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Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://archive.org/details/progressreporton62hurs 
 
State of Illinois 
 Henry Horner, Governor 
 Department of Registration and Education 
 John J. Hallihan, Director 
 
 Division of the 
 
 STATE GEOLOGICAL SURVEY 
 
 M. M. Leighton, Chief 
 
 Urbana, Illinois 
 
 :o, 62 CIRCULAR July 1940 
 
 PROGRESS REPORT ON THE 
 INVESTIGATION OF THE PROPERTIES OF 
 ILLINOIS SHALES AND CLAYS AS MORTAR MIX 
 
 By 
 
 R. K. Hursh, J. E. Lamar, and R. E. Grim 
 
 Cooperative Investigation 
 
 of the 
 
 Illinois State Geological Survey 
 
 and the 
 
 Department of Ceramic Engineering of the 
 
 University of Illinois 
 
■INTRODUCTION 
 
 The use of clay materials as an Ingredient in cement mortars 
 is not a new idea. Many instances of such a practice have been noted 
 over a Ions period of years but: the possibilities of commercial devel- 
 opment of clays as mortar mix materials have been seriously considered 
 only in recent years. Such a development has taken place in some 
 regions and with marked success. 
 
 A number of experimental studies have been made on the 
 properties of mortars containing clay materials. These have demon- 
 strated the practicability and desirability of the use of clays and 
 shales of certain regions or localities, In these investigations, 
 the characteristics of the clay materials themselves and the rela- 
 tion of their specific properties to their effects In mortar mixtures 
 have not received adequate consideration* The results, therefore, 
 'have applied to the particular clays investigated and have not been 
 entirely conclusive as regards the advantages or disadvantages of clay 
 materials from other regions. 
 
 The present investigation was undertaken by the Illinois 
 State Geological Survey in cooperation with the Department of Ceramic 
 Engineering at the request of the Illinois Clay Manufacturers ' Asso- 
 ciation and of members of the Structural Clay Products Institute. 
 
 In planning the investigation it was felt that, in certain 
 respects, the study should be more comprehensive than previous work 
 has been. In particular, the physical and mineralogical character- 
 istics of the materials should be determined in order to inquire 
 into the effects which these might have on the properties of mortars 
 and to disclose whether or not certain types of clay or shale might 
 be more desirable than others c 
 
 Samples of various clays and shales of the State were col- 
 lected by the staff of the Geological Survey. Physical tests to de- 
 termine the particle-size characteristics of these materials were 
 made by Dr. R. M. Grogan under the direction of Mr. J. E. Lamar, Head 
 of the Industrial Minerals Division, and mineralogical examinations 
 were made by Dr. R. A, Rowland under the supervision of Dr. R. E. Grim, 
 Petrographor The investigation of the properties of mortar mixtures 
 in which these clay materials were incorporated has been conducted in 
 the laboratories of the Department of Ceramic Engineering by Mr. P. E. 
 Buckles under the direction of Professor R. K. Hursh. 
 
 Samples and Sampling 
 
 The -samples for this investigation were selected on the 
 premise that the materials studied should include: (1) Samples rep- 
 resentative of the various kinds of shales, underclays ; . and surface 
 clays now in use in Illinois for the manufacture of clay products; 
 
(2) samples of Illinois shales, clays, or other materials not used fo: 
 making clay products but which are of interest because of their min- 
 oral or mechanical composition; (3) samples giving a resonably com- 
 plete representation of the kinds of clay minerals found in Illinois 
 clays and shales as well as the amounts of clay minerals and the 
 various combinations in which they occur; and (4) samples giving a 
 reasonably complete representation of the various ranges in particle 
 3ize distribution existing In the clays and shales of Illinois. 
 
 By selecting samples on the above basis, it was believed 
 that practically all types of clays and shales occurring in Illinois 
 would bo represented and that the data resulting from the testing of 
 those samples could be interpreted to evaluate the suitability of the 
 bulk of Illinois' clay and shale deposits for mortar mix. Thus it 
 was felt that the clay products industry of the State as a whole 
 would be served adequately without an investigation of overwhelming 
 proportions and prohibitive duration. 
 
 Prom a more purely scientific angle it was also felt that 
 samples chosen as indicated above would provide a sound basis for de- 
 termining the significance of particle size distribution and clay 
 mineral composition In relation to the various important properties 
 of the mortars in which clay or shale mortar mixes are used. 
 
 With the foregoing factors in mind, 22 samples were se- 
 lected for study. With the exception of the sample of gumbotil, all 
 materials are in actual commercial use for the manufacture of clay 
 products or other purposes. The samples included 10 samples of shale 
 from sources well distributed throughout the State and covering a 
 wide range in the amount of clay minerals content present and in 
 particle size distribution or texture; throe samples of underclays, 
 or fireclays as they are sometimes known, of varied clay mineral com- 
 position and texture; three samples of till, a pebbly, mostly limy, 
 clay of glacial origin; one sample of gumbotil, a non-limy clay occur 
 ring extensively in southern and western Illinois and resulting from 
 the weathering of glacial till under conditions of poor drainage for 
 a long period of time; one sample of Illinois fuller's earth, used 
 for decolorizing oil and for other purposes; one sample of southern 
 Illinois kaolin, a material with a high percentage of the clay min- 
 eral kaolinite; one sample of "Goal Measures" clay with an unusual 
 mineral composition; one sample of loess, a wind-transported and 
 deposited material found extensively along the major rivers of 
 western and southern Illinois; one sample of crude silica, a material 
 consisting almost exclusively of various sized aggregates of exceed- 
 ingly minute quartz particles. The last sample was included to permi 
 evaluation of the possible significance of non-clay materials as 
 mortar mix. 
 
