THE UNIVERSITY OF ILLINOIS LIBRARY 6?>\.5 Ec Digitized by the Internet Archive in 2016 with funding from University of Illinois Urbana-Champaign Alternates https://archive.org/details/secretsofpracticOOeckh \ Secrets of Practical Cement Construction PRICE $1.50 The Cement Institute • » 708 N. 7th St. SAINT - - LOUIS. - - MISSOURI Copyriglif 1906 by Fred. Eckhard Saint Louis = INDEX = = ^Le.^ % Basement Floors Beam and Floor Slabs Bridge Construction Bridge — One Span Creek Bridge — Flat Span Highway Building Blocks Building Block Machines Appearance and Use City Specifications — Concrete for — Cost of Efflorescence — Facing of Hardening Materials Mixing Standard Specifications ■—“Strength of — Tamping — how to Use of Rich Mixtures Facing Waterproof Qualities Colored Mortar Table Column Construction Fence Posts .... Freezing— How to Prevent Measuring for Mixing Mixing • Re-Inforced Concrete Building Re-inforced Designing Table 6 32 37 37 39 - 10 to 28 17 24 27 11 22 18 21 18 15&16 16 10 19 17 & 18 20 21 - 1 to 3 45 34 9 1 1 1 28 to 37 46 to 47 « ■■ f— < 5 JUJO INDEX = Concluded Sidewalks — Excavation — Sub-Foundation — Top Dressing Silos of Concrete Stable Floors and Driveways Steps Structural Details Water-proofing Building Blocks 3 to 36 33 1 to 3 3 Miscell; Illustrations- Hydrated Lime — How to make 2 Milk of Lime 3 Properly Graded Materials 2 Barn 43 Beam and Floor Slabs 32 & 34 Columns 34 Creek Bridge 37 Facing Plate 43 Flat Span Bridge 39 Gateway 44 Re-Inforced Building 29 Re-Inforcement for Bridges 41 Sidewalk Construction - 4 Silo Construction 11 Stirups — Fig. 4 - 29 Steps - 36 Structural Details 33 CD CO tO OO N MEASURING. Measure all parts in a barrel with the bottom out is a convenient way to measure sand gravel or crushed rock. Four bags of cement equals a barrel of cement. In estimating do not make the mistake so often made thinking that five barrels crushed stone (or gravel), three barrels sand and one barrel (4 bags) cement will make ten barrels con- crete, as the sand and cement do not take up any space, but simply fills in between the broken stone (or gravel), unless one-half or three-fourths rough stuff is used. MIXING. A watertight mixing board should be used, made of one-inch lumber, well cleated at bottom, with a 3x4 scantling around the outside of top, so as to prevent the mixture from leaving the mixing board. First place the sand on the board, then the cement, then mix the sand and cement thoroughly until the mass is of an even color, then wet and mix thor- oughly, then add crushed rock, or gravel. This method is for course rock, or gravel, say about 2-inch stuff. One-half or three-quarter inch rock or gravel should be mixed with the sand and cement in the dry state all at one time, and then add water. This will save labor. Do not make the concrete sloppy, have it just wet enough that when well tramped the water will come to the surface. A sprinkling can is a good way to add water, as it will not wash away the cement. Do not use a hose until you have become experienced. FREEZING. The best method to keep cement work from freezing is to warm the sand and stone and use hot water to mix. This will make the cement set quickly. Frost will not injure cement after it has set, but avoid cement work in cold weather if possible, as frost will prevent the bond- ing of the different layers and cause the outside to scale. Another method is to use about ten pounds of salt to a barrel of cement. WATERPROOFING. If it is desired to make a leaner concrete the following methods of waterproofing may be used with success. Hydrated lime slightly delays the setting of the cement and it will effervesce to an extent, -but the ultimate formation of the carbonate of lime closes the pores in the con- crete and makes it impermeable permanently. 1 HYDRATED LIME. Place the lime in a shallow box exposed to the air as much as pos- . sible, but protected from rain, sprinkle with a sprinkling can just a little every day, so as to cause the lime to fall to dust (hydrated lime)., Care must be taken not to use too much water, so as to cause the lime to cook. (See page for manner of mixing hydrated lime with cement.) WATERPROOF QUALITIES. The chief fault of concrete building blocks, as ordinarily made, is their tendency to absorb water. In this respect they are generally no worse than sandstone or common brick; it is well known that stone or brick walls are too permeable to allow plastering directly on the inside surface, and must be furred and lathed before plastering, to avoid dampness. This practice is generally followed with concrete blocks, but their use and popularity would be greatly increased if they were made sufficiently waterproof to allow plastering directly on the inside surface. For this purpose it is not necessary that blocks should be perfectly waterproof, but only that the absorption of water shall be slow, so that it may penetrate only part way through the wall during a long-continued rain. Walls 'made entirely water-tight, are, in fact, objectionable, owing to their tendency to “sweat’* from condensation of moisture on the in- side surface. For health and comfort walls must be slightly porous, so that any moisture formed on the inside may be gradually absorbed and carried away. Excessive water absorption may be avoided in the following ways: 1. — Use of Properly Graded Materials. — It has been shown that po- rosity and permeability are two different things; porosity is the total proportion of voids or open spaces in the mass, while permeability is the rate at which water, under a given pressure, will pass through it. Per- meability depends on the size of the openings as well as on their total amount. In two masses of the porosity or percentage of voids, one con- sisting of coarse and the other of fine particles, the permeability will be greater in case of the coarse material. The least permeability, and also the least porosity, are, however, obtained by use of a suitable mixture of coarse ^nd fine particles. Properly graded gravel or screenings, containing plenty of coarse fragments and also enough fine material to fill up the pores, will be found to give a much less permeable concrete than fine or coarse sand used alone.. 2 MILK OF LIME Used in place of clear water in mixing facing for cement blocks. Mix lime and water as you would whitewash. This will lighten the color of your block as well as make them waterproof. United States government engineers have used this process in forti- fication work. One specification prepares a’ wash of one pound con- centrated lye and five pounds of alum in two quarts of water to one part, which is added to ten pounds of cement, light colored preferred. The wash should be applied on a bright day, as the sun will bleach the wash, making the work a very light co.lor. Wet the wall before applying this wash. For cistern work the usual wash is simply cement grout, applied with a brush in one or two coats, usually to a well trowled surface. FOR CEMENT BUILDING BLOCKS. Take 5 per cent solution of ground alum in watej* and a 7 per cent solution of common yellow soap and water. Use the alum solution in mixing mortar half as much as the. usual" percentage of' water, then add the other half in the form of the soap solution. Use this for the facing- mixture only. Twenty pounds of alum to a barrel of water and five bars of soap to a barrel of water makes a good solution. When a concrete block building has already been erected, a wash composed of barium hydrate 5 ounces to each gallon of water may be used. Apply to the surface of the wall. Several coats should be applied at intervals. The solution must be used fresh, as it soon be- comes turbid if left in the air. This solution is cheap and effective. It fills and seals the pours by absorbing carbonic acid from the air. CONCRETE SIDEWALKS. A useful and comparatively simple application of concrete is in the construction of sidewalks, for which .purpose it has been used with marked success for a number of years. EXCAVATION AND PREPARATION OF SUBGRADE. The ground is excavated to subgjade and well consolidated by ram- ming to prepare it for the subfoundation of stone, gravel or cinders. The depth of excavation will depend upon the climate and nature of the ground, being deeper in localities where heavy frosts occur, or where the ground is soft, than in climates where there are no frosts. In the former case the excavation should be carried to a depth of 12 inches, whereas in the latter from 4 to 6 inches will be sufficient. No roots of trees should be left above subgrade. } THE SUBFOUNDATION. The subfoundation consists of a layer of loose material, such as broken stone, gravel or cinders. Spread over the subgrade and well tamped to secure a firm base for the main foundation of concrete, which is placed on top. It is most important that the subfoundation be well drained to prevent the accumulation of water, which, upon freezing, would lift and crack the walk. For this purpose it is well to provide drain tile at suitable points to carry off any water which may collect under the concrete. An average thickness for subfoundation is 4 to 6 inches. Although in warm climates, if the ground is firm and well' drained, the subfoundation may be only 2 to 3 inches thick, or omitted altogether. THE FOUNDATION. The foundation consists of a layer of concrete deposited on the sub- foundation and carrying a surface layer, or wearing coat, of cement mortar. If the ground is firm and the subfoundation well rammed in 4 place and properly drained, great strength will not be required of the concrete, which may, in such cases, be mixed in about the proportions 1-3-6, and a depth of only 3 to 4 inches will be required. Portland cement should be used and stone or gravel under 1 inch in size, the con- crete being mixed of medium consistency, so that moisture will show on the surface without excessive tamping. THE TOP DRESSING OR WEARING SURFACE. To give a neat appearance to the finished walk, a top dressing of cement mortar is spread over the concrete, well wo'rked in, and bro ught to a perfectly smooth surface with straight edge and float. This mortar should be mixed in the proportion of 1 part cement to 2 parts sand, sharp, coarse sand or screenings below one-fourth inch of some hard, tough rock being used. The practice of making the 'concrete of natural cement and the wearing surface of Portland is not to be commended, owing to a tendency for the two to separate. A cord stretched between stakes will serve as a guide in excavating, after which the bottom of the trench is well consolidated by ramming, any loose material below subgrade being replaced by sand or gravel. The material to form the subgrade is then spread over the bottom of the trench to the desired thickness and thoroughly compacted. Next, stakes are driven along the sides of the walk, spaced 4 to 6 feet apart, and their tops made even with the finished surface of the walk, which should have a transverse slope of one-fourth inch to the foot for drain- age. Wooden strips at least 1^2 inch thick and of suitable depth are nailed to these stakes to serve^ as a mold for the concrete. By carefully adjusting these strips to the exact height of the stakes they may be used as guides for the straightedge in leveling off the concrete and wearing surface. The subfoundation is well sprinkled to receive the concrete, which is deposited in the usual manner, well tapnped behind a board set vertically across the trench, and leveled off with a straightedge, as shown, leaving one-half to one