acid. Warm until all effervescence has ceased, uncover, add a few drops of nitric acid, and evaporate to dryness. Bake on the hot-plate or sand-bath until all odor of hydro- chloric acid has disappeared, or safer still, heat in an air-bath at IIo° C. for one hour after the residue has become perfectly dry. Cool the dish and add 5 cc. of dilute hydrochloric acid, set on the hot-plate, covered with a watch-glass for five minutes, then add 50 cc. of hot water and filter, after digesting until all except silicious matter dissolves. Wash thoroughly, ignite and weigh as “insoluble silicious matter.” Silica Should it be desirous to know the silica in the “insoluble silicious matter” fuse it with ten times its weight of pure dry sodium carbonate, first over a Bunsen burner turned low, and then, after slowly raising the flame of this latter to its full height, over a blast-lamp until the contents of the crucible are in a state of quiet fusion. Remove the crucible from the lamp and run the fused mass well up on its sides by tilting and revolving the crucible while held with the crucible tongs. While still hot dip the crucible three-quarters of the way up in a pan of cold water which will frequently cause the mass to loosen from the crucible. Wash off any material spattered on the crucible cover into a casserole or dish with hot water, and add the mass in the crucible if it has become detached. If not, fill the crucible with hot water and set on the hot-plate until the fused mass softens and can be removed to the casserole. Dissolve any particles of the mass in hydrochloric acid, that adhere too firmly to the crucible to be removed by gentle rubbing with a rubber-tipped rod. When the hot water has thoroughly disin- tegrated the fused mass, cover the casserole or dish with a watch-glass and strongly acidify the contents with hydrochloric acid. Heat until all effervescence ceases and everything dissolves except the silica. Wash off the watch-glass into the dish and evaporate the solution to dryness. Heat for one hour at 110° C. in the air-bath, or on the hot-plate at not too high a temperature until all odor of hydrochloric acid has disap- peared from the dry mass. Cool, add Io co. of hydrochloric acid and 50 THE AN ALYSIS OF THE RAW MATERIALS 525 cc. of water, warm until all soluble salts are in solution, filter, wash well with hot water, dry, ignite, and weigh as silica, SiO2. Fe2O3,4 l,Oa,CaO, MgO. Mix the two filtrates from the silica separations and proceed to de- termine iron and alumina, lime and magnesia, as directed in the method “By Ignition with Sodium Carbonate.” When the amount of sodium carbonate added to the “insoluble silic- ious matter” is greater than o.5 gram, it is best in very accurate work, instead of mixing the two filtrates from the silica, to determine the iron, alumina, lime, and magnesia in each solution separately, since the large lime precipitate is almost sure to be contaminated with sodium salts if the two filtrates are mixed. Determination of Organic Matter, Insoluble Silicious Matter, Ferric Oaſide and Alumina, Lime and Magnesia. Weigh I gram of the finely ground dried limestone into a porcelain dish or casserole; cover with a watch-glass and add 30 cc. of water and Io ce. of concentrated hydrochloric acid. Warm until all effervescence ceases, uncover and evaporate to dryness on a water-bath. Heat the dish for one hour, after the residue becomes thoroughly dry, at IIo° C. in an air-bath. Cool the dish and add 5 cc. of hydrochloric acid and 50 cc. of hot water. Heat until all soluble salts dissolve, filter upon a Gooch crucible or a small counterpoised filter-paper. Wash well with hot water, dry at Ioo? C. in an air-bath and weigh as “organic matter” plus “insoluble silicious matter.” Now ignite until all carbonaceous matter is destroyed, and cool and weigh as “insoluble silicious matter.” This weight subtracted from the preceding one gives the “organic matter.” If the silica in the “in- soluble silicious matter” is desired, fuse the latter with ten times its weight of sodium carbonate and proceed as described in the preceding scheme for the analysis of limestone “By Solution in Hydrochloric Acid.” Heat the filtrate from the “organic matter” and the “insoluble silic- ious matter” to boiling, add ammonia in slight but distinct excess, and proceed to determine the ferric oxide and alumina, lime and magnesia, as directed on page 52I. The Determination of Alkalies, Sulphuric Acid, Carbon Dioxide Combined Water and Loss on Ignition For the determination of these constituents refer to the meth- ods given under cement. Use the fusion method for sulphur and employ only 3% gram for a sample in determining carbon dioxide. 526 PORTLAND CEMENT RAPID DETERMINATION OF LIME AND MAGNESIA S. B. Newberry" suggests the following rapid scheme for de- termining lime and magnesia in limestone, etc. “Prepare N/5 hydrochloric acid and N/5 caustic soda solutions, and standardize with pure, transparent Iceland spar. One-half gram of spar should exactly neutralize 50 cc. of acid. “Weigh out 9% gram of finely ground limestone, transfer to an Erlenmeyer flask of about 500 cc. capacity, provided with rubber stopper and thin glass tube about 30 inches long to serve as a condenser, as described on page 236. Run into the flask 60 cc. N/5 acid; attach the condenser and boil gently, allowing no steam to escape from the tube, for about two minutes. Wash down the tube into the flask with a few ce. of water from wash-bottle; remove the condenser and cool the solution thor- oughly by immersing the bottom of the flask in cold water. When quite cold, add five drops of phenolphthalein solution, (I gram in 200 cc. alcohol), and titrate back to first pink color with N/5 soda solution. It is important to recognize the point at which a faint pink color first appears throughout the solution, even though this may fade out in a few seconds. If alkali be added to a permanent and strong red color, the lime will come too low. Let us call the amount of acid used the first acid, and the alkali used to titrate back the first alkali. “Transfer the neutral solution to a large test-tube, 12 inches long and I inch inside diameter, marked (with a paper strip or otherwise) at IOO ce. Heat to boiling, and add N/5 soda solution, about I ce. at a time, boiling for a moment after each addition, till a deep red color, which does not become paler on boiling, is obtained. This point can be easily recognized within one-half ce. after a little practice. Note the number of ce. Soda solution added to the neutral solution, as second alkali. Dilute to IOO co., boil for a moment and set the tube aside to allow the precipitate to settle. When settled, take out 50 cc. of the clear solution by means of a pipette, and titrate back to colorless with N/5 acid. Multiply by 2 the number of ce. acid required to neutralize, and note as second acid. * Cement and Engineering News, March, 1903, p. 35. THE AN ALYSIS OF THE RAW MATER [ALS 527 e “The calculation is as follows: Second alkali — second acid, × 2 × 0.40 = % MgO. First acid – (first alkali + second alkali — second acid), × 2 × 0.56 = % CaO. “Example: To 94 gram limestone were added 60.00 cc. acid, (first acid). To titrate back to first pink, II.60 cc. alkali were required, (first alkali). The solution was then transferred to test-tube, boiled, and 3.55 alkali added to permanent deep red color, (second alkali). After diluting to IOO co. and settling, 50 cc. of the red solution required O.45 cc. acid to decolorize it, (O.45 × 2 = O.90 = second acid). 3.55 – O.90, X 2 × 0.40 = 2. I2 % MgO. 60.00 – (11.60 + 3.55 – O.90) × 2 × 0.56 = 51.24% CaO.” NOTES “Nitric acid may be used in place of hydrochloric; the latter appears, however, to give slightly better results. “Not more than I ce. excess of alkali should be added in precipitating the magnesia; the ‘second’ should therefore not exceed I. Larger excess of alkali tends to throw down lime. “The settling usually requires only a few minutes, unless much mag- nesia is present; it may be greatly hastened by allowing the test-tube to stand two or three minutes, then immersing the lower part for a moment in cold water. “If results are desired in percentages of magnesium carbonate and calcium carbonate the factors O.84 and I.oO are to be substituted for o.40 and 0.56, respectively. “The tendency of the method is to give slightly too high results on magnesia and too low results on lime. This is partly due to the forma- tion of calcium carbonate, by the action of the carbon dioxide of the air, during the precipitation of the magnesia. By the use of a large test-tube, as above described, this error is so far reduced as to be insignificant. Another source of shortage of lime is to be found in the presence, in certain materials, of Small proportions of lime in a form insoluble in dilute acid.” In determining lime in cement-rock or in cement mixtures made from clay containing calcium silicates this method always gives low results for the above reason. To use the method on such material it is necessary to determine a “correction factor” by comparison between the lime found by this method and that on page 523, in a series of standard samples. By subtracting the lower from the higher results, a constant is obtained which is to be added to all results obtained by titration with the acid and alkali. 528 PORTLAND CEMENT Modification by Brandenburg and Avakian Messrs. Brandenburg and Avakian, of the Cowell Portland Cement Co., modify Newberry's method as follows: Prepare 2/5 N acid (HCl) and alkali (NaOH) solutions adding 2 cc. of a I per cent solution of phenolphthalein to each liter of stand- ard acid. Standardize against Iceland spar as usual. Weigh I gram of the sample into a 300 cc. Erlenmeyer flask and add 60 cc. of the standard acid. Attach to the condenser described on page 514 and boil two or three minutes. Instead of titrating hot as in ordinary acid and alkali determinations of lime, cool the solution under the tap and when cold titrate rapidly, yet carefully, with the 2/5 N alkali until the first pink color is ob- tained and record the number of ce. Of alkali so used as “A.” Attach flask to the condenser again and heat just to boiling, having ready I.5 grams of Solid Sodium oxalate. Add the latter to the solution in the flask and boil for a minute or two. Re- move the flask from the condenser and flame and add to the solu- tion a decided and measured excess of 2/5 N alkali. Record the number of co. of alkali so used as “B.” Attach flask to condenser, boil the contents for two or three minutes, remove from the flame, cool under the tap, transfer con- tents to a 200 cc. graduate, fill to the mark with water and shake thoroughly. Filter through double filter-paper into a IOO ce. graduate, discarding the first and probably turbid filtrate. Filter off IOO ce., transfer to a clean Erlenmeyer flask and titrate care- fully back with the 2/5 N acid. Note the number of ce. of acid so used, double this reading and record as “C.” The results are calculated as follows: CaCO, = 60 — (A + B — C) X factor. MgCO2 = (B — C) X factor. For Example: If 60 cc. of 2/5 N acid are used to dissolve the sample, 9.85 cc. of alkali to back titrate (A), 40.0 cc. to precipitate the magnesia (B) and 31.7 to back titrate C; then CaCO3 = 60 — (9.85 –– 40 – 31.7) × 2 = 41.85 × 2 = 83.70 %. THE ANALYSIS OF THE RAW MATERIALS 529 MgCOs = (40 – 31.7) × 1.69 = 8.3 × 1.69 = I4.03 %. The above example assumes acid and alkali are exactly 2/5 N strength. NOTES The titration of the solution with alkali should not be continued after the “first pink” is reached, even though the color fades. Any additional alkali after the “first pink” will be consumed for precipitation of the magnesia. The object of the addition of oxalate, according to the authors, is to form calcium oxalate and thus render the excess alkali added later in- active and remedy the error in the older method due to the precipita- tion of the calcium by the alkali. Should magnesia be precipitated by the oxalate no error will occur as the magnesium oxalate is converted to the hydrate by the excess alkali later employed. METHODS FOR CLAY AND SHALE Finely grind the sample of clay and heat at IOO9 to IIo° C. for one hour in an air-bath. Transfer I gram of the dried clay to a fairly large platinum crucible. Mix with it by stirring with a Smooth glass rod IO grams of sodium carbonate and a little so- dium nitrate. Heat over a Bunsen burner, gently at first, for a few minutes and then to quiet fusion over a blast-lamp. Run the fused mass well up on the sides of the crucible and allow to cool. Nearly fill the crucible with hot water and set on the hot-plate for a few minutes. Pour the solution and as much of the mass as has become detached from the crucible into a casserole or better a platinum dish. Repeat this treatment until the mass has become thoroughly disintegrated. Treat what remains in the crucible with dilute hydrochloric acid and pour the acid into the casserole or dish. Clean out the crucible with a rubber-tipped rod and after acidifying with hydrochloric acid evaporate the contents of the casserole to dryness. Proceed as in A or B. A is the shorter method but B is the more reliable. A. Heat in an air-bath at I IO* C. for one hour, or until all odor of hydrochloric acid has vanished. Cool, moisten the mass with dilute hydrochloric acid, add a little water and again evaporate to dryness. Now add 30 cc. of dilute hydrochloric acid, digest at a gentle heat for a few moments and add IOO to I50 cc. of hot water. Allow to stand a few minutes on the hot-plate and filter. 530 PORTLAND CEMENT Wash the residue thoroughly with hot water, ignite over a Bun- sen burner until all carbon is burned off, and then for five min- utes over a blast-lamp, and weigh as SiO2. B. The residue, without further heating, is treated at first with Io ce. of dilute HC1. The dish is then covered and digestion al- lowed to go on for ten minutes on the bath, after which the solu- tion is diluted slightly, filtered, and the separated silica washed thoroughly with hot water. The filtrate is again evaporated to dryness, the residue, without further heating, taken up with acid and water, and the small amount of silica it contains separated on another filter-paper. The two papers containing the residue are transferred wet to a weighed platinum crucible, dried, ignited, first over a Bunsen burner until the carbon of the filter is com- pletely consumed, and finally over the blast for fifteen minutes. The precipitate is then weighed as SiO2. This precipitate is more or less contaminated by iron oxide and alumina. In accurate work the amount of these must be determined in the following manner and deducted from the weight of SiO, as found above. Moisten the weighed silica with a few drops of dilute sulphuric acid and half fill the crucible with hydrofluoric acid. Evaporate to dryness by placing over a burner in an inclined position so that the low flame plays upon the side of the crucible and the evaporation takes place only from the surface. Ignite and weigh. The dif- ference between the two weights is the silica, SiO2. Ferric Oazide and Alumina Add a few drops of bromine water and heat the filtrate from the silica, which should measure about 150 cc., to boiling, and add ammonia in slight but distinct excess; boil for a few moments and allow the precipitate to settle. Filter and wash several times with hot water. Remove the filtrate from under the funnel and dissolve the precipitate of iron and alumina in a mixture of 15 cc. of dilute nitric acid and 15 cc. of cold water, by pouring back and forth through the filter as long as any precipitate remains. Wash the filter-paper well with cold water, dry, place in the weighed platinum crucible containing the residue from the puri- fication of the silica if this has been done, and set aside. Repre- cipitate the iron and alumina in the filtrate as before by adding a THE ANALYSIS OF THE RAW MATERIALS 53 I slight but distinct excess of ammonia, filter, and wash once with hot water. Place in the crucible with the other paper and ignite, using the blast as in determining silica and weigh as Fe,0s + Al,Os (TiO, H- P.O. -- Mn,0,). Determine the ferric oxide in the precipitate as in A, B or C below and subtract the amount from this weight; the difference will be the Al2O3 (TiO2 + P.O; + Mn2O,). A. Fuse the ignited precipitate with sodium carbonate, treat the fused mass with hot water and wash it out into a small beaker, allow the residue to settle and decant off the clear supernatant liquid through a small filter, leaving the residue in the bottom of the beaker. Wash the filter-paper once and pour a little hot con- centrated hydrochloric acid through the filter into the beaker con- taining the residue. Heat gently, but do not boil. When all the residue is dissolved, determine the iron in the solution by re- duction with stannic chloride and titration with potassium bichro- mate as directed on page 463. B. The precipitate is fused with 3 or 4 grams of potassium bi- sulphate at a very low temperature and the melt is dissolved in water acidified with sulphuric acid. The solution is then reduced with zinc or hydrogen sulphide, (preferably the latter since clays sometimes contain considerable titantic oxide), and the iron de- termined as directed on page 459. C. Weigh out a fresh sample of Ø gram. Mix intimately with 2 grams of precipitated calcium carbonate and 2 grams of sodium carbonate. Ignite for fifteen minutes in a large platinum crucible over a good blast-lamp. Cool the mass and dissolve in dilute hydrochloric acid. If much silica separates out evaporate to dryness and filter. Otherwise add ammonia in excess to the solution, filter off the precipitated Fe2O3, dissolve the latter in an excess of hydrochloric acid, and determine the iron as directed on page 463 or dissolve in Sulphuric acid and determine as directed on page 459. Lime Heat the filtrate from the iron and alumina to boiling and add an excess of a saturated solution of ammonium oxalate. Stir and boil for a few minutes and set aside for several hours to allow 532 PORTLAND CEMENT the complete precipitation of the lime. Filter, wash, dry, and ignite over a blast-lamp until the weight is constant. Weigh as calcium oxide, CaO. Or determine volumetrically with perman- ganate as described on page 455. Magnesia To the filtrate from the calcium oxalate add sufficient hydro- chloric acid to make it slighly acid and then 30 cc. of sodium phosphate solution. Concentrate the solution to about 200 cc. by evaporation and cool. Then add ammonia drop by drop, with constant stirring until the liquid is slightly ammoniacal and the precipitate begins to form. Stop adding ammonia and stir for five minutes, then add one-tenth the volume of the liquid of strong ammonia and continue the stirring for five minutes more. Allow the solution to stand in a cool place over night, filter, wash with a mixture of 1,000 cc. water, 500 cc. ammonia (sp. gr. O.96), and I50 grams ammonium nitrate. Dry, ignite (do not use the blast-lamp), and weigh as magnesium pyrophosphate, Mg,F,C). Multiply this by O.36219 for magnesium oxide, MgO. NOTES Clay is practically unacted upon by hydrochloric acid and requires fusion with alkaline carbonates for its decomposition. Should the solution, on evaporation to dryness, show a tendency to climb the sides of the dish, greasing the latter lightly with vaseline or paraffine will remove the difficulty. The amounts of lime and magnesia in clays are small, so that the filtrate and washings from the second ammonia precipitation of the iron and alumina may be rejected and the lime and magnesia determined in the first filtrate only. For the same reason it is unnecessary to re- precipitate the calcium oxalate, although the solution is largely con- taminated by sodium salts from the alkaline fusion. Determination of the Alkalies To determine the alkalies use I gram of the clay, I gram of ammo- nium chloride and 8 grams of calcium carbonate and proceed as directed for determining the alkalies in cement on page 486. Determination of Free, Hydrated and Combined Silical To ascertain how much of the silica found exists in combination with the bases of the clay, how much as hydrated acid, and how much * Cairns' Quantitative Chemical Analysis, page 68. THE ANALYSIS OF THE RAW MATERIALS 533 as quartz sand or as a silicate present in the form of sand, proceed as follows.” Let A represent silica in combination with the bases of the clay. Let B represent hydrated silicic acid. Let C represent quartz sand and silicates in the form of sand, e. g., feldspar sand. Dry 2 grams of the clay at a temperature of Ioo” C., heat with sul- phuric acid, to which a little water has been added, for eight or ten hours, evaporate to dryness, cool, add water, filter out the undissolved residue, wash, dry, and weigh (A + B -- C). Then treat it with sodium carbonate. Transfer it, in small portions at a time, to a boiling solution of sodium carbonate contained in a platinum dish, boil for some time and filter off each time, still very hot. When all is trans- ferred to the dish, boil repeatedly with strong solution of sodium car- bonate until a few drops of the liquid finally passed through the filter remain clear on warming with ammonium chloride. Wash the residue, first with hot water, then (to insure the removal of every trace of sodium carbonate which may still adhere to it) with water slightly acidified with hydrochloric acid, and finally with water. This will dis- solve (A + B) and leave a residue (C) of sand, which dry, ignite, and weigh. To determine (B), boil 4 or 5 grams of clay (previously dried at IOoº C.) directly with strong solution of sodium carbonate in a platinum dish as above, filter and wash thoroughly with hot water. Acidify the filtrate with hydrochloric acid, evaporate to dryness, and determine the silica as usual. It represents (B) or the hydrated silicic acid. Add together the weights of (B) and (C), thus found, and sub- tract the sum from the weight of the first residue (A + B -- C). The difference will be the weight of (A) or the silica in combination with the bases of the clay. If the weight of (A -- B -- C) found here to be the same as that of the silica found by fusion in a similar quantity in the analysis of the clay, the sand is quartz, then the sand contains silicates. The weight of the bases combined with silica to form silicates can be found by subtracting the weight of total silica found in I gram in the regular analysis, from the weight (A + B -- C) in I gram. NOTES The following scheme is much less trouble than that described above and gives the silica present as sand and silicates undecomposable by sul- phuric acid and that in combination with the alumina or combined silica. Heat I.25 grams of the finely ground and dried (at Ioo° C.) clay with I5 cc. of concentrated sulphuric acid to near the boiling-point of the acid and digest for from ten to twelve hours at this temperature. * Compare Fresenius' Quantitative Analysis, 5th Ed., 1865, Sec. 236. 35 534 PORTLAND CEMENT Cool, dilute and filter. Wash and ignite the residue to a constant weight. Call this weight A. After weighing brush the residue which consists of silica present as sand and undecomposable silicates and silica from the decomposition of the silicates of alumina, into an agate mortar, grind very finely and weigh O.5 gram of it into a platinum dish con- taining 50 cc. of boiling caustic potash solution (of 1.125 sp. gr.). Boil for five minutes, filter, wash, first with hot water and then with water containing a little dilute hydrochloric acid and then again with hot water, dry and ignite to a constant weight. Call this weight B. Multi- ply A by 0.4 (to correct the I.25 grams of clay used to correspond to the 0.5 gram of the residue taken for treatment with caustic potash solution) and subtract B from the product. Multiply the difference by 2GO for the per cent of silica combined with alumina in the clay. This deducted from the total silica found by analysis gives the silica as sand and un- decomposable silicates. Determination of Coarse Sand In examining clay to be used for cement manufacture, it is not so important to know the chemical condition in which the silica exists as its physical state, i. e., whether the sand grains are large or small. Pure quartz sand if sufficiently finely powdered will combine with lime at the temperature of the rotary kiln, so that what is more requisite in clay to be used for cement manufacture is that the sand shall be present in fine grains. To test the clay, along this line, weigh IOO grams of clay into a beaker and wet with water. Triturate to a thin slip with a glass rod and wash into a No. IOO test sieve. Now place the sieve under the tap and wash as much of the clay as possible through the meshes of the sieve with a gentle stream of water. Dry the sieve on a hot-plate and brush out the dry residue failing to pass through it on to the balance pan and weigh. The weight in grams gives the percent- age of the clay failing to pass a No. 100 sieve. The clay may also be tested in a similar manner on the No. 200 sieve and the residues may be subjected to chemical analysis. Marls are examined by the same method to determine fineness. Determination of Water of Combination Should the clay contain very little organic matter, iron pyrites or calcium carbonate, heat I gram of the previously dried cement for twenty minutes to a bright redness over a Bunsen burner. THE ANALYSIS OF THE RAW MATERIALS 535 The loss in weight will represent the water of combination. If, however, the clay contains much organic matter, calcium carbon- ate or iron pyrites, the water of combination should be de- termined by absorption in a weighed calcium chloride tube as described for cement analysis on page 475. Many chemists simply heat I gram of dried clay over a blast for twenty minutes reporting the loss of weight as loss on igni- tion. This loss, of course, comes from combined water and car- bon dioxide driven off (from the decomposition of carbonates), organic matter burned and iron pyrites changed from iron sul- phide, FeS2, to ferric oxide. Sulphur and Iron Pyrites For the determination of sulphur in clay, proceed as directed for determining this constituent in cements by fusion with sodium carbonate and potassium nitrate. Multiply the weight of barium sulphate by O.257OI and report as iron pyrites, FeS2, or by O. I3738 and report as sulphur. If reported as FeS2 multiply the percentage of this latter by O.90836 and deduct from the Fe,Oa. Rapid Determination of Silica, Iron Oxide and Alumina Weigh O.5 gram of the finely ground sample of clay into a platinum crucible and mix with it intimately, by stirring with a glass rod rounded at the ends, I gram of precipitated calcium carbonate such as is used for alkali determination and 9% gram of finely powdered dry sodium carbonate. The mixing must be thorough. Brush off the rod into the crucible with a camel's hair brush and place the covered crucible over a Bunsen burner turned low. Gradually raise the flame till the full heat is attained, keep at this temperature for two or three minutes, and then remove to the blast-lamp and ignite strongly for five minutes. Cool the crucible by plunging its bottom in cold water and place it on its side in a platinum or porcelain dish or casserole. Add IO cc. of water and Io co. of dilute (I : I) acid. As soon as the mass is dissolved out of the crucible remove the latter, rinse it off into the dish removing any solid particles with a policeman and evapo- rate the solution to dryness. Heat the dish at 120° C. until all 536 PORTLAND CEMENT odor of acid has disappeared. Cool, add 20 cc. of hydrochloric acid (I : I), cover and boil a few minutes, add 50 cc. of water, boil a few minutes longer, filter, wash and ignite, first over the burner, until carbon is all burned off, and then over the blast for ten minutes. Cool and weigh as silica, SiO2. Iron Oaxide and Alumina Heat the filtrate to boiling, after adding a few drops of bromine water, add ammonia in slight but distinct excess and again heat to boiling. Continue boiling for two or three minutes and after allowing the precipitate to settle, filter and wash once with hot water. Invert the funnel over the beaker in which the precipita- tion was made and wash the precipitate back into this with a stream of hot water from a wash-bottle. Dissolve in dilute nitric acid, heat to boiling and reprecipitate with ammonia. Boil for a few minutes, allow the precipitate to settle, and filter. Wash once with hot water, ignite (using the blast finally) and weigh as Oxides of alumina and iron, Al,Oa -- Fe2O3. METHODS FOR GYPSUM OR PLASTER OF PARIS Determination of Silica, Iron Oride, Alumina, Lime and Magnesia Weigh O.5 gram of the finely ground Sample into a platinum dish or porcelain casserole and add 20 cc. of dilute hydrochloric acid (I : I). Evaporate to dryness and heat the residue, at IIo° C. until all odor of hydrochloric acid has vanished from the con- tents of the dish. Cool and add IO ce. of dilute hydrochloric acid, cover with a watch-glass and heat for five minutes. Dilute to 50 cc. and heat a little longer. Filter, wash the precipitate well with hot water, ignite and weigh. Report as insoluble silicious matter or proceed as follows: Ignite O.5 gram of the sample with }} gram of pulverized sodium carbonate first over a burner and then over a blast. Place the crucible in a dish or beaker and dissolve out the mass in a little dilute hydrochloric acid. Evaporate the solution to dryness and heat, at IIO* C., until all odor of hydro- chloric acid has disappeared from the dry mass. Dissolve in a THE ANALYSIS OF THE RAW MATERIALS 537 little hydrochloric acid and water, as before, filter, wash, ignite and weigh as SiO2. Heat the filtrate from the SiO, or that from the “insoluble silicious matter,” as the case may be, to boiling, precipitate the iron and aluminum as oxides with ammonia and proceed as in the analysis of cements on page 441. - Determination of Sulphuric Acid Weigh O.25 gram of the finely ground sample into a beaker and dissolve in 5 cc. of dilute (I : I) hydrochloric acid, by the aid of heat. Dilute to IOO ce. with hot water. Digest for a few minutes and filter. Wash the paper and residue thoroughly, with hot water, until the filtrate measures about 250 cc. Heat this latter to boiling and add, with constant stirring, 20 cc. of barium chlor- ide solution, also boiling hot, and stir for five minutes. Remove from the source of heat and allow to stand over night in a warm place. In the morning, filter through a double filter-paper or a “Shimer filter tube” and wash well with hot water. Ignite (without using the blast) and weigh as BaSO,. This weight multiplied by O.343OO gives the SOs in the sample or by O.62184 the (CaSO4) H2O or by O.7375 the CaSO4·2H2O. Do not for- get a quarter gram sample has been taken. The above method is that generally employed. The writer, however, prefers to separate the lime from the solution before precipitating the sulphur. His method is as follows:–Weigh O.25 gram of the sample into a small beaker and add 5 cc. of dilute (I : I) hydrochloric acid. Heat until solution is complete. Dilute to IOO cc. make alkaline with ammonia and add an excess of ammonium carbonate solution. Boil for a few minutes and filter. Wash the residue with hot water and redissolve in 5 cc. of acid. Again neutralize with ammonia and add ammonium carbonate solution. Filter and wash the residue with hot water a few times. Combine the filtrates from the two precipitations. Acidify with hydrochloric acid, using an excess of about 3 or 4 cc. Heat to boiling and precipitate the sulphur as directed above with barium chloride. * See page 472. 