 With a few exceptions, samples consisted of 200 pounds of 
 dried brick taken at random from dryer cars. It was felt that such 
 samples would be reasonably representative of the raw materials in us 
 and would be similar to the dryer waste which in some places is an 
 important source of clay from which mortar mix is made. 
 
A few shale samples contained small amounts of barium car- 
 bonate that had been added to reduce scumming. Such samples wore 
 duplicated by additional 200-pound samples of barium-free shale from 
 storage bins so that both barium-containing and barium-free material 
 would be available for study. For the most part the samples were 
 supplied directly by various clay manufacturers and producers. 
 
 PARTICLE SIZE CHARACTERISTICS OF SAMPLES 
 By J. E. Lamar 
 
 It is well known that the properties of clays and shales 
 vary with the particle size of their constituent mineral grains. It 
 seemed desirable, therefore, to make particle size measurements of the 
 samples used in this investigation with tho particular aim of deter- 
 mining the effect of particle size on the quality of a clay or shale 
 for mortar mix and whether particle size will serve as a means of 
 distinguishing between suitable and unsuitable clays and shales. 
 
 The particle size of a clay or shale is difficult, if not 
 impossible, to measure in absolute terms. Tho violence of tho dis- 
 persion method used, and the length of time during which a sample Is 
 subjected to a dispersing procedure will influence the extent to which 
 a shale or clay is broken down towards its ultimate particle size.. 
 Tho present study makes no claims to have reached ultimate particle 
 size but the dispersion processes employed are believed to give re- 
 sults satisfactory for all practical purposes and to be at least as 
 severe as any conditions producing dispersion likely to be encountered 
 in actual use of clays or shales as mortar mix. 
 
 Method of Analysis 
 
 Particle size analyses were made by the "hydrometer" method 
 using a Casagrande type hydrometer. This procedure has been investi- 
 gated and described by a number of different writers and has been 
 found accurate and comparatively rapid. Briefly, it consists of 
 measuring by means of a hydrometer the amount of a sample of known 
 weight which remains in suspension in water after certain stated 
 periods of time and from these data drawing a curve showing particle 
 size distribution. 
 
 Each sample analyzed consisted of a representative fraction 
 of the original 200-pound sample which had been ground to pass an 8- 
 mesh sieve. Preparation of samples for analysis involved the use of 
 sodium oxalate to give maximum dispersion and five cycles of soaking 
 and shaking in an end-over-end shaker, each cycle consisting of four 
 hours shaking and 20 hours soaking, making a total of 20 hours of 
 shaking and 100 hours of soaking for each sample. At an appropriate 
 place in the dispersion procedure the samples were rubbed lightly on 
 a 270-mesh sieve to break up unslaked pieces. 
 
4 
 
 After the hydrometer analyses were completed, the plus 270- ; 
 rush material was recovered by wet screening and was dried and weighed 
 The character of this coarse portion of tho samples was identified 
 under the microscope and proved to bo largely grains of quartz, silt- 
 stone, clay ironstone, and brown ferruginous material. 
 
 All samples were run in duplicate and close checks were ob- 
 tained in all cases. The data given are the averages of the results 
 of the duplicate analyses . 
 
 Results of Tests 
 
 Results of the particle size analyses are shown graphically 
 in figures 1 and 2. Each group of bars represents one sample and tho 
 length of each bar shows the amount of material of a certain sizo. 
 The key in figure 1 gives the size of the material represented by 
 
 each .bar. 
 
 These bar charts show that the samples studied have a diver- 
 sity of particle size distributions. Of the shales, samples 5, 20, 
 and 21 (figure 1) contain a large amount of fine material and very 
 little coarse material, in contrast with shales 4, 8, and 18 which 
 have a relatively small amount of fine material and a large amount of 
 medium and coarse material. Other shale samples show .intermediate 
 characteristics. 
 
 The charts of the fireclays, tills, etc. (figure 2), show a 
 similar diversity of particle sizes. The kaolin, fuller's earth, 
 and "Coal Measures" clay have very large amounts of fine materials 
 whereas other samples contain moderate amounts or comparatively small 
 amounts . 
 
 It is probable that the particle size character of clays 
 and shales bears a relationship to their suitability for mortar mix. 
 Evaluation of this relationship involves the consideration of many 
 complex factors and is not feasible at the present stage of this in- 
 vestigation, 
 
SHALES 
 
 40 
 
 nil lill Idl. 
 