inch for the wearing surface. Three- eighths inch sand joints are provided at intervals of 6 to 8 feet, to pre- vent expansion cracks, or, in case of settlement, to confine the cracks to these joints. This is done either by depositing the concrete in sec- tions, or by dividing it into such sections with a spade when soft and filling the joints with sand. The location of each joint is marked on the wooden frame for future reference. Care must be exercised to pre- vent sand or any other material from being dropped on the concrete, 5 and thus preventing a proper union with the wearing surface. No sec- tion should be left partially completed to be finished with the next batch or left until the following day. Any concrete left after the completion of a section should be mixed with the next batch. It is of the utmost importance to follow up closely tl;e concrete work with the top dress- ing in order that the two may set together. This top dressing should be worked well over the concrete with a trowel, and leveled with a straight- edge, to secure an even surface. Upon the thoroughness of this opera- tion often depends the success or failure of the walk, since a good bond between the wearing surface and concrete base is absolutely essential. The mortar should be mixed rather stiff. As soon as the film of water begins to leave the surface, a wooden float is used, followed up by a plasterer’s trowel, the operation being similar to that of plastering a wall. The floating, though necessary to give a smooth surface, will, if continued too long, brings a thin layer of neat cement to the surface and probably cause the walk, to crack. The surface is now divided into sec- tions by cutting entirely through, exactly over the joints in the concrete. This is done with a trowel guided by a straightedge, after which the edges are rounded off with a special tool called a jointer, having a thin s-hallow tongue. These sections may be subdivided in any manner de- sired for the sake of appearance. A special tool called an edger is run around the outside of the walk next to the mold, giving it a neat rounded edge. A toothed roller having small projectigns on its face is frequently used to produce slight indentations on the surface, adding somewhat to the appearance of the walk. The completed work must be protected from the sun and kept moist by sprinkling for several days. In freezing weather the same, precautions should be taken as in other classes of concrete work. CONCRETE BASEMENT FLOORS. Basement floors in dwelling houses as a rule require only a moderate degree of strength, although in cases of very wet basements, where water pressure from beneath has to be resisted, greater strength is re- quired than would otherwise be necessary. The subfoundation should be well drained, sometimes requiring the use of tile for carrying off the water. The rules given for constructing concrete sidewalks apply equally well to basement floors. The thickness of the concrete foundation is usually from 3 to 5 inches, according to strength desired, and for average work a 1-3-6 mixture is sufficiently rich. Expansion joints are frequently omitted, since the temperature variation is less than in outside work, but since this omission 'not infrequently gives rise to unsightly cracks, their use is recommended in all cases. It will usually be sufficient to divide 6 a room of moderate size into four equal sections, separated by one-half inch sand joints. The floor should be given a slight slope toward the center, or one corner, with provision at the lowest point for carrying off any water that may accumulate. CONCRETE STABLE FLOORS AND DRIVEWAYS. Concrete stable floors and driveways are constructed in the same general way as basement floors and sidewalks, but with a thicker foun- dation, on account of the greater strength required. The foundation : : may well be 6 inches thick, with a 1 inch wearing surface. An objection' sometimes raised against concrete driveways is that they become slippery when wet, but this fault is in a great measure overcome by dividing the wearing surface into small squares about 4 inches on the side, by means of triangular grooves three-eighths of an inch deep. This gives a very neat appearance and furnishes a good foothold for horses. 7 Reinforced concrete silos may be built Monolithic, but hollow cement building blocks will make the neatest and most serviceable silo and at the same cost Monolithic building requires greater skill than building blocks on account of cracks caused by contraction and expansion, and if too much water is used in mixing the concrete shrinkage cracks will appear. Farmers are beginning to use Portland cement concrete for silos, in which root crops and green fodder is stored for winter use, even green grass may be kept in these silos. Heretofore silos have been constructed of wood, brick or stone, all of which concrete is fast super- seding. For small silos plain Monolithic structures are built, for larger silos a simple form of reinforced concrete is coming into use, usually expanded metal or plain iron telegraph wire is the reinforcing member. A silo ten feet in diameter by fifteen feet high should have the foundations carried down below the frost line, the footing being about two feet wide at the base, contracting to sixteen inches at the top of the wall, upon which a wall ten inches thick will answer. Reinforced with sheets of expanded metal placed about one inch from the outer face of the wall and reinforced by heavy wire wound around the ex- panded metal and spaced two inches from centers for the first five feet of the structure for a circular tank or silo, a core is erected against which the concrete is deposited, a ring or circular form capable of being raised from time to time as the concrete is tamped in place. : : : The outer circular form as well as the inner core and the method of supporting the outer form by barrels and loose brick piers each time it is raised. This form is in two pieces, capable of being brought close together, in order to diminish the thickness of the wall which, being ten inches at the base, may be contracted to five inches at the top. The expanded metal sheets should lap five to six inches at the ends. The heavier the reinforcement the thinner may the walls be con- structed. In finishing the last ten inches of wall three-eighth inch iron bolts ten inches long should be imbedded in the top, projecting four inches out of the concrete, to be used for anchoring the roof, which is usually of wood. The mixture for the concrete may be one cement, three sand, and four gravel. Where hand mixing is the process, deposit the sand and gravel, over which spread the cement and turn not less than three times dry, then add water, just sufficient that when thor- oughly mixed the concrete will ball in the hand, deposit in place and ram or tamp well. In finishing the last ten inches of the wall at the 8 top eight or ten turns of wire should be laid or wound around the ■expanded metal for additional strength. A silo fifteen feet high with an internal diameter will have a capacity of about 1,179 cubic feet. Doors or openings are sometimes left in the silo walls for convenience of filling or removing the contents. For this purpose frame should be inserted, as is done in ordinary brick building construction, and the doors hung after the structure is finished- Concrete silos when prop- erly built are practically indestructible. FENCE POSTS. Fence posts should be stronger than building blocks, as a greater strain is put to them, for they often receive sudden jolts; various de- vices have been invented for attaching fence wire to the post, the con- cern you buy your mold from will advise you which is the best adapted to their particular make. A concrete not weaker than four parts of coarse, sharp sand to one part of Portland cement should not be used fbr posts. Although a post may be hard and apparently strong when one week old, it will not attain its full strength in that length of time and must be handled with the utmost care to prevent injury. Carelessness in hand- ling green posts frequently results in the formation of fine cracks, which, though unnoticed at the time, give evidence of their presence later in the failure of the post. Posts should be allowed to cure for at least sixty days before being placed in the ground, and for this purpose it is recommended that when moved from the molding platform they be placed upon a smooth bed of moist sand and protected from the sun until thoroughly cured. During this period they should receive a thor- ough drenching at least once a day. The life of the molds will depend upon the care with which they are handled. A coating of mineral oil or shellac may be used instead of soap -to prevent the cement from stick- ing to the forms. As soon as the molds are removed they should be cleaned with a wire brush before being used again. The cost of rein- forced concrete fence posts depends in each case upon the cost of labor and materials, and must necessarily vary in different localities. An estimate in any particular case can be made as follows: One cubic yard of concrete will make 20 posts, measuring 6 inches by 6 inches at bot- tom, 6 inches by 3 inches at top, and 7 feet long, and if mixed in the proportions \-2]/ 2 -S, requires approximately. Materials for 1 cubic yard of concrete: 1 barrel of cement. 3 barrels of sand. 5 barrels of gravel. To this must be added the cost of mixing concrete, molding and handling posts. STANDARD SPECIFICATIONS FOR CEMENT BLOCKS. One of the most important subjects to be considered by the. cement block industry is standard specifications for cement building blocks that will meet the 'approval of municipal corporations, engineers, archi- tects and the private consumer. Such specifications will inspire confi- dence and result in the real advancement of the industry. A block with a mixture of 1 cement to 4 sand and gravel will meet all of the require- ments for strictly first-class material. It will be dense, fairly waterproof and sound in every way, provided the curing is properly done. While a weaker mixture, say 1 to 7, will be amply strong where the aggregates are properly graded, there is yet an element of danger in new and inex- perienced men, the richer the mixture in cement the sooner will the block be ready to set in the wall, thus a saving of . time in completing the work. Blocks in which cement has been skimped has now and then re- sulted in giving the industry a black ’eye. It is this identical bad work that has made the insurance companies timid in giving reasonable rates. Bad news travels fast. So does bad work. In every community there are men who are ever ready to pick flaws in concrete construction, especially where the cement block is displacing wood, stone and brick the cement block is therefore on trial and will be compared with other forms and materials of construction. It behooves the cement block manufacturer not to skimp the materials, but always to turn out strictly high grade work, and he will be the gainer in the end and overcome the kickers who are constantly crying down the innovation the cement block is effecting in the building industry. This is particularly true of a certain class of old line architects who still cling with Chinese persist- ence to the materials of their fathers, shutting their eyes to the living, breathing present with its potent array of force which are constantly undermining and transforming old ideas. Unfortunately, owing to poor workmanship and lack