538 PORTLAND CEMENT Determination of Water Weigh I gram of the finely ground sample in a weighed platinum crucible and heat" for one hour at IOO-IoS9 C. Cool and weigh. The loss in weight represents the “moisture” or “water below IoS9 C.” Determine the combined water and carbon dioxide as directed for cement on page 475, or: a- Place the crucible over a Bunsen burner and heat at a low red temperature for thirty minutes. The loss in weight represents “water of combination” or “water above IoS9 C.” If the heating has been too high, some sulphuric acid will have also been lost. To check this, dissolve the sample out of the crucible, after igni- tion, with hydrochloric acid. Dilute to about IOO ce. and filter into a 200 cc. flask. Wash well with hot water and dilute with water to the mark. Measure of this volume 50 cc. dilute to 250 cc. and determine the SO, as directed previously. If loss has occurred, this determination will give a lower figure than the other. In this case deduct the difference between the percentages found by the two trials from percentage of loss in weight over the burner for the percentage of water of combination. If the heating of the crucible over the Bunsen burner has been done at a heat not higher than cherry-red there should be no loss of sul- phuric acid, however. Determination of Carbon Dioxide Determine carbon dioxide as directed on page 483, for cement, using the evolution method. * See page 485. PHYSICAL TESTING CHAPTER XIX INSPECTION OF CEMENT Standard Specifications and Tests for Portland Cement” 1.” Definition.—Portland cement is the product obtained by finely pulverizing clinker produced by calcining to incipient fusion an intimate and properly proportioned mixture of argil- laceous and calcareous materials, with no additions subsequent to calcination excepting water and calcined or uncalcined gypsum. I. Chemical Properties 2. Chemical Limits.--The following limits shall not be ex- ceeded : Loss on ignition, per cent . . . . . . . . . . . . . . . . . . . . . . . . . . 4.00 Insoluble residue, per cent . . . . . . . . . . . . . . . . . . . . . . . . . o.85 Sulfuric anhydride (SOs), per cent . . . . . . . . . . . . . . . . 2.OO Magnesia (MgO), per cent . . . . . . . . . . . . . . . . . . . . . . . . 5.CO II. Physical Properties 3. Specific Gravity.—The specific gravity of cement shall be not less than 3. Io (3.07 for white Portland cement). Should the test of cement as received fall below this requirement a second test may be made upon an ignited sample. The specific gravity test will not be made unless specifically ordered. 4. Fineness.-The residue on a standard No. 200 sieve shall not exceed 22 per cent by weight. * These specifications were approved March 31, 1922, as “American Standard” by the American Engineering Standard Committee. * Where numbers occur in front of paragraphs, these appear in the Standard specifications, the original numbering being retained to facilitate references. 54O PORTLAND CEMENT 5. Soundness.-A pat of neat cement shall remain firm and hard, and show no signs of distortion, cracking, checking, or dis- integration in the steam test for soundness. 6. Time of Setting.—The cement shall not develop initial set in less than forty-five minutes when the Vicat needle is used or sixty minutes when the Gillmore needle is used. Final set shall be attained within ten hours. 7. Tensile Strength.--The average tensile strength in pounds per square inch of not less than three standard mortar briquettes (see Section 50°) composed of one part cement and three parts standard sand, by weight, shall be equal to or higher than the following: Tensile t g Asºº º } Storage of briquettes strength, 1b. y per Sq. in. 7 I day in moist air, 6 days in water 2OO 28 I day in moist air, 27 days in water 3OO 8. The average tensile strength of standard mortar at twenty- eight days shall be higher than the strength at seven days. Standard Specifications for Packages, Marking and Storage 9. Packages and Marking.—The cement shall be delivered in suitable bags or barrels with the brand and name of the manu- facturer plainly marked thereon, unless shipped in bulk. A bag shall contain 94 pounds net. A barrel shall contain 376 pounds net. Io. Storage.—The cement shall be stored in such a manner as to permit easy access for proper inspection and identification of each shipment, and in a suitable weather-tight building which will protect the cement from dampness. Standard Specifications for Inspection and Rejection II. Inspection.—Every facility shall be provided the pur- chaser for careful sampling and inspection at either the mill * See page 640. PHYSICAL TESTING 54 I or at the site of the work, as may be specified by the purchaser. At least ten days from the time of sampling shall be allowed for the completion of the seven-day test, and at least thirty-one days shall be allowed for the completion of the twenty-eight-day test. The cement shall be tested in accordance with the methods here- inafter prescribed. The twenty-eight-day test shall be waived only when specifically so ordered. I2. Rejection.—The cement may be rejected if it fails to meet any of the requirements of these specifications. I3. Cement shall not be rejected on account of failure to meet the fineness requirement if upon retest after drying at IOO9 C. for one hour it meets this requirement. I4. Cement failing to meet the test for soundness in steam may be accepted if it passes a retest using a new sample at any time within twenty-eight days thereafter. I5. Packages varying more than 5 per cent from the specified weight may be rejected; and if the average weight of packages in any shipment, as shown by weighing fifty packages taken at random, is less than that specified, the entire shipment may be rejected. Methods of Inspection It is now the custom to test carefully all cement to be used upon important work. Most of the large cities of the country maintain well equipped laboratories and systematically inspect all cement used upon the various municipal works undertaken by them. The Bureau of Standards in Washington tests all cement used by the national government in fortifications, dry-docks, public buildings, etc. Various private laboratories also make a specialty of inspecting the cement to be used in big buildings, reservoirs, retaining walls, etc., for private corporations, while the railroads, most of them, have well equipped laboratories for testing such materials, cement among them, as they purchase. Cement may be inspected either at the mill before shipment, or at the place where it is to be used, after receipt. The actual tests, of course, may be made at either of these points, or the samples can be properly labelled and sent some distance to a convenient 542 PORTLAND CEMENT laboratory. The New York Rapid Transit Railroad (Subway) Commission pursued the former of these two plans and inspected the cement at the mill itself. The Philadelphia Rapid Transit Company, on the other hand, followed the latter plan and in- spected the cement as received in Philadelphia. Both plans can be made to give entire satisfaction. Where the product of one mill alone is to be used for the work, the testing laboratory may be located at the mill from which the cement is supplied. Otherwise, it should, of course, be lo- cated at Some convenient point to which samples can readily be Sent. The suggestion has been made that the cement companies furnish the inspector testing appliances, quarters, etc., for doing this work. This seems to be asking rather much of the manu- facturers, as their laboratories are, most of them, already over- crowded and the presence of an outsider, in the one part of the plant where trade secrets are likely to be exposed, is not desirable. Inspection at the Mill Where cement inspection is done at the mill certain bins are set aside by the proper authority at the cement mill, and the spouts leading into these are closed by means of a wire and lead seal such as is used in closing box cars; the idea of sealing the spouts is to prevent the bins from being emptied and refilled without the knowledge of the inspector. Any method which will insure against this, such as sealing wax and string will answer as well as the lead seal and wire. In some cases, it may be sufficient to rely upon the honesty of the mill authorities and to merely accept their word or promise that the bin has not been tampered with. Or an affidavit may be secured from the stock-house foreman to this effect. After selecting the bin and insuring against its being emptied and refilled, it must be carefully sampled. How this is to be done will depend somewhat upon the size and shape of the bin. Since cement when freshly ground and hot flows not unlike a liquid, the cement first run into the bin will be almost all of it deposited in a layer on the floor of the bin. For this reason, the PHYSICAL TESTING 543 means used for sampling the bin must be such that the cement at the bottom of the bin is included in the sample. One page 548, a rod suitable for sampling shallow bins is described. This is probably as satisfactory as any sampling device can well be, pro- vided the bins are not too deep. The taking of a sample from the floor of a bin may necessitate the use of a sledge hammer to drive the rod through the mass of cement in the bin. If the inspector is permanently located at the mill, the sample can be taken easiest, when the bin is being filled, by means of an auto- matic sampler such as is described on page 496. The importance of sampling the floor of a bin will be under- stood, when it is known that, in a bin of unsound cement, a sample taken only a few days after the bin has been filled and representing only the surface layer of cement will often be sound, while one representing the bottom layer may be unsound after even a month's seasoning. A shallow rectangular bin should be sampled in at least four places—the four corners—and may be sampled in as many more as the inspector sees fit. A sample drawn from the four corners of shallow bins, filled by a spout in the middle, will be repre- sentative. The feet and legs of the man taking the sample may be protected as he walks over the surface of the cement by thrusting them in clean new cloth cement bags (a few of which can be found around all mills) and tying them securely around the legs above the knee. The cement sample should be placed in clean cloth bags, which should be properly closed and sealed and expressed or conveyed to the testing laboratory. If the in- specting laboratory is located at the mill, paper bags or tin buckets may be used for this purpose. Small milk cans holding about 2 quarts will be found excellent for transporting samples, as the tops can be wired down tight and the samples are pro- tected from changes due to exposure to air in them. The objection has been raised to the use of cloth bags, that an unsound cement would probably be seasoned sound after a two or three days’ journey in them and Some inspectors use tin buckets or cans, with tightly fitting covers for this purpose. On the other hand, if an unsound sample is made sound by exposure in 544 PORTLAND CEMENT cloth bags after a few days’ journey by express, the inspector may rest assured that the body of the bin will be seasoned equally well by an equally long journey by freight in a box car. Also cement occasionally leaves the mill “slow-setting” and arrives at the work “quick-setting,” so that shipment of a sample in cloth should give a line on the likelihood of the main body of the cement doing this. When the sample arrives at the testing laboratory, its receipt is properly recorded together with such data as the brand, manufacturer, bin, date sampled, etc., after which, to readily identify briquettes, etc., it is given a running number. The sample is then carefully mixed, and a sufficient quantity of this for the necessary tests is taken and passed through a 20-mesh sieve to remove lumps, after which it is submitted to the tests called for by the specifications. The large sample is then stored away in a tin can or a fruit jar for future reference, retests, etc. When the results of the tests are at hand, the laboratory noti- fies its agent at the mill, who in turn informs the authorities of the cement company that such and such a bin is ready for ship- ment, and when cement is needed it is also the duty of the mill inspector to see that the cement is packed from accepted bins and accepted bins only. This system usually necessitates the holding of a bin for from five to six weeks, if the specifications call for a twenty-eight-day test, or about two weeks if only the seven-day test is relied upon. This often puts the manufacturer to much inconvenience and trouble, but, from the standpoint of the consumer, seems to be preferable. On the other hand the manufacturer has the satis- faction of knowing that, after the cement is once shipped, it is off his hands for good and all with no chance for complaint from the purchaser. Another form of inspection at the mill consists in sampling the cars as they are filled. This is usually done by taking a small quantity of cement from one in every forty bags packed. These small samples are then either mixed or not as desired and sent to the laboratory for tests. (See directions for sampling, page 546). The car is not held for the result of these but is PHYSICAL TESTING 545 immediately billed to its destination. By the time it has reached this, the seven-day tests will usually have been completed. If the tests are satisfactory the car can be immediately unloaded and used. This method is employed by most testing laboratories. Inspection on the Work When the cement is inspected as it arrives at the work, the cars are unloaded and 'sampled—one bag out of every forty (or one barrel in ten) being selected and a sample drawn from it as indicated on page 547. These samples may be either mixed or kept separate in clean paper bags. The contents of each car should be piled in such a way that it may be kept to itself and marked by a properly tagged board or sign. When the work permits the use of a large store house, this should be divided into bins holding a carload, 200 barrels or 1,000 bags. The cement should be held in storage until the results of the tests are known when, if these are satisfactory, the contractor or fore- man may be notified that he can use the cement from such and such a pile or bin. When a car of cement fails to pass the specifications, the manu- facturer is usually notified at once that such cement has been found unsatisfactory. He will then probably ask for a retest, which should be made from new samples, drawn in the presence of his representatives, and, if possible, the tests also should be repeated in the presence of this representative. If this latter can not be done, the sample should be divided into three parts and placed in tin cans or fruit jars and closed up tight. One of these samples should be tested by the manufacturer and, unless his re- sults agree with those of the consumer, the third sample should be sent to some reliable, competent third party with the agree- ment of both manufacturer and consumer to stand by his results. Should the cement finally be found unsatisfactory, it is usually returned to the manufacturer, who replaces it with another con- signment or else it is used on Some unimportant part of the job. Unsound cement may be held until it has been seasoned sound and quick-setting cement may often be made slow-setting by a small addition (O.5 per cent) of plaster or slaked lime. In both 546 PORTLAND CEMENT instances, the resulting concrete will be satisfactory and the manufacturer will usually be willing to bear the expense of stor- age, or addition of plaster or lime, rather than pay the double freight, necessary to its replacement with other cement. When the cement supplied by a manufacturer habitually fails to pass the specifications under which it is sold, he deserves little consideration from the engineer or inspector, but, when the failure of a brand to meet specifications is a rare incident, the engineer can afford to be lenient, if his work is not en- dangered thereby, especially if the average quality of the cement is far above that asked for by him, in his specifications. Standard Methods of Sampling The methods of sampling recommended by the standard speci- fications are as follows: 16. Number of Samples.—Tests may be made on individual or composite samples as may be ordered. Each test sample should weigh at least 8 pounds. 17. (a) Individual Sample.—If sampled in cars one test sample shall be taken from each 50 barrels or fraction thereof. If sampled in bins one sample shall be taken from each IOO barrels. (b) Composite Sample.—If sampled in cars one sample shall be taken from one sack in each forty sacks (or I barrel in each Io barrels) and combined to form one test sample. If sampled in bins or warehouses one test sample shall represent not more than 200 barrels. 18. Method of Sampling.—Cement may be sampled at the mill by any of the following methods that may be practicable, as ordered: * (a) From the Conveyor Delivering to the Bin.-At least 8 pounds of cement shall be taken from approximately each IOO barrels passing over the conveyor. (b) From Filled Bins by Means of Proper Sampling Tubes.— Tubes inserted vertically may be used for sampling cement to a maximum depth of IO feet. Tubes inserted horizontally may PHYSICAL TESTING 547 be used where the construction of the bin permits. Samples shall be taken from points well distributed over the face of the bin. (c) From Filled Bins at Points of Discharge.—Sufficient cement shall be drawn from the discharge openings to obtain samples representative of the cement contained in the bin, as determined by the appearance at the discharge openings of indi- cators placed on the surface of the cement directly above these openings before drawing of the cement is started. 19. Treatment of Sample.—Samples preferably shall be shipped and stored in air-tight containers. Samples shall be passed through a sieve having 20 meshes per linear inch in order to thoroughly mix the sample, break up lumps and remove foreign materials. The knowledge usually sought by a test and analysis of cement is the average composition and properties of a given lot or bin. In order that it shall give this, it is necessary that the small sample used in the tests shall fairly represent the whole quantity, possibly many tons. In a large lot of cement, it often happens that a small sample, or even a large sample, taken from one place in the bin or one barrel in the consignment, will not repre- sent the cement, since this particular point in the bin, or this special barrel, might be better or worse than the remainder, hence the directions to take at least twenty samples in a car of 200 barrels, or to sample at frequent places in a bin. Samplers Practically all cement in the United States is now packed in Bates Valve bags, the sampling from which is easy. This is usually done by means of a small brass tube from 18 to 20 inches long, both ends of which are left open but one end of which is bevelled at an angle of about 45°. This tube is simply thrust into the bag through the valve of the latter and the cement which it retains is withdrawn for the sample. The tube should be thrust into the bag from valve to center not across the end of the bag. In sampling cement from a barrel a small brass tube with a slit cut down the middle may be used. The slit is neces- 548 PORTLAND CEMENT sary as the cement becomes packed in the tube when it is thrust into the cement and it is necessary to run a lead pencil or nail up and down the opening to get the cement out. The tube for this purpose need not be over two feet long and its upper end should be screwed into a T, the latter forming a handle. The forms of grain and Sugar Samplers sold by dealers in apparatus for cement testing may be used for sampling bags and barrels. In sampling cement packed in Bates valve bags, this can be done without untying the bags by thrusting a brass tube into the Hº " ", !!! Fig. 157.—Jointed Rod for Sampling Stock House Bins. contents of the bag through the valve. The spill from the tube of this machine will also make a good average sample of bags as packed. For sampling bins of cement in the stock houses at the mill the depth of the former, often eight or more feet, makes their proper sampling a difficult matter unless a specially devised sampling rod is at hand. In order to get an average of the bin it is necessary to draw portions from it at all depths and at both ends. An excellent apparatus for doing this, consists of a long iron rod such as is shown in Fig. 157. PHYSICAL TESTING 549 It is made of I-inch wrought iron piping and in sections of about four feet each, to allow of its being readily carried about from one mill to another. The couplings are long and are turned down so as to taper at either end. In the end of the rod is fastened a steel point and slots about one-fourth inch in width and fourteen inches in length are cut in each section as shown in the illustration. One side of each slot is made to project slightly beyond the side of the pipe and sharpened, as shown in the section A-B. In using the rod, as many sections are used as may be necessary to reach to the bottom of the bin. These are joined, the whole is thrust into the bin until it reaches the bottom, the rod is filled by turning it a few times, then withdrawn, turned upside down and the cement shaken out of it into a bag by rapping it against the side of the stock house. A rod made with the slot running its entire length and termi- nating in a T, with two pieces of short pipe screwed into it to form a handle, is sometimes used to sample bins. The main trouble with this rod is that such a long slot weakens the sampler, and unless made of very heavy pipe it soon twists out of shape. Grain Samplers may also be used to sample bins but are seldom made long enough to reach to the bottom of the bins. Fig. I58 shows a sampler designed by Mr. Wm. P. Gano, Fig. 158.—Sampler Designed by Mr. W. P. Gano. chief chemist of the Pennsylvania Cement Company, and made by Riehlé Bros. Testing Machine Company. It consists of two brass tubes, Io feet long, one of which fits snugly into the other. The outside tube is 134 inches outside diameter. Two brass handles are pinned, one to each tube, and the outside tube is provided with a bronze point. The outside tube is No. 20 brass and the 36 550 PORTLAND CEMENT inside No. 16. Both tubes are provided with twenty-seven open- ings, 2% inches long by 9% inch wide. These slots are made at corresponding points in the two tubes. One edge of each slot in the outside tube is flared outward and provided with a cutting edge. A VA-inch brass set screw working in a slot shows when the openings are opposite. The sampler is thrust down into the cement with the inner tube turned so that the openings are closed. When the bottom of the bin is reached, the handles are turned so that the openings are opened and the tube is turned round a few times. The flared edges of the openings then scrape the cement into the tube. This sampler is one of the best for obtaining a sample from bins. Where cement can be sampled as it goes into the bin, as is done regularly by the manufacturer, some form of automatic sampler such as described on page 496 should be installed and no mill is complete which is not so equipped. Silo bins are usually sampled as they are filled, or after filling by drawing cement from the discharge openings. In doing the latter, a ball, or other indicator, is placed in the middle of the top of the bin and cement is drawn out at the bottom until the ball appears at the discharge. The cement drawn out is sampled at frequent intervals meanwhile. Uniform Specifications and Methods of Testing In order to bring about uniformity, both in the matter of in- spection and of the specifications under which cement is sold, committees have been appointed by various scientific societies, chief of which have been the American Society for Testing Ma- terials and the American Society of Civil Engineers. The latter society appointed a committee, Some forty years ago, to con- sider methods of testing cement and received its report in 1885. Later, another committee was appointed, which reported January 21, 1903. This report was amended at various times to keep it up to date and the methods of test recommended by it are now considered the standard ones. The American Society for Testing Materials turned its atten- tion to the drafting of a uniform set of specifications for cement, PHYSICAL TESTING 55I and its committee first reported, June 17, 1904. Since this time the report has been amended a number of times. The important amendments consisted in altering the requirements as to specific gravity and tensile strength. This set of specifications has been endorsed with subsequent revisions by The American Institute of Architects, The American Railway Engineering and Mainte- nance of Way Association, The Association of American Port- land Cement Manufacturers, and The American Society of Civil Engineers, and later when this was formed by the Engineering Standards Committee and hence may be considered the “Stand- ard Specification.” In the following sections under the heading “Specification” are given the requirements as defined by the above set of specifica- tions while under the heading, “Method of Operating the Test,” is given the method of testing recommended. Tests to be Made The qualities which are requisite for a good Portland cement are those which insure that concrete made from it shall be of sufficient strength to withstand any and all strains, stresses and shocks to which it may be submitted, not only when first made and allowed to harden, but after the lapse of many years. The tests now applied to cement all aim to search out these qualities, or show their absence, and may be classed under two general heads, i. e., those designed to show the strength of concrete made from the cement, and those designed to show its endurance. Under the first head come the tests for tensile strength, com- pressive strength, fineness to which the cement is ground, as this influences its sand-carrying capacity and hence its strength, and time or rate of setting, as quick-setting cement may not give sufficient time for proper manipulation of the concrete and slow- setting cement may take too long to get its strength. Under tests for endurance come the various so-called soundness tests, and possibly chemical analysis as the quantities of magnesia and of sulphur trioxide present are supposed to have an influence upon endurance. 552 PORTLAND CEMENT Ordinarily cement is tested as to its: (I) Soundness. (2) Time of setting. (3) Tensile strength with sand. (4) Fineness to which it has been ground. (5) Specific gravity. Other tests are those of compressive and transverse strength, adhesion, resistance to abrasion, etc. CHAPTER XX SPECIFIC GRAVITY Standard Specification and Method of Test Standard Specification for Specific Gravity The specific gravity of the cement, thoroughly dried at IOO9 C., shall be not less than 3. IO (3.07 for white Portland cement). Should the test of cement as received fall below this require- ment a second test may be made upon an ignited sample. The specific gravity test will not be made unless specifically ordered. Standard Method of Operating the Test 28. Apparatus.