 18 
 
 SHALES 
 
 40 
 
 t 30 
 
 KEY 
 
 20 
 
 U 
 
 u 
 °- 10 
 
 CO 
 
 z 
 o 
 cr 
 o 
 
 
 
 Bttnfe 
 
 8 
 
 SHALES 
 
 i i i i i i i + 
 
 CM ST I s - O O O CO 
 — OJ <tf «o 
 ' ' i l i I I I I I 
 
 T= TRACE 
 
 Fig. 1. - Chart showing the particle size character of the shale samples 
 
 Lengths of the vertical "bars indicate the amount of material present 
 within the size ranges given in the "Key." The numbers helow each- 
 graph indicate sample numbers. 
 
40 
 
 I- 30 
 
 Z 
 
 UJ 
 
 u 
 
 20 
 
 Ixl 
 
 
 
 
 
 
 
 tvj kAi 
 
 rwl nvJ 
 
 II 
 
 UNDERCLAY 
 
 14 
 UNDERCLAY 
 
 I 
 UNDERCLAY 
 
 CRUDE SILICA 
 
 GLACIAL TILL 
 
 GLACIAL TILL GLACIAL TILL 
 
 GUMBOTIL 
 
 10 
 KAOLIN 
 
 7 13 
 
 FULLER'S EARTH COAL ME AS. CLAY 
 
 Fig. 2. - Chart showing the particle size character of the underclays , 
 tills, and other samples studied. The "Key" is given in figure 1. 
 
MINERALOGICAL CHARACTER OP THE CLAYS AND SHALES 
 
 By Ralph E. Grim 
 
 5 
 
 Clays and. shales are aggregates of very small crystalline 
 particles of one or more members of a small number of minerals known 
 as the clay minerals. Analyses of many clays and shales have shown 
 that there are three important groups of clay minerals and these are 
 listed in table 1. In addition to the clay minerals, clays and shales 
 also contain variable quantities of quartz, pyrite, organic material, 
 limonite, etc. Of these non-clay mineral constituents, quartz is usu- 
 ally the most abundant, so that in a general way clays and shales are 
 composed of clay mineral flakes of the order of size of 0.001 mm. or 
 1/25000 in., together with variable quantities of grains of quartz. 
 
 Table 1. — Important Clay Minerals 
 
 Name 
 
 Ideal Composition 
 
 Occurrence 
 
 Kaolinite 
 
 Illite 
 
 Montmoril- 
 lonite 
 
 (0H) 8 Al 4 Si 4 10 
 (0H) 4 Ky(Al 4 -Fe -Mg -Mg ) (Si 
 
 0H) 4 Al 4 Si 8 2Q 
 
 China clay, under- 
 clays, etc. 
 
 •Al )0 Shales, underclays, 
 o-y y <M surface clays 
 
 Bentonite, fuller's 
 earth, surface 
 clays 
 
 Composition of Clay Materials 
 
 Following are brief statements of the general composition of 
 certain types of clay materials. Most of the shales that have been 
 studied are composed essentially of flakes of illite ranging in size 
 from about 0.001 mm. to 0.020 mm. Some, shales contain almost no 
 quartz whereas others contain 50 per cent or more in grains from about 
 0.002. mm. to 0.2 mm. China clays are composed largely of flakes of 
 kaolinite, ball clays of kaolinite with some illite, fireclays of ka- 
 olinite with some Illite. Like the shales the fireclays also contain 
 quartz in amounts varying up to more than 50 per cent. Also in the 
 fireclays the relative amounts of illite and, kaolinite vary; thus 
 some fireclays are known that are composed almost entirely of kaolin- 
 ite whereas others contain about equal amounts of kaolinite and illite. 
 The clay mineral In most fuller's earth and bentonites . is montmoril- 
 lonite. Surface clays in Illinois frequently contain illite as the 
 essential clay mineral constituent; grains of quartz and also of cal- 
 cite, if the clay is calcareous, are usually abundant. Gumbo til, the 
 clayey material produced by the ancient weathering of till, contains 
 illite and montmorillonite, and occasionally small amounts of 
 kaolinite . 
 
Properties of the Clay Mineral s 
 
 The clay minerals have different physical properties, and 
 the physical properties of any clay or shale depend largely on the 
 character of the clay minerals that compose it. The amount and kind 
 of non*-clay minerals are also important; for example, a clay contain- 
 ing 50 per cent quartz will not have the same properties as one con- 
 taining only 10 per cent quartz. Some of these properties are no 
 doubt related to the satisfactory use of a clay for mortar mix, and 1 
 is one of the objectives of this work to investigate this point. 
 
 Montmorillonite is found in extremely small particles 
 (frequently less than 0.0001 mm.) or in larger flakes that are easily 
 broken down, namely, in pugging, to this extremely small size. Clays 
 composed of montmorillonite have high plastic properties, high bond- 
 ing strength, high shrinkage, and are not refractory. 
 
 .Kao Unite occurs in., particles larger than those of mont- 
 morillonite (usually larger than 0.001 mm.) and the particles are not 
 easily reduced in size on working as in pugging. Kaolinite clays 
 tend to have lower shrinkage', bonding strength, and plastic properti* 
 than montmorillonite clays. They are also more refractory. 
 