of artistic de- sign, a large part of the hollow block buildings hitherto erected have fallen far short of the excellence above described. A multitude of men 10 without capital and inexperienced in the use of cement have embarked in the business of block making, attracted by the glowing prospects of profits held out by the army of block machine agents. As a result, great quantities of inferior blocks, weak, porous and unsound, have been and are being turned out, and have been erected by careless and unskilled builders into defective and ugly structures. This state of affairs is an injury to competent and conscientious block manufacturers, and an obstacle to the adoption of a most excellent and promising building material. Blocks of first-rate quality can easily and cheaply be made, with small outlay for machinery, provided certain simple rules are intelli- gently followed. It is the purpose of this paper to state briefly the causes of faults in concrete blocks, and the precautions by which good and reliable work may be assured. CONCRETE. Concrete is an artificial stone consisting of coarse and fine fragments, such as sand, gravel and broken stone, united by cement to a solid mass. The strength of concrete depends greatly upon its density, and this is secured by using coarse material which contains the smallest amount of voids or empty spaces. Different kinds of sand, gravel and stone vary greatly in the amount of voids they contain, and by judiciously mixing coarse and fine material the voids may be much reduced and the density increased. The density and percentage of voids in concrete ma- terial may be determined by filling a box of one cubic foot capacity and weighing it. One cubic foot of solid quartz or limestone, entirely free from voids, would weigh 165 pounds, and the amount by which a cubic foot of any loose material falls short of this weight represents the pro- portion of voids contained in it. For example, if a cubic foot of sand weighs 115j/2 pounds, the voids would be 49j4-165ths of the total volume, or 30 per cent. Experiments have shown that the strength of concrete increases greatly with its density; in fact, a slight increase in weight per cubic foot adds very decidedly to the strength. The gain in strength obtained by adding coarse material to mixtures of cement and sand-is shown in the following table of results of experi- ments made in Germany by R. Dykerhoff. The blocks tested were 214- inch cubes, 1 day in air and 27 days in water: 1 2 33 2,125 1 2 5 12.5 2,387 1 3 — 25 1,383 1 3 9.5 1,515 1 4 20 1,053 1 4 8^4 7.4 1,204 11 These figures show how greatly the strength is improved by adding- coarse material, even though the proportion of cement is thereby re- duced. A mixture of 1 to \2]/ 2 of properly proportioned sand and gravel is, in fact, stronger than 1 to 4, and nearly as strong as 1 to 3, of cement and sand only. In selecting materials for concrete, those should be chosen whicu give the greatest density. If it is practicable to mix two materials, as sand and gravel, the proportion which gives the greatest density should be determined by experiment, and rigidly adhered to in making concrete, whatever proportion of cement it is decided to use. Well proportioned dry sand and gravel or sand and broken stone, well shaken down, -should weigh at least 125 pounds per cubic foot. Limestone screenings, owing to minute pores in the stone itself, are somewhat lighter, though giving equally strong concrete. They should weigh at least 120 pounds per cubic foot. If the weight is less, there is probably too much fine dust in the mixture. The density and strength of concrete are also greatly improved by use of a liberal amount of water. Enough water must be used to make the concrete thoroughly soft and plastic, so as to quake strongly when rammed. If mixed too dry it will never harden properly, and will be light, porous and crumbling. Thorough mixing of concrete materials is essential, to increase the density and give the cement used a chance to produce its full strength. The cement, sand and gravel should be intimately mixed, dry, then the water added and the mixing continued. If stone or coarse gravel is added, this should be well wetted and thoroughly mixed with the mortar. MATERIALS FOR CONCRETE BUILDING BLOCKS. In the making of building blocks the spaces to be 'filled with con- crete are generally too narrow to permit the use of very coarse material, and the block-maker is limited to gravel or stone not exceeding y 2 or Y inch in size. A considerable proportion of coarse material is, how- ever, just as necessary as in other kinds of concrete work, and gravel or screenings should be chosen which will give the greatest possible density. For good results, at least one-third of the material, by weight, should, be coarser than % inch. Blocks made from such gravel or screenings, 1 to 5, will be found as good as 1 to 3 with sand only. It is a mistake to suppose that the coarse fragments will show on the surface; 12 if the mixing is thorough this will not be the case. A moderate degree of roughness or variety in the surface of blocks is, in fact, desirable, and would go far to overcome the prejudice which many architects hold against the smooth, lifeless surface of cement work. Sand and gravel are, in most cases, the cheapest material to use for block work. The presence of a few per cent, of clay or loam is not harmful provided the mixing is thorough. Stone screenings, if of good quality, give fully as strong concrete as sand and gravel, and usually yield blocks of somewhat lighter color. Screenings from soft stone should be avoided, also such as contain too much dust. This can be determined from the weight per cubic foot, and by a' sifting test. If more than two-thirds pass j^-inch, and the weight (well jarred down) is less than 120 pounds, the material is not the best. Cinders are sometimes used for block work; they vary greatly in quality, but if clean and of medium coarseness will give fair results. Cinder concrete never develops great ‘ strength, owing to the porous character and crushability of the cinders themselves. Cinder blocks may, however, be strong enough for many purposes, and suitable for work in which great strength is not required. Lime. — It is well known that slaked lime is a valuable addition to cement mortar, especially for use in air. In sand mixtures, 1 to 4 qr 1 to 5, at least one-third of the cement may be replaced by slaked lime without loss of strength. The most convenient form of lime for use in block-making is the dry-slaked or hydrate lime, now a common article of commerce. This is, however, about as expensive as Portland cement, and there is no great saving in its use. Added to block concrete, in the proportion of % to V 2 the cement used, it will be found to make the blocks lighter in color, denser, and decidedly less permeable by water. Cement. — Portland cement, today, is the only hydraulic material to be seriously considered by the block-maker, and at present prices there is nothing gained by attempting the use of any of the cheaper substitutes. Natural and slag cements and hydraulic lime are useful for work which remains constantly wet, but greatly inferior in strength and durability when exposed to dry air. A further advantage of Portland cement is the promptness with which it hardens and develops its full strength; this quality alone is sufficient to put all other cements out of consideration for block work. 13 PROPORTIONS. There are three important considerations which must be kept in view in adjusting the proportions of materials for block concrete — strength, permeability, and cost. So far as strength goes, it may easily be shown that concretes very poor in cement, as 1 to 8 or 1 to 10, will have a crushing resistance far beyond any load that they may be called upon to sustain. Such con- cretes are, however, extremely porous, and absorb water like a sponge. It is necessary, also, that the blocks sh'all bear a certain amount of rough handling at the factory and while being carted to work and set up in the wall, and safety in this respect calls for a much greater degree of hardness than would be needed to bear the weight of the building. Again, strength and hardness, with a given proportion of cement, depend greatly on the character of the other materials used; blocks made of cement and. sand, 1 to 3, will not be so strong or so impermeable to water as those made from a good mixed sand and gravel, 1 to 5. On the whole, it is doubtful whether blocks of satisfactory quality can be made, by hand mixing and tamping, under ordinary factory conditions, from a poorer mixture than 1 to 5. Even this proportion requires for good results the use of properly graded sand and gravel or screenings, a liberal amount of water, and thorough mixing and tamping. When suitable gravel is not obtainable, and coarse mixed sand only is used, the proportion should not be less than 1 to 4. Fine sand alone is a very bad material, and good blocks cannot be made from it except by the use of an amount of cement which would make the cost very high. The mixture above recommended, 1 to 4 and 1 to 5, will necessarily be somewhat porous, and may be decidedly so if the gravel or screenings used is not properly graded. The water-resisting qualities may be greatly improved, without loss of strength, by replacing a part of the cement by hydrate lime. This is a light, extremely fine material, and a given weight of it goes much further than the same amount of cement in filling the pores of the concrete. It has also the effect of making the wet mixture more plastic and more easily compacted by ramming, and gives the fin- ished blocks a lighter color. The following mixtures, then, are to be recommended for concrete blocks. By “gravel” is meant a suitable mixture of sand and gravel, or stone screenings, containing grains of all sizes, from fine to j4-inch: 1 to 4 Mixtures, by Weight. Cement 150, gravel 600. Cement 125, Hyd. lime 25, gravel 600. Cement 100, Hyd. lime 50, gravel 600. 14 1 to 5 Mixtures, by Weight. Cement 120, gravel 600. Cement 100, Hyd. lime 20, gravel 600. Proportion of Water. — This is a matter of the utmost ^consequence, and has more effect on the quality of the work than is generally sup- posed. Blocks made from too dry concrete will always remain soft and weak, no matter how thoroughly sprinkled afterwards. On the other hand, if blocks are to be removed from the machine as soon as made, too much water will cause them to stick to the plates and sag out of shape. It is perfectly possible, however, to give the concrete enough water for maximum density and first-class hardening properties, and still to remove the blocks at once from the mould. A good proportion of coarse material allows the mixture to be made wetter without sticking or sagging. Use of plenty of water vastly improves the strength, hard- ness and waterproof qualities of blocks, and makes them decidedly lighter in color. The rule should be: Use as much water as possible without causing the blocks to stick to the plates or to sag out of shape on removing from the machine. The amount of water required to produce this result varies with the materials used, but is generally from 8 to 9 per cent, of the weight of the dry mixture. A practical block-maker can judge closely when the right amount of water has been added, by squeezing some of -the mixture in the hand. Very slight variations in proportion of water make such a marked difference in the quality and color of the blocks that the water, when the proper quantity for the materials used has been determined, should always be accurately measured out for each batch. In this way much time is saved and uncertainty avoided. Facing. — Some block-makers put on a facing of richer and finer mixture, making the body of the block of poorer and coarser material. As will be explained later, the advantage of the practice is, in most cases, questionable, but facings may serve a good purpose in case a colored or specially waterproof surface is required. Facings are generally made of cement and sand or fine screenings, passing a I^-inch sieve. To get the same hardness and strength as a 1 to 5 gravel mixture, at least as rich a facing as 1 to 3 will be found necessary. Probably 1 to 2 will be found better, and if one-third the cement be replaced by hydrate lime the waterproof qualities and appearance of the blocks will be improved. A richer facing than 1 to 2 is liable to show greater shrinkage than the body of the block, and to adhere imperfectly or develop hair-cracks in consequence. 