-The determination of specific gravity shall be made with a standardized Le Chatelier apparatus which conforms to the requirements illustrated in Fig. I59. This apparatus is standardized by the U. S. Bureau of Standards. Kerosene free from water, or benzine not lighter than 62° Baumé, shall be used in making this determination. 29. Method.—The flask shall be filled with either of these liquids to a point on the stem between zero and one cubic centi- meter, 64 grams of cement, of the same temperature as the liquid, shall be slowly introduced, taking care that the cement does not adhere to the inside of the flask above the liquid and to free the cement from air by rolling the flask in an inclined position. After all the cement is introduced, the level of the liquid will rise to some division of the graduated neck; the difference between read- ings is the volume displaced by 64 grams of the cement. The specific gravity shall then be obtained from the formula: -> ... Weight of cement (g.) Specific gravity = Displaced volume (cc.) 30. The flask, during the operation, shall be kept immersed in water, in order to avoid variations in the temperature of the liquid in the flask, which shall not exceed O.5° C. The results of re- peated tests should agree within O.O.I. 554 PORTLAND CEMENT 31. The determination of specific gravity shall be made on the cement as received; if it falls below 3. Io, a second determination shall be made after igniting the sample as described on page 434. * - sº m º ºs m. 5cm -------- k §:... * 3. | 13cm-2TS | {NSA; ---, `) (' § : f Y § : | ſ––––. : Ground Gas, .. | SS ; Jºopper-" # — — — — — : C!C § : +1 — — — º HT : : Hº : i = 6 cc ! E21 >% gºy § ! = 20°C (0 ; E. 20 º : E : : = 18 : Hall —–3. § * . SS rº) | º –––3 & % - § : (Z : | º: : —| — — —#- : Haye fivo CR/cc 2 ~ Š | 6radwańons erfema , YE- ſcrapa. y t above /a/7a' A E } & 9623C/ſy J. S be/ow 0/Mark -------AE aſ?'0 —º ! §§ | \––– º – Capac, s | : of Buſk s ! approx. | p 250cc ..., * No. A Š T 20°C § | ; : J º : : | N-- - * F --- - Hy- Y. | }<------------------ 8 cm -------->| | re------------ 9 cm -------------- -> Fig. I 59.—Le Chatelier’s Specific Gravity Bottle, Standard Form. SPECIFIC GRAVITY 5 5 5 Notes A convenient method for cleaning the apparatus is as follows: The flask is inverted over a large vessel, preferably a glass jar, and shaken vertically until the liquid starts to flow freely; it is then held still in a vertical position until empty; the remaining traces of cement can be removed in a similar manner by pouring into the flask a small quantity of clean liquid and repeating the operation. Kerosene will be found the most convenient liquid for use in taking the specific gravity of cement. It is cheap and may be easily obtained. To free it from water, place in a large bottle, together with some quicklime or a lump of calcium chloride and shake well. Allow the lime to settle, keep tightly corked and draw or pour off the oil carefully for use. It is most important to have the temperature of the liquid the same at the time the two readings are made hence the immersion of the flask in a cylinder of water. The importance of this will be understood when it is pointed out that a change of I* C. will effect the volume by O.22 cc. or a specific gravity reading by o.O35. A rise in temperature will make the observed specific gravity too low and vice versa. The flask should be allowed to remain in water for at least one-half hour before the first read- ing is taken and fifteen minutes before the second is made, checking the temperature of the water before each reading. The inside stem of the flask above the bulb should be wiped perfectly dry after the bulb is filled with kerosene by means of a swab of absorbent cotton on a wire, a thin roll of filter paper or a clean cloth. A convenient method of dropping the cement in the flask is to place the weighed sample of cement on a sheet of glazed paper across the middle of which a trough has been made by folding in the palm of the hand and gradually drawing the cement into the flask in small lots by means of a flattened wire. The latter may also be used to dislodge any cement which sticks to the neck of the flask, or the flask itself may be rapped on a piece of sheet cork or blotting paper on top the table for this pur- 556 PORTLAND CEMENT pose. This gentle rapping is also resorted to for the purpose of dislodging any air bubbles carried down by the cement. The old style Le Chatelier apparatus had only one graduation below the bulb and it was necessary therefore to fill the flask to exactly this point before introducing the cement. This may be most conveniently done by means of a pipette. The writer when employing the old style bottle usually filled the bottle to a little above the graduation below the bulb, and after allowing the flask to remain in the water bath for one-half hour, the ex- cess of kerosene was sucked off until the level reached the lower graduation on the stem by means of a piece of glass tubing drawn out to form a pipette. In order to protect the inside of the neck of the flask from wetting when withdrawing the pipette this was covered by means of a thin roll of filter paper inserted in the stem and reaching down to the bulb. The table following will be found useful in calculating the specific gravity. TABLE XLV-VALUES OF SPECIFIC GRAVITY IN TERMs of THE READ- INGs of THE LE CHATELIER APPARATUS, when USING 64 GRAMs of CEMENT. CC, O. O.O O.O2 O.O4 o.O6 o.O3 I9.50 3.282 3.279 3.275 3.272 3.269 o.60 3.265 3.262 3.258 3.255 3.252 O.7O 3.249 3.246 3.242 3.239 3.236 O.80 3.232 3.229 3.225 3.222 3.219 O.90 3.216 3.21.3 3.209 3.2O6 3.203 2O.OO 3.2OO 3. IQ7 3. I94 3. IQO 3.187 O. IO 3.184 3.181 3.178 3. I74 3. I7I O.2O 3.168 3. I65 3. I62 3. I59 3.156 O.30 3. I53 3. I50 3. I47 3. I43 3. I40 O.40 3. I37 3. I34 3. I31 3.I28 3. I25 O.5O 3. I22 3. II9 3.II6 3. II3 3. IIO o.60 3. IO7 3. IO4 3. IOI 3.098 3.095 O.7O 3.092 3.089 3.086 3.083 3.080 O.80 3.077 3.074 3.07I 3.068 3.065 O.90 3.063 3.059 3.056 3.054 3.05.I 2I.OO 3.048 3.045 3.042 3.O39 3.036 O.IO 3.033 3.030 3.027 3.025 3.022 O.2O 3.OI9 3.016 3.OI3 3.OII 3.008 O.30 3.005 3.002 3.OOO 2.997 2005 SPECIFIC GRAVITY 557 TABLE XLV.-VALUES OF SPECIFIC GRAVITY IN TERMS OF THE READ- INGS OF THE LE CHATELIER APPARATUS, when USING 64 GRAMs of CEMENT.—(Continued). Cc. O. OO O.O2 O.O4 o.oé o.O8 O.40 2.992 2.989 2.986 2.983 2.98o O.50 2.977 2.974 2.97I 2.969 2.966 O.60 2.963 2.960 2.957 2.955 2.952 O.70 2.949 2.946 2.944 2.942 2.939 O.80 2.936 2.933 2.930 2.928 2.925 O.90 2.922 2.919 2.917 2.914 2.912 All apparatus purchased for the determination of specific gravity should be tested as to the accuracy of the graduation by sending to the U. S. Bureau of Standards for this purpose. Or the maker may be made to furnish a certificate from the bureau as to the accuracy of the apparatus. We have frequently found apparatus which gave incorrect results owing to faulty gradu- ations. The older editions of this book give methods for check- ing the accuracy of the apparatus. ** Other Methods Other forms of apparatus which have been used for taking the specific gravity of cement are those of Schumann, Candlot and Jackson. These are all described in the preceding editions of this book. Their use has been superseded by the standard Le Chatelier apparatus described above. When this apparatus is not at hand the specific gravity of cement may be determined by the use of the ordinary pycnometer or specific gravity bottle by the following method: First weigh the bottle, empty, then fill the bottle with water and weigh. Then dry and fill with kerosene and weigh. Calcu- late the specific gravity of kerosene from the formula * = *-*. y w — p where a = specific gravity of kerosene, B = weight of bottle full of kerosene, W = weight of bottle full of water, and p = weight of the empty bottle. - Now introduce a weighed portion of the cement into the bottle, fill with kerosene, and weigh. The specific gravity of the cement may then be found by the formula 558 PORTLAND CEMENT x ==< *- B -- C — D. where B = weight of the bottle full of kerosene, C = weight of the cement. D = weight of the bottle and the cement and the kerosene, a = specific gravity of the kerosene as found above, and X = specific gravity of the cement. Turpentine or benzine may be used in place of kerosene. Observations on Specific Gravity Neither the French nor German specifications have any require- ments as to specific gravity. The English specifications place the minimum limit for fresh cement at 3.15 and for cement four weeks old at 3.IO. While a minimum specific gravity clause is a feature of many specifications for Portland cement, there is probably no test of less value or which taken by itself might lead to more faulty con- clusions. Originally in the Standard Specifications for cement under the heading “General Observations,” appeared the following para- graph: “Specific Gravity is useful in detecting adulteration and under- burning. The results of tests of specific gravity are not neces- sarily conclusive as an indication of the quality of a cement, but when in combination with the results of other tests may afford valuable indications.” Shortly after the publication of this report the writer began a series of experiments in connection with one of his assistants, Mr. L. C. Hawk, to determine the causes which tend to lower the specific gravity of Portland cement and the actual value of the test. The Committee on Technical Research of the Associa- tion of American Cement Manufacturers took up the subject and their two reports will be found in the proceedings of this associa- tion. Butler, an English chemist, also made experiments along the same line which he described in the proceedings of the Institute of Civil Engineers. SPECIFIC GRAVITY 559 Effect of Burning on Specific Gravity Naturally the first condition to receive attention by Meade and Hawk was the degree of burning. This was done in the following manner: A kiln was detected turning out under-burned clinker, and from this kiln twelve samples were drawn as the kiln was heated up to slightly above normal temperature. From these samples, four were selected as representing (I) very soft under- burned clinker, (2) slightly under-burned clinker, (3) normally burned clinker and (4) very hard burned clinker. These clinkers were then ground as rapidly as possible to pass a standard IOO- mesh sieve and the specific gravity at once taken. The need of haste was occasioned by the fact that under-burned clinker rapidly absorbs carbon dioxide and water from the air, which lowers its specific gravity. The specific gravity of the three samples was found to be : I. Very soft under-burned clinker . . . . . . . . 3.208 2. Slightly under-burned clinker . . . . . . . . . . 3.222 3. Normally burned clinker . . . . . . . . . . . . . . 3.214 4. Very hard burned clinker . . . . . . . ... . . . . . 3.234 The ground clinker was also mixed with 2 per cent plaster of Paris, and made into pats which were subjected to the steam test. At the end of two hours the pat made from the very soft under-burned clinker had entirely disintegrated. At the end of five hours the pat from the slightly under-burned clinker had be- come checked and partially disintegrated. The other two pats not only stood the steam test satisfactorily, but five hours longer in boiling water had no effect upon them. Thus we see that al- though the difference in specific gravity is only O.O26, the degree of burning in the four samples was markedly different. The author has frequently taken the specific gravity of under- burned clinker and in no case has he ever found it below that of the standard specifications. The experiments made by the members of the Association of American Cement Manufacturers conducted at six different mills, gave an average of 3.14 for the specific gravity of the under- burned cements and 3.18 for that of the hard burned ones. 560 PORTLAND CEMENT Effect of Adulteration on the Specific Gravity The effect of adulteration can of course be calculated accu- rately. The substances most available for adulteration of Portland cements in this country are natural cement, raw material or limestone and slag. Rosendale or natural cement has probably been used more than any of the others. Its specific gravity ranges between 2.8 and 3.1. In detecting a mixture of Rosen- dale cement and Portland cement the value of the test will de- pend entirely upon the specific gravity of the Rosendale. In the case of a natural cement with a specific gravity of 2.9 it would, of course, be possible to mix as much as one part Rosen- dale to two parts Portland, while with natural cements of higher density more Rosendale could be used. The raw material or cement-rock of the Lehigh district has a specific gravity of about 2.7, hence very little of it could be used without lowering the specific gravity appreciably. Its dark color would also cause its presence to be suspected and chemical analysis would readily detect it. Limestones average in specific gravity about 2.8, so that only about 20 per cent of the mix- ture could be used without lowering the specific gravity be- low that called for by the standard specifications. In the case of blast furnace slag, the density of which is somewhere around 3.0 large quantities could be used without detection by the specific gravity test. The writers recently had a sample of basic slag containing 36 per cent silica, of which the specific gravity was 3.05. A mixture of one part of this slag and one part of Portland had a density of 3.12. It would seem therefore that while the test would be of value in detecting additions of limestone or cement-rock, it is by no means an infallible one or even a reliable one for detecting ad- mixture of Rosendale or slag. Effect of Seasoning Cement or Clinker on Specific Gravity It has long been known that the storage of cement causes a lowering of its specific gravity. This is easily explained by the fact that cements on exposure to air absorb carbon dioxide and SPECIFIC GRAVITY 56I water, forming calcium carbonate and calcium hydroxide. The former has a density of 2.7O and the latter of 2.08. The effect of storage on cement is shown by the following: TABLE XLVI.-EFFECT OF SEASONING ON SPECIFIC GRAVITY OF CEMENT. Specific gravity Sample No. . . * * * * * s = e tº a g º e I 2 3 4 5 When made 3. IQ 3.2 I 3.16 3. I5 3.2O After 28 days, undried 3. II 3. I2 3. IO 3.09 3.08 After 28 days, dried at IOO’ C. 3.16 3.18 3. I4 3. I2 3. I4 After 6 months, undried 3.08 3.O4. 3.08 3.03 3.O4 After 6 months, dried at 100° C. 3. I3 3.09 3. I2 3.09 3.09 After 6 months, ignited 3.18 3.21 3.18 3. I5 3. I9 Reference to the above table shows that samples 2, 4 and 5 would have failed to come up to the standard specific gravity Specifications after six months, and yet, briquettes made of the samples at the same time the specific gravity determinations were made, showed the cement to be at its best, after storage for that length of time. A sample of cement had a specific gravity of 3.21 when fresh and after lying in a warehouse three years had a specific gravity of only 3.02. Its properties at the end of that period were ex- cellent and the only noticeable change in its condition was that it was slightly caked. It is now generally conceded that the seasoning of cement is an advantage, and many tests by various operators show that cement gives its best strength after a storage of from three to six months. Yet it is probable that cement which has been stored this length of time will have a specific gravity of less than 3. Io. If the cement does not absorb some carbon dioxide and water no benefits will be derived from seasoning, and if it does absorb them the specific gravity is bound to be lowered thereby. The absorption of 3 per cent carbon dioxide and water is sufficient to lower the specific gravity of cement below 3.I.O. An under-burned cement which failed when freshly made to stand a five hours’ steam test without complete disintegration had 562 PORTLAND CEMENT a specific gravity of 3.185. After being seasoned one month it stood five hours' steam and boiling tests perfectly, but its specific gravity had fallen to only 3,082. Similarly it has been found that seasoned clinker made a cement of lower specific gravity than would have been the case if the clinker had been ground fresh from the kilns. Other- wise the cement is excellent. For example, a sample of clinker fresh from the coolers gave a specific gravity of 3.18; after be- ing exposed out of doors for one month the specific gravity fell to 3.04, and after two months’ exposure to 2.96. The cement made from the exposed clinker had neat strength of 677 pounds at the end of seven days and 765 pounds at the end of twenty- eight days, and a sand strength of 330 pounds in Seven days and 394 pounds in twenty-eight days. It will be seen therefore that seasoning or storage of the cement has a much greater effect upon the specific gravity than under-burning or adulteration. Specific Gravity Upon Dried and Ignited Samples If a sample which has been kept for some time is dried at IOO9 C., its specific gravity will be found to be higher than it was in the undried condition, (Refer to Table XLVI), but still not as high as when it was freshly made. If this sample is subjected to a strong ignition in a platinum crucible over a good blast lamp, its specific gravity will still further increase and may even be more than the original specific gravity of the freshly made ce- ment. The new specifications propose in cases where the specific gravity of cement falls below the limit prescribed by the specifica- tions that the samples should be ignited and the specific gravity of the ignited sample taken. We have made a large number of de- terminations of specific gravity upon seasoned cements from which we find that practically all samples of cement when ignited give a specific gravity of between 3. I5 and 3.22 and that most of them give around 3.20. This conclusion was also reached by the Committee on Technical Research of the Association of American Portland Cement Manufacturers, and by Butler. SPECIFIC GRAVITY 563 Upon igniting a mixture of 40 per cent Rosendale and 60 per cent Portland cement having a specific gravity of 2.985 be- fore ignition we were surprised to obtain a specific gravity of 3.2O. This result was checked with practically the same result. A mixture of 40 per cent cement-rock and 60 per cent Portland cement which had a specific gravity of 2.95, gave after ignition 3.2O. This would prove that the ignition of the cement and de- termination of the specific gravity of the ignited sample fails to give any indication of adulteration even where this has taken place to a considerable extent. A former requirement, that cement which falls below a specific gravity of 3.IO shall also not show more than 4 per cent loss on ignition, will serve to detect additions of limestone but will not of slag or Rosendale cement, since these substances themselves show very small loss on ignition. Seasoning will also cause high loss on ignition and a well-seasoned cement or one made from seasoned clinker might easily show a loss on ignition of more than 4 per cent. If this loss on ignition is a good part of it water, the inspector may safely conclude that no adulteration has been practiced. In conclusion it may be said that the specific gravity determina- tion is of little value in determining whether cement has been under-burned or not. The experienced cement chemist at the mill can see at a glance by looking at the clinker if it is under- burned, and the engineer or inspector can judge better by the test for soundness. It is also for the reasons given above, no indication of adulteration. If, however, the specific gravity of a cement is low, it is well to examine it a little more closely, to see if it is adulterated, by the methods outlined in Chapter XXV, on “Detection of Adulteration.” Manufacturing Conditions Affecting Specific Gravity The above paragraphs will indicate fairly well the conditions met with in manufacturing which are likely to make a cement fail to meet the specific gravity test. The percentage of iron in the cement has a slight influence on specific gravity—the effect of a high percentage of iron being to raise the specific gravity. 564 PORTLAND CEMENT Low specific gravity, except in the case of white cements, how- ever, is not apt to be due to a low iron content in the cement. The respective percentages of the other elements seem to have little influence on the specific gravity of cement within the limits usually met with in standard Portland cement. Where the specific gravity of cement is low this is most likely to be the result of seasoning of either the cement or the clinker before grinding and the remedy in this case is obvious. Where water is sprayed on the clinker, or the latter is “seasoned” out of doors, sufficient hydration may take place to cause the resulting cement to fall below the specifications when tested as received. It ignited, however, the cement should pass the test satisfactorily. CHAPTER XXI FINENESS Standard Specification and Method of Test Specification.—The residue on a standard No. 200 sieve shall not exceed 22 per cent by weight. - 32. Apparatus. Method of Operating the Test.—Wire cloth for standard sieves for cement shall be woven (not twilled) from brass, bronze, or other suitable wire, and mounted without distortion on frames not less than 1% inches below the top of the frame. The sieve frames shall be circular, approximately 8 inches in diameter, and may be provided with a pan and cover. 33. A standard No. 200 sieve is one having nominally an O.OO29-inch opening and 200 wires per inch standardized by the U. S. Bureau of Standards, and conforming to the following re- quirements: The No. 200 sieve should have 200 wires per inch, and the number of wires in any whole inch shall not be outside the limits of 192 to 208. No opening between adjacent parallel wires shall be more than O.OO5o inch in width. The diameter of the wire should be O.OO2I inch and the average diameter shall not be out- side the limits O.OO19 to O.OO23 inch. The value of the sieve as determined by sieving tests made in conformity with the stand- ard specifications for these tests on a standardized cement which gives a residue of 25 to 20 per cent on the No. 200 sieve, or on other similarly graded material, shall not show a variation of more than 1.5 per cent above or below the standards maintained at the Bureau of Standards. 34. Method.—The test shall be made with 50 grams of cement. The sieve shall be thoroughly clean and dry. The cement shall be placed on the No. 200 sieve, with pan and cover attached, if desired. The sieve shall be held in one hand in a slightly inclined position so that the sample will be well distributed over the sieve, at the same time gently striking the side about one hundred and fifty times per minute against the palm of the other hand on the up stroke. The sieve shall be turned every twenty-five strokes 37 566 PORTLAND CEMENT about one-sixth of a revolution in the same direction. The oper- ation shall continue until not more than O.O5 gram passes through in one minute of continuous sieving. The fineness shall be de- termined from the weight of the residue on the sieve expressed as a percentage of the weight of the original sample. 35. Mechanical sieving devices may be used, but the cement shall not be rejected if it meets the fineness requirement when tested by the hand method described in Section 34. Notes Foreign Specifications for Fineness The English, German and French specifications all call for fineness tests to be made on sieves having 900 to 4,900 meshes per square centimeter respectively. The former is equivalent to 76 meshes to the linear inch and the latter to 180 meshes to the linear inch. The diameter of the wire used in the former is o.OO2 inch and in the latter O.OO44 inch. This makes the open- ings in the English 18O-mesh sieve O.OO36 inch square while in the U. S. Standard 200-mesh sieve they are O.OO29 inch square. The requirements of the three foreign specifications referred to are as follows: Highest residue on sieve _900-mesh 4900-mesh % % England 3 I8 France IO 3O Germany 5 *=º All of the above three specifications call for the test to be made on IOO grams. Errors in Sieves In purchasing sieves for making the fineness test, care must be exercised to see that they are within the limits prescribed by the standard rules, for there are many So-called standard sieves on the market which are anything but standard. I have seen a No. IOO test sieve bearing the name of a well-known firm, which FINENESS 567 makes a specialty of supplying apparatus for cement testing, that was made of wire cloth containing, to the linear inch, 90 meshes one way by 93 the other. Not only may standard sieves not contain the proper number of meshes but the wire from which the cloth is woven may be larger or smaller than the size called for in the standard method. This will reduce or increase, as the case may be, the size of the openings of the sieve. Not only may the sieves vary from the standard by reason of incor- rect mesh, but also by reason of irregular spacing. That is, the wires may be nearer together in some places than in others, leaving large openings at the latter points for the cement to drop through. On purchasing sieves they should be examined as to the regu- larity of the spacing by holding them to the light and also the number of meshes to the inch should be counted. For this latter purpose, small magnifying glasses such as are used for testing linen are convenient. These consist of a small lens, mounted on Fig. 160.-Scale for fineness determination. a stand, in the base of which is an opening exactly one-half inch square. The opening is placed over various parts of the sieve and the number of meshes counted. Where such an instrument is not at hand, an opening of this size may be cut in a piece of card- board and the meshes counted by the aid of a small reading or pocket magnifying glass. Sieves may also be calibrated by com- 568 PORTLAND CEMENT paring them with other sieves of known value. Or a sample of standard ground quartz may be kept for this purpose. Any holes or irregularities in test sieves should be stopped up with solder. A convenient balance for use in making sieve tests is shown in Fig. 160. The beam is graduated into I/IOOO of a pound, hence if one-tenth pound (= about 45 grams) is taken for the test each of the small divisions on the beam will represent O. I per cent residue. Other Methods Methods of Sieving, Sieves, Etc. Where many sievings have to be made every day, the use of a sieve without top and bottom is the general plan. In this case the sieving is done over a large piece of paper or oilcloth. When it is desired to ascertain if the operation has been completed, the material on the paper is rolled to one side by lifting the edge of the paper, thus exposing a clean surface over which the sifting may be continued and the amount passing through the sieve ob- served. An experienced operator will be able to tell, by his eye and sense of time, when the operation is finished, without re- course to balance and weights. In place of striking the sieve against the palm of the hand some operators bounce one side of it, gently up and down, on a small block of wood, taking care not to bounce any of the material over the top of the sieve. The use of shot also greatly hastens the operation of sieving, as the bounc- ing of these latter, on the wire cloth of the screen, keeps the meshes of the latter open. To separate the shot from the coarse material preparatory to weighing the latter, pass the mixture through a IO- or 20-mesh screen. When tests are made by using sieves without a top the sides of these should be high in order to avoid bouncing the material out of the apparatus. If the sieving is done by bouncing the sieve up and down on a block the sides of the sieve should be at least six inches high. FINENESS 569 It is important that the sieve be rotated as indicated during sieving. Griesenauer found that the results of the test are ma- terially affected by the position of the warp and the shoot wires with reference to the motion of the sample across the wires. With the same standard sieve he found a difference of 1.38 per cent between the tests made with the sieve in the two positions. Various forms of mechanical shakers for doing away with the manual labor incident to hand sieving have been devised and are quite generally used in spite of the fact that the hand method is specified by the standard methods of testing. One of the best forms of mechanical shaking sieves is that shown in Fig. 161. This apparatus is manufactured by the W. S. Tyler Company, Cleveland, O., and is known as the “Ro-tap Testing Sieve Shaker.” This machine operates as its Fig. 161.