 Illite may occur (1) in particles of very small size or in 
 particles that are easily broken down to an extremely fine particle 
 size, or (2) in larger flakes that resist reduction in size. Clays 
 composed of the former variety are plastic and have high shrinkage 
 and high bonding strength. Materials composed of the latter variety 
 have low shrinkage, low bonding strength, and low plastic properties 
 In general, illite clays or shales are not refractory. 
 
 Analytical Results 
 
 It is possible to classify clay materials on the basis of 
 their clay mineral composition and also on the basis of the relative 
 abundance of quartz. The Illinois Geological Survey has determined 
 the composition of all the important kinds of clays and shales in th< 
 State. Using these analytical data as a basis the samples included 
 in the present Investigations were selected so that they would repre- 
 sent the range in composition of clays and shales found in Illinois. 
 The purpose of this selection was twofold: first, to place the in- 
 vestigation on a fundamental rather than empirical basis by providing 
 for the study of the basic factors that determine the satisfactory 
 use of a material for mortar mix; second, to permit a prediction to 
 be made of the probable worth of any clay or shale in the State for 
 mortar mix. ■ This f ollows . f rom the fact that if v/e know what com- 
 position a material jnust have to be used satisfactorily for mortar 
 mix, we can predict 'the probable value of a clay or shale for this 
 use by determining its composition. 
 
Table 2 presents data on the character and. abundanc 
 clay minerals and the amount of quartz In the samples invest! 
 The shales range in composition from about 85 to 45 per cent 
 the remainder being chiefly quartz. The illite in the shales 
 variety that occurs in relatively large particles which do no 
 down easily into extremely small ones. The underclays show a 
 in clay 'mineral content of from 60 to 70 per cent and a varia 
 the relative abundance of illite from 10 per cent to 30 per c 
 the total clay. The clay mineral in the glacial till is 111! 
 probably of the variety occurring in large flakes which are r 
 to break-down. The non-clay portion of the glacial tills con 
 addition to quartz, grains of calcite making up about 15 per 
 the total samDle. 
 
 e of the 
 gated. 
 
 illite, 
 is the 
 
 t break 
 range 
 
 tion in 
 
 ent of 
 
 to, 
 
 esistant 
 
 tains in 
 
 cent of 
 
 The kaolin sample is almost pure kaolinite and is distinc- 
 tive because the kaolinite occurs in flakes smaller than those fre- 
 quently characteristic of this mineral. Sample 13 contains only about 
 10 per cent non-clay mineral and the illite is of the variety that 
 breaks down easily into extremely small particles when worked with 
 water. The fuller's earth is illustrative of clays composed chiefly 
 of montmorillonite . Samples 16, 19, and 15 are examples of fine- 
 grained materials with large amounts of non-clay minerals. Gumbotil 
 (sample 16) is also important because of the presence of a small 
 amount of montmorillonite. It is known that this clay mineral, even 
 though present in only small amounts, has a very great effect on the 
 physical properties of a clay. 
 
 The study of the possible relation between the mineral 
 compositions of the clays and shales and the properties that determine 
 their suitability for mortar mix, which is one of the objectives of 
 these researches, cannot be made until all the analytical data are at 
 hand. Consequently, the results of this part of the work cannot be 
 presented prior to the final report. 
 
 Table 2. --Mineral Composition of Samples Investigated 
 
 Maximum , 
 Sam- Clay Size of Chief size of 
 
 pie Clay minerals minerals clay non-clay non-clay 
 no. per cent minerals-"- minerals mineral Comments 
 
 0' illite 
 
 illite (10) 
 
 1 kaolinite (90) 
 
 2 illite 
 
 illite 
 
 60 
 
 medium 
 
 quartz 
 
 
 .05 mm. 
 
 70 
 
 fine 
 
 quartz 
 
 
 .2 mm. 
 
 45 
 
 fine 
 
 quartz 
 calcite 
 
 70 
 
 i ^0 
 
 2 mm. 
 
 60 
 
 fine 
 
 calcite 40 
 (Continued on page 8) 
 
 and limonite 
 
 quartz 60 .5 mm. Contains 
 
 limonite 
 
8 
 
 Tablo 2. --(Continued) 
 
 
 
 
 
 
 Kaximum 
 
 
 Sam- 
 
 
 Clay 
 
 Size of 
 
 Chief 
 
 size of 
 
 
 ple 
 
 Clay minerals minerals 
 
 clay 
 
 non-clay 
 
 non-clay 
 
 
 no. 
 
 pe 
 
 r cent 
 
 minerals- 
 
 c minerals 
 
 mineral 
 
 Comments 
 
 4 
 
 illite 
 
 45 
 
 coarse 
 
 quartz 
 
 .2 mm. 
 
 Contains 
 limonite 
 
 5 
 
 illite 
 
 85 
 
 fine 
 
 quartz 
 
 1 mm. 
 
 Contains 
 limonite 
 
 6 
 
 illite 
 
 85 
 
 medium 
 
 quartz 
 
 .15 mm. 
 