15 Poured Work. — The above suggestions on the question of propor- tions of cement, sand and gravel for tamped blocks apply equally to concrete made very wet, poured into the mould, and allowed to harden a day or longer before removing. Castings in a sand mould are made by the use of very liquid concrete; sand and gravel settle out too rapidly from such thin mixtures, and rather fine limestone screenings are gen- erally used. MIXING. . To get the full benefit of the cement used it is necessary that all the materials shall be very thoroughly mixed together. The strength of the block as a whole will be only as great as that of its weakest part, and it is the height of folly, after putting in a liberal measure of cement, to so slight the mixing as to get no better result than half as much cement, properly mixed, would have given. The poor, shoddy apd crumbly blocks turned out by many small-scale makers owe their faults chiefly to careless mixing and use of too little water, rather than to too small proportion of cement. The materials should be mixed, dry, until the cement is uniformly distributed and perfectly mingled with the sand and gravel or screenings; then the water is to be added and the mixing continued until all parts of the mass are equally moist and every particle is coated with the ce- ment paste. Concrete Mixers. — Hand-mixing is always imperfect, laborious and slow, and it is impossible by this method to secure the thorough stirring and kneading action which a good mixing machine gives. If a machine taking 5 or 10 horse power requires five minutes to mix one-third of a yard of concrete, is of course absurd to expect that two men will do the same work by hand in the same time. And the machine never gets tired or shirks if not constantly urged, as it is the nature of men to do. It is hard to see how the manufacture of concrete blocks can be success- fully carried on without a concrete mixer. Even for a small business it will pay well in economy of labor and excellence of work to install such a machine, which may be driven by a small electric motor or gasoline engine. In w r ork necessarily so exact as this, requiring perfectly uniform mixtures and use of a constant percentage of water, batch mixers, which take a measured quantity of material, mix it, and discharge it, at each operation, are the only satisfactory type, and continuous mixers are unsuitable. Those of the pug-mill type, consisting of an open trough with revolving paddles and bottom discharge, are positive and thorough 16 in their action, and permit the whole operation to be watched and con- trolled. They should be provided with extensible arms of chilled iron, which can be lengthened as the ends become worn. Concrete Block Systems. — For smaller and less costly buildings, separate blocks, made at the factory and built up into the walls in the same manner as brick or blocks of stone, are simpler, less expensive and much more rapid in construction than monolithic work. They also avoid some of the faults to which solid concrete work, unless skillfully done, is subject, such as the formation of shrinkage cracks. Tamped Blocks From Semi-Wet Mixtures. — These are practically always made on a block-machine, so arranged that as soon as a block is formed the cores and side-plates are removed and the block lifted from the machine. By far the larger part of the blocks on the market are made in this way. Usually these are of the one-piece type, in which a single block, provided with hollow cores, makes the whole thickness, of the wall. Another plan is the two-piece system, in which the face and back of the wall are made up of different blocks, so lapping over each other as to give a bond and hold the wall together. Blocks of the two-piece type are generally formed in a hand or hydraulic press. Various shapes and sizes of blocks are commonly made; the build- ers of the most popular machines have, however, adopted the standard length of 32 inches and height of 9 inches for the full-sized block, with thickness of 8, 10 and 12 inches. Lengths of 24, 16 and 8 inches are also obtained on the same machines by the use of parting plates and suitably divided face plates; any intermediate lengths and any desired heights may be produced by simply adjustments or blocking off. Blocks are commonly made plain, rock-faced, tool-faced, paneled, and of various ornamental patterns. New designs of face plates are con- stantly being added by the most progressive machine-makers. The fol- lowing illustrations show some of the forms of blocks most commonly made: Block Machines. — There are many good machines on the market, most of which are of the same general type, and differ only in me- chanical details. They may be divided into two classes: those with vertical and those with horizontal face. In the former the face plate stands vertically, and the block is sitnply lifted from the machine on its base plate as soon as tamped. In the other type the face plate forms the bottom of the mould; the cores are withdrawn horizontally, and by the motion of a lever the block with its face plate is tipped up into a 17 vertical position for removal. In case it is desired to put a facing on the blocks, machines of the horizontal-face type are considered the more convenient, though a facing may easily be put on with the vertical-face machine by the use of a parting plate. Tamping of Concrete Blocks. — This is generally done by means of hand-rammers. Pneumatic tampers, operated by an air-compressor, are in use at a few plants, apparently with considerable saving in time and, labor and improvement in quality of work. Moulding concrete by pres- sure, either mechanical or hydraulic, is not successful unless the pressure is applied to the face of a comparatively thin layer. If compression of thick layers, especially of small width, is attempted, the materials arch and are not compacted at any considerable depth from the surface. Moulding blocks by pressure is therefore practiced only in the two-piece system, in which the load is applied to the surface of pieces of no great thickness. Hand tamping must be conscientious and thorough, or poor work will result. It is important that the mould should be filled a little at a time, tamping after each addition; at least four fillings and tamp- ings should be given to each block. If the mixture is wet enough no noticeable layers will be formed by this process. Hardening and Storage. — Triple decked cars to receive the blocks from the machines will be found a great saving of labor, and are essen- tial in factories of considerable size. Blocks will generally require to be left on the plates for at least. 24 hours, and must then be kept under roof, in a well-warmed room, with frequent sprinkling, for not less than five days more. They may then be piled up out of doors, and in dry weather should be wetted daily with a hose. Alternate wetting and drying is especially favorable for the hardening of cement, and concrete so treated gains much greater strength than if kept continuously in water or dry air. Blocks should not be used in building until at least four weeks from the time they are made. During this period of seasoning, blocks will be found to shrink at least 1-16 inch in length, and if built up in a wall when freshly made, shrinkage cracks in the joints or across the blocks will surely appear. Efflorescence, or the appearaace of a white coating on the surfaces, sometimes takes place when blocks are repeatedly saturated with water and then dried out; blocks laid on the ground are more liable to show this defect. It results from diffusion of soluble sulphates of lime and alkalies to the surface. It tends to disappear in time, and rarely is suffi- cient in amount to cause any complaint. 18 PROPERTIES OF CONCRETE BLOCKS. Strength. In the use of concrete blocks for the walls of buildings, the stress to which they are subjected is almost entirely one of compression. In compressive strength well-made concrete does not differ greatly from ordinary building stone. It is difficult to find reliable records of tests of sand and gravel concrete, 1 to 4 and 1 to 5, such as is used in making blocks; the following figures show strength of concrete of approximately this richness, also the average of several samples each of well-known building stones, as stated by the authorities named: Limestone, Bedford, Ind. (Ind. Geo. Survey) 7,792 lbs. Limestone, Marblehead, Ohio (Q. A. Gillmore).- 7,393 lbs. Sandstone, N. Amherst, Ohio (Q. A. Gillmore). 5,831 lbs. Gravel Concrete, 1:1. 6:2.8, at 1 yr. (Candlot) 5,500 lbs. Gravel Concrete, 1:1. 6:3. 7, at 1 yr. (Candlot) 5,050 lbs. Stone Concrete, 1:2:4 at 1 yr. (Boston El. R. R.) 3,904 lbs. Actual tests of compression strength of hollow concrete blocks are difficult to make, because it is almost impossible to apply the load uni- formly over the whole surface, and also because a block 16 inches long and 8 inches wide will bear a load of 150,000 to 200,000 lbs., or more than the capacity of any but the largest testing machines. Three one- quarter blocks, 8 inches long, 8 inches wide and 9 inches high, with hol- low space equal to one-third of the surface, tested at the Case School of Science, showed strengths of 1,805, 2,000 and 1,530 lbs. per square inch, respectively when 10 weeks old. Two blocks6 x 8 9 inches, 22 months old, showed crushing strength of 2,530 and 2,610 lbs. per sq. inch. These blocks were made of cement 1%, lime y 2 , sand and gravel 6, and were tamped from damp mixture. It is probably safe to assume that the minimum crushing strength of well-made blocks, 1 to 5, is 1,000 lbs. per square inch at 1 month and 2.000 lbs. at 1 year. Now a block 12 inches wide and 24 inches long has a total surface of 228 sq. inches, or, deducting 1-3 for openings, a net area of 192 inches. Such a block, 9 inches high, weighs 130 lbs. Assuming a strength of 1.000 lbs. and a factor of safety of 5, the safe load would be 200 lbs. per sq. inch, or 200x192=38,400 lbs. for the whole surface of the block. Dividing this by the weight of the block, 130 lbs., we find that 295 such blocks could be placed one upon another, making a total height of wall of 222 ft., and still the pressure on the lowest block would be less than one- 19 fifth of what it would actually bear. This shows how greatly the strength of concrete blocks exceeds any demands that are made upon it in ordinary building construction. The safe load above assumed, 200 lbs., seems low enough to guard against any possible failure. In