--Tyler Ro-tap testing sieve shaker. name indicates so as to give the sieve the same circular and tapping motion given testing sieves in hand sieving. The results are comparable with careful hand sieving and are better than can be obtained with any but the most conscientious operators. A 57O PORTLAND CEMENT sieve test with this machine requires 20 minutes. The machine will hold six sieves of regulation height or three sieves with pan attached making it passible to test three samples at once, or one sample through six different size sieves. Determining the Flour in Cement A number of devices have been proposed for determining the flour in cement. The chief difficulty with them all seems to be standardization. Each one will give a different result from the other, as we would suppose, for there is no specification as to what is meant by flour, and each apparatus takes out a size differ- ent from the other. Practically all of these forms of apparatus depend upon the suspension of the finer particles of the cement in air, benzene, kerosene, water, etc. A number of them were described in The Engineering Record of August 20, 1904, page 234. As we have said, the difficulty with all of them is that each would report a different percentage of the cement as flour. Even if they were so calibrated as to give concordant results, these figures would mean nothing more than the sieve test carried a little further. We do not know how fine cement has to be ground in order to “carry sand,” although we know that it must be ground con- siderably finer than merely sufficient for it to just pass the 200- mesh sieve. For experimental purposes it is highly important to obtain some form of apparatus which will enable the finer particles of the cement to be sorted out and graded, in order that the point of fineness at which the sand carrying capacity begins to approach that of ordinary commercial cements may be deter- mined. Such an apparatus, after this point has been determined, would have a practical value, because of two cements the one having the greatest percentage of such “active” particles would be the best ground. The Germans now employ a sieve having 250 meshes to the inch as a standard in place of the No. 200 American standard. Messrs. J. Gantois et Cie of St. Die, France (Ebstein Bros., 60 Grant St., New York) advertise a 3OO-mesh sieve. Both of these sieves will be found of use in studying the fineness of FIN ENESS 57I cement. Neither of them however is fine enough to pass only active material and reject all coarse or inactive particles and for this latter recourse must be had to one of the suspension methods given below. Something may be gained by determining the fine- ness on the No. 100, No. 200 and No. 250 sieves and plotting the results into a curve of which one set of ordinates represents the percentage of material passing and the other the area of the openings of the screens. Suspension Method The form of apparatus devised by the author for determining the flour in cement by suspension in a liquid is modeled after Fig. 162.—Apparatus for determining flour in cement 3 oo by suspension in liquid. 572 PORTLAND CEMENT the silt cylinders used for soil analysis. Fig. 162 shows the apparatus. It consists of a cylinder of at least 300 millimeters height and not too great diameter provided with a cork or stopper for closing it and a siphon for drawing off the liquid and suspended matter. The lower end of the siphon is closed by a rubber tube and pinch-cock and the upper one is bent as shown. Strips of paper or file marks are made on the cylinder, one near the top and the other exactly 200 millimeters below this one. In use, IOO grams of cement are introduced into the cylinder and the latter filled with kerosene freed from water (as described on page 555 under specific gravity) to the upper mark and shaken well. It is then placed on a block, the siphon, which should be full of kerosene inserted until its opening is level with the lower mark, and exactly ten seconds after the cylinder was placed on the block the pinch-cock is to be opened and the liquid siphoned off to the lower mark. This process is repeated until the liquid above the lower mark settles practically clear in ten seconds. The residue in the cylinder, or else the suspended matter, is then col- lected on a filter and its weight determined. From this the per- centage of flour is calculated and reported as “particles having a settling value in kerosene of less than 20 millimeters per second.” These can be again divided into two portions, by allowing fifteen seconds to settle, when the value will be 200--15 or I3% milli- meters per second, etc. If desired, the size of the largest of these particles can then be measured under the microscope. - The Griffin-Goreham Flourometer The Griffin-Goreham standard flourometer is shown in Fig. 163 and is used to some extent in England. The Braun Appa- ratus Company, Los Angeles, Cal., are the American importers. This apparatus consists of two parts. An aerometer or blower and the apparatus proper or flourometer. The blower consists of the customary bell and water tank and is merely used to furnish a constant supply of air to the apparatus. The flourometer itself (Fig. 164) consists of a long brass tube, T resting upon a stand. FINENESS 573 The separation of the coarse and fine particles takes place in this. The tube is surmounted by a double walled dome, W, covered with a top, O. The walls of this dome are perforated Fig. 163.-Griffin-Goreham flourometer. and the spaces in between them (W) are filled with cotton. This serves to catch all the dust and prevents this being blown into the laboratory. The lower part of the brass tube, T, terminates in a cone-shaped brass casting, F, which rests upon the stand. A three-way stop-cock provided with a pointer to show the direction of the opening, is placed at the lower end of the cone and beneath this a glass tube R, which serves to catch the coarse particles. The sample of cement should be dried for an hour at 11oº. The pointer of the stop-cock should be at right angles to the brass tube T. The tube T is removed and about one gram of the cement is then introduced into the funnel F. The bell of the 574. PORTLAND CEMENT aerometer is now raised to its full extent and the air pressure noted. - The pointer of the stop-cock is next turned parallel with the tube and the air allowed to blow through the apparatus for ten minutes. At the end of this time the air pressure is turned off, when the coarse particles from which the cement has been sepa- © G Fig. 164.—Details of the Griffin- Goreham flourometer. rated drop into the receptacle R. This residue is weighed and the difference is of course flour. Any blower which will furnish air at a steady and standard pressure may be used in place of the aerometer described. Two large cans set at constant vertical distances apart, such as one on the table and one on the floor, for instance, will serve, the upper one being filled with water which flows into the lower, forcing out the air in the latter. The objection to all these water blowers is of course the fact that the air is more or less FINENESS 575 damp. Best results will be obtained by passing the air through a rather large drying tower filled with calcium chloride or better still pumice stone drenched with strong sulphuric acid. The Pierson Air Analyser This apparatus has been considerably improved by the U. S. Bureau of Standards. Figure 165 represents the Bureau of Standards old type air analyser." According to correspondence between the author and the head, the Bureau is developing a new type of apparatus but is not as this book goes to press ready to give out information as to this. Referring to Fig. 165, I is a reostat in series with the motor armiture affording speed control, 2 is a % horsepower motor, 3 is a blower with a rated capacity of I2 cu. ft. per minute at 4 lbs. pressure, 4 is a grease trap, 5 is an automatic pressure regu- lator, 6 is a mercury gauge for indicating the pressure of the air delivered to the analysis. 7 is a detachable glass bulb provided with a set of three interchangeable nozzles which afford separa- tion of the cement into portions corresponding to 350, 500 and IOOO mesh sieves respectively. 8 Separating stack, 9 supporting tripod, Io electric tapper to minimize adherence of dust to sep- arating stack, I I dust collector consisting of a flannel sack which when the apparatus is in use is drawn up over the frame. The sieve relations are based on two dimensional microscopic measurements of cement particles. The relative sizes of the sep- aration of the standard No. 200 sieve and the air analyses by this system of measurements are as follows: No. 200 sieve O. II min. No. 350 sieve (air analyses) o.O6 mm. No. 500 sieve O.O4 mm. No. IOOO sieve - O.O2 IT1111. This method of designating the air analyser separations in terms of sieve mesh is for comparative purposes only as such fine sieves cannot be constructed. I have found such apparatus in general more satisfactory than the Gary-Lindner apparatus described below. On the other hand * U. S. Patent No. 1, 186,525 to J. G. Pearson. Also Bureau of Standards Tech- nologic Paper No. 48. 576 PORTLAND CEMENT the Gary-Lindner apparatus is of course suitable for collecting a quantity of flour of various degrees of fineness and testing this Fig. 165.-The Pearson Air Analyses of the U. S. Bureau of Standards. with sand for strength. At the present time no very satisfactory apparatus is at hand and no one of the three methods given FINENESS 577 can be said to give entirely satisfactory results. Some idea, how- ever, can be formed as to the relative amount of flour by studying various cements under exactly the same conditions, and the writer has employed them to advantage in studying the various types of grinding machinery with reference to the relative amount of flour produced by these latter. The Gary-Lindner Apparatus The apparatus (Fig. 166) consists of three glass tubes, a, the lower ends of which are united by pieces of large rubber tubing to three glass funnels into which small glass tubes have been melted. Through these small tubes air is supplied. The cement Fig. 166.—The Gary-Lindner apparatus for flour. must be first dried perfectly. Twenty grams of the cement to be tested are placed in the funnel I, then air is blown in at a pressure of IOO millimeter water column. The glass cocks permit the ad- justment of the air supply to each funnel; the pressure is noted 578 PORTLAND CEMENT on the U-manometer. The funnels I, II, III will enter into oper- ation one after the other and at the end there will remain a quantity of powder in each of the funnels. The finest flour will pass out of the glass tube III and will be arrested in the glass receptacle, IV. If the air pressure is produced by a hydraulic blower, the air must be dried before entering the funnels, as de- scribed above. Observations on Fineness Effect of Fineness on the Properties of Portland Cement The effect of the fineness to which Portland cement clinker is ground upon the physical properties of the resulting cement is well understood as the following quotation from the Progress Report of the American Society of Civil Engineers will show : “18. Significance. It is generally accepted that the coarser particles in cement are practically inert, and it is only the ex- tremely fine powder that possesses adhesive or cementing quali- ties. The more finely cement is pulverized, all other conditions being the same, the more sand it will carry and produce a mortar of a given strength.” The two properties of cement most affected by the fineness of the product are the setting time and the sand carrying capac- ity. All the properties of the cement are of course influenced to some degree. Influence on Color The color of clinker itself is practically black. As the clinker is ground the color becomes lighter, until at a fineness of 75 per cent passing the No. 200 test sieve, the color of the commercial product, a light buff, is reached. Cement ground so fine that 95 or Ioo per cent of it will pass the No. 200 test sieve is of a somewhat lighter shade than cement ground to the ordinary fineness of 75 per cent passing this sieve. At the same time, no manufacturer would care to go to the increased expense of grinding the cement to such an extreme degree of fineness merely for the sake of a slightly lighter color, nor would even FIN ENESS 579 sidewalk and concrete block men care to pay the increased cost of such cement simply to obtain cement of a slightly lighter shade. Influence on Soundness Fine grinding will to some extent help the soundness of the cement. This is shown by Table XLVII. This gives four instances in which soundness was helped by fine grinding, but in order to obtain four instances many samples of unsound cement were ground, and the majority of them failed to become sound even after being ground to an impalpable pow- der. Fine grinding and seasoning, however, usually produced the desired results. That is, an unground cement after season- ing, say one week, failed to pass the boiling test, but the same cement ground so fine that none of it remained on the No. 200 test sieve passed the test after seasoning one week. The grind- ing no doubt here breaks up the small pieces of clinker and allows the air to slake out the injurious component. In this connection, it may be said, that if the coarse particles, i. e., those remaining on the No. 200 sieve, are separated from the cement and ground to a fineness of 75 per cent through the No. 200 sieve, the resulting product is usually unsound. It is also usually quick-setting, due to the fact that the sulphate nearly all passes into the fine powder. If I per cent of plaster of Paris is added to the powder, its setting time is normal but it is still un- sound. If the powder is then seasoned for a few days it be- comes sound. TABLE XLVII.-SHow ING EFFECT OF FINE GRINDING OF CEMENT on SOUNDNESS. Result of five hour steam test (A. S. C. E.) As received Ground to pass No. 200 sieve . Ground to an impalpable powder I Checked Sound . . . . . . 2 Checked Sound . . . . . . 3 Checked Slightly checked Sound 4 Checked Slightly checked Sound 580 PORTLAND CEMENT It would, however, be a waste of energy for the manufacturer to make a sound cement by grinding one unsound at ordinary fineness to say IOO per cent passing a No. 200 test sieve, as by grinding the much softer raw materials to a fineness of only 95 to 98 per cent through the IOO-mesh sieve he would be practi- cally sure of obtaining the same results, provided the composition of the mixture and the burning of the clinker were satisfactory. At the same time, if the manufacturer found it advantageous to grind his cement to a fineness of 90 to 95 per cent through a No. 200 test sieve, he would find that it has some beneficial effect upon the soundness also, and that this effect was most marked where the cement had a chance to season or age as it usually does. Influence on Setting Time The influence of fineness upon the rate of set of cement is in some instances quite marked; in other instances this is much less noticeable. If any effect is produced at all, and there generally it, it is to make the cement quicker setting, in some instances, so quick-setting as to be unfit for use: and often, where this is the case, additions of plaster of Paris fail to retard the set suffi- ciently to allow the cement to be used. In Table XLVIII are given a number of instances illustrating the influence of fine grinding upon setting time. TABLE XXIX.-INFLUENCE OF FINE GRINDING OF CEMENT UPON ITS SETTING TIME. Per cent passing a No. 200 sieve. 75 8O 85 90 95 IOO Cement number Setting time (initial set) in minutes I 255 246 I92 75 I2 2 2 IO5 IO6 IOO IOO 22 6 3 I2O II5 IOO 95 6O 35 4 240 2OO I8O II5 60 30 5 24O 2IO I IO 55 I5 5 6 200 I90 I75 IOO 25 2 7 IOO IOO 90 8O 25 5 8 II5 IO5 IOO 75 30 IO The question of the influence of fine grinding upon the set is an important one, for upon this will depend to a large degree FINENESS 581 the ability to grind cement to the point where all of it is rendered useful, and where it contains no inert matter except that present chemically and not due to coarseness. The composition of the cement unquestionably has something to do with the effect of fine grinding. High-alumina and low-lime cements seem to have their setting time most affected by finer grinding. High lime, Soft-burned and low-alumina cements do not seem to be so much affected. Cements low in lime are often quick-setting, and if a sample of cement is sieved through a No. 200 test sieve and analyses are made of both the coarse residue and the fine portion passing, the former will in most cases be found lower in lime than the latter. It is natural that the softer portions of the clinker should consti- tute the greater part of the impalpable powder in ordinary Port- land cement. When the cement is ground still finer the harder portions are broken up, and these harder portions are probably responsible for the “quick set” of finely ground cement, owing to the fact that they are lower in lime and are burned to a high degree of vitrification. It is certainly possible, even probable, that if it is found advantageous to grind cement to a much greater degree of fineness than is now practiced, it will also be found necessary to grind the raw material to a higher degree of fine- ness, in order to allow the making of very highly basic cement, in which the highest possible amount of lime is obtained. If it is desirable to get rid of all the physically inert material by fine grinding of the clinker, it is also equally desirable to have in the cement all of the chemically active element possible. I am strongly inclined to believe that it will be possible to grind cement very fine without influencing the set unfavorably, by properly adjusting the composition of the clinker and the degree of burning. If the finer particles of cement, not merely the particles which pass a No. 200 sieve but the impalpable dust, are separated from the cement, it will usually be found that this very fine material sets normally, showing that it is possible to grind some part of the cement at least to an impalpable powder. It is also now generally agreed that it is this fine powder which is the active constituent in cement. Hence it follows that the 38 582 PORTLAND CEMENT active portion of cement is not quick-setting even when finely ground, and that there is some undesirable element in the coarser and at present inert particles of the cement which is liberated or rendered active by the grinding. The problem will there- fore undoubtedly be to keep out the undesirable element from the clinker and to increase the desirable one. I have no doubt that by the time grinding machinery has been perfected which will reduce cement to the fineness of IOO per cent through a No. 200 test sieve on a commercial basis, the chemical side of the ques- tion will have been solved. Indeed, experiments which I have made indicate a solution of the problem. Under present con- ditions it would be practically impossible to produce commercially a cement much finer than 90 per cent passing a No. 200 sieve, if indeed it would be possible to reach even this fineness, and at this nothing more than a slight shortening of the setting time of properly proportioned cements should be met with. The Structural Materials Laboratory, Chicago, found" that the normal consistency of cement is increased with the fineness of grinding and that about O. I per cent of water (in terms of the weight of cement) must be added for each I per cent re- duction in residue on the No. 200 sieve. Effect of Fineness upon Strength A number of experiments made by the author to determine the effect of finer grinding upon the tensile strength of Portland cement proved the following general facts. I. That the neat strength is lowered by finer grinding. 2. That the sand strength is increased by finer grinding. Table XLIX gives the results obtained in one of the most care- fully made of these tests. Referring to Table XLIX we see that the neat strength is de- creased by fine grinding. This decrease is as follows: Grind- ing to 85 per cent fine decreases the seven-day neat tensile strength 17 per cent from the figures of the 80 per cent fine. Grinding to 90 per cent fine decreases the strength 21 and 20 per cent respectively for the same periods. Grinding to 95 per 1 Bºul. No. 4, Structural Materials Laboratory. FIN ENESS 583 TABLE XLIX.—STRENGTH OF THE SAME CEMENT GROUND To VARIOUS DEGREES OF FINENEss. Per cent passing a No. Ioo sieve 93.9 95.8 97.4 99.0 | IOO.o Age in days Neat or sand Per cent passing a No. 200 sieve 8O 85 90 95 IOO Tensile strength in 1bs. per sq. in. I • - - - - - - - - - - - - - - - - - - - - - Neat 369 24I 308 || 282 200 7 . . . . . . . . . . . . . . . . . . . . . . Neat 955 || 796 || 749 || 627 | 558 28. . . . . . . . . . . . . . . . . . . . . . Neat 963 | 849 || 775 | 626 594 7 - - - - - - - - - - - - - - - - - - - - - - I : 3 sand 235 | 284 || 35I 363 382 28. . . . . . . . . . . . . . . . . . . . . . I : 3 sand 297 || 353 || 468 || 498 || 576 7 - - - - - - - - - - - - - - - - - - - - - - I : 4 sand I6O | 204 || 234 247 | 263 28. . . . . . . . . . . . . . . . . . . . . . I : 4 sand 224 266 324 377 392 NotE:—Each value is based on five briquettes. Each portion is from same lot of cement. One operator made all tests. cent fine decreases the strength 34 and 35 per cent and grind- ing to IOO per cent fine decreases it 42 and 38 per cent. In gen- eral it will be seen that the decrease in neat strength due to fine grinding is about the same for both the seven-day and the twenty- eight-day periods. Referring to the sand tests it will be seen at a glance that the increase in sand strength due to finer grinding is large. Increas- ing the fineness from 80 to 85 per cent, increases the seven-day I :3 sand strength 21 per cent; further grinding to 90 per cent increases it to 45 per cent; grinding to 95 per cent increases it to 54 per cent, while grinding to IOO per cent increases it to 63 per cent over the 80 per cent strength. The I:4 sand strength is increased by practically the same percentage. The increase upon the twenty-eight-day Sand tests due to finer grinding is even larger. In this series of tests the original cement gained but little neat strength between these two periods. Fine grinding will decrease not only the neat strength but also the percentage of gain between 584 PORTLAND CEMENT these two periods as well. An example of this is given below. In this experiment a lot of cement, just as received from the TABLE L.—SHOWING EFFECT OF FINER GRINDING ON LONG-TIME TESTs of CEMENT. Tensile Strength in Pounds per Square Inch. Néat I day 7 days 28 days 3 mos. 6 mos. I year 2 years As received 327 630 725 72O 760 825 850 Ground to pass a No. 200 sieve 2IO 525 540 540 560 575 560 I : 3 mortar I day 7 days 28 days 3 mos. 6 mos. I year 2 years As received tº º tº 278 357 387 390 4IO 425 Ground to pass a No. 200 sieve tº º º 48o 555 575 615 623 640 mills, was divided into two parts, one of which was tested just as it was and the other was ground to completely pass a No. 2OO sieve, and then tested. Table L, gives the results obtained On the two samples. Limitations of the Sieve Test The fineness to which cement is ground is an important point. Since cement is always used with sand, the strength of the mor- tar increases with the fineness of the cement, because the greater is the covering power of the cement, i. e., the more parts of cement come into action with the sand. A test for fineness is nearly always included in cement specifications, as the indications from a fair degree of fineness coupled with proper tensile strength are that the cement will give good results when used with sand. - At the same time the most rigid fineness specification could be filled by a cement which would be many degrees too coarse. Some of the older specifications could be easily filled by a product which would show almost no setting qualities and no sand-carrying ca- pacity. If a sample of clinker is crushed in an iron mortar by a pestle and sieved as fast as it is ground through a IOO-mesh FIN ENESS 585 screen, a product will be obtained IOO per cent of which will pass a IOO-mesh screen. Many of the older specifications call for only 90 per cent. If a pat is made of this cement it will just about cohere. If, however, the fine particles are sieved through a 200- mesh screen and the flour washed off the coarse particles by ben- zine and the latter driven off by heat, the product will still all pass a IOO-mesh sieve, and yet will have no setting properties. If another sample is ground in a mortar and sieved after every few strokes of the pestle through a 200-mesh screen, it will all pass a 2OO-mesh sieve and yet will nevertheless be almost worthless as a cement. When washed free from its flour with benzine it will just about hold together. In the writer's laboratory there was a Braun's gyratory muller for grinding samples, in which the grind- ing is done by an enclosed round pestle revolving in a semi-hemi- spherical mortar. In the bottom of the mortar is a hole which can be stopped by a plug. The grinding may be done in two ways, one by feeding the sample into the hopper in the cover and allow- ing it to work its way out at the bottom, then sieving out the fine material from the coarse, and returning the latter through the grinder, and so on until all has passed the sieve. The other, by placing the plug in the bottom of the mortar and allowing the pestle to work upon the material until the latter has reached the desired fineness. Two samples of cement were prepared from the same lot of clinker by these methods. One sample, the one made by passing the clinker through the muller and sieving out the 2OO-mesh particles after each grind, would, of course, all pass a 2OO-mesh sieve. The other sample, the one made by grinding the whole sample to the desired fineness without screening, tested 96 per cent through a IOO-mesh sieve and 76.5 per cent through a 2OO-mesh sieve. Sand briquettes were made of these two lots of cement with the following results. 7 days 28 days 3 months 6 months pounds pounds pounds pounds Samples made by grinding and Broke in Broke in Broke in screening to fineness (all 200-mesh) clips Clips Clips 28 Grinding to fineness without screening . . . . . . . . . . . . . . . . . . . . . . . 2 [5 295 324 3.18 586 PORTLAND CEMENT The cementing value of Portland cement depends upon the per- centage of those infinitesimal particles which we call flour. No sieve is fine enough to tell the quantity of these present. At the same mill it is probable that the sieve test is relative but to the engineer who is called upon to examine the product of many mills using different systems of grinding the sieve test, is hardly to be expected to give the relative percentage of flour in each. The product of the Griffin mill and of the ball and tube mill probably differ much in the percentage of flour present, even when testing the same degree of fineness on the 200-mesh sieve. Even with the ball and tube mill system one ball mill and two tube mills would probably give a product with a higher percentage of flour than one tube mill and two ball mills, even when the cement was ground to the same sieve test. The size screen on the ball mills probably also influences the percentage of flour in a product of a certain fineness. Effect of Fineness of the Cement on the Resulting Concrete The Structural Materials Laboratory, Chicago, has made a careful study of the effect of the fineness of cement on the prop- erties of concrete: Their conclusions follow. - In general, the strength of concrete increases with the fineness of a given lot of cement, for all mixes, consistencies, gradings of the aggregate, and ages of concrete. The cements with resi- dues lower than about 10 per cent were inclined to give erratic results in the strength tests; one lot showed an abnormal increase, and two a pronounced decrease in strength as compared with the other tests on coarser cements in the same lot. For residues higher than IO per cent the strength of concrete varies approximately inversely as the residue on the No. 200 sieve. Fine grinding of cement is more effective in increasing the strength of lean mixtures than rich ones. Fine grinding of cement is more effective in increasing the strength of concrete at seven days than at ages of twenty-eight days to one year. * Bull. No. 4, Structural Materials Laboratory. D. A. Abrams, Lewis Inst. FINENESS 587 For the usual range of consistencies the effect of fineness of cement is independent of the consistency of the concrete. The rate of increase in strength with fineness is lowered for very wet mixtures. –3322 `s D 4000 F- § § 3,500 | 1 *~ O § YS Jºy §§ || || 3220 S. § I S. § `s Sº S § \; Nº. S l § N ^ 3 & 2OOO § Š _/50o == T- ZOOO * f | H t + /O /2 /4 /6 /8 20 22 24 Azzezess, Mºeszo'oe C/7 A/? zoo. A/ 5/eve Fig. 167.