 Contains a 
 bundant li- 
 onite (5+^ 
 
 7 
 
 illite 
 
 60 
 
 coarse 
 
 quartz 
 
 .15 mm. 
 
 Contains 
 limonite 
 
 8 
 
 illite 
 
 70 
 
 coarse 
 
 quartz 
 
 .5 mm. 
 
 
 9 
 
 montmor ill onite 
 
 75 
 
 fine 
 
 quartz 
 
 .2 mm. 
 
 Contains glu 
 conite, f eld 
 spar, & coar3 
 mica 
 
 10 
 
 kaolinite 
 
 95 
 
 fine 
 
 quartz 
 
 .06 mm. 
 
 
 11 
 
 kaolinite (50) 
 illite (50) 
 
 60 
 
 medium 
 
 quartz 
 quartz 65 
 
 .3 mm. 
 
 Contains 
 
 12 
 
 illite 
 
 40 
 
 fine 
 
 calcite 35 
 
 .2 mm. 
 
 limonite 
 
 13 
 
 illite (80) 
 kaolinite (20) 
 
 90 
 
 medium 
 
 quartz 
 
 .06 mm. 
 
 Contains ap- 
 preciable 
 
 pyrite 
 
 14 
 
 illite (35) 
 kaolinite (65) 
 
 60 
 
 medium 
 
 quartz 
 
 . 15 mm. 
 
 Contains a- 
 
 preciable 
 
 pyrite 
 
 15 
 
 kaolinite 
 illite 
 
 5 
 
 fine 
 
 
 
 Non-clay mat'- 
 rial is crypo 
 crystalline 
 silica in f 
 gregate fori 
 
 16 
 
 montmor ill onite 
 
 40 
 
 fine 
 
 quartz 
 
 1 mm. - 
 
 
 17 
 
 illite 
 
 50 
 
 coarse 
 
 quartz 
 
 .25 mm. 
 
 
 
 
 (Con 
 
 tinued on 
 
 page 9) 
 
 
 
Table 2 .-- (Continued) 
 
 9 
 
 Maximum 
 Sam- Clay Size of Chief size of 
 
 pie Clay minerals minerals clay non-clay non-clay 
 no . per cent minerals*- minerals mineral Comments 
 
 18 illite 
 
 19 illite 
 
 20 illite 
 
 21 illite 
 
 60 
 
 medium 
 
 quartz 
 
 20 
 
 fine 
 
 quartz 
 
 75 
 
 medium 
 
 quartz 
 
 75 
 
 coarse 
 
 quartz 
 
 .2 mm.. Contains 
 
 trace of cal- 
 cite & few 
 larger pebbles 
 
 •15 mm. 
 
 Contains 
 .3 mm. limonite 
 
 .3 mm. Contains 
 limonite 
 
 •«- Coarse =+0.02 mm.; medium = 0.02 mm. -0.005 mm.; fine - -0.005 mm. 
 
 PROPERTIES OF MORTAR MIXTURES 
 CONTAINING ILLINOIS CLAYS AND SHALES 
 
 By R. K. Hursh 
 
 The proportion of clay which may he satisfactorily incor- 
 )orated in the mortar is a most important consideration . Whether or 
 lot certain types of clay material could be used in larger amounts 
 :han others and the practicable limit for each material were questions 
 :o which these experiments were directed. For each sample a series of 
 lixtures was prepared in which the clay and cement proportions were 
 raried while a standard proportion of sand was maintained. These mix- 
 tures covered a range which, it was felt, extends beyond the practica- 
 )le maximum, clay content for actual use. Comparison of the clay- 
 :ement-sand mortars with lime-cement-sand mortars and with commor- 
 :ially prepared masonry cement mortars has also been made. 
 
 It has been the practice, in other investigations and in 
 ;eneral commercial use of clays in mortars, to grind the material very 
 finely. It seemed desirable to determine what effect on the mortars 
 ; ould result if the clay or shale were not so finely ground. The cost 
 f fine-grinding is an important factor in the practicability of com- 
 .ercial development of these materials for mortar mix in many of the 
 lants which do not, at present, have equipment for such preparation 
 f the material. Successful use of clays of relatively coarse grind 
 n mortars has been reported. A series of tests have, therefore, 
 ,een made of mortars in which the clay portion was ground only in the 
 ry-pan to pass an 8-mosh screen. For comparison, tests have also 
 ieen made on mortars in which the same clays and in like proportions 
 ,avo been U3ed but with relatively fine-ground clay material passing 
 ho 80-mesh sieve e A few additional tests wore also made with clay 
 Laterial ground even more finely . 
 
10 
 
 Tost Procedure 
 
 ■ 
 So far as possible, standard methods of test procedure, ap-j 
 proved by the American Society for Testing Materials, have been used 
 in the investigation. Such standards are not available for testing 
 some properties or characteristics, such as plasticity, and in these 
 cases, suitable test procedures must be developed to give comparative 
 data. 
 
 Materials and Mi.xturus .--A single brand of a standard Port- 
 land cement was used and a sand from the Ottawa district which con- 
 formed to the A.S.T.M. specification of C-41 for mortar sand for com- 
 pression tests. The sizing specification for such sand and the scree 
 analyses of two lots of sand used in these tests are shown in table 2 
 
 Table 3. 
 