Taylor and Thompson’s work on con- crete a safe load of 450 lbs. for concrete 1 to 2 to 4 is recommended; this allows a factor of safety of S]/ 2 . On the other hand, the Building Code of the City of Cleveland permits concrete to be loaded only to 150 lbs. per sq. inch and limits the height of walls of 12-inch blocks to 44 ft. The pressure of such a wall would be only 40 lbs. per square inch; ad- ding the weight of two floors at 25 lbs. per sq. ft. each, and roof with snow and wind pressure, 40 lbs. per sq. ft., we find that with a span of 25 ft. the total weight on the lowest blocks would be only 52 lbs. per sq. inch, or about one-twentieth of their minimum compression strength. Blocks with openings equal to only one-third the surface, as required in many city regulations, are heavy to handle, especially for walls 12 inches and more in thickness, and, as the above figures show, are enor- mously stronger than there is any need of. Blocks with openings of 50 per cent, would be far more acceptable to the building trade, and if used in walls not over 44 ft. high, with floors and roof calculated as above for 25 feet span, would be loaded only to 56 lbs. per square inch of actual surface. This would give a factor of safety of 18, assuming a minimum compression strength of 1,000 lbs. There is no doubt that blocks with one-third opening are inconven- iently and unnecessarily heavy. Such a block, 32 inches long, 12 inches wide, and 9 inches high, has walls about Z l / 2 inches thick, and weighs 180 lbs. A block with 50 per cent, open space would have walls and parti- tions 2 inches in thickness, and would weigh about 130 lbs. With proper care in manufacture, especially by using as much water as possible, blocks with this thickness of walls may be made thoroughly strong, sound and durable. It is certainly better for strength and water-resisting quali- ties to make thin-walled blocks of rich mixture, rather than heavy blocks of poor and porous material. 2. — Use of Rich Mixtures. — All concretes are somewhat permeable by water under sufficient pressure. Mixtures rich in cement are of course much less permeable than poorer mixtures. If the amount of cement used is more than sufficient to fill the voids in the sand and gravel, a very dense concrete is obtained, into which the penetration of water is extremely slow. The permeability also decreases considerably with age, owing to the gradual crystallization of the cement in the pores, so that 20 concrete which is at .first quite absorbent may become practically imper- meable after exposure to weather for a few weeks or months. There appears to be a very decided increase in permeability when the cement is reduced below the amount necessery to fill the voids. For example, a good mixed sand and gravel weighing 123 lbs. per cubic foot, and therefore containing 25 per cent, voids, will give a fairly impermeable concrete in mixtures up to 1 to 4, but with less cemoii will be found quite absorbent. A gravel with only 20 per cent, voids would give about equally good results with a 1 to 5 mixture; such gravel is, however, rarely met with in practice. On the other hand, the best sand, mixed fine and coarse, seldom contains less than 33 per cent, voids, and con- crete made from such material will prove permeable if poorer than 1 to 3. Filling the voids with cement is a rather expensive method of se- curing waterproof qualities, and gives stronger concretes than are needed. The same may be accomplished more cheaply by replacing part of the cement by slaked lime, which is an extremely fine-grained material, and therefore very effective in closing pores. Hydrate lime is the most convenient material to use, but nearly as costly as Portland cement at present prices. A 1 to 4 mixture in which one-third the cement is re- placed by hydrate lime will be found equal to a 1 to 3 mixture without the lime. A 1 to 4 concrete made from cement 1, hydrate lime >4, sand and gravel 6 (by weight), will be found fairly water-tight, and much superior in this respect to one of the same richness consisting of cement 1 ^ 2 , sand and gravel 6. 3. — Use of a Facing. — Penetration of water may be effectively pre- vented by giving the blocks a facing of richer mixture than the body. For the sake of smooth appearance, facings are generally made of cement and fine sand, and it is often noticed that these do not harden well. It should be remembered that a 1 to 3 sand mixture is no stronger and little if any better in water absorption than a 1 to 5 mixture of well graded sand and gravel. To secure good hardness and resistance to moisture a facing as rich as 1 to 2 should be used. General Hints on Waterproof Qualities. — To obtain good water- resisting properties, the first precaution is to make the concrete suffic- iently wet. Dry-tamped blocks, even from rich mixture, will always be porous and absorbent, while the same mixture in plastic condition will give blocks which are dense, strong, and water-tight. The difference in this respect is shown by the following tests of small concrete blocks, made by the writer. The concrete used was made of 1 part cement and 5 parts mixed fine and coarse sand, by weight. 21 No. 1. — With 5 per cent, water, rather dryer than ordinary block concrete, tamped in mould. No. 2. — With 10 per cent, water, tamped in mould. No. 3 — With 25 per cent, water, poured into a mould resting on a flat surface of dry sand; after 1 hour the surface was troweled smooth; mould not removed until set. These blocks were allowed to harden a week in moist air, then dried. The weights, voids, and water absorption were as follows: This method will always show hair or shrinkage cracks on the face of blocks. 1 2 3 Damp-tamped. Wet-tamped. Poured. Weight per cubic foot, lbs 112.2 125-9 112.0 Voids, calculated, per cent, of volume . 25.7 22.9 12.5 Water required to fill voids, per cent, of wt 9.6 9.4 12.5 Water absorbed after 2 hours, per cent of wt . 8.6 6.4 10.0 The rate at which these blocks absorbed water was then determined by drying them thoroughly, then placing them in a tray containing water 14 inch in depth, and weighing them at intervals. Water absorbed 1 2 3 per cent, by weight. Dainp-tamped. Wet-tamped. Poured. V 2 hour .. 2.0 0.8 1.8 1 “ . 3.2 1.0 2.5 2 “ 4.1 1.4 3.2 4 “ 5.2 1.9 3.8 24 6.1 3.0 7.0 48 “ .... 6.4 4.1 7.5 These figures show that concrete which is sufficienttly wet to be thoroughly plastic absorbs water much more slowly than dryer concrete, and prove the importance of using as much water as possible in the damp-tamping process. COST. The success of the hollow concrete block industry depends to a great extent on cheapness of product, since it is necessary, in order to build up a large business, to compete in price with common brick and rubble stone. At equal cost, well-made blocks are certain to be preferred, owing to their superiority in strength, convenience, accurate dimensions. 22 and appearance. For the outside walls of handsome buildings, blocks come into competition with pressed brick and dressed stone, which are, of course, far more costly. Concrete blocks can be sold and laid up at a good profit at 25 cents per cubic foot of wall. Common red brick costs generally about 12 dollars per thousand, laid. At 24 to the cubic foot, a thousand brick are equal to 41.7 cu. ft. of wall; or, at $12, 29c. per cu. ft. Brick walls with pressed brick facing cost from 40c. to 50c. per cubic foot, and dressed stone from $1 to $1.50 per foot. The factory cost of concrete blocks varies according to the cost of materials. Let us assume cement to be $1.50 per barrel of 380 lbs., and sand and gravel 25c. per ton. With a 1 to 4 mixture 1 barrel cement will make 1,900 lbs. of solid concrete, or at 130 lbs. per cu. ft., -14.6 cubic feet. The cost of materials will then be Cement, 380 lbs $1.50 Sand and gravel, 1,520 lbs 0.19 Total $1.69 or 11.5c. per cu. ft. solid concrete. Now, blocks 9 inches high and 32 inches long make 2 square feet of face of wall, each. Blocks of this height and length, 8 inches thick, make 1 1-3 cubic feet of wall; and blocks 12 inches thick make 2 cubic feet of wall. From these figures we may calculate the cost of materials for these blocks, with cores or open- ings equal to 1-3 or the total volume, as follows: Per cu. ft. of block, 1-3 opening 7.7 cts. Per cu. ft. of block, y 2 opening . 5.8 Block 8 x 9 x 32 inches, 1-3 opening 10.3 Block 8 x 9 x 32 inches, y 2 opening 7.7 Block 12 x 9 x 32 inches, 1-3 opening 15.4 Block 12 x 9 x 32 inches, y 2 opening 11.6 “ Tf one-third of the cement is replaced by hydrate lime the quality of the blocks will be improved, and the cost of material reduced about 10 per cent. The cost of labor required in manufacturing, handling and deliver- ing blocks will vary with the locality and the size and equipment of fac- tory. With hand-mixing, 3 men at average of $1.75 each will easily make 75 8-inch of 50 12-inch blocks, with 1-3 openings, per day. The labor cost for these sizes of blocks will therefore be 7c. and lO^c. respecttively. At a factory equipped with power concrete mixer and cars for transport- ing blocks, in which a number of machines are kept busy, the labor cost will be considerably less. An extensive industry located in a large city 23 is, however, subject to many expenses which are avoided in a small country plant, such as high wages, management, office rent, advertising, etc., so that the total cost of production is likely to be about the same in both cases. A fair estimate of total factory cost is as follows: Material. Labor. Total. 8 x 32 inch, 1-3 space 10.3 7 17.3 cts. 8 x 32 inch, Yz “ 77 6 13.7 “ 12 x 32 inch, 1-3 “ 15.4 10.5 25.9 “ 12 x 32 inch, “ 11.6 9 20.6 “ With fair allowance for outside expenses and profit, 8-inch blocks may be sold at 30c. and 12-inch at 40c. each. For laying 12-in. blocks in the wall, contractors generally figure about 10c. each. Adding 5c. for teaming, the blocks will cost 55c. each, erected, or 27^c. per cubic foot of wall. This is less than the cost of common brick, and the above fig- ures show that this price could be shaded somewhat, if necessary, to meet competition. APPEARANCE AND USE. Since concrete blocks are, as has been shown, more convenient, more efficient, and cheaper than any other building material, it would naturally be expected that they would quickly take the place of wood, brick and stone and be generally adopted for all ordinary construction. The growth of the block industry has, indeed, been rapid, but it plays as yet but a small part in the building operations of the country. It is evident on all sides that concrete blocks meet with opposition and sus- picion on the part of architects and builders, and in consequence are much less generally adopted than their merits appear to warrant. * Tt is neither just nor expedient to attribute this opposition to prejudice against a new material. Rather should we try to find and remove the grounds pn which such opposition is based. My observation leads me to believe that architects and engineers have no prejudice against concrete, but on the contrary, welcome it as a building material by means of which they can obtain results never before within their reach. And they are also keenly watching the block industry, and are ready to adopt block con- struction as soon as they are offered a product which meets their ideas as to utility and beauty. Fortunately, no material is so elastic in its capabilities as concrete, and no other can with so little effort be adapted to produce any effect 24 desired. It is hardly to