-Effect of fineness of cement on COn Crete (From Prof. Abrams' test A-1). Ordinary concrete mixtures at twenty-eight days show an in- crease in strength of about 2 per cent for each I per cent re- 588 PORTLAND CEMENT duction in the residue of the cement on the No. 200 sieve. At Seven days, three months and one year the corresponding in- creases in strength are about 2.5, I.7 and I.4 per cent. The decreased benefit of fine grinding of cement with the age of the concrete does not bear out accepted opinion that the coarser particles of cement do not hydrate, but indicates that the principal result of finer grinding is to hasten the early harden- ing of the concrete. * For the richer mixtures and the consistency necessary for building construction, the fineness of the cement has no appreci- able effect on the workability of concrete as determined by the “slump” test. For leaner mixtures and wetter consistencies the finer cements showed a somewhat greater “slump” than the COa1‘Ser CementS. - The unit weight of cement decreases with fineness. For the cements used in these tests the weight varied from 76 (residue of 2.4 per cent) to IO8 pounds per cubic foot (residue 43.3 per cent). For the usual range in fineness the weight is lowered about three-fourth pound per cubic foot for each I per cent re- duction in the residue on the No. 200 sieve. Fig. 167 shows graphically the influence of finer grinding of cement on the strength of concrete and is taken from the above- mentioned bulletin. Effect of Manufacturing Conditions on Fineness Theoretically provided the cement mill is equipped with the proper grinding machinery it is within reasonable limits entirely a matter of choice with the manufacturer how fine the cement is to be ground. As the grinding of the clinker is one of the most expensive operations in the manufacture of cement, how- ever, this choice is generally influenced by considerations of economy. Poor equipment often makes the grinding of cement expensive and limits the manufacturer to a fineness approximat- ing too closely the lower limits of the specifications for the comfort of the chemist who is responsible for the quality of the product. In the chapters of this book devoted to “Grinding Ma- chinery” and “Grinding the Clinker,” the mechanical aspects of FIN ENESS 589 the problem are fully dealt with and to these the reader is re- ferred for a discussion of the proper machinery, etc., to be em- ployed in grinding clinker. The chemical composition of the clinker itself has an import- ant bearing on the facility with which it can be ground. A high percentage of iron in the clinker will make the latter very hard to grind and will increase materially the repairs on the mills used for grinding. It is quite probable that other things being equal the facility with which clinker can be ground increases as the iron oxide content decreases. On the other hand, clinker high in lime (or with a high lime ratio) is easier to grind than one low in lime. Attention to this has been called in the chapter on “Grinding the Clinker” and the matter discussed quite fully then. High silica cements are easier to grind than those high in alumina. This may be due, however, to the greater likelihood that the latter are burned to a higher degree of vitrifaction. The degree of burning of course influences the facility with which clinker can be ground, the harder burned material being naturally the more difficult to pulverize. The statement is also made that the clinker of the wet process is more easily ground than that from the dry. Hot clinker is harder to grind than that which is perfectly cold, as is also damp or wet clinker. Clinker which has been seasoned out of doors, or where moisture can reach it, is more easily ground than fresh clinker, provided it is not damp when fed to the grinding mills. CHAPTER XXII TIME OF SETTING Standard Specification and Method of Test 6. Specifications.—The cement shall not develop initial set in less than forty-five minutes when the Vicat needle is used or sixty minutes when the Gillmore needle is used. Final set shall be attained within ten hours. Normal Consistency 36. Miring Cement Pastes and Mortars.-The quality of dry material to be mixed at one time shall not exceed 1,000 grams nor be less than 500 grams. The proportions of cement, or cement and sand, shall be stated by weight in grams of the dry materials; the quantity of water shall be expressed in cubic centi- meters (I ce. Of water = I gram). The dry materials shall be weighed, placed upon a non-absorbent surface, thoroughly mixed dry if sand is used, and a crater formed in the center, into which the proper percentage of clean water shall be poured; the ma- terial on the outer edge shall be turned into the crater by the aid of a trowel. After an interval of one-half minute for the ab- Sorption of the water the operation shall be completed by con- tinuous, vigorous mixing, Squeezing and kneading with the hands for at least one minute." During the operation of mixing, the hands should be protected by rubber gloves. 37. The temperature of the room and the mixing water shall be maintained as nearly as practicable at 21° C. (70°F.). 38. Apparatus.-The Vicat apparatus consists of a frame A (Fig. 168) bearing a movable rod B, weighing 3OO grams, one end C being I centimeter in diameter for a distance of 6 centi- meters, the other having a removable needle D, I millimeter in * In order to secure uniformity in the results of tests for the time of setting and tensile strength, the manner of mixing above described should be carefully followed. At least one minute is necessary to obtain the desired plasticity which is not appreci- ably affected by continuing the mixing for several minutes. The exact time necessary is dependent upon the personal equation of the operator. The error in mixing should be on the side of overmixing. TIME OF SETTING 59 I diameter, 6 centimeters long. The rod is reversible, and can be held in any desired position by a screw E, and has midway be- tween the ends a mark F which moves under a scale (graduated to millimeters) attached to the frame A. The paste is held in ITTÜV （-ºil iſ Fig. 168.-Vicat apparatus for determining setting time and normal consistency. a conical, hard-rubber ring G, 7 centimeters in diameter at the base, 4 centimeters high, resting on a glass plate H about IO centimeters square. - 39. Method.—In making the determination, 500 grams of cement, with a measured quantity of water, shall be kneaded into a paste, as described in Section 36, and quickly formed into 592 PORTLAND CEMENT a ball with the hands, completing the operation by tossing it six times from one hand to the other, maintained about 6 inches apart; the ball resting in the palm of one hand shall be pressed into the larger end of the rubber ring held in the other hand, completely filling the ring with paste; the excess at the larger end shall then be removed by a single movement of the palm of the hand; the ring shall then be placed on its larger end on a glass plate and the excess paste at the smaller end sliced off at the top of the ring by a single oblique stroke of a trowel held at a slight angle with the top of the ring. During these operations care shall be taken not to compress the paste. The paste con- fined in the ring, resting on the plate, shall be placed under the rod, the larger end of which shall be brought in contact with the surface of the paste; the scale shall be then read, and the rod quickly released. The paste shall be of normal consistency when the rod settles to a point Io millimeters below the original surface in one-half minute after being released. The apparatus shall be free from all vibrations during the test. Trial pastes shall be made with varying percentages of water until the normal consistency is obtained. The amount of water required shall be expressed in percentage by weight of the dry cement. 40. The consistency of standard mortar shall depend on the amount of water required to produce a paste of normal con- sistency from the same sample of cement. Having determined the normal consistency of the sample, the consistency of stand- ard mortar made from the same sample shall be as indicated in Table LXIII,” the values being in percentage of the combined dry weights of the cement and standard sand. Determination of Time of Setting 45. The following are alternate methods, either of which may be used as ordered: 46. Vicat Apparatus.-The time of setting shall be determined with the Vicat apparatus described in Section 38. (See Fig. 168). 47. Vicat Method.—A paste of normal consistency shall be molded in the hard-rubber ring G as described in Section 39, and * See page 642 for table giving percentage of water for sand mortars. TIME OF SETTING 593 placed under the rod B, the smaller end of which shall then be carefully brought in contact with the surface of the paste, and the rod quickly released. The initial set shall be said to have occurred when the needle ceases to pass a point 5 millimeters above the glass plate in one-half minute after being released; and the final set, when the needle does not sink visibly into the paste. The test pieces shall be kept in moist air during the test. This may be accomplished by placing them on a rack over water contained in a pan and covered by a damp cloth, kept from con- tact with them by means of a wire screen; or they may be stored in a moist closet. Care shall be taken to keep the needle clean, as the collection of cement on the sides of the needle retards the penetration, while cement on the point may increase the pene- tration. The time of setting is affected not only by the percent- age and temperature of the water used and the amount of knead- ing the paste receives, but by the temperature and humidity of the air, and its determination is therefore only approximate. 48. Gillmore Needles.—The time of setting shall be deter- mined by the Gillmore needles. The Gillmore needles should pre- ferably be mounted as shown in Fig. 169. º | HRTI */IWS —I Fig. 170.--Test-piece for use with Gilmore needles. 4– I Tº | | Fig. 169.-Gilmore Needles for determining setting time. 49. Gillmore Method.—The time of setting shall be deter- mined as follows: A pat of neat cement paste about 3 inches in diameter and one-half inch in thickness with a flat top (Fig. 594 PORTLAND CEMENT I70), mixed to a normal consistency, shall be kept in moist air at a temperature maintained as nearly as practicable at 21° C. (70°F.). The cement shall be considered to have acquired its initial set when the pat will bear, without appreciable indenta- tion, the Gillmore needle one-twelfth inch in diameter, loaded to weigh one-fourth pound. The final set has been acquired when the pat will bear without appreciable indentation, the Gill- more needle one-twenty-fourth inch in diameter, loaded to weigh I pound. In making the test, the needles shall be held in a vertical position and applied lightly to the surface of the pat. Notes Foreign Specifications for Setting Time Both the English and German standard specifications call for the use of the Vicat needle. The German specifications pre- Scribe that “normal” Portland cement shall not receive its initial Set in less than one hour, and fix no period within which the final set shall take place. The English standard specifications divide cement into three grades, “Quick,” “Medium” and “Slow.” The requirements for the three are as follows:– “Quick,” initial Setting time not less than two minutes, final setting time not less than ten, nor more than thirty minutes; “Medium,” initial set- ting time not less than ten minutes, final setting time not less than thirty minutes nor more than two hours; “Slow,” initial set not less than twenty minutes, final setting time not less than two, nor more than seven hours. The French Specifications require the cement to have an initial set of not less than twenty minutes and a final set of not less than three hours for cement to be used in Sea-water or two hours for cement to be used in fresh-water, or more than twelve hours for both classes. The determination of the time of setting is only approximate, being materially affected by the temperature of the mixing water, the temperature and humidity of the air during the test, the per- centge of water used, and the amount of molding the paste re- CelVeS. TIME OF SETTING 595 The cheapest form of moist closet consists simply of a wooden box provided with a door and shelves and painted on the inside * * * * ** = <= ** * * * * * * * * * * * * = I i | ::::::::::------------J * * - - - - - - - - - - - - - - - | ;:---------------------> -: * - - - - - - - - - - - - - --— | | r:-------> -- - - - - - -1 - º | !-- - - - - - - - - - - - - - - | ſ | j-": : - - --~~~~~~~: il-3 t | g * * *m, º sº sº sº sº sº as sºme * * * * * * i t ! F-S" - tº---> --> --~~~~~! ! ſ * * Izº ..* * * * * ! F--. -* * - - - - - - ---, | t * - * - - - - - - - - - - -- | $ f ----------- +------ Fig. 171.-Cheap form of moist closet. with black asphaltum varnish or other good water-proof paint (see Fig. 171). In the bottom of this box should be placed a tin pan containing a sponge, and water should always be kept in this pan. The shelves should be removable and may be made of plate-glass or wood. The shelves should be so placed as to allow a free circulation of air through all parts of the closet. Instead of being painted the box may be lined with thin sheet Z111C. A common tin bread-box makes a very good moist closet where only a few pats and briquettes have to be tested. This is provided with a few cleats and a perforated tin shelf is made to fit into the box, and rests on these cleats. Water is poured into the bottom to a depth of a half inch and the test pieces are placed on the shelf. In order to prevent rusting, this box also should be painted inside with black asphalt varnish. In large laboratories moist closets made of Soapstone have been employed. Such a closet, used in the Municipal Labora- tories of the city of Philadelphia, is shown in Fig. 172. This closet is made of one and one-fourth inch soapstone (with the exception of the doors, which are made of wood covered with 596 PORTLAND CEMENT zinc) and is in two sections for the reason that it was found that as the height of the closet was excessive, the humidity varied considerably between top and bottom. On the sides of each closet are fastened cleats to hold the shelves, which are of glass or wood. Mr. Ernest B. McCready described in the Proceedings of the American Society for Testing Materials, Vol. VII, a moist closet - sº; | Fºsses º º C º º: º ji | † #gº; Hºff | gº : | ; º º | § #. º | | |li §i) | g | º sº * ºftº: º sº . #: º i |# º a.º. sº º º | ''. sºjº” Jº Fig. 172.-Moist closet of soapstone. made of cement which is employed in his laboratory. Such a closet can be constructed in any cement testing laboratory from waste cement, the forms being made by a local carpenter. A I to 2 sand mortar was used and the walls reinforced with one- half inch mesh galvanized wire netting. Other Methods The test proposed by General Gillmore, U. S. A., for determin- ing setting properties is the one most used in this country. (See Sections 48 and 49 of Standard Specifications). The Gillmore needles, or wires, are much more convenient to use where many samples have to be tested, as the pats themselves do not have to be lifted from the moist closet or table, in order to TIME OF SETTING 597 apply the needle. While the Vicat needle unquestionably is a much more Scientific instrument and should be used where great nicety is required in making the test, as in settling disputes, etc.; still for ordinary inspection work, where all that is needed is the assurance that the cement will not set before it is laid in position in the job, and that after it is so placed it will harden in a rea- sonable time, the simpler and less expensive Gillmore needles will answer the purpose just as well as the more expensive Vicat ap- paratus. The Gillmore needles are the ones generally used by both manufacturrs and engineers in determining the setting time of cement, and most of those called upon to test and use cement are familiar with the terms initial, and final set as defined by these needles. Setting time is influenced by so many things besides those over which the Vicat needle has control, that the personal equation is as much an element in determinations made with this apparatus as in those made with the Gillmore needles. The “ball” test for determining the proper consistency is much used in commercial laboratories, using the Gillmore needles to de- termine set, and in spite of its crudeness, gives results which agree fairly well with those determined by the Vicat apparatus. It consists in forming the mortar into a ball and dropping it from a height of one foot. This fall should not materially flatten nor crack the ball, the former denoting too much water in the mortar and the latter not enough. In most plant laboratories, and indeed in many testing labo- ratories where Gillmore's needles are used, it is the practice to test the setting time of cement upon a smaller batch of mortar than that prescribed by the standard rules. Often the same test piece which is employed for setting time is used to determine soundness also (see Chapter XXIII). This plan consists in weigh- ing out from 50 to IOO grams of cement. This is placed upon the mixing slab and a smaller crater is formed in the center of this. The water is next added in a measured amount. The cement is rolled into the crater and the mixture is worked back and forth with a trowel until the proper plasticity is Secured. The working usually takes from one to three minutes depending upon the operator and the quickness of his movements. The 39 598 PORTLAND CEMENT cement is then formed into a small cake which is placed on a small glass plate (about 4 by 4 inches) and flattened out with the trowel as shown in Fig. 173, so as to present a smooth surface to the needle. If the pat is also to be used for the steam test, it is drawn out to a thin edge as shown in Fig. 170. For this latter test the pat is allowed to stand in the moist closet, after (((( ))))) Fig. 17.3.−Test piece often employed for determining setting time. the setting time has been taken, until the next day, when it is boiled or steamed. Observations on Setting Time The rapidity with which cement sets furnishes us with no in- dication of its strength. The test is usually made to determine the fitness of the material for a given piece of work. For ex- ample, in most submarine work a quick-setting cement is desired, that is, a cement which loses its plasticity in less than half an hour, while for most purposes where sufficient time will be given the cement to harden before being brought into use, a slow-set- ting cement will usually answer better, or one that sets in an hour or more. The slow-setting cements can be mixed in larger quantities than the quick-setting ones, and do not have to be handled so quickly, so that for most purposes where permissible they are used. When cement sets hard a few minutes after the mortar is mixed it is said to have a “flash” set. Some cements are so quick setting that they even set up under the trowel and on working get dryer instead of more and more plastic. Factors Influencing the Rate of Setting The rate of set is determined by a number of things, chief of which are temperature and the percentage of water used in making the mortar:-The higher the temperature the quicker TIME OF SETTING 599 the set and the larger the percentage of water the slower the set. Temperature has a very marked influence, and many cements which are suitable for use in this country could not be used in the tropics. Similarly in the early spring and late fall when the temperature out of doors is from 20° to 30° F. below that indoors, cement which tests quick setting in the laboratory may give perfect satisfaction when used at the outside temperature. This influence is shown by the results given below: TABLE LI.-INFLUENCE OF TEMPERATURE ON THE RATE OF SETTING OF PORTLAND CEMENT. Sample No. I 2 3 4. Temp. o F.1 H M H M. H M H M Initial set 3 O 5 O 2 O 2 IO 35 Final set 8 O IO-H | . . 6 O 6 O Initial set I 5 3 O I I5 I 5 45 Final set 3 I5 7 3O 3 3O 3 I5 6o Initial set O 3O 2 3O O I5 O 3 Final set I IO 6 O I O O IO 8O Initial set O 4. 2 OO O 2 Final set O IO 5 3O O 5 Initial set O 45 IOO Final set 3. I O * Of room during setting time and of cement and of water used to gauge pats. The percentage of water used to gauge the pats, or in actual work to make the mortar, affects the setting time, as well as the early strength of the concrete, very greatly. A wet mixture sets very slowly, while a dry one sets much more promptly. In the manufacture of hollow building blocks, where the piece must be removed from the molds at once, only as Small a quantity of water as is actually needed to do the work is used, and the mix- ture of about the consistency of damp sand is rammed into the molds; while in some forms of concrete construction, the mor- tar is made decidedly plastic, and may be actually poured into the forms. It is then left several days to harden before the latter 6OO PORTLAND CEMENT are removed. Below are given some results on the effects of various percentages of water on the setting time of Portland Cennent : TABLE LII.—INFLUENCE OF VARIOUS PERCENTAGES OF WATER USED To GAUGE THE PATs on THE SETTING TIME OF PORTLAND CEMENT. Per. Sample No. I 2 3 4 cent- age of water IH. M. H M FH. M FI M Initial set O IO 2 IO O IO O 25 I4 Final set 2 45 6 O O 35 O 55 6 Initial set O 2O 2 2O O IO O 25 I Final set 3 5O 6 O O 35 I O S Initial set I 5 2 2O O IO tº e 35 I Final set 5 O 6 I5 O 35 I I5 Initial set 2 IO 2 4O O 8 I 25 2O Final set 6 2O 6 I5 O 3O 4 O Initial set 4. 2O 3 O O 5 2 I 5 22 Final set 8 O 6 5O O 3O 5 O 2 Initial set 5 I O 5 O O 2O 3 O 4 Final set I2–H 8 3O O 5O 6 IO Another factor which influences very greatly the rapidity of the set of cement is the humidity or the amount of water vapor contained in the air. It has been found that cement will al- ways set much more slowly in a moist closet than it will when left in the open air and for this reason test pieces upon which the setting time is to be made, should always be kept in a moist closet and should not be allowed to remain for more than a minute at any one time out of this. Rise in Temperature During Setting It was formerly the practice to determine the rise in tempera- ture during setting, any considerable increase being considered as indicative of free lime in the cement, the supposition being that the rise is caused by the heat formed by the hydration of TIME OF SETTING & 6OI the lime. No conclusion could be more erroneous. From the examination of many samples of Portland cement, every detail of whose manufacture was known, I am not afraid to say posi- tively, that the rise of temperature during setting is not only not indicative of free lime, but usually comes from the reverse, not enough lime. Those cements which show the greatest increase in temperature during the process of setting are usually the quick- setting cements. These cements usually are low in lime and burned very hard. Many samples of such cements show a rise of temperature distinctly perceptible to the hand, and yet boiling for many hours will fail to distintegrate the pat or warp or check it in any manner. In many instances, the addition of a small quantity (% per cent) of finely ground lime or I or 2 per cent of slaked lime will slow the setting of the cement and in this case no rise of temperature will be met with, showing that the pres- ence of free lime is not the cause of the rise in temperature during setting. On the other hand many samples which fail badly after even a few hours of the steam test, show no greater rise in temperature than the normal. When there is a consider- able rise in temperature during the setting of a slow-setting cement, something is probably wrong with the cement, but when the rise is met with, in connection with quick set, it is no evidence of free lime, and the conclusion that it is, is unwarranted by facts. In this connection, it is well to remark that practically all of the silicates and aluminates of lime met with in cement clinker give off heat when mixed with water and during the process of hydration. The tricalcium aluminate under this condition gives off so much heat that the mass actually boils. Influence of Sulphates on Setting Properties If Portland cement clinker is ground just as it comes from the coolers, without the addition of any foreign substance, the re- sulting cement is entirely too quick-setting to allow of its being properly worked. It is therefore the general practice to either grind a small percentage, usually 2 or 3 per cent of gypsum with the clinker or else to add to the cement just before it is shipped, a corresponding percentage of finely ground plaster of Paris, in 6O2 PORTLAND CEMENT order to regulate the set so as to give time for working, tamping and troweling. At some mills coarsely ground plaster of Paris or calcined plaster as the manufacturers call it, is added to the clinker before grinding. Le Chatelier made many experiments on the effect of the addi- tion of gypsum and plaster of Paris to Portland cement. He concluded that the governing action which it exercised over the cement was due to the formation of certain soluble compounds between the sulphuric acid of the calcium sulphate and the very active calcium aluminates of the cement which cause quick-set- ting. He also stated that either gypsum or plaster of Paris could be added to slow the set and that the addition could be made either before or after burning. Since, however, calcium sulphate is decomposed at temperatures decidedly below that at which Portland cement is burned there would be a decided disadvantage, owing to loss of SOs, in adding gypsum before burning. Indeed from experiments made by the writer if all the sulphur entering the kiln came out with the clinker as calcium sulphate there would be no need to add either gypsum or plaster of Paris. In spite of Le Chatelier's experiments, it has been a theory generally held in this country that gypsum would not retard the set of cement, but that the only form of sulphate of lime which would do this is plaster of Paris; and that where gypsum is ground in with the clinker, this is transformed into plaster of Paris, the heat generated during grinding being sufficient to drive off the water and make the change from CaSO4·2H2O to (CaSO,), H2O. It is true that in many cases the heat generated by the friction of the grinding machinery is sufficient to drive off the water, as the writer has frequently tested cement fresh from the tube mill and found it over 130° C., the temperature at which gypsum loses three-quarters of its water of crystallization. In- deed Shenstone and Cundall state that gypsum begins to lose its water of crystallization at 70° C. in dry air. To test these various contrary theories and statements the writer and his assistant, Mr. W. P. Gano, carried out the follow- ing experiments:* * Meade and Gano, Chemical Engineer, I, 2, p. 92. TIME OF SETTING 603 A sample of cement was prepared by grinding fresh normal clinker in the usual way without the addition of any retarder. To separate portions of this were added in different percentages finely ground— - (I) Plaster of Paris, (CaSO4)2.H2O, containing 53.18 per cent SOa. (2) Gypsum CaSO4·2H2O, containing 44.22 per cent SOs. (3) Dead burned gypsum, CaSO4, containing 55.21 per cent SOa. The results are given in the tables below: The first column shows the percentage of gypsum, etc., added to the cement. By percentage is not meant the percentage of gypsum in the mixture, but the percentage of the weight of cement of gypsum which is added. For instance, 2 per cent means 2 grams of gypsum added to IOO grams of cement, etc. The second column shows the percentage of water used for the pat, being the amount necessary to obtain a mortar of normal consistency, as determined by the ball test. The third column shows the “initial set” or the time necessary for the cement to harden sufficiently to bear the light Gillmore wire, one-twelfth inch in diameter, loaded with one-fourth pound. The fourth column shows the “final set” or the time necessary for the cement to harden sufficiently to bear the heavy Gillmore wire, one-twenty- fourth inch in diameter, loaded with one pound. TABLE LIII.—SHOWING THE EFFECT OF PLASTER OF PARIS ON THE SETTING TIME OF CEMENT. Percentage ºr ...º.º. Initial set Final set added make pats Hollrs Minutes Hours Minutes O 25 O 2 O 6 O.5 23 O 5 O IO I.O 23 O 50 4 O I.5 23 2 50 6 O 2.O 22 3 O 6 I5 3 22 I 45 5 2O 4 22 O 35 4 O 5 22 O I6 2 O IO 22 O I6 I 30 20 22 O 9 O 2O 6O4 - PORTLAND CEMENT TABLE LIV.—SHow ING THE EFFECT of GYPSUM ON THE SETTING TIME OF CEMENT. Percentage Percentage of of water itial * gypsum used to Initial set Final set added make pats Hours Minutes Hours Minutes I 23 O 2 O IO 2 23 2 40 5 50 3 22 2 5O 5 5O 5 22 3 I5 6 OO IO 22 3 O 5 40 20 22 3 2O 6 OO Referring to the tables it will be seen that there is little choice in the three forms of calcium sulphate so far as efficiency goes, all doing the work of retarding the set about equally well. This is to be expected. If the retardation is due to chemical action there is no reason why any one of the three forms should not be as efficient as the others, because they all have approximately the same solubility, that of I part in 400-500 parts of cold water. The solution of any of the four would merely be one of a mix- ture of two kinds of ions, CaO and SOa, and the SO, anions would be as free to react on the aluminates of lime if their source was gypsum as they would if they came from plaster of Paris. TABLE LV.—SHowING THE EFFECT OF DEAD BURNED GYPSUM ON THE SETTING TIME OF CEMENT. Percentage Percentage buria gyp- °. º Initial set Final set sum added make pats. Hours Minutes Hours Minutes I 23 O 6 O IO 2 23 I 45 5 IO 3 23 I 47 5 3O 5 23 2 O 5 3O IO 23 I 50 5 O 2O 23 2 2O 5 O It will be noticed, by reference to Table LIII, that 2 per cent plaster of Paris produced the maximum retardation of the set. Larger quantities than this had the effect of quickening the set of the cement. This maximum of course varies with different cements, but with all it will be found that there is a point beyond which additions of plaster will be attended with shortening instead of further lengthening the setting time of the Cement. TIME OF SETTING 605 As we have said many manufacturers prefer to add plaster of Paris to cement just before it is shipped. If it is properly mixed with the cement there are certainly points in favor of adding the sulphate here. We do not see, however, why finely ground gyp- sum would not do the work just as well, saving the cost of cal- cining. On the other hand if the gypsum is added to the clinker, it is sure to be finely ground and thoroughly disseminated throughout the cement, two things necessary with any form of sulphate, if it is to act as a retarder. There will be no danger of the gypsum failing to do its work, whether the temperature is low or high during grinding, because dehydration is not necessary. It must be remembered, however, that plaster of Paris contains more sulphuric acid than gypsum, 290 parts of the former being equivalent to 344 of the latter or a ratio of 87: IOO so that plaster of Paris weight for weight is the more effective of the two. Influence of Calcium Chloride on Setting Time Another substance which will retard the setting of cement is calcium chloride, though the writer has never heard of its being used in practice. Candlot made many experiments upon the effect of chloride of calcium on the setting of ground cement clinker. Below are some of his results: TABLE LVI.