 Percenta g e retained on designated screen 
 Screen size A.S.T.M. 
 
 U.S. series specification Test samples 
 equivalent C-41 1 2 
 
 100 98 t 2 97.0 97.0 
 
 50 72+5 76.0 67.0 
 
 30 2+2 0.5 
 
 16 O 
 
 Mortar mixtures were prepared in the proportions of one (l) 
 part by weight of cementing material (cement plus clay) to three (3) 
 parts by weight of mortar sand. Those proportions correspond to the 
 A.S.T.M.. Specification C91-38T for compressive tests on mortars. The 
 amount of sand was the same in all the mixtures, 75 per cent of the 
 total. 
 
 The proportions of clay and cement were varied so that, foi 
 each clay, four mortars were made with ratios of clay to cement of 
 20:80; 30:70; 40:60; 50:50 respectively, the proportions being by 
 weight. Tests have boon made with both coarsely- and finely-ground 
 clays in these proportions. 
 
 The water requirement for each mixture to give standard 
 consistency was determined by means of the flow table. For prepara- 
 tion of compression test specimens, a flow of 65-80 per cent is des- 
 ignated. Experimental mixtures were made up with varying water con- 
 tent until the proper amount of water to give the desired flow was 
 found. 
 
11 
 
 Co mpre ssive Strength . --Strength of mortars' in compression 
 is determined by tests on 2-inch cubes. These are made, by a stand- 
 ardized procedure, in metal molds with mortars of a standard, con- 
 sistency. The cubes are left in the molds for 48 hours in a damp 
 closet with regulated temperature and humidity. They are then re- 
 moved from the molds and stored for an additional five days in the 
 damp closet. Specimens are then tested, without drying, for the 
 seven-day strength of the mortar. For longer curing periods, the 
 mortar cubes are removed from the damp closet at the end of the seven- 
 day period and are immersed and kept under water for the additional 
 time, after which they are tested, without drying, for compressive 
 strength. In the present investigation, compressive tests were made 
 on six cubes of each mixture after seven days and on another six 
 cubes after 28 days. Individual specimens which showed a variation 
 of more than 10 per cent from the average were discarded. The test 
 pieces showed excellent uniformity and only a few were eliminated. 
 
 Water Retention . --The water retentivity of a mortar is con- 
 sidered to be in a measure an Index to its workability, which is an 
 essential property of a mortar. It also indicates somewhat the re- 
 sistance of the mortar to drying out in contact with absorbent masonry 
 units with consequent weakening of the bond. 
 
 The water retention test is made by subjecting a layer of 
 the mortar, made up to a consistency giving a flow of 100-115 per 
 cent, to a suction equivalent to a two-inch column of mercury for a 
 period of one (1) minute. After the suction treatment a flow test is 
 made, and the result is recorded In percentage of the original flow. 
 Federal Specification SS-0-181b requires that the final flow be at 
 least 65 per cent of that before the suction test. The water reten- 
 tion tests are not completed at this time and only part of these data 
 are given. 
 
 Further tests on the mortars include time-of-set, volume 
 changes in setting and due to subsequent wetting and drying, and some 
 bonding or adhesion tests of typical mortars with brick masonry. Re- 
 sults of these tests will be reported at a later date. 
 
 Results 
 
 Compressive Strength . --The average compressive strength of 
 mortars in which the various shales were used to replace 20, 30, 40 
 and 50 per cent of Portland cement in a 1:3 mixture are shown by 
 curves in figure 3. The solid lines marked 7-C and 28-C represent 
 the seven-day and 28-day tests of mortars in which coarsely-ground 
 shale passing an 8-mesh sieve was used. Similar data for the more 
 finely-ground material passing an 80-mesh sieve are shown by the 
 dotted curves 7-F and 28-F. The sample number of each shale ac- 
 companies the corresponding curves. For comparison, the strength 
 tests for mortars containing hydrated lime in the same proportions as 
 the shales are shown in the curves under L. The seven- and 28-day 
 strength of a commercial masonry mortar are shown by points 7-M and 
 28-M respectively on this diagram. The strength data for a 1:3 
 
12 
 
 cement-sand mortar are also shown by points 7-PC and 28-PC at the 
 left-hand margin. 
 
 Data for the underclays and glacial tills are presented in 
 the curves of figure 4 and those for other miscellaneous samples in 
 figure 5. 
 
 With 20 per cent clay and 80 per cent cement, there is a 
 slight gain in strength at seven days over the use of cement alone ir 
 the 1:3 mortar in shale samples 6, 8, and 17; about equal strength 
 with samples 5, 7 , and 4; and lower compressive strength with other 
 shales. One of the underclays (14) shows about equal strength with 
 the 20:80 ratio, and all of the glacial tills are only slightly 
 lower in strength than the cement-sand mortar when used in this pro- 
 portion. Fuller's earth (9), silica (15), loess (19) and two of the 
 underclays (l and 11) show definitely lower values of strength at 
 seven days, even with the smallest amounts replacing cement in the 
 mortar. 
 