be expected that the block of the present day will be the block of the future; the type which is most economical, prac- tical and beautiful will gradually come to the front, and that which is costly, clumsy add ugly will become a thing of the past. To make a success of the business we must keep our eyes open, watch what others are doing in the way of invention and improvement, and study the wants of customers. And we must not hesitate to throw our old block machines into the scrap heap when we are sure we have found a better apparatus and process. The objections which architects and builders make to blocks now on the market are chiefly the following: Poor workmanship, Fixed dimensions, Too great weight, Unpleasing appearance. As to workmanship, shoddy, weak and crumbling blocks are far too often met with. Good concrete should be hard and dense, _ and should give out a musical tone when struck with a hammer. If your blocks sound dead when struck, and break easily with an earthy fracture, you are either using too poor a mixture or working too dry, probably the lat- ter. It does not pay, for the sake of low factory cost, to turn out work of this kind. If there is any money to be made in the block business it will be made by furnishing a good article at a living price, and in no other way. Will any one argue that it pays to make rotten blocks at a factory cost of two cents less than good ones? My belief is that the ten- dency of the future will be toward the use of wetter concrete, and the adoption of a process which makes this possible. As to fixed dimensions of blocks, the standard length of 32 inches, divided into halves, thirds and quarters, is very convenient, and is gener- ally confirmed to by architects for simple work, without much objection. To be fully successful, however, and to overcome all prejudice, the block-maker must be ready to furnish any size or shape that may be called for to suit architects’ designs. It would be very pleasant if we could confine ourselves to the standard size and let customers “take it or leave it.” But such an attitude bars the way to any wide use of blocks in varied and attractive buildings, and cannot be maintained with- out loss of trade. Architects want also courses of greater or less height than the 9 inch standard, and all manner of cornices, copings, columns and capitals. This may frighten the timid and conservattive block-maker, but it is in that direction that success lies, and the pro- duction of these special shapes requires only ingenuity, courage and me- 25 chanical skill. Until we can say to the architect “Design whatever you like, we’ll make it for you," he will shy at us and our product. He will, of course, readily appreciate that special shapes cost more than standard, and if he knows he can get just what he wants he will be conveniently and cheaply furnished. Preference should be given, therefore, to the machine which per- mits the greatest variety of sizes and shapes to be easily made. And the greatest business success is likely to come "to the manufacturer who shows the least inclination to get into a rut, and is most ready to adapt his product to the wants of his patrons. The objection to the weight of the one-piece block comes chiefly from masons and contractors. Hoisting 12 x 32 inch blocks weighing 180 lbs. to the upper floors of a building, and handling them onto the wall, is a considerable taslc, and it is largely on this account that the half-block of the two-piece system, 24 inches long, weighing only 64 lbs., is received with so much favor. It must be remembered, however, that the two- piece blocks make a wall with over 50 per cent, opening, and a one-piece block of the same thickness of walls — 2 inches — would also be lighter to handle and doubtless very popular. My belief is that the one-piece block of the future will be 24 inches long and with a thickness of walls of not over 2 inches. Such a block, 12 inches wide and 9 inches high, will weigh only 97 lbs., and if well and honestly made will bear rough handling and any possible load. Finally, it is to the appearance of concrete blocks, as ordinarily made and used that architects and other persons of taste and judgment make the greatest objection. Anything that savors of imitation that pretends to be what it is not, will always be hated and condemned by all who know the difference between the good and the bad. The com- mon rock-faced block is an imitation of the cheapest form of quarry stone and a poor imitation at that, for no two natural stone blocks are alike in surface; while even if you have half a dozen rock-face plates of the same size of block, and strive to shuffle up the product of these plates in the yard and on the work, you will never see a building in which, here and there, blocks from the same plate are not found one above or beside the other. And it is surprising how unerringly the eye will pick out the spots where this occurs, and what a feeling of “some- thing lacking” is awakened. It is bad art, and quite indefensible. The “rock-faced galvanized iron” of our country store-fronts is no more a glaring fraud. The rock-faced block must go. 26 Now let us inquire what constitutes imitation, and how concrete may be made to stand on its merits and look like what it really is. In the first place, concrete must always look like stone, because it is stone. An artificial stone, consisting of grains of sand and gravel or limestone crystals bound together by a little Portland cement, cannot help look- ing like natural sandstone or limestone made up of the same materials bound together by carbonate of lime or soluble silicates slowly de- posited in its pores. We need never be afraid that concrete will be con- demned for its stony look, since that is its nature. All we need to avoid ir givng the work an appearance which is unnatural to concrete, such as the rock-face. Smooth, ribbed and paneled surfaces, also good or- namental patterns for friezes or cornices, are entirely legitimate, and equally characteristic of stone, metal, terra cotta or concrete. Forms of beauty may properly be reproduced in any material; the only thing to be avoided is pretense — the attempt to deceive the observer into the belief that the material he sees is something different from what it really is. The surface which best pleases the eye of artist and architect is a rough and varied one, rather than the smooth, dead look which rich cement mixtures have. The film of cement which coats the face of the work is certainly monotonous and unattractive. This can be cheap- ly removed by washing with very weak acid, and very beautiful ef- fects are thus obtained, especially with crushed stone or gravels con- taining pebbles of various colors. CITY SPECIFICATIONS FOR CONCRETE BLOCKS. In order to guard against the use of blocks of poor quality and to insure safe construction of block buildings, a number of cities have adopted specifications for the acceptance and use of building blocks of concrete. The building regulations of New York City* in regard to all materials used as substitutes for brick or stone are extremely severe, requiring tests to be made on blocks the size and shape of an ordinary brick, which must show an average modulus of rupture of 450 lbs. in transverse test, average compression strength of 3,000 lbs., water absorption not over 15 per cent, loss of not more than 33 per cent strength after freezing and thawing 20 times,- and no disintegration after heating 1 hour to 1,700 degrees F. and plunging into cold water. The City of Philadelphia* for a time followed these requirements, but has lately modified them, and provides that tests of hollow con- crete blocks shall be made on full-sized specimens. The most impor- tant requirements are: 27 Rlocks to be made «of Portland cement with not more than 5 parts sand and gravel or crushed rock; hollow space to be not over 33 per cent (20 and 25 per cent in lower parts of high walls); maximum load 111 lbs. per square inch of wall ;' crushing strength 1,000 lbs. per square inch of total surface of block including openings; absorption, freezing and fire tests as* in New York requirements. According to the Cement Age, concrete blocks in the Philadelphia market have shown compression strength of 1,200 to 1,600 lbs., absorp- tion of about 5 per cent, little loss of strength on freezing, and have passed the fire test well. The City of Newark, N. J., requires that blocks shall be not poorer than 1 to 4; they must be no more than 36 inches long and 10 inches high, and not less than 8 nor more than 16 inches wide; the hollow spaces must not exceed one-third; they must not be used until 30 days old, and must show a crushing strength of 1,500 lbs. per square inch. These various city requirements seem generally reasonable and certainly abundantly severe. It is difficult to see, however, why the hollow spaces should be limited to one-third or less when strength is fully provided for by a compression requirement of 1,000 lbs. on the whole area of the block. If blocks with thinner walls will show this strength, there appears to be no ground for prohibiting them. THE REINFORCED CONCRETE FACTORY FOR THE AMERI- CAN OAK LEATHER CO., CINCINNATI. I At least seven such structures, including warehouses, factories, office buildings and stores, were then in process of erection. The ten- dency in Cincinnati recently has been to build the exterior walls of hol- low blocks, and the structural portions of the building, that is, the col- umns, beams and floors, of reinforced concrete. This is due to economi- cal considerations. Because of the cost of lumber and of the labor of placing and removing wall forms and the necessity of specially treating the face of the concrete, or else veneering it with stone or brick, it is often cheaper to build the entire wall, except the trimmings, of. hollow blocks. Among the pioneers in reinforced concrete construction is the Ferro- concrete Construction Co., the builders of the famous sixteen-story In- galls office building and several other structures, including the factory of the American Oak Leather Co., also in Cincinnati. 28 The building is designed for heavy loading, and in anticipation of the presence of piles of leather on all or nearly all the floors at the same time, this heavy loading was carried through to the foundations. The design of the floor plan and the connection of the building with an old one belonging to the same company required a large variety of sizes of floor panels, each of which was especially designed in thickness and re inforcement for its particular load. The building is seven stories high above the basement, and the base- ment floor is full of tanks and vats and troughs, all of reinforced con- crete, for use in the operations incident to the preparation of leather. Fig. 1 is a typical section across the building. The main portion of the structure represented by the three bays at the right is 58 ft. wide by 269 ft. in length. Wings, eight stories high above the basement and pro- jecting at each end of the building carry the reinforced concrete stair- ways and also connect with the old building. The columns vary in size in accordance with the spans they carry, ranging from 10x10 in. to 32x36 in. The principal girders, that is, the girders across the building, range in size from 8x20 in. to 14x20 in. and 10x24 in. The longitudinal beams which butt into the principal girders range from 6x16 in. to 8x20 in. The floor slabs vary with the span from 4 to 7 in. in total thickness. For a reinforced concrete building nearly as many carpenters are required as laborers, and one of the first essentials for economical con- struction is the design of the forms to reduce the quantity of lumber to a minimum, and the construction of these forms at the smallest possible labor cost. In the present case one of the first operations was the erec- tion of a shanty occupying half of the street next to the site, which was fortunately on an unfrequented highway, and equipping it with power saws and other woodworking machinery. Here all the forms required in the construction of the building were made, and the general repairing was done. Structural Details. — Twisted steel was used for reinforcement. The square rods were twisted, cut to length, and bent to shape at the per- manent shop of the contractors in the city. The twisting machine twists three “30-ft. rods of the smaller sizes at the same operation. As the opera- tion of twisting a set of three rods occupies two men with the machine but slightly over one minute (not including the carrying to and from the machine), the cost is scarcely appreciable, while the twisting produces a deformed rod capable of greater adhesion and with an increased elastic limit. The high elastic limit was utilized by the designers in the as- sumption of a higher allowable unit pull in the steel and thus a smaller percentage of the metal in the beams and slabs. 