-INFLUENCE OF CALCIUM CHLORIDE ON THE SETTING TIME OF PORTLAND CEMENT. Solution of CaCl2 I 2 Gr. per liter h. m. h. m. h. m. h. m. 2 0.05 I.O5 8.00 I.34 5 o.O8 IO.OO I2.OO 2.OO IO 8. I8 IO.OO I4.OO 5.50 2O I.OO I2.OO IO.30 8.OO 4O 4.35 8.OO 6.30 8.35 6O 3.2O 6.00 4.00 6.co IOO O.O3 O.2O O.30 3.30 2OO O.O3 O.O.Q O.O5 O.25 3OO O.O2 O.08 O.03 O.05 Carpenter" also made some experiments on grinding the clinker and calcium chloride together. His results are given below and show that chloride of calcium has effect in retarding the time of setting and exerts the greatest effect when about one-half of I per cent by weight of the chloride of calcium is employed: 1 Sibley, Journal of Engineering (Cornell University), January, 1905. 606 PORTLAND CEMENT TABLE LVII.-INFLUENCE OF CaCl2 GROUND DRY witH THE CLINKER. Per cent Per Cellt Initial set Final set of CaCl2 of water minutes minutes O.O 29.8 II5 274 O.5 34. I I60 272 I.O 29.8 I67 234 I.5 26.4 I27 2I2 2.O 25.4 ge IO3 I8O 2.5 26.4 45 I82 3.0 26.4 97 185 3.5 26.4 63 I5O 4.5 28.6 73 I60 5.0 . 29.8 76 84 5.5 29.8 68 I45 6.o 29.8 Influence of Hydration Various authorities have at different times suggested the pos- sibility of retarding the set of cement by the use of water alone or with gypsum. Ware' states that in his experience he found that a certain lot of seasoned clinker also low in lime which under normal conditions gave quick-setting cement when ground either alone or with gypsum would give normal cement when ground under conditions which would permit of hydration. He found that it made little difference how the water was added. He tried the following methods all of which were successful. (I) The clinker was ground hot, the heat liberating the water from the gypsum. (2) Water was sprinkled on the cold clinker. (3) Steam was turned into the conveyor leading from the mills. The method finally adopted was to heat the clinker and grind while still hot with gypsum which had been thoroughly wetted. Ware also stated that in the laboratory quick-setting cement could often be made slow setting by simply dropping it through a 30-inch vertical tube through which a cloud of steam was rising. He also succeeded in making quick-setting cement normal by rapidly mixing by hand 3 per cent of water with the ground cement and then grinding in a laboratory pebble mill for a short time in order to further mix it. * Ware, Concrete-Cement Age, April, 1913. TIME OF SETTING 607 Bambier found he could slow the setting time of cement by passing Superheated steam into the tube mill by means of a pipe inserted through the head. The writer has had some ex- perience with this method as it was tried at one mill with which he was associated. It does cut down to some extent the amount of gypsum required but at this mill the results obtained indicated that the method was not reliable where no gypsum was used. The practice is of value, however, in curing unsound cement. Quickening the Setting Time Certain reagents if added to cement have the property of quick- ening the set of the latter. The alkalies have this property to a marked degree. Even a small percentage of sodium carbonate added to cement will quicken the set of the latter quite appreci- ably. Commercial “soda ash” is crude sodium carbonate and where it is desired to hasten the set of cement, this chemical is usually employed. There are some objections to its use, however, chief of these are the absence of any authoritative research work to show the effect of such additions on the strength and per- manency of the resulting concrete. The alkali is also likely to appear as an efflorescence on the surface of the concrete. Effect of Storage of Portland Cement on Its Setting Properties No property of Portland cement is harder to control than its “set,” or gives the manufacturer more trouble. This is not so much because of any difficulty in the way of making a slow-set- ting cement, as it is of making one which will stay slow-setting under all ordinary conditions of storage and aging. Every manu- facturer can cite instances of cement which left the mill having the proper setting time, and yet which turned up at the job with a “flash” set. Bins of freshly made cement will frequently test slow-setting and yet, after seasoning. Some weeks, will show quick set on again testing. - The converse of this is also true, some cements which, when freshly made are quick-setting, will in time become slow-setting, and again slow-setting cements may become quick-setting and then slow-setting again. As a usual rule a cement which is slow- 608 PORTLAND CEMENT setting when freshly made and which becomes quick-setting on storage is under-limed, and the trouble can usually be remedied by increasing the percentage of lime in the cement. High-limed, well-burned and made cements do not usually show this fault. What percentage of lime it is necessary to carry in order to avoid this trouble is a question every mill must decide for itself, but, in general, it may be said that cements high in alumina will require a high percentage of lime to overcome this fault, and in some instances the margin between the minimum of lime to in- sure against quick set and the maximum allowed by a good hot test is very narrow. The table below illustrates the changes in the setting time of cement, due to aging. TABLE LVIII.—INFLUENCE OF AGING OF THE SET OF PORTLAND CEMENT. I 2 3 4 5 6 7 Sample No. *=== H | M | H | M | H | M | H | M | H | M | H | M |H| M Fresh Initial set || 2 |50 || 3 || IO || 4 || IO || 2 |40 | - || 2 | . . Io |. 4 TeSI 1 - - - - - - - - Final set | 6 || O || 6 || 40 || 8 || o|| 6 || I5 | . I5 | . |25 |. IO Initial set | 1 |3O | . . . IO || 2 | 15 3 | 2 || - || 5 || || 4 I week old. . . . . set 4 || O 25 || 6 || o 8| . . Io | . 15|. IO Initial set | O || 3 | . . | 5 | I 25 3 | " | I5 3O || || 4 2 weeks old. | #. sº | 3 |}|...| 1 || 3 4O 8| - |35 | 1 || 5 || | Io Initial set | O || 3 | . . 5 | . 30 5 I | 3O | I 50 | | I5 4 weeks old. | F. s. 7 | . . . I5 | I 50 II || 4 || IO || 4 || 45 || |3O Initial set | . 3O | . . || 4 | . Io 3| I 35 | 2 | O |2|4O 3 months old. Final set | 1 || 5 | . . . I5 | . 30 8|| 4 || O || 6 || Io |6 || 5 Initial set | . |25 | . . . 20 e ſe 3 || 2 | IO || 2 || O |2| IO 6 months old. Final set | I |I5 I* | IO* | . . . . 8|| 6 || o|| 6 || Io 5|4o Initial set | . |25 | . . 55 || 2 | 20 4 || 2 | O | I 4O |2| I5 I year old . . . . Final set | 1 |Io || 2 || 30 || 5 |45 IO || 5 || 30 || 5 || 5 ||6 || 5 The reason commonly given for the quickening of the set of Portland cement is that the plaster of Paris (CaSO4), H2O, has hydrated and reverted to gypsum, CaSO,.2H2O. It is a fact, however, as is generally well known, and as we have mentioned before that gypsum is practically as efficacious a retarder as plaster of Paris. Not only will the mineral gypsum slow the set of cement but the artificial gypsum, formed when plaster hydrates or sets, will also act in the same manner, as the following re- sults will show. TIME OF SETTING 609 TABLE LIX.—THE EFFECT OF “SET’’ PLASTER OF PARIS ON THE SETTING TIME OF CEMENT. Percentage of Percentage of “set” plaster water used to Initial set Final set of Paris added make pats Hours Minutes Hours Minutes O 25 O 2 O 6 I 23 O 8 O 40 2 23 I 45 5 O 3 23 2 O 5 2O 5 23 I 45 6 O IO 23 I 55 5 35 2O 23 2 I5 5 50 In view of the fact that both gypsum and set plaster of Paris, which is merely plaster of Paris reverted into gypsum, will slow the set of cement, there can be nothing in the theory that plaster loses in time its control, over cement, for the only change which the plaster can undergo is to absorb water from the air forming gypsum. We must therefore seek for another solution of the matter. Mr. Clifford Richardson suggested one, in his paper on the “Constitution of Portland Cement,” read before the Associa- tion of Portland Cement Manufacturers, at Atlantic City, June, I904. His theory being that the tension in the solid solution of calcium silicates and aluminates, which constitutes cement, is re- leased by changes in temperature, etc., setting free some alumi- nate which makes the cement quick-setting again. Against this latter theory are several facts, chief of which is that cements kept in air-tight vessels do not get quick-setting. The writer has many times divided a sample of cement, which from its analysis led him to believe it would develop a “flash” set on aging, into two portions, storing one in a small paper bag and the other in an air-tight fruit jar, and, in no case, has he ever observed the sample in the jar to become quick-setting, although in most cases that in the bag developed an initial set of from two to ten minutes after a week's time. In making this test three pats were always made of each sample, both before and after aging, and the bag and jar were placed side by side on the shelf, where both would be subjected to the same changes of temperature, etc. 6IO PORTLAND CEMENT Influence of Slaked Lime on Setting Time When cement has become quick-setting from storage it can generally be made slow-setting again by simply adding I or 2 per cent of slaked lime, or by gauging the pat with lime-water. This seems to lead to the conclusion advanced by Candlot that the quickening of the set of cement on exposure to air is due to the change of the small percentage of free or of hydrated lime al- ways present in cement to the inert carbonate. This change is brought about by the carbon dioxide of the air, consequently, when not exposed to the air, the cement does not become quick- setting. Slaked lime will not itself slow the setting of unsul- phated cement, and calcium sulphate must be present in some form or other, so that it is probably a mixture of calcium sul- phate and calcium hydrate which retards the hydration of the aluminates, and consequently the activity of the cement. Cement which has become quick-setting may also be made slow-setting again by addition of a small percentage of plaster of Paris. One-half of I per cent is usually sufficient for this purpose. When bins of cement have become quick-setting, from age, it is usual to bring the setting time back to normal by such means. Usually a square box made to hold so much plaster of Paris (when struck off level) is added to every barrow of cement as it is wheeled from the bin to the conveyor, or else a box is dumped into the conveyor at stated intervals of time. The screw conveyor then does the mixing and usually does it pretty thoroughly, too. Some mills are provided with automatic scales and mixers for doing this work, but these are usually installed only in those mills which use plaster of Paris and make the addition before packing, instead of grinding gypsum in with the clinker. Quick-setting cements may also be rendered slow-setting by mixing them with slow-setting ones, but this must be carefully done to see that both bins are drawn from in the desired propor- tions. The property slaked-lime has of slowing the setting time of cement which has quickened with age does not seem to be utilized as much as it might be. I know of one cement mill where TIME OF SETTING 6 II hydrated lime was added for a short time for this purpose and of another which contemplated doing so. Most manufacturers, however, have found it simpler to add a little more plaster of Paris to such cement as becomes quick-setting, just before it is packed and so bring back its setting time to the normal. The con- tractor or engineer, however, might in many cases add hydrated lime to the cement and so relieve the manufacturer of the ex- pense of taking the cement back to the mill in order to plaster it. On small jobs, where water is added to the concrete from barrels, the addition of a few lumps of lime to the contents of the barrel would make the cement slow-setting, and the resulting concrete would be as strong as if no lime had been added. Sidewalk makers and other users of cement who do not test their purchases may safeguard themselves against using quick-setting cement un- awares by the use of lime in this way or by mixing hydrated lime with the mortar. Manufacturing Conditions Effecting Setting Time Theoretically, the setting time of cement should be controlled by the amount of gypsum added. From a perusal of the pre- ceeding paragraphs, however, it will be apparent that other con- ditions will influence this materially. The specifications allow as much as 2 per cent sulphur trioxide in the cement. Cement clinker burned with coal ordinarily contains from O.3 to O.5 per cent sulphur trioxide and gypsum when pure 46 per cent of this constituent; so ordinarily the maximum amount of pure gypsum which can be added without having the cement exceed the limits of the specifications is 3.4 to 3.8 per cent of the weight of the clinker (12% to 14% pounds per barrel of cement). It has been found that unless the clinker is of proper chemical composition and has been properly burned it is not possible to slow the set of the resulting cement to the requirements of the specifications with this amount of gypsum. The influence of both alumina and lime on the setting time of cements has been pointed out in Chapter II of this book. Gen- erally speaking cements high in alumina are apt to be quick- 612 PORTLAND CEMENT setting or to become so when aged. On the other hand, high silica cements are not so likely to show this tendency. The percentage of lime in the cement has a marked influence on its setting time. High limed and well burned cements made from finely ground raw materials are slow setting after a moder- ate amount of gypsum has been added, nor do they usually be- come quick-setting on aging. What percentage of lime it is nec- essary to carry at any individual works in order to avoid quick- setting cement is a question each mill must find out for itself, but in general it may be said that cements in which the ratio CaO : SiO, H–Al,O, + Fe,O, is two or better will be satisfactory. Cements high in alumina will require a high percentage of lime to overcome the tendency to become quick-setting and in some in- stances the margin between the minimum of lime to insure against quick set and the maximum allowed by a good hot test is very narrow. It is particularly desirable that the clinker be uniform in composition. Low lime clinker mixed with high lime material may apparently be of satisfactory chemical composition, due to averaging, and yet the influence of the low lime material will be sufficient to make the cement quick-setting. Mixtures of underburned and normal or very hard burned clinker are also apt to be quick-setting, consequently uniform burning is desirable if the set of the cement is to be regular. When cement is quick-setting or becomes so, even after the maximum amount of gypsum allowable is added, it will generally be found that the trouble can be remedied by increasing the per- centage of lime in the cement, by more careful burning and by fine grinding of the raw materials, one or all. CHAPTER XXIII SOUNDNESS Standard Specification and Method of Test Specification.--A pat of neat cement shall remain firm and hard, and show no signs of distortion, cracking, checking, or dis- integration in the steam test for soundness. Method of Test 41. A steam apparatus which can be maintained at a tem- perature between 98 and IOO’C., or one similar to that shown in Fig. 174, is recommended. The capacity of this apparatus may be increased by using a rack for holding the pats in a vertical or inclined position. 42. A pat from cement paste of normal consistency about 3 inches in diameter, V4 inch thick at the center, and tapering to a thin edge, shall be made on clean glass plates about 4 inches square, and stored in moist air for twenty-four hours. In mold- ing the pat, the cement paste shall first be flattened on the glass and the pat then formed by drawing the trowel from the outer edge toward the center. 43. The pat shall then be placed in an atmosphere of steam at a temperature between 98 and IOO’ C. upon a suitable support I inch above boiling water for five hours.” 44. Should the pat leave the plate, distortion may be detected best with a straight edge applied to the surface which was in con- tact with the plate. * Unsoundness is usually manifested by change in volume which causes distortion, cricking, checking or disintegration. Pats improperly made or exposed to drying may develop what are known as shrinkage cracks within the first twenty-four hours and are not an indication of un- soundness. These conditions are illustrated in Fig. 175. The failure of the pats to remain on the glass or the cracking of the glass to which the pats are attached does not necessarily indicate unsoundness. 40 614 PORTLAND CEMENT 'quouuoo go ſsaq ssºupunos ºuļxſeu lloj stų eluddy—"#4 i '51） un 14 do L 'pºsſº ſºq az Ajdovapyoçº paeſy|×- -• • • ► - - - …» - *º'qissodawºwał pogºry ºg aſ suſpaçº ffy|<„ 02→!?k‘9}{409 apºstº pºucº， ºg és uża' żożg 6，76%）|----#/[3A3（1-\u04su09 ***)/22/ç/oºppuu ºq oſ sądu påſøy -*į，• 7** --> -> ======= <----Y.ºſº •~~~~）; „žysºwyoazº aww ua/pozyupaypoOO:ſſ:Ķī£ „žyo 322€/%,ººººººº， aguſia，-º; — — — —**§.§! pºzvawoº, ſºyo ºppu ºqo, yºus S}{!§ §. - ► ►►*.|GSÇ`, J.ļºuſ S/#ø2nøy!#№ ò |-$$/， /{ĶY }<！-----------5, 62 - ---- - - - --------->|g. ģ}}}~ |-Ģș∞::-*i!§ }}}}}} }ș tuo tae uxo}\ogGJøddogº <-tºqqºyſ-- |--*- |º 9p || S‘+ldol-l | K„ ſºº （- , ------>|k ----. $/ -------->{ » çº-x-ae） {-x-） ';§ 3}Č5 2}}/07. .*-+-+ -º- º,} /a497?days&o?† į ſae – †} 44 1/24/221/i/o|- ^~| -----...ºf● ~/º/adºſ_ - - ~~№.- say6uy -vºdºo3 ſa peſſ --§.• Avaza/º/oº”, ae-Ý-;.ſº6a'o',/ º <-WTTT-T-T), ºſ gaeſåſ, ? 8./JAMu.au/. £�cae-*-_©�• / wo pºtiwn, ºãº Go!...” | º º sº e º ºs Checked 28 . . . . . . O. K. . . . . . . . . Checked 90 ' ' ' ' ' ' | . . . . . . . . . . . . . . . . . . . . O. K. * Samples were seasoned in a small paper bag on a shelf in the laboratory. Cement which has seasoned sound is just as good as one which was sound when freshly made, and the writer does not think the engineer need concern himself whether the manufacturer prefers to make cement which is sound when fresh, or whether he pre- fers to age it sound in his stock-house. So long as it is sound when he uses it, he is secure, and possibly the softer burned 632 PORTLAND CEMENT clinker, usually unsound when freshly ground, will grind with a greater percentage of flour, increasing the sand carrying capacity of the cement. Effect of Fine Grinding of the Raw Materials on Soundness In order for cement to stand the boiling test when fresh from the grinding mills, the raw materials must be finely ground. The unsoundness due to coarse grinding of the raw materials is prob- TABLE LXI.-SHOWING EFFECT OF FINENESS OF GRINDING OF CLINKER ON SoundNEss. Fineness --- Result of Condition of cement as tested 5-hour steam test Residue | Residue (A. S. C. E.) No. Ioo | NO. 200 As received from the mills, tested one day old . . . . . . . . . . . . . . . . . . 8.5 27.0 | Partially disintegrated As received from the mills, tested again after seasoning one week 8.5 27.0 | Partially disintergated As received from the mills, tested again afterseasoning one month 8.5 27.0 | Badly checked Portion of sample passing No. 200 sieve, tested one day old . . . . . . O. O o.O | Sound Sample ground to all pass a No. 200 sieve, tested one day old ... o.o o.o | Slightly checked Sample ground to all pass a No. 200 sieve, tested one week after grinding . . . . . . . . . . . . . . . . . . . . . O. O o.o | Sound ably the hardest form of unsoundness to cure by aging. This is particularly so if the clinker has been burned very hard, as the coarse pieces of limestone, calcined to free lime, are locked up in a case of clinker. If this case is not broken in grinding, the free lime is left surrounded by a wall of clinker and will be very slowly acted upon by the moisture of the air. The experiment in Table LXI seems to prove this very thing. Laboratory records show the unsoundness of this sample to have been due to coarse grinding or the raw mixture. The fine particles passed the boil- ing test fresh, the coarse ones failed even on grinding, but on aging one week, the ground particles stood the test. Aging the SOUNDNESS 633 cement, however, for two weeks failed to make it sound, because the free lime was locked up in the coarse particles, where hydra- tion could only take place very slowly, but, on grinding the coarse particles, the air had a chance to get at the free lime and convert it to the innocuous hydroxide. The effect of fine grind- ing of the cement itself on soundness has been discussed in Chapter XXI. Effect of Sulphates on Soundness Pats allowed to harden in steam or hot water will often pass the boiling test where pats hardened in air will not. It must be remembered that checking is caused by slaking after the pats are fully hardened. If they are placed in steam to harden the moist air merely accelerates the slaking of the lime, doing the work be- fore the pat hardens, just as heat hastens any chemical action. The addition of sulphates, either as gypsum or plaster of Paris, aids the cement in standing the boiling test, probably because it delays the set until after the lime has slaked. The rendering of the free lime inert by the formation of compounds with the lime by the gypsum seems hardly probable, since the lime and gypsum could not react unless both were in solution, and if the water could get at the free lime to dissolve it, slaking would take place on adding water only, and the harmless hydroxide would be formed. The early hardness due to gypsum can hardly play any part, since cements breaking as high as 600 pounds in twenty-four hours may fail on the boiling test, while briquettes breaking at I 50 pounds may be sound. My own experiments go to show that anything which will delay the setting of cement until after the free lime has slaked, or that will hasten the slaking of the free lime before the pat sets, will make cement sound. The table given below shows the effect of additions of plaster on the boil- ing test: * See also Taylor, Proceedings, 4 m. Soc. Test. Mat., III (1903), 377, and Butler, Portland Cement, p. 174. 634 PORTLAND CEMENT TABLE LXII.-SHowING EFFECT OF ADDITIONS OF GYPSUM OR PLASTER OF PARIs on SoundNESs. Result of 5-hour steam test (A. S. C. E.)” Per cent Sample SO .Sv3 o.5 per cent 1.0 per cent 2.0 per cent 3.o per cent plaster added plaster added plaster added | plaster added Cement . . . . . . . I. 2 I Sound . . . . . . . . . . . . . . . . . . . . Cement . . . . . . . I.43 Checked Sound | . . . . . . . . . . . . . Cement . . . . . . . I. I8 Checked Checked Sound . . . . . . . Cement . . . . . . . I.36 Checked Checked Checked Sound Ground clinker o.31 Checked Checked Sound . . . . . . . * All samples were unsound without addition of plaster of Paris. Value of Accelerated Tests At the 1903 meeting of the American Society for Testing Ma- terials, Mr. W. P. Taylor, of the Philadelphia Municipal Testing Laboratory, read a very carefully prepared paper upon the boil- ing test” in which he compared the results of neat briquettes and neat pats with the results of the boiling test. As is usual, he considered a falling off of the strength of neat briquettes on long time tests and a cracking and warping of the neat cold water pat as being positive evidence of the presence of injurious constit- uents in the cement. He gives these figures: “Of all the sam- ples failing to pass the boiling test 34 per cent of them developed checking or curvature in the normal pats or a loss of strength in less than twenty-eight days. Of those samples that failed in the boiling test but remained sound for twenty-eight days, 3 per cent of the normal pats showed checking or abnormal curvature in two months, 7 per cent in three months, IO per cent in four months, 26 per cent in six months, and 48 per cent in one year; and of these same samples 37 per cent showed a falling off in tensile strength in two months, 39 per cent in three months, 52 per cent in four months, 63 per cent in six months, and 71 per cent in one year. Or taking all these together, of all the samples that failed in the boiling test 86 per cent of them gave evidence in less than a year's time of possessing some injurious quality. * Proceedings, Amer. Soc. Test. Mat., III (1903), 374. SOUNDNESS 635 “On the other hand, of those cements passing the boiling test but one-half of I per cent gave signs of failure in the normal pat tests and but I.3 per cent showed a falling off in strength in a year's time.” It is unfortunate that the test which seems to be accepted by the majority as a standard is the long time cold water pat, a test requiring such length of time for its completion as to practically forbid its use. The conditions of the case demand a rapid test in order that the consumer may not be required to store the cement for a long period of time while he awaits the results of his cold water pats. Unquestionably much good concrete has been made from so- called unsound cement, and this is the key to the whole objection to the hot test. It is probable that much of the first American Portland cement would not have passed the steam test, yet it is upon the merits of the work done with this cement that engineers are now using American instead of imported cement. Butler gives a strong plea for the Faija test and states that in the twenty years this test has been in use, no cases of failure in work by ce- ment passing this test have come under his observation. If the Faija test is severe enough to exclude all bad cements, then the steam tests is needlessly severe as it rejects many cements which pass Faija's test. Some experiments' which were made by Mr. W. P. Gano, Chief Chemist of the Pennsylvania Cement Company, are in- teresting in this connection. He found by an extensive series of experiments that concrete would itself become sound, or in other words, that hydration could take place without necessarily caus- ing destruction of the concrete. His experiments consisted in making a large number of test pats of each sample of unsound cement. One of these was subjected to the boiling test after twenty-four hours in moist air. The other pats were set aside in either air or water and subjected to the boiling test at intervals of a week or more. He found that the boiling test had less and less effect on the pats until eventually a period was reached when the pats stood the test perfectly. This would seem to indicate that * Engineering News, Vol. I, XVII, No. 21, p. 980. 