 All of the clay materials cause a progressive decrease in 
 mortar strength as the percentage of clay is increased. The change 
 is approximately proportionate to the amount of clay added. The de- 
 crease in strength is slightly less pronounced in shales 5, 7, and 
 and in Underclays 1 and 11 than in the other materials, as indicated 
 by the slope of the lines in figures 3 and 4. 
 
 As would be expected, there is a definite gain in strength 
 in the period from seven to 28 days, during which the test cubes wore 
 immersed in water. The amount of gain is smaller for shales 20 and 
 17 and for the kaolin (10) than for the other materials. The numeric 
 value of the increase in strength is greatest for the smaller clay 
 additions but the gain is in nearly the same ratio to the seven-day 
 strength for almost all mixtures with a given clay. Three of the mix- 
 tures containing the coarse-ground clay in the 20:80 ratio to cement 
 showed higher strength at 23 days than did the 1:3 cement mortar. 
 These contained shales 6 and 3 and undorclay 14. 
 
 More finely-ground clay (passing an 80-mesh sieve) gave 
 mortars of lower strength than did the 8-mesh material in all cases 
 except three. In some instances, the decrease was considerable, oitl: 
 at seven or 28 days or both. Only the mortars containing shales (20 
 and 17) or glacial till (3) developed somewhat higher strength with 
 the finer clay material. With the exception of the 20:30 mixture of 
 shale (17), all of the mortars containing the finely-ground clay 
 showed lower strength in both the seven-day and 28-day tests than thi' 
 of a 1:3 cement-sand mortar. So far as mortar strength is concerned., 
 the fine grinding of the clay portion gives little, if any, advanta 
 It is evident that there is sufficient slaking of most of the clays, 
 even "the harder shales, in the mixing of the mortars to obviate the 
 need of finer grinding. 'These results indicate that a portion of the 
 clay, at least, functions as an aggregate in the same manner as the 
 sand. Probably the gradation in particle ■ sizing of the clay portion 
 will have a significant effect in relation to the density developed 
 by the packing of the particles in the mortar mixture. The amount oJ 
 slaking and break-down of the clay in wetting and mixing is a factor 
 in this connection. 
 
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13 
 
 It Is possible that other properties of the mortar, such as 
 weather resistance, may be affected, to a greater extent by the use of 
 finer clay material and to such a degree that It may be desirable. 
 This must be determined in further investigation. 
 
 The maximum amount of clay that may be safely incorporated 
 In a mortar mixture will bo determined, to a considerable degree,, by 
 the strength that will be developed in setting. Definite strength 
 requirements are not included in some of the specifications for 
 masonry mortars. 
 
 Federal Specification SS-C-181b for masonry cement requires 
 a minimum strength of 250 lbs. per sq. in. at seven days and 500 lbs. 
 per sq, in. at 28 days for Type I, which is intended for use where not 
 exposed to frost action* For general masonry use, Type II materials 
 should have a minimum compressive strength of 500 lbs. at seven days 
 and 1000 lbs. at 28 days. 
 
 In Brick Engineering, _/ it is suggested, in connection with 
 weather resistance, that the minimum strength at seven days should be 
 600 lbs* per sq. in. In specifications for lime-cement-mortars, 
 three classes and their requirements are designated. 
 
 The 1:1:6 mortar (cement , lime-putty, and sand by volume) 
 (minimum compressive strength at seven days = 400 lbs. per sq. in.) 
 is suitable for general use above grade and is recommended specifically 
 for parapet walls, chimneys, and exterior walls subject to severe ex- 
 posure, also for structural clay tile construction. 
 
 The 1:2:7-9 (cement, lime-putty, sand) mortars, having a 
 minimum seven-day strength of 150 lbs. per sq. in., are suitable for 
 non-load-bearing walls not subjected to severe exposures, also for 
 load-bearing walls in which unit compressive stress is not excessive. 
 The l:|-:2^~3 mortar (cement, lime-putty, sand) with a minimum strength 
 of 15C0 lbs. per sq. in. at seven days, is suitable for general use 
 and is recommended specifically for reinforced brick masonry and for 
 plain masonry below grade or in contact with earth, such as in founda- 
 tions, retaining walls, walks, sewers, manholes, and catch basins. 
 
 For every clay tested, mortar strength was sufficient, even 
 with equal parts of clay and cement, to exceed the requirement for 
 Typo I in the Federal Specification, The strength requirements for 
 Type II mortars, suitable for general use, are fulfilled by mortars 
 in which clay material replaces 40 per cent of the cement for all the 
 shales, underclays, glacial tills, and other materials except fuller's 
 earth. In the 50:50 mixtures, shale (20) was slightly below the 28- 
 day requirement and materials 9, 10, and 13 were also somewhat de- 
 ficient in 28-day strength. 
 
 The strength of mortars in which 40 per cent or more of these 
 clay materials replaced cement was equal to or greater than that of the 
 commercial masonry cement for nearly every sample. It is evident that 
 relatively large quantities of these shales and clays can be incor- 
 porated in mortars for ordinary masonry purposes and that they will bo 
 
 l/Brick Engineering, H. C. Plummor and L. J. Reardon - Structural Clay 
 Products Institute, p. 51, 1939. 
 