30 (By practical experience it has been shown that a twisted rod is weaker than an untwisted rod; by twisting, the rod is deformed and nat- urally weaker.) A cutter designed with a multiple lever, so as to be operated by one man, cuts single rods up to y% in. square, and smaller rods in lots of two or more. All rods are bent cold. The small rods up to about Y in. square, which comprise all the steel which requires bending except the bent bars in the girders, are bent by hand with the aid of a special vise. For rods larger than y in. a machine designed for the purpose bends the rod to any angle and at the same time keeps all the bends in the same rod in a plane. As usual in concrete building construction, the concrete was mixed on the ground and elevated to the floor where it was required. However, instead of following the more common practice of an elevator running in a frame which is raised from story to story as the building advances, an immense derrick with an 80-ft. boom was set on top of a tower con- sisting of a pyramidal frame of timber with its diagonal braces carefully bolted. The base of the derrick was thus 55 ft. above the ground and so high that buckets could be emptied upon the roof. This derrick was used not only for hoisting the concrete, but for raising the form timber and handling other material and tools. It was thought when the building was begun that it would be the best plan to dump the concrete from the bucket at various places on the floor where it was required, the boom being long enough to swing over a considerable area of the floor. This worked well in the lower stories, but for the upper floors and the roof, where the swing of the boom be- came limited, it was found more economical to dump the concrete into a hopper to be wheeled in barrows to place. Fig. 2, which is taken on the fifth floor, shows the operation of dumping the hoisting bucket into the hopper. By this plan less time was consumed in placing the bucket, and no tag-rope man was required, as the engine-man could swing the boom to a certain point on the wall which brought the bucket directly over the hopper. The concrete is composed of Portland cement, sand and broken stone in proportions 1:2:4. The sand and broken stone were stored in bins within less than 50 ft. of the mixer, and wheeled in barrows, which were also used for measuring, along an elevated run to a mixer. From the mixer the concrete fell into the derrick bucket which rested on an iron truck on wheels, about twice the length of the bucket, so that the 31 empty bucket could be set by the derrick on one end of the truck while the other bucket was being filled, and then as. soon as the full bucket was removed, the truck was pushed by the attendant to bring the empty bucket under the mixer. The steel in the columns, consisting generally of vertical round rods with hoops placed around them every foot in height, was set as soon as the concrete of any floor was laid, the column forms were built around it, and the floor slab and girder forms placed and carefully supported and braced by vertical struts and diagonals. The forms were thus built and the steel placed in the beams and slabs so that the concrete was poured in one-half of the floor while the forms were being built for the other half of the story. The concrete was mixed wet enough to pour into the columns and a very fine face was obtained on the sides of the posts by the use of long- handled wooden paddles. The thickness of the floor slabs were gauged by 1x2 in. wood strips with blocks nailed on the under side of them at occasional intervals to bring the top of the strip to the required surface level. These were placed crosswise of the floor about every 15 ft. and the concrete poured between them, and screened with a long straight edge. The strips were immediately removed, and their location filled with concrete by men wearing rubber boots who walked through the soft material. As soon as the concrete was sufficiently set, the surface 32 finish was spread and finally floated. The rate of speed on the building was a half story per week. Design. — The general floor plan is shown in Fig. 3, which shows the forms and the steel in place for the 50-ft. span girders and the floor' TYPE M TYPE N Fi g. 6 in the west end of the building. These girders are 14 in. wide and 36 in. deep, and the span is 50 ft. in the clear. 33 Fig. 3 Fig. 8 shows girder and floor slab construction. Fig. 4 shows how stirrups are placed on girder rods. The surfaces W Hoops 12" 0.0 h o) COL. 33 34 of the girders and floors show the knots and other impressions from the lumber of the forms, but a close examination fails to detect any of the irregularities and stone pockets so often found in structures of this char- acter. In general, there were four principal rods in each beam and two of these were bent up diagonally so as to reach the top of the beam or to extend over the supports. Typical forms of these bent bars are shown in Fig. 6. The live loads assumed in the design are as follows: First floor, lower section, 500 lbs. per square foot; floors over 50-ft. span 150 lbs.; other floors, 200 lbs.; roof, 100 lbs. The girders are calculated fur 80 per cent of the live load. The columns take the total dead load, and also are assumed to carry the following percentages of the live load com- ing from the girders: On the roof, 100 per cent; seventh floor, 100 per cent; sixth floor, 90 per cent; fifth floor, 80 per cent; fourth floor, 70 per cent; thi-rd floor, 60 per cent; second floor, 50 per cent; first floor, 50 per cent. Typical column reinforcement adapted for different sectional dimen- sions is shown in Fig. 7. In general, the vertical rods, which are round, have a sectional area of about 1 to 2 per cent of the cross section of the column. The size of the rods is reduced from story to story, ranging on an average from about 2 in. in the lower floors to *4 in. in the upper stories. The foundations for the columns are reinforced, and as they are built in advance of the columns, short vertical rods about 3 ft. long are set into them, which project up about 2 ft. into the column. The lower ends of these “stubs” are set upon plates which hold them in position, and form a bearing upon the concrete. For the columns at one end of the building an inverted beam foun- dation was required because the footings could not project beyond the building line. This foundation, supporting two polumns, was heavily re- inforced at the top with sixteen 24-in. and 1-in. rods, and provided with stirrups as in ordinary beam construction. Note. — The contractors collect in one table and the above diagram all the data for the reinforcement of all beams and girders. For example, the beam a is shown in this table to have bent reinforcement of type R, of the dimensions tabulated, as well as straight bars and stirrups. This tabulation and diagram keep the floor plans free from lettering about details. The stairs are reinforced as shown in Fig. 9, which run up in the wings at each end of the building are generally in double flights with 35 winders or platforms connecting them. They are usually enclosed on three sides by the brick wall of the building. The plan and elevation of one of the flights with winders is shown in Fig. 1. In the more usual pattern, with a platform at the half-story, no post is required. A large portion of the basement is occupied with tanks or vats for use in the leather processes. These pickling vats are each 8 ft. long, 6 ft. deep, with walls only 2 x / 2 in. thick, constructed all of concrete. The plan of the vats in three of the bays running across the build- ing, which also gives a section of a vat wall and of one of the drains below the vats. The vats are built in groups, there being a group of six vats in each bay. Each group is built at one operation, so that there will be no joint, and the exterior walls of the group, that is, the walls on a line with the columns both ways, are thus double, but separated so as to permit shrinkage. The bottom of the vats are about 6 ft. above the ground, and they are supported by small columns at each intersec- tion. The troughs or drains which run under the vats are of unique con- struction. They are built as V-shaped troughs of mortar, 2 in. thick and 8 in. deep, reinforced with J^-in. longitudinal rods and also with 14-in. hoops which are allowed to project about 2 ft. above the sides when the trough is finished. The floors of the vats constitute the tops of these troughs. In some cases a thin oak veneer is sprung across the top of the drain to serve as a form for the concrete, and the floors of the vats are then spread over this and over the surface of floor between the drains, and the ends of the hoops which project above the sides of the drain are bent down into this floor so that the drains are in effect suspended from the floor and form a part of it. As is stated above, the walls of the building are of brick (hollow blocks 36 would have lessened the cost of the building 10 per cent), but the water table, the sills and the caps of the windows and doors are formed o* concrete laid in place. No mortar surface is given to them, but the ag- gregate is sand and rather fine broken stone, and care is used in placing it against the form. After removing the forms, the surfaces are carefully dressed by pol- ishing with a piece of sandstone so that they can scarcely be distinguished from cut stone trimmings. SPECIAL FALSEWORK FOR A CONCRETE BRIDGE. The Cobbs Creek bridge at Media, Pa., near Philadelphia, carries a double track electric railway and a highway about 19 ft. above the creek level by a single skew span 46 ft. 2 in. in the clear. The arch is a false ellipse of reinforced concrete. The intrados is a three-centered curve having a total rise of 17 ft. 5 in. from skewback to crown. The central part has a radius of 30 ft. 8 in., forming a segment subtended by a chord 30^2 ft. long. At each end this segment is tangent to a segment of 15 ft. 4*4 in. radius, which is continued beyond the springing fine nearly to the intersection with the inclined plane of the footing. The extrados is of similar construction with center