636 PORTLAND CEMENT those compounds causing unsoundness in the boiling test very frequently hydrate in a perfectly harmless manner and whatever expansion does occur will be taken care of by the elasticity of the concrete. In this connection, it should be remembered that as the concrete becomes older it becomes stronger and consequently better able to withstand any strains to which it may be put by expansives within itself. All cement probably contains some free lime. From the nature of the case this must be so, since cement raw materials are not ground to a degree of fineness nor carried to a state of fusion which would permit of every molecule of lime coming in contact with a molecule of silica or of alumina. Now there are limits be- yond which if the uncombined or free lime goes, certain results will take place. Let us suppose that with a very small percentage present the cement will fail on the boiling test but pass satisfac- torily five hours in steam, and if a still larger percentage is pres- ent it will fail in the steam but pass the Faija test. Now, again, let us suppose that a neat mixture with a certain small percentage of free lime is sound, with a larger percentage a 3: I sand mix- ture is sound, with a still larger percentage a I : 3: 8 concrete is sound. (It is well understood that the tendency of cement to dis- integrate is greater in a neat paste than in a sand mixture, and anyone with experience in cement testing knows of cases where neat briquettes had disintegrated in time and yet the sand ones were sound and strong). Now how do we know that the limit of lime which may be present in good cement (that is cement which will make enduring concrete) is coincident with that maximum which may be present for a sound boiling test? Nearly all advocates of the steam test have tried to prove these two limits coincident by comparing the steam test with the results of neat pats and neat briquettes. Usually the coincidence of a failure on the boiling test with either a warping or cracking of the neat pats or a loss of strength in the neat briquettes on long time tests is considered competent evidence in favor of the boil- ing test. In reality cement is seldom used neat. A cement which fails on the boiling test, whose neat briquettes fall off in strength after seven or twenty-eight days, yet whose sand briquettes in- SOUNDNESS 637 crease in strength as they grow older, has certainly given evidence that it will make good concrete. In weighing evidence for any test it must be remembered that we do not make the soundness test to see if neat briquettes will fail in strength as they age or if neat pats will warp and decay, but whether sidewalks, piers, abut- ments, foundations, walls, floors and buildings of concrete, not neat cement, will be permanent, and the thing therefore to com- pare the boiling test with, is concrete. Not until we can com- pare our laboratory records with many examples of both failures and successes in actual work will we have reliable data for form- ing our conclusions as to the reliability of the various tests for soundness. Experiments made by a committee of the Society of German Portland Cement Manufacturers in connection with the Royal Testing Laboratory at Charlottenburg forced them to report in 1900 and again in 1903 that none of the so-called accelerated tests for consistency of volume was adapted to furnish a reliable and quick judgment in all cases concerning the applicability of a cement. The experiments which they made consisted in putting the cement into actual work and observing it during a period of four years. The committee recommended the twenty-eight-day cold water pat as a standard test. If this test is taken as a stand- ard the hot test will reject many good cements. Manufacturing Conditions Influencing the Soundness As has been previously pointed out, the manufacturing con- ditions which are most likely to cause unsoundness are those of too much lime in the cement, improper burning and too coarse raw material. In this connection, it should be remembered that there is a relation between these conditions as has been pointed out on pages I46 and 284. The effect of lime on cement has been quite fully dealt with previously. The chemist who would have a satisfactory product can not, however, always cure unsoundness by resorting to the expedient of lowering the percentage of lime carried in the mix, because if he does this, he is likely to have a product which is quick-setting or of low strength, possibly both. Unsoundness 638 PORTLAND CEMENT does frequently occur from too much lime where the fault is due to the inability of the chemist to have his raw mixture of the de- sired proportions. This is particularly true where unsoundness is caused by occasional excess of lime due to irregularity in the raw materials themselves. There is a tendency on the part of manufacturers to go over to the wet process under the belief that it is easier to control the composition of the mix with this process than with the dry. In the matter of chemical control, there are unquestionably much better facilities provided at most wet process plants than there are in the general run of dry process mills. At the same time if proper facilities are provided, the dry process can be made to give fully as good results along this line as the wet process. The remedy for an irregular mix is usually the employment of a large Stone store house or else silos such as are described on page I2O, in which the raw material can be properly blended before being sent to the kilns. Irregular burning is one cause of unsoundness. Generally speaking, all manufacturers aim to burn to about the same degree of hardness. Like many other manufacturing processes, how- ever, the burning is dependent on the care with which it is done, or in other words, on the skill and attentiveness of the burners. The trouble is generally less a matter of the hardness to which it is aimed that the clinker be burned than of the fact that oc- casionally large amounts of underburned material are allowed to pass out of the kiln. The remedy in this case is obvious. Coarse raw material probably causes more unsoundness than any other condition and generally speaking where plants are having continued trouble with the boiling test it is due to too coarse raw material. There has within the last ten years been a very marked change in the attitude of manufacturers in this re- spect, due very largely to the introduction of more efficient pul- verizing machinery. There are now many plants where the raw materials are ground to a fineness of 85 per cent passing the No. 200 sieve. SOUNDNESS 639 While on the subject of fineness, it is well to point out that the ground raw material should be free from any considerable per- centage of grit and it is well to test this through a 20-mesh sieve. There should be practically no residue on this sieve. The general practice of seasoning clinker is an aid to sound- ness and a great deal of clinker which would not give sound cement if freshly ground will produce sound cement if seasoned for two or three weeks either in the open or where moisture can get to it. Mention has already been made of the practice of in- troducing steam into the tube mill, where these are used for grinding, and this practice is a material aid to soundness. There are objections to it, however, on the ground of inconvenience and possibly interfering with the efficiency of the tube mill itself. Where the sulphur trioxide is not too near the limit, unsound- ness may be often cured, as pointed out previously, by raising the percentage of this in the cement. CHAPTER XXIV TENSILE STRENGTH Standard Specification and Method of Test Specification.—7. The average tensile strength in pounds per Square inch of not less than three standard mortar briquettes (see Sec. 50) composed of one part cement and three parts stand- ard sand, by weight, shall be equal to or higher than the follow- 1ng: Age at test, e Tensile strength, days Storage of briquettes 1bs. per sq. in. 7 I day in moist air, 6 days in water 2CO 28 I day in moist air, 27 days in water 300 8. The average tensile strength of standard mortar at twenty- eight days shall be higher than the strength at seven days. Method of Operating Test 50. Form of Test Piece.—The form of test piece shown in Fig. 182 shall be used. The molds shall be made of non-corrod- ing metal and have sufficient material in the sides to prevent spreading during molding. Gang molds when used shall be of the type shown in Fig. 183. Molds shall be wiped with an oily cloth before using. 51. Standard Sand.—The sand to be used shall be natural sand from Ottawa, Ill., screened to pass a No. 20 sieve and retained on a No. 30 sieve. This sand may be obtained from the Ottawa Silica Company, at a cost of three cents per pound, f. o. b. cars, Ottawa, Ill. 52. This sand, having passed the No. 20 sieve, shall be con- sidered standard when not more than 5 grams passes the No. 30 sieve after one minute continuous sieving of a 500-gram sample. . 53. The sieves shall conform to the following specifications: TENSILE STRENGTH Fig. 182.—Details for Briquette. Fig. 183.−Gang mold. 642 PORTLAND CEMENT TABLE LXIII.—PERCENTAGE OF WATER FOR STANDARD MoRTARs. Percentage of water Percentage of water Percentage of water Percentage of water for neat cement for one cement for neat cement for one cenlent Paste of normal Three standard Ottawa Paste of normal Three standard Ottawa consistency sand consistency Sa Il I5 9.O 23 I0.3 I6 9.2 24 IO.5 I7 9.3 25 IO.7 I8 9.5 26 IO.8 IQ 9.7 27 II.O 2O 9.8 28 II.2 2I IO.O 29 II.3 22 IO.2 3O II.5 The No. 20 sieve shall have between 19.5 and 20.5 wires per whole inch of the warp wires and between 19 and 21 wires per whole inch of the shoot wires. The diameter of the wire should be ooſó5 inch and the average diameter shall not be outside the limits of O.OI6O and O.OI7o inch. The No. 30 sieve shall have between 29.5 and 30.5 wires per whole inch of the warp wires and between 28.5 and 31.5 wires per whole inch of the shoot wires. The diameter of the wire should be O.OI Io inch and the average diameter shall not be out- side the limits O.OIO5 to O.OII5 inch. 54 Molding.—Immediately after mixing, the standard mortar shall be placed in the molds, pressed in firmly with the thumbs and smoothed off with a trowel without ramming. Additional mortar shall be heaped above the mold and smoothed off with a trowel; the trowel shall be drawn over the mold in such a man- ner as to exert a moderate pressure on the material. The mold shall then be turned over and the operation of heaping, thumbing and smoothing off repeated. 55. Testing.—Tests shall be made with any standard machine. The briquettes shall be tested as soon as they are removed from the water. The bearing surfaces of the clips and briquettes shall be free from grains of sand or dirt. The briquettes shall be carefully centered and the load applied continuously at the rate of 600 pounds per minute. 56. Testing machines should be frequently calibrated in order to determine their accuracy. TENSILE STRENGTH 643 57. Faulty Briquettes.—Briquettes that are manifestly faulty, or that give strengths differing more than 15 per cent from the average value of all test pieces made from the same sample and broken at the same period, shall not be considered in determining the tensile strength. Storage of Test Pieces 58. Apparatus.-The moist closet may consist of a soapstone, slate or concrete box, or a wooden box lined with metal. If a wooden box is used, the interior should be covered with felt or broad wicking kept wet. The bottom of the moist closet should be covered with water. The interior of the closet should be pro- vided with non-absorbent shelves on which to place the test pieces, the shelves being so arranged that they may be with- drawn readily. 59. Methods.—Unless otherwise specified, all test pieces, im- mediately after molding, shall be placed in the moist closet for from twenty to twenty-four hours. 60. The briquettes shall be kept in molds on glass plates in the moist closet for at least twenty hours. After from twenty to twenty-four hours in moist air the briquettes shall be immersed in clean water in storage tanks of non-corroding material. 61. The air and water shall be maintained as nearly as prac- ticable at a temperature of 21°C. (70°F.). Notes Standard Sand Up to the adoption of the above standard rules, crushed quartz such as is used in the manufacture of sandpaper, and of the same size as is specified for the present standard sand, was used, having been recommended by a former committee of the Amer- ican Society of Civil Engineers. Where the value of the cement is desired with regard to some particular piece of work, the sand used for the test may be the sand that is to be used for the work. In this case it is the mortar that is tested rather than the cement. Just as a series of tests 644 PORTLAND CEMENT made with a standard sand and various brands of cement would give the comparative value of the cements, so a series of tests with an established brand of cement and various sands will give the comparative value of the sands. Cement, when tested with the natural Ottawa sand, usually shows a greater strength than when tested with crushed quartz. In the case of seven-day breaks, the higher figure may be as much as 40 per cent above the lower. The reason" for this difference is due to the shape of the sand grains. The Ottawa sand being round, it compacts much more closely and has a lower per- centage of voids than crushed quartz, as the latter has sharp and angular grains, which mass and wedge, leaving more space be- tween the sand particles. Other Forms of Briquettes Fig. 184 shows the form of briquette recommended in the re- port of a former committee on a uniform system for tests of cement of the American Society of Civil Engineers," which is similar to the present standard except that the latter has rounded * *.sº e ! *- /* +-* * | i | | -- I so ‘y | * J | * * Fig. 184.—Old standard Fig. 185.-German standard form of briquette. form of briquette. corners. Fig. 185 shows the form which is the standard in Germany. The dimensions of the two forms are given in the drawings. As will be seen, the weakest section of briquettes of either form is at the center and is one inch in cross-section, 1 Brown, Proceedings of Am. Soc. for Test. Mat., IV (1904), 124. 1 This committee presented its report at the annual meeting of the society, Janu- ary 21, 1885, and was then discharged. TENSILE STRENGTH 645 in the case of the United States standard; and 5 square centi- meters in that of the German. Comparative tests show the American standard to give the higher result of the two. In the case of briquettes of neat cement, this difference amounts sometimes to as much as 30 or 40 per cent of the lower. The standard British form of briquette is the same as the A. S. T. M. form. Molds Other types of briquette molds are shown in Fig. 186. The first form is held together by levers, the bearing surfaces of which are the ends of threaded pins. By turning the pins as they wear, the molds can be kept tightly closed. The second form is held together by a clamp provided with a thumb screw but in the writer’s opinion has no advantage over the standard form and the disadvantage of an extra part—in the case of a gang mold two extra parts. The third form is provided with an eccentric bear- ing so that when it is revolved in a half circle, or over, to the Fig. 186.--Other forms of briquette molds. other side from that shown, the two halves of the mold are Separated, thus facilitating the removal of the briquettes. All these types are adapted to three-gang molds. Fig. 187 shows form of gang mold which is extensively used. Where molds are for more than three briquettes it is advisable to bore a hole through from side to side of the mold, between the Second and third openings, so as not to interfere with the briquettes, and to run a bolt provided with a thumb-screw 42 646 PORTLAND CEMENT through this. The mold will be considerably stiffened thereby and springing will be guarded against. Molds are usually made of gun-metal, brass, bronze or some alloy of copper which does not rust on exposure to moisture. Mr. Force, Engineer of Tests of the Lackawanna R. R., tried Fig. 187.-Good form of gang mold. aluminum molds but found that while they were light and stiff enough, the test-pieces stuck to them badly. To clean the molds, lay them all flat on the table without the clamps just as if briquettes were to be made and scrape off any hardened cement with a piece of sheet zinc or other soft metal. Then brush off with a stiff bristle brush and wipe with a piece of oily waste. Turn the molds over and repeat the process on the other face. Now separate the molds and place the halves in a long line with the mold part forming a trough, brush with Fig. 188.-Scraper for cleaning molds. a stiff brush and wipe off with oily waste. Briquettes should not be allowed to become too hard before removing from the molds. The specifications require that the briquettes be left in the molds for at least twenty hours and this is long enough if the cement is normal. TENSILE STRENGTH 647 Fig. 188 shows a scraper for cleaning molds. This consists of a block of wood 5 × 3 inches, rounded to form a handle, into which is fixed a piece of zinc. Mixing In place of a glass plate, a sheet of brass %-inch thick makes an excellent mixing surface. Slate and soapstone slabs are also used. Both, however, absorb water and draw it away from the briquettes. This can be avoided by keeping a damp cloth over that part of the table used for mixing when not in service. Or G/ 2 sº sº sº sº º sº as * * sº 77%2 || | * = * * * z_j *~ 2 ,’ N–Z N Z ºr--> M%zsfe GT-d Cozz Fig. 189.—Table for mixing mortar and making briquettes and pats. melted paraffine may be poured over the heated slab and allowed to soak in and the whole then cooled. The excess of paraffine is, of course, to be scraped off with a metal scraper. Fig. 189 shows a convenient table for mixing mortar and mak- ing briquettes and pats. It consists of a table arranged with glass or brass plates or slate slabs at either end and the central 648 - PORTLAND CEMENT part of the table raised four or five inches above the ends as shown. The space between the shelf and the glass plate is left open so that the surplus mortar, etc., used in making a set of briquettes may be swept through this and into a waste can placed below. A piece of tin bent to form a trough, as shown, con- ducts the waste into the can. Above the first shelf, which is used for the scales, measuring cylinders, pat glasses, etc., a second shelf is supported by four uprights—one at each corner. At each end of this shelf are to be placed 2 gallon bottles pro- vided with siphons of glass and rubber as shown. These siphons are closed by pinch-cocks, as shown. Drawers may be placed in front of the table for holding such articles as trowels, spatulas, etc. Four 2-gallon bottles should be provided, and while two are in use on the table the other two should be full and standing nearby to get the room temperature. Instead of kneading the cement mortar with the hands as prescribed by the standard rules, many testers use a trowel, working the mortar back and forth on the table, under the trowel. Percentage of Water The percentage of water used in gauging the mortar for the test pieces has a considerable influence on the strength of the cement. This is shown by the table given below which is taken TABLE LXIV.-INFLUENCE OF VARIOUS PROPORTIONS OF WATER ON THE NEAT STRENGTH OF PORTLAND CEMENT. (E. S. LARNED). Tensile strength Cement Water 24 7 28 3 6 I2 brand per cent hours days days months months months I5 37I 655 875 94I 720 787 I6 303 750 973 IOO8 735 8I6 Giant I8 260 649 773 83I 645 748 Portland 2O 233 500 693 716 62I 676 22 I84 546 636 658 6OI 589 24 I67 539 649 644 629 755 I3 366 775 859 IO67 892 832 I4 4O4 780 891 972 852 781 Atlas I6 363 6O2 725 844 806 723 Portland I8 308 570 723 785 728 724 2O 225 590 718 760 674 636 22 II6 554 649 73I 643 604 24 42 5IO 691 695 632 574 TENSILE STRENGTH 649 from a paper by Mr. E. S. Larned on the subject. It will be noticed that in the case of both cements, the dryer mixtures give the higher results. This is probably due to the fact that the dry mixtures require hammering or ramming to get them in the molds, while the wet mixtures were merely forced in with the thumb as they were too soft for this treatment. Other experi- menters, however, have found results differing in some particu- lars from Mr. Larned, and while agreeing with him that the dryer mixtures give higher short time tests, their experiments show the differences on long time tests to be slight and usually in favor of the wet mixtures. This has also been the writer’s experience, but in his case both the dry and the wet mixtures were merely pressed into the molds with the thumbs. Table LXIII gives the percentage of water to be used in standard mortars. This table is calculated from the formula: o.67 P AV -- I In which Y is the percentage of water required for sand mortar, P is the percentage of water required for neat cement paste of normal consistency, N is the number of parts of sand to one of cement by weight and K is a constant which for standard Ottawa sand has the value 6.5. This table differs quite materially from the one formerly used. The former methods (Am. Soc. Civil Engrs.) called for a much dryer mortar as the following Table LXV will show. Y = +A . TABLE LXV.—CoMPARISON BETweeN OLD AND NEW SPECIFICATIONS FOR PERCENTAGE OF WATER FOR STANDARD MORTARs. Percentage of water for neat cement Paste of normal Percentage of water for one part cement to three of standard Ottawa sand by weight consistency Old specifications Present specifications I8 8.5 9.5 IQ 8.7 9.7 2O 8.8 9.8 2I 9.O IO.O 22 9.2 IO.2 23 9.3 IO.3 24 9.5 IO.5 25 9.6 IO.7 26 9.8 IO.8 27 IO.O II.O 28 IO.2 II.2 * Proceedings, Amer. Soc. Test. Mat., III (1903), 4o 1. 650 PORTLAND CEMENT The old figure is based on a value for K of 5.5. Feret who originally devised this formula in a somewhat different form used a value for K of 6.0 for mortars of plastic consistency and 4.5 for mortars of dry consistency. Storage of Briquettes The briquettes may be placed in water either flat or on edge. The latter gives more surface exposed to the water. The tanks in which the briquettes are immersed may be made of galvanized iron and of any desired size. They are usually, however, from 2 to 6 inches deep. Where space is limited, they may be placed one above the other on a suitable framework. When much testing has to be done, a good form of trough for the storage of briquettes is made of stout 2-inch board lined with sheet zinc. These troughs may be placed one above the other on a suitable wood frame. A small stream of water should be kept running through them all the time. This can be done by arranging overflow tubes so that the water will flow from the upper trough into the next one below, etc. Quite frequently the briquette trough is placed in the cellar Fig. 190.-Marking briquettes. and is made of concrete. In one of the writer’s laboratoriess such a trough is employed. It is raised about 2 feet from the floor and is 8 inches deep. The water level is maintained at about 6 inches. The temperature of this cellar is very even TENSILE STRENGTH 651 both in summer and winter. In making the trough, a very dense concrete was used so as to be sure of no leakage from it into the cellar. After the briquettes have attained their initial set they should be marked with an identifying number. Where neat briquettes are made these may be marked by a steel die as shown in Fig. I90. Sand briquettes may be marked by putting a thin layer of neat cement about 1/16 inch thick on one end and marking this. When briquettes are to be broken at short periods a grease pencil such as is used for marking china may be used for marking, but where long time tests are made steel dies should be used. In storing the briquettes in the troughs, it will be found most convenient to put all the briquettes to be broken in seven days, in order of making, in one part of the trough, and those for twenty- eight days in another, etc. The briquettes may be placed edge- wise, in pairs, one on top of the other; and where the sand bri- quettes are not marked, it will be found a good plan to place the meat briquettes over the corresponding sand ones. The number of briquettes to be made, and the time when these are to be broken, will vary with circumstances. Usually in cement inspection work only seven-day and twenty-eight-day sand tests are made but in research work briquettes are often made to be broken at periods of twenty-four hours, seven days, twenty- eight days, three months, six months, one year, two years, five years and ten years. Uusually from three to five briquettes, both sand and neat, are broken at each period, except at twenty-four hours, when only neat briquettes are broken. In temporary and field laboratories the long time tests are, of course, omitted. Three briquettes are usually considered enough to test the strength of cement at any period, though in some laboratories only two of each kind are broken. m The briquettes should always be put in the testing macnille and broken immediately after being taken out of the water, and the temperature of the briquette and of the testing room should be constant, between 60° and 70° F. Seven days neat briquettes kept in the room and allowed to dry out for twenty-four hours 652 PORTLAND CEMENT before breaking, in many instances, break at less than half the strain of those kept in water the full period. Sand briquettes, however, seldom show any very marked difference. Testing Machines The Fairbanks' cement testing machine is much used for ce- ment testing because of its simplicity and automatic action. It is shown in Fig. 191. It consists of a cast iron frame A, made in one piece with a shot hopper B. To this frame are hung the Fig. 191,-Fairbanks cement testing machine. two levers D and C. From the end of the upper lever the weight is applied by allowing shot to flow from the hopper into the bucket F. The tension is applied to the briquette held in the * The Fairbanks Scale Co., New York, N. Y. TENSILE STRENGTH 653 clips N and N by means of the lower lever C. The lower clip is attached, by means of a ball joint, to a screw with a hand wheel P, for lowering or raising, when putting in the briquette and taking up the slack. There is also a counterbalance E, for bringing the levers and bucket into partial equilibrium so that the final adjustment can be made with the ball L. The shot hopper is provided with a lever and gate J, which cuts off the shot as soon as the specimen breaks. The shot is weighed by hanging the bucket on the opposite end of the lever D, by means of a sliding poise R. To operate the machine: Hang the cup F on the end of the beam D as shown in the illustration. See that the poise R is at the zero mark, and bal- ance the beam by turning the ball L. Fill the hopper B with fine shot, place the specimen in the clamps N N, and adjust the hand wheel P so that the graduated beam D will rise to the stop K. Open the automatic valve J so as to allow the shot to run slowly into cup F. When the speci- men breaks, the graduated beam D will drop and automatically close the valve J. As the load is applied, the beam D will begin to drop. When it reaches a point midway in the guide K, jointly engage the hand wheel T and turn slowly so as to keep the beam D from striking the bottom of the guide and cutting off the flow of shot before the briquette breaks. Remove the cup with the shot in it, and hang the counterpoise weight G in its place. Hang the cup F on the hook under the large ball E, and pro- ceed to weigh the shot in the regular way, using the poise R on the graduated beam D, and the weights H on the counterpoise weight G. The result will show the number of pounds required to break the specimen. The flow of shot can be regulated by the valve, M. Many operators prefer to operate this machine by applying sufficient force at the start to take care of the elasticity of the cement and by so doing no attention is needed while the briquette 654 PORTLAND CEMENT is breaking unless the beam falls to the bottom of the guide when the flow of shot will be cut off. This method of procedure is convenient but is likely to result in premature breaks, particularly if the operator is inexperienced or the cement is weak. In the Fairbanks machine there is an error due to the fact that some time (in which shot is falling into the bucket) is taken by the beam to fall to the valve checking the shot stream; this Fig. 192.-Riehlé U. S. standard automatic cement tester. stream of shot extending from the valve opening to the surface of the shot in the bucket must fall into the latter and be weighed as part of the load which broke the specimen, though this shot was not in the bucket when the specimen broke. Fig. 192 shows the Riehlé automatic testing machine." In this machine the initial load is avoided by an ingenious arrangement consisting in balancing a bucket of shot against a weight, and then applying the load by allowing the shot to run out of the bucket. This load acting through the levers breaks the briquette. The beam should be kept horizontal by means of the lever and worm * Riehlé. Bros. Testing Machine Co., Philadelphia, Pa. TENSILE STRENGTH 655 gear so that the pointer and mark on the beam are at all times practically coincident. At the instant that the test piece breaks, the flow of shot is shut off by means of a piston valve. The shot flowing out of the kettle is caught in a large cup resting on a spring balance, which shows at all times the load which has been applied to the briquette. As soon, therefore, as this latter breaks, the operator can see at a glance the strain required to do this. Fig. 193.-Olsen shot machine. These machines have come into very extensive use of late years, as they have many points of advantage over the older forms. For instance there is no initial load applied. The break- 656 PORTLAND CEMENT ing stress is read directly as soon as the briquette breaks and there is no transferring of the shot from one end of the beam to the other in order to weigh it. The weight and impact of the flowing column of shot is also done away with. The Olsen shot machine" is shown in Fig. 193. It is somewhat similar to the Riehlé machine, although in the author's opinion the latter possesses some points of advantage over the former. In this machine the valve is different from that of the Riehlé. Fig. 194-Olsen-Boyd automatic cement tester. In the Olsen machine the briquette is placed in the clips and the load applied by means of the small hand wheel located below these. This small wheel is so arranged that it will automatically slip on the adjusting screw as soon as the predetermined initial * Tinius Olsen Co., Philadelphia, Pa. TENSILE STRENGTH 657 load has been applied to the briquette. The cut-off of shot is effected by the upper grip striking the horizontal arm which extends just above it, and thus releasing the curved arm carried on the spindle immediately on the left. This curved arm in turn strikes the valve and closes it. The newest type of cement tester to be brought out is the Olsen-Boyd machine (Fig. 194). This is also made by Tinius Olsen Testing Machine Company, Philadelphia. This machine has all the advantages of the shot type of machine but does not employ any shot. This is desirable since the shot have to be returned to the kettle after each test and during this transfer are apt to be spilled. In this machine the initial load is applied as with the shot type of machine by means of the lower hand wheel. A ratchet ar- rangement at the base can be set so as to cut off the pressure here at any desired initial load even though the operator con- tinues to turn the hand wheel. This guards premature breaks. The breaking load is applied by means of the weight at the right of the machine which moves downwards, the motion being con- trolled hydraulically so as to give a uniform rate of loading of 6OO pounds per minute or any other rate desired. The load is indicated continuously as applied by means of the pointer and dial, the former remaining at the maximum point of load when the briquette breaks. After the briquette is broken and is re- moved from the clips, the pointer is set at zero by pushing up the plunger shown below the dial and the weight to the right is raised to the initial point by the hand wheel when it is auto- matically latched in place. These operations can be quickly done, when the machine is ready for another test. In spite of the short time in which this machine has been on the market it is ex- tensively used. Ratc of Siress Whatever machine is employed to break the briquettes the load is to be applied at the rate of 600 pounds per minute. The standard load for many years was 400 pounds per minute but the committee of the American Society of Civil Engineers in their 658 PORTLAND CEMENT report of 1903 increased this to the above figure. The more rapidly the load is applied to a cement briquette, the higher the breaking figure which will be obtained. Any of the automatic shot testing machines described above can be set so that the load will be applied at a uniform rate. Clips Some of the various forms of clips are shown in the following illustrations. Fig. 195 shows that recommended by the former Fig. 195.-Old standard clip. lſº agº. ---1.25°---ſº- 0.25° One inch Fig. 196.-Standard form of clip. TENSILE STRENGTH 659 committee of the American Society of Civil Engineers. This form does not seem to be very satisfactory as the bearing surface is insufficient and the briquette is likely to break from the crush- ing of its surface at the point of contact. A later form of clip Fig. 196 is much more to be preferred. It affords sufficient bear- ing surface without binding. Various authorities at different times have advocated cushion- ing the grips by placing blotting paper between the jaw of the grip and the briquette, or stretching rubber bands around the Fig. 197.-Rubber cushioned clip. jaws, so as to soften the point of contact of these with the test piece. Mr. W. R. Cock' advised the use of a rubber bear- ing as shown in Fig. 197. In this clip the line of contact be- tween the grip and the briquette is a rubber tube mounted on a Fig. 198–Roller clips. pin. These tubes are readily replaced for a few cents when worn out. These cushion clips usually give results which are only 80 to 90 per cent of those obtained with the standard clips. The cushion clips are also troublesome. * Engineering News, Dec. 20, 1890. 660 PORTLAND CEMENT Roller clips (Fig. 198) are now as stated much used. Roller bearings are likely to wear flat unless they are kept clean and can revolve freely. This it is hard to do. Roller clips do not give breaks that are any higher than those obtained with the Standard rigid form. The general impression seems to be that clip breaks are due to cross strains and hence give figures below the true breaking strength of the cement. In fact, experiments prove that clip breaks are on an average from 2 to 5 per cent higher than breaks obtained at the cross-section. The roller clip shown in Fig. 198 has a solid back which pre- vents the briquette from being shoved too far back in the clip. This or some form of stop is desirable with any form of clip. In order that the stress upon the briquette shall be along the proper lines great care must be exercised in properly center- ing the briquette in the clips, and the form of the latter must be such that it does not clamp the head of the briquette thus pre- venting the test piece from adjusting itself to an even bearing. At the same time the surface of contact must be sufficient to prevent the briquette from being crushed at this point. Striking the happy medium has so far proved not any too easy. The clips are usually suspended by conical bearings which permit them to turn so as always to transmit the stress in a direct line between the bearings. Other Methods Foreign Specifications The British test briquette is of the same form and dimensions as our own. Their sand is a natural sand also, but the British specifications call for both neat and sand tests. The molds are filled by hand with a special form of spatula. The requirements call for a minimum neat strength at Seven days of at least 450 pounds and a I 3 sand strength of 200 pounds. The twenty- eight-day neat test must not be less than 500 pounds and the in- crease in strength from seven to twenty-eight days must not be less than TENSILE STRENGTH 661 25 per cent if the 7 day test is between 400 and 450 lbs. 20 per cent if the 7 day test is between 450 and 500 lbs. 15 per cent if the 7 day test is between 500 and 550 lbs. Io per cent if the 7 day test is between 550 and 600 lbs. 5 per cent if the 7 day test is over 600 lbs. The sand strength at twenty-eight days must not be less than 250 pounds and the increase in strength from seven to twenty- eight days must not be less than 25 per cent if the 7 day test is between 200 and 250 lbs. 15 per cent if the 7 day test is between 250 and 300 lbs. Io per cent if the 7 day test is between 300 and 350 lbs. 5 per cent if the 7 day test is over 350 lbs. The standard German specifications, like our own, call for no neat test. The form of briquette has been shown in Fig. 185. The Steinbrüch mixer and the Bohmé hammer are employed for mixing the mortar and tamping the molds respectively. The specifications call for a sand strength of at least I2 kilograms per square centimeter which is equivalent to 171 pounds per square inch. The specifications require no twenty-eight day tensile strength test but do require a seven and twenty-eight-day compressive I :3 sand test equivalent to I,708 pounds and 2,846 pounds per square inch minimum respectively for the two periods. The standard French specifications call for both neat and sand tests. The form of briquette is the same as that shown in Fig. 185. The mortar is hand mixed and the molds hand filled. The requirements are: Kilos per sq. cm. Lbs. per sq. in. 7 days neat 25 356 28 days neat 35 498 Increase between 7 and 28 days neat 3 42.7 7 days I : 3 sand 8 II4 28 days I : 3 sand I5 2I3 Increase between 7 and 28 days sand 2 28.4 The above specifications are the minimum and the engineer can increase them if he should so desire. Lack of Uniformity in Tensile Tests In cement testing, the personal equation enters very largely into the results. In a paper" by Prof. James Madison Porter, of * Engineering News, March 7, 1895. 43 662 PORTLAND CEMENT Lafayette College, he gave a series of results upon the same cement by nine different operators, tested by the method of the Society of Civil Engineers as they understood it. The results varied from 75 to 247 pounds per square inch. The first Com- mittee on a Uniform System for Tests of Cement of the Ameri- can Society of Civil Engineers, in their report, says: “The testing of cement is not so simple a process as it is thought to be. No small degree of experience is necessary before one can manipulate the materials so as to obtain even approximately accurate results. “The first test of inexperienced, though intelligent and careful persons, are usually very contradictory and inaccurate, and no amount of experience can eliminate the variations introduced by the personal equations of the most conscientious observers. Many things, apparently of minor import- ance, exert such a marked influence upon the results, that it is only by the greatest care in every particular, aided by experience and intelligence that trustworthy tests can be made.” The personal equation probably plays its most important part in the gauging of the cement, the making of the mortar, and the molding and breaking of the briquettes. In order to eradicate these variations of treatment, machines have been introduced upon the market to do the work automatically and so do away with whatever variations the operator may introduce into the hand work, principally among which are the Steinbrüch and the Faija mixers and the Bohmé hammer. None of these machines, however, give test pieces which are more uniform than hand , made ones. Machines for Mixing the Mortar and Making Briquettes The Steinbriich mixer is much used in Germany. It consists of a horizontal circular casting having on its upper side near the outer edge a groove or trough in which a wheel whose rim corresponds with the groove of the pan rests. Both the pan and the wheel revolve and the mortar is rubbed between the surfaces of the wheel and the trough. Ploughs keep the mortar in th center of the trough. *- The Faija mixer is the design of the late Henry Faija, of Eng- land and is listed in the catalogue of Riehlé Bros. Testing Ma- chine Company, of Philadelphia. TENSILE STRENGTH 663 The Taylor mixer is the design of Mr. W. P. Taylor and was used by him while in charge of the Municipal Cement Testing Laboratory of Philadelphia. It is listed in the catalogue of Tinius Olsen Testing Machine Company, Philadelphia. The Bohme hammer" consists of a tilt hammer with automatic action, which hammers the cement mortar into the mold. It is listed by both of the firms mentioned above. The Olsen molding machine fills the mold by compression applied by a hand wheel through a plunger. It is made by Tinius Olsen Testing Machine Company. None of these machines have been used to any extent for testing cement in this country. Those who are interested in machines for mixing the mortar and molding the briquettes are referred to the earlier editions of this book or to the standard English and German works on cement testing. Observations High Tensile Strength of Unsound Cement Much attention was formerly paid to neat strength but as the result of the opposition of the writer and other cement experts to this practice, the neat test has now been dropped from the standard specifications. Unsound cements often give notoriously high results, and the addition of plaster or gypsum will also in- crease the neat strength. In both of these instances there is apt to be on long time breaks a falling off in strength, permanent in the former case and usually only temporary in the latter case. This is illustrated by the following table taken from a paper by Mr. W. P. Taylor, on “Soundness Tests of Portland Cement,” TABLE LXVI.—CoMPARISON OF THE TENSILE STRENGTH OF BRI- QUETTES PAssING AND FAILING IN THE BoILING TEST. Failing Passing I : 3 I : 3 Age - Neat sand - Neat sand 1 day 530 tº tº º 39 I * : * 7 days 817 I97 643 237 28 days 749 273 727 303 2 months 7I3 274 732 3I2 3 months 7O2 242 749 3I4 * Trans., Am. Soc. C. E., 3, p. 1. * Proceedings, Amer. Soc. Test. Met., III (1903), 381. 664 PORTLAND CEMENT read in 1903. This table was compiled from over 200 nearly con- secutive tests of a single brand, IOO of them failing in the test, IOO passing. It will be noticed that the early strength of the neat tests of those samples failing to pass the test is much the greater, while the opposite is true of the sand samples. Relation Between Neat and Sand Strength That the sand strength and neat tests do not necessarily bear any relation to each other, the Table LXVII will show. The TABLE LXVII.-SHOWING LACK OF ANY RELATION BETweeN NEAT AND SAND STRENGTH. Fineness Tensile strength Tensile strength Cement Boiling Through through 7 days 28 dav's No. test No. IOO NO. 200 Neat I : 3 Neat I : 3 I O. K. 99.O 8O.O QI5 303 IOI3 353 2 O. K. 99.O 80.0 790 285 853 320 3 O. K. 99. I 85. I 933 298 990 340 4 O. K. 98.8 83.3 O3O 288 963 330 5 O. K. 94.8 78.8 733 27O 825 360 6 O. K. 95.O 79.O 748 28O 62O 275 7 O. K. 96.5 74.O 818 273 858 360 8 O. K. 97.O 74.0 8OO 260 IOI3 28O Q O. K. 95. I 7O.O QIO I90 Io38 266 IO O. K. 95.0 7O.O 683 I8O 750 320 II O. K. 98.o 82.5 IOO8 2OO III5 282 I2 O. K. 97.9 82.5 855 283 97O 333 I3 O. K. 94.8 75.O 6IO 350 8Io 440 I4 O. K. 92.0 7O.O 544 2O6 884 26I I5 O. K. 93.4 70.4 7OI 217 893 3IO I6 O. K. 93.8 74.2 68O 359 791 4IO I7 O. K. 97. I 82.5 855 283 97O 333 I8 O. K. 97.4 82.7 QIO 255 97O 305 sand strength seems to depend largely upon the fineness, yet dif- ferent brands of cement giving similar residues on the test sieves will not necessarily show the same relation between neat and sand test. This latter may, of course, be due to differences in the amount of flour, which is not shown by the sieve test, as well as to peculiarities of composition, physical structure, etc., of the clinker from which the cement is ground. The opinion is also becoming more and more general that there is little relation between the tensile strength of sand bri- TENSILE STRENGTH 665 quettes and of concrete. This is illustrated by the tests given in Table LXVIII. Each cement in this is a sample of a different brand and the four represent cement made in different sections of the country and from several kinds of material. From this and from numerous other tests which have been made it would appear that while the sand test is of value in determining whether cement is fit for use or not, it should not be used as a basis for comparatively valueing cements. It will also be seen that the tests are much nearer together at twenty-eight days than at seven days, and also that the difference between the compressive strength of the four cements at twenty-eight days is slight, the lowest figure being only about Io per cent less than the highest. TABLE LXVIII.—Coyſ PARISON BETweeN TENSILE STRENGTH OF I : 3 SAND MORTAR AND COMPRESSIVE STRENGTH OF CONCRETE. Setting Tensile strength Compressive strength time Fineness I : 3 sand I : 2 : 3 concrete In "1. Fin'1. No. 200 7 days 28 days 7 days 28 days Cement min. min. % lbs. 1bs. lbs. 1bs. A 2IO 38o 8O. I 235 382 1805 2403 B 2OO 355 80.0 28O 342 I37O 228o C 225 4OO 76. I 249 390 957 216I D I65 360 83.5 246 290 I625 2328 CEMENT's ARRANGED IN ORDER OF STRENGTH. Tensile strength. I : 3 sand Compressive strength 1 : 2 : 4 concrete 7 dav's 28 days 7 days 28 days % of % of % of % of Cement flighest Cement highest Cement highest Cement highest B IOO C IOO A IOO A IOO C 89 D IOO D QO D 97 D 88 A 98 B 76 B 95 A 84 B 88 C 53 C 90 Effect of Seasoning and Hydration on Strength The Structural Materials Research Laboratory" has made an extensive investigation of the effects of storage on the strength of concrete. This covered a period of five years and three dif- ferent lots of Portland cement, the cement being stored under cover in standard cotton sacks. As the result of this investiga- tion it was found that there is an appreciable loss in the strength of Portland cement due to storage and that the loss of strength 1 Bul. No. 6, Structural Materials Laboratory, Lewis Inst., Chicago. 666 PORTLAND CEMENT *= –42- &222 60%2/7 32% ºgºź” C2/* zºº/ Cºe/2262/27.5 N £ºg &eaſº-//7-22/27. %22 S. 3 N Q _%2% is ~ © jºss'; te >< <- ^- $ zºo 2=>s-> **-x § /ø/2 O - ---O S T--—H.--O S } &% Ş / --> º % JZ222 /2,~~~zzazoº & 2// cººz76°/2/3. t § 3%.3%% Ş | w) 4/2007 § Ns § 3/22/2 & J– Ža 7 § § W - – –o *** - – - – -OT C2/272^2/ Jºž/zz/- 4/eaſ/is Fig. 199.-Effect of storage of cement on its strength. TENSILE STRENGTH 667 is greater for the first three months of storage than for latter three months periods. It was also found that the earlier tests showed a much greater loss in strength due to storage than tests at later ages. Chemical analyses made during this investigation show that the deterioration of cement in storage is due to absorption of atmospheric moisture which in time causes a partial hydration of the cement. Fig. 199 gives a graphic summary of the re- sults of this experiment and illustrates the falling off in strength due to storage. These experiments were made on a small quantity of cement. The rate of seasoning of a large quantity of cement stored in bulk in a silo or bin at the plant would not be so rapid. Mani- festly cement stored in a low rectangular bin would season much more slowly than if stored in sacks around which the air could circulate. Similarly the seasoning in a tall silo would be less rapid than in a low bin. The rate of seasoning would depend on the surface exposed to the atmosphere and the humidity and temperature of the latter. Observations which the writer has made seem to indicate that the same phenomena holds good for the seasoning of clinker also and that cement made from seasoned clinker if ground to the same degree of fineness will not show the same strength as that made from the same clinker ground immediately after burn- ing. In considering the effect of seasoning clinker on the strength of cement, it should be remembered, however, that seasoning of the clinker makes this easier to grind and consequently allows a finer product to be economically made. Drop in Tensile Strength A point which has often been brought against cement, and American cements in particular, is that there is a permanent drop in tensile strength after the twenty-eight day neat test. In fairly quick-setting cements with their usual low-lime content and to which the normal amount of gypsum or plaster has been added, this drop is rarely met with and is probably then due to improper 668 PORTLAND CEMENT manipulation of the test. In cements high in lime, without being necessarily unsound, or in cements to which a large addition of plaster or gypsum has been made, this drop is often met with. In unsound cements it is usually met with, often after the seven- day test. It does not necessarily follow that any drop in strength indi- cates a disrupting action, because as cement briquettes get older they get more and more brittle, and consequently tensile stresses break them more easily. Particularly is this true if the clips TABLE LXIX.—SHowING Loss IN STRENGTH OF NEAT BRIQUETTES AND GAIN IN SAND BRIQUETTES AFTER SEVEN-DAY TEST. o Tensile strength Z. t Boiling Neat I : 3 sand # test § 7 days 28 days | 3 mos. 6 mos. I yr. 7 days 28 days měs. mº, I year I O. K. 657 615 650 | 680 || 7 I I 240 302 || 360 | 381 405 2 || O. K. 915 | 845 | 730 || 760 | 755 || 3 IO || 360 || 375 || 378 || 415 3 || O. K. IO58 || Io23 | 890 | 852 || 783 | 200 || 263 || 425 || 4 io || 463 4 || O. K. 865 | 727 | 730 650 | 728 317 | 353 390 | 400 || 416 5 O. K. 708 || 656 | 661 | 663 | 665 20 ! 279 | 402 || 455 520 6 || O. K. 735 | 704 | 684 | 688 || 658 290 4o 426 443 477 7 O. K. 916 | 845 816 || 825 | 802 301 || 360 424 || 45o 456 8 || O. K. IOI 2 | 875 | 890 92 I | 944 || 306 || 374 || 381 || 4 Io 467 9 || O. K. 912 815 826 814 | 827 292 || 327 | 368 381 381 IO | O. K. 856 || 303 || 8IO | 8 || 4 || 81 I 275 || 361 || 369 || 391 || 418 II Check’d II.50 || 775 6Io 615 674 || 235 | 315 366 || 381 427 I 2 { { 947 || 8 || 6 || 702 || 3 IO | Dis. 2 IO | 246 247 || 311 || 312 I3 { { 812 || 3O4 || 318 || 3o I | 204 || 294 || 316 || 32 I | 330 || 327 I4 { { 955 || 8 | I | 8 ||6 || 802 || 503 || 274 || 321 375 || 4 ||6 || 427 I5 { { 927 802 || 765 612 344 213 227 264 || 375 || 414 I6 { { 6IO || 3 || 4 || I9 I 78 95 224 || 237 || 24I 256| 281 17 6 & II IO || 765 342 | Dis. |Dis. 275 298 || 3 15 362 396 exert any twisting action and the load is not evenly applied. Also cement is never used neat and in the vast majority of cases when a cement shows a slight falling off in neat strength, the sand strength increases with age. This is shown in Table LXIX. Humphreys states that the compressive strength of neat cement does not experience this drop when the cement is sound even if the tensile strength does fall off somewhat after the twenty- TENSILE STRENGTH 669 eight day test; an important fact, if true, as cement is seldom if ever used in tension. Coarse grinding of the cement has some influence on the in- crease in strength with age. A very fine cement increases neat very little after seven days, while a coarser one keeps on increas- ing. This is no doubt due to the fact that the coarse particles are acted on much slower than the fine ones, and solution and crys- tallization of these go on after the finer ones are all hydrated. The following experiment was made with the same cement. Cement A is just as it comes from the mills. Cement B is cement A with the coarse particles (residue on a No. 200 sieve, re- moved): Age 7 days 28 davs 3 mos. 6 mos. Q moS. Cement A, 1bs. 618 695 675 25 750 Cement B, 1bs. 518 546 535 5IO 549 Of seventy-six samples of the same brand of cement, each one containing from 63.25 to 63.75 per cent lime when freshly ground and passing the boiling test, those ground to a fineness of 80-85 per cent through a No. 200 sieve showed an increase of only 3.4 per cent neat strength between the periods of seven and twenty- eight days; while those ground to a fineness of 70-75 per cent through a No. 200 sieve gained 18.3 per cent in this time. When a cement gives a high neat break on seven days, and passes the steam test when received, failure to show a marked increase in twenty-eight days should not be taken as an indication of a poor Cement. Manufacturing Conditions Influencing Strength The chief manufacturing conditions which influence the strength of cement are the “lime ratio,” the fineness to which the cement is ground and the percentage of sulphur trioxide which it contains. The first two will play a very important part in the strength of the cement and the latter to a limited extent. The effect of fineness on the properties of cement has been quite fully discussed. Formerly a fineness of 75 per cent passing the 200-mesh sieve was considered ample. To-day, however, a finer product is being demanded and under present conditions 670 PORTLAND CEMENT most manufacturers are grinding cement to a fineness of at least 80 per cent passing the No. 200 sieve, the general range being between 80 and 85 per cent. If the cement has been properly proportioned as regards chemical composition and the setting time and soundness are satisfactory, a fineness of 80 will be ample to secure the strength required by the standard specifica- tions. If a stronger product is desired, it will probably be found easier to secure this by fine grinding rather than by unusual chemical composition. With regard to chemical composition, the influence of alumina in securing early strength has been discussed in Chapter II of this book. It is doubtful, however, if increasing the alumina beyond a ratio of I alumina to 2% of silica will be generally advisable unless the manufacturer desires to go to the special high alumina cements. Increasing the alumina beyond this point will very probably result in quick-setting cement and difficulty in burning the clinker uniformly which would probably affect the soundness. Where the silica-alumina ratio is greater than 4 to I, it will probably be found advisable to increase the alumina, otherwise efforts to increase strength had better be directed towards a finer cement or a higher lime ratio. Where cement has been ground to a proper degree of fineness and does not show the desired strength, it is probable that the percentage of lime is too low. In this event, the trouble will be detected by chemical analysis and the remedy will be evident. It is, of course, difficult to give any fixed rules relative to how high the lime should be carried because this must be governed to some extent by the soundness test. Generally, however, a cement which has a lime ratio" of less than I.9 will show low strength. This is particularly true of high silica cements or cements in which the alumina is low. & In connection with chemical composition it should be remem- bered that increasing the lime ratio will make the clinker easier to grind and consequently a finer product can be obtained with the same expenditure of power, etc. % Lime T e 1 t I t a *, * % Silica-i- ſº Alumina-H # Iron oxide should not be less than 1.9 TENSILE STRENGTH 67 i Increasing the percentage of sulphur trioxide will often re- sult in a slight gain in strength. As a general thing, if the cement has been properly proportioned the necessary strength will be obtained with a percentage of sulphur trioxide not exceeding 1.5. In extreme cases if found to be of assistance in increasing strength and where other means are not available, the percent- age of sulphur trioxide in the cement might be increased with this end in view. Generally, however, it will be better to secure the strength by increasing the fineness or the lime ratio. MISCELLANEOUS CHAPTER XXV THE DETECTION OF ADULTERATION IN PORTLAND CEMENT The detection of adulteration in Portland cement is a prob- lem which the American chemist rarely, if ever, has to solve. The writer does not recall a single instance which has come under his observation during the last fifteen years where cement has been even suspected of being adulterated. Some twenty years ago a few manufacturers at times did grind together a mixture of Rosendale or Natural cement clinker, and sell either as a blend (“Improved Cement”) or sometimes as straight Port- land cement. While depreciating this practice, it is only fair to the manufacturers who did this to say that for the most part they honestly believed they were making a superior product by so doing. As the result of the activities of the Portland Cement Association to discourage this practice and the fact that engi- neers gradually came to look upon those brands of cement with suspicion whose makers even burned Rosendale cement, these blended cements have entirely disappeared from the market. When adulteration is suspected, the cement should be subjected to a microscopic test and if evidence of this is found a more careful investigation can be made. º Cements have been adulterated with natural cement, blast- furnace slag, ground limestone, shale, ashes, etc. Some of these substances are so similar to Portland cement that chemical an- alysis fails to show their presence. It is, therefore necessary to direct special tests to their detection. When present in small quantities, it is probable that even such tests will fail to show positively an adulterated cement. Microscopic Test The microscope furnishes us with a very good means of detect- ing added material in cement. Butler" recommends that those 1 Portland Cement, 2nd Edition, p 304. MISCELLANEOUS 673 particles which pass a 76 sieve and are retained upon a 120 sieve be examined with a low power (say one-inch) objective. The particles of pure, well-burned cement clinker of this size will then appear dark, almost black in color, resembling coke somewhat, and will possess the characteristic spongy honey-combed appear- ance of cement clinker. The particles of less well-burned clinker, always present in cement, will, when examined in the same way, present the same shape and structure, but will differ in color, being light brown and semi-transparent, resembling gum arabic. Intermediate products range from black to light brown. These particles are always of a more or less rounded nature. Particles of slag of the same size viewed under the same conditions differ somewhat in color, according to the nature of the slag. Usually the particles are light colored, of angular fracture, and instead of the particles presenting a rounded appearance the edges are sharp like flint. Not to be mistaken for the slag, however, are the particles of pebbles from the tube mills used to grind the clinker. These latter may be distinguished from the slag by pick- ing out the particles in question with a pair of pincers, crushing them in a small agate mortar and treating them with hydrochloric acid. The slag is readily attacked while the débris from the pebbles is not attacked. Particles of iron from the crushers are also present in the residue caught upon the I2O sieve. These may be identified by their black metallic appearance and their behavior with the magnet. Neither of these can, of course, be considered as adulterants. Limestone and cement-rock if present are in more or less flattened particles, and the latter is always dark gray in color. Both of these may be readily detected by effervescence with dilute acids. The foreign particles may also be picked out of the residue with a pair of tweezers, ground finely and identified by chemical analysis. Tests of Drs. R. and W. Fresenius Drs. R. and W. Fresenius," at the request of the Association of German Cement Manufacturers, made investigations into the sub- ject of cement adulteration looking to a method of detecting the 1 Ztschr. anal. Chem., 23, p. 175, and 24, p. 66. 674 PORTLAND CEMENT same. They experimented upon twelve samples of pure Portland cement from Germany, England and France, and compared the results of tests upon these with the results obtained by similar tests upon three kinds of hydraulic lime, three kinds of weathered slag, and two of ground slag. The cements were of various ages and had been exposed to the air for various lengths of time. On the next page are tabulated their experiments for comparison. Proposed Tests As the result of these experiments they proposed the following tests for the detection of adulteration: I. The specific gravity. This must not be lower than 3.IO. 2. The loss on ignition. This should be between O.3 and 2.59 per cent; certainly not much more. 3. The alkalinity imparted to water. One-half gram of cement should not render 50 cc. of water so alkaline as to require more than 6.25 cc. nor less than 4 cc. of decinormal acid to neutralize. 4. The volume of normal acid neutralized. - One gram of cement should neutralize from 18.8 to 21.7 cc. of normal acid. 5. The volume of potassium permanganate reduced. One gram of cement should reduce not much more than O.OO28 gram of potassium permanganate. 6. The weight of carbon dioxide absorbed. * Three grams of cement should not absorb more than O.OOI8 gram of carbon dioxide. The tests I, 3, 4, and 5 are for the detection of slag and I, 2, 3 and 6 for the detection of hydraulic lime. Drs. R. and W. Fresenius also tried these tests upon experi- mental mixtures containing IO per cent of slag or hydraulic lime, and in each case were able to detect the impurity. MISCELLANEOUS 675 TABLE LXX.—ADULTERATION IN PORTLAND CEMENT. I 2 3 4 5 2 Tº c t 'S º ### #5 8 > - O Description : 5. ãº; a ; : $43 º bO • *4 * * 5 || 2 #5, ‘sº O é 5 Pºž : rºd - --, § * +: ; ºn ‘g ... 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