and end radii of 40 ft. and 16 ft. 10 in. respectively. The end segments do not, however, extend quite to the springing line but just above that point are tangent to reversed curves which diverge from the intrados so as to give the footings a width of 6 ft. 8 in. in a plane perpendicular to the direction of the re- Fig. 13 sultant. The radial thickness of the arch ring varies from 10 in. at the crown to 18 in. at the extremities of the center segments and to about 4 ft. at the springing line. 37 The reinforcement is made wholly of plain round bars of medium steel in two sets, one of them near the upper and the other near the lower surface of the concrete. In the lower set there are eighty curved rods \y A in. in diameter and 30 ft. long which reach from the footing to a point near the crown where they overlap 40 rods of the same diameter 24 ft. long. The upper bars correspond to them in relative positron and number, but are only in. in diameter at the crown, those at the end being 1^-in. rods. The rods in both sets are crossed by horizontal *4- in. rods parallel to the axis of the arch and spaced 15 in. apart on centers. Each footing is reinforced by forty ^-in. rods 6 *4 ft. long and 12 in. apart, perpendicular to the resultant. These are crossed by two full- length in. horizontal transverse rods at the extremities of the curved rods in the upper and outer sets of the arch ring. The arch is 40 ft. long inside the parapet walls, and its axis is inclined 74 deg. with that of the roadway. At each end the spandral walls, which are not shown in the accompanying photograph, are continuous with the intersecting wing walls, the latter being oblique both to the axis of the street and to the axis of the stream. The bridge contains about 200 cu. yd. of 1:3:5 concrete mixed wet by hand, Vulcanite Portland cement a;id broken stone varying from 54 to ^4 i n - in diameter being used. There are about 30 tons of steel in the reinforcement and the arch was built in ten working days after the completion of the falsework. The stream was considered treacherous and subject to unexpected floods, and as the contractors did not know the character of the bottom it was decided not to trust falsework bents placed in the bed of the stream. The locality was not such that it was convenient or economical to drive piles, and it was therefore decided to support the bridge during construction on falsework trusses, as shown in the illustration. Sheeted pits were excavated to rock at a depth of 8 to 10 ft. below the surface of the ground and from 6 ft. below water level. These were drained without serious difficulty by a centrifugal pump and the lower ends of the arch ring, which really acted as skewback piers, were built in them about up to the springing line. They were allowed to set and serve as supports for the falsework, which was made of simple wooden trusses about 3 ft. apart. Each truss was built of 3xl0-in. planks spiked together at intersections and serving to support the top chord; which was com- posed of scarf boards carefully cut to the curve of the intrados. The trusses were built in place and the light radial members seen in them are small strips of wood put in place before the completion of the truss to support the scarf boards temporarily until the connections were com- pleted and the structural developed full strength. The trusses were 38 braced together by intermediate horizontal planks and by the lagging, which consisted of square-edge boards planed on the upper surface. Outside forms were built in three sections at each end of the arch and the concrete was rammed in them to points above the haunches, as in- dicated by the angles of the extrados between the face rings. By dar- ing out the wedges under the falsework, the latter was released three weeks after the concrete was laid, without causing any appreciable set- tlement in the arch. A FLAT SPAN REINFORCED CONCRETE BRIDGE AT MEMPHIS • A 100-ft. through span, reinforced-concrete highway bridge, carried by two longitudinal girders, without any dependence on arch action, has recently been built at Memphis, Tenn. The bridge replaces an old wood- en structure and spans a 100-ft. right-of-way on which six tracks of lour different railroads are laid. The railroad tracks closely parallel one side of a "cemtery so that the approach to one end of the bridge is within the grounds of the latter, the level of the grounds being about 15 ft. above the tracks. Owing to the necessity of providing a clearance of at least 19 ft. over all of the tracks on the right-of-way, and to very strong objections to a slightly graded approach that would have been required in the cemetery grounds if an arched bridge which would pro 1 - vide such a clearance had been built, a practically flat span had to be de- signed and has been erected. 39 rise is largely introduced near the abutments. The two longitudinal girders are, designed to carry the floor, which is also reinforced and is suspended from them. Each end of both girders is designed to act as a cantilever beam for 21 ft. from the abutments. Between the outer ends of the two cantilever parts of each girder the latter is designed to act as a simple beam, with a span of 58 ft. carried by the cantilevers. The bridge has a total width of 31 ft. made up of a 16-ft. roadway, with a walk on each side, one girder being between the roadway and each walk. The girders are 3 ft. 6 in. wide and have a total height of 6 ft. 6 in., including a 6-in. coping. The girders being designed to act as Cantilevers toward the abutments, tension stresses are produced near their upper surfaces in this portion of them and the concrete has been reinforced accordingly. This reinforcement consists of thirty lj4-in. bars, placed in four horizontal rows as shown in one of the accompany-’ ing illustrations. These bars are 40 ft. long, extending 4 ft. beyond the outer end of the cantilever section of the girder and 15 ft. back into the e nd of the girder over the abutment. The simple beam portion of each girder is reinforced near the bottom by twenty-four 1^-in. bars in three rows. This reinforcement is 66 f»t. long and extends 4 ft. into the outer end of each of the cantilever sections supporting the simple beam. Two planes of no moment occur in each girder, one at the junction between the end of each cantilever and the adjoining end of the simple beam. Heavy shearing stresses are, therefore, introduced at these points. These stresses are overcome by thirty short, inclined 1 ^ 2 -in. bars placed in the vicinity of each of the planes of no moment. Each cantilever is anchored to its abutment by a cluster of lj/ 2 -in. bars, which extend from a central point near the top of the girder and over the haunch of the arch down into the concrete of the abutment, ra- diating in the latter to secure more complete anchorage. Several light street railway rails were also placed in each girder back of the point of support to bond the masonry of the girder and the abutment together. The abutments had to be designed to provide anchorages for the cantilevers, the thrust from the arch being considered of little conse- quence. The section of the girders is extended well back from the point of support of the cantilevers and down to the bottom of the abutments. Between the girders the abutments are hollow, having a retailing wall at the front, with a wide, flat floor cantilevered back from the rear face of the wall. This floor is reinforced near the lower surface with light rails, the ends of which extend into the girder abutments. The front wall thus retains an earth load on the floor and provides an additional anchorage. 40 The bridge floor is 13 in. thick and is reinforced with I-beams placed transversely. Each beam is attached on the center line of both bridge gird- ers to two 1-in. tie rods. These rods extend up into the girder and are anchored just below the coping on the latter. to a longitudinal y 2 x6- in. steel bar imbedded in the concrete. The floor is thus suspended from the girders and is not designed to be self-supporting due to any arch action that may occur in it. It is designed to carry a uniform live load of 200 lb. per square foot. This load is small, however, as compared with the dead load of the bridge, amounting to 3 cu. yd. of concrete per linear foot of span, which the girders are required to carry. 41 The erection of the forms for the span was rendered difficult and ex- pensive by the necessity of maintaining traffic on the six railroad tracks. The dead load of the bridge to be carried by these forms was approxi- mately 1,000,000 lb. Spans of as much as 20 ft. were required in the falsework for the centering in order to clear the tracks. The bents of the forms were built of 12xl2-in. timbers, heavily X-braced. Resting on the caps of these bents were 5xl6-in. stringers, placed clo-sely together, which carried the lagging. The concrete was mixed fairly wet in the proportions of 1 of Port- land cement, 2 l / 2 sand and 5 of small broken stone. Corrugated bars were used for reinforcement, except as mentioned. One girder was built in a single day and the other the following day, each of the girders be- ing considered as a separate structure during the construcion. After the concrete had set three months the forms were removed without any set- tlement occurring, insofar as it was possible to discover. No cracks are apparent in the structure, except a very few small ones in the coping, which is not reinforced and has no expansion joints. The bridge cost $17,500 complete, including the asphalt pavement on the roadway, a cut-stone veneer on the posts at the ends of the girders and the iron railing along the walk on each side. The forms required $4,000 of this amount, owing chiefly to the difficulty of erecting them so they would not interfere with traffic on the tracks. The girders and the floor of the span contain about 200 and the abutments 800 cu. yd. of concrete. The latter quantity could be greatly reduced in proportion to the former in a structure with several spans of the same type, since the reinforcement at the top of the cantilever sections of the girders could be extended through adjoining spans and the heavy anchorage required in a structure with a single span avoided. 42 Method of Facing Concrete Work (this Plate is made of Sheet Iron) Barn 43 44 Colored Hlortars Colors given to Portland Cement Mortars, containing two parts sand to one cement. Remember that wet mortars give a darker color but dries out lighter. White Cement Blocks are made by using lime-stone siftings. White sand or Marble dust for the facing. Weight of Coloring Matter to 100 pounds of Cement Dry Material Used ' -1 3/5 Pound 1 l/5 pounds 1 4/5 pounds 4/5 Pound Lamp Black Light Slate Light Gray Blue Gray Dark Blue Slate Prussian Blue Light Green jSlate Light Blue Slate Blue Slate Bright Blue Slate Ultra Marine Blue Light Blue Slate Blue Slate Bright Blue Slate Yellow Ochre Light Green Light Buff Burnt Amber Light Pink Slate Pinkish Slate Dull Lavender Pink Chocolate Venetian Red Slate Pink Tinge Bright Pinkish Slate Light Dull Pink Dull Pink Chattanooga Iron Ore Light Pinkish Slate Dull Pink Light Terra Cotta Light Brick Red Red Iron Ore Pinkish Slate Dull Pink Terra Cotta Light Brick Red 45 Tabic for Designing Reinforced Concrete Beams and Slabs Proportion of Concrete 1:2:4. See important foot-note. .5 0 ’5 Q£ C cn o — z -o ” QJ O EQi-g ' o o ■jS J 5 H j|“J EQi GO ^ Q 0 ■a *•« g_E S' £ -5 10 oCQ Q ‘S CO CD tC X co cd © © r'. 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