14 
 
 i'u..'.'.'. t as high In strength as are prepared mortars now on the market 
 and in general use. 
 
 
 ■ If a minimum compressive strength of 1500 lbs. per sq. in. 
 at seven days is satisfactory for mortars subject to the most severe 
 requirements of ordinary masonry, the present tests show that con- 
 siderable amounts of the majority of the clays tested may be used. Ir 
 most cases, the compressive strength does not fall below this, value 
 untiL the ratio of clay to cement reaches 30:70 to 35:70 by weight. 
 These mortars would contain the following proportions by weight of 
 the three ingredients: 1 cement - 0.43 clay - 4.29 sand; and 1 cement 
 - 0.54 clay - 4.62 sand, respectively. 
 
 Water Requirement for Standard Consistency . --The water re- 
 quirement for the specified consistency for compressive strength , .. 
 specimens Is somewhat lower than would probably be used- in mortars 
 for masonry purposes. These stiffer mortars, with a flow of 65-80 
 per cent, are more suitable for molding the two-Inch cubes thsn would- 
 be a mortar of 100-115 per cent flow, specified for water retention 
 tests. The latter is about the consistency used by the brick mason, 
 -^he water requirement for 100-115 per cent flow is found to be about 
 1 to 3 per cent higher than that for 65-80 per cent flow 7 in some of 
 the mortars containing various proportions of clay 'materials . 
 
 A considerably larger amount of water is needed in the clay^ 
 cement mortars than when cement alone is used with the sand. The re- 
 quirement ' increases with larger proportions of clay, as shown in. 
 figure l 6« In general, the clays which require the larger amounts of 
 water to produce the desired mortar consistency give lower-strength 
 mixtures than do the clays requiring less water. This is particularly 
 noticeable with fuller's earth (9), and to a less degree with the 
 kaolin (10) and the "Coal Measures" clay (13). The effect in the 
 latter two is best seen in the diminishing gain in strength from 
 seven to 28 days as the proportion of clay is increased. In the 
 shales, the differences in water requirement of up to 40 per cent 
 mixtures is not great and little effect on mortar strengths is evi- 
 dent or should bo expected. 
 
 It would be expected that a high water addition in the 
 mortar would cause lower strength, due to a greater degree of poros- 
 ity. The effect might be offset by shrinkage in setting and drying, 
 but this would be objectionable in a masonry mortar. On the other 
 hand, higher water content should tend to give a greater yield or 
 volume of mortar per unit weight of solid material. The relative 
 yield of the different mixtures has not been determined. 
 
 Water Retention . — The results of water retention tests' for 
 a number of the samples are shown with the strength data in figures 3, 
 4, and 5. The values for mortars containing the various proportions 
 of the 8-mesh clay material are shown by curves marked R-C . Results 
 with 80-mesh clay material arc shown for three samples by dotted 
 curves R-F. The value for the masonry mortar is -shown in Figure 1 
 with the lime-cement mortar data (L) by the point R-M. 
 
PER CENT WATER REQUIRED FOR 65-80% FLOW 
 
15 
 
 Some of the samples show high values of water retention, 
 considerably above that of the lime-cement mortars. Those compare 
 well with the prepared masonry mortar which showed a value of 73.3 per 
 cent. The other samples show values equal to or only slightly lower 
 than does the hydrated lime. 
 
 It has been noted that a water retention value of 65 per 
 cent is considered desirable. Largo proportions of some of the clay 
 materials will be required to give this value while others can be 
 used in lesser amounts. This indicates that increase in water 
 retentivity will be obtained at the sacrifice of mortar strength and 
 vice versa. Further tests on water retention, now in progress, will 
 give desirable information on this relationship and, possibly, on 
 some influences of the specific properties or characteristics of the 
 clay materials themselves. None of the lime-cement mortars, made 
 with the one sample of hydrate which was used, gave a water retention 
 value of 65 per cent. 
 
 Discussion of Results 
 
 It is evident from the data on compressive strength of the 
 mortars that a considerable proportion of the Illinois clays and shales 
 are suitable for use as plasticizers in masonry mortar. It is in- 
 dicated that they are equal to or superior to hydrated lime, when 
 used in the same proportions, in producing mortars of satisfactory 
 strength and that many are superior to the lime-cement mortars from 
 the standpoint of water retention. In the testing procedure, it was 
 observed that the workability of the clay mortars was generally much 
 better than that of the lime mortars. 
 
 Clays which require large amounts of water to give a suit- 
 able working consistency are likely to produce mortars of inferior 
 strength. However, most of the clays and shales which are most 
 likely to be considered for use as mortar mix are satisfactory in 
 this respect. 
 
 A considerable amount of most of the shales and clays may 
 be incorporated in mortar without reducing the strength below the 
 minimum requirements of specifications in common use. In general, 
 these clay materials may replace 30 to 35 per cent by weight of the 
 cement in 1:3 mortars intended for severe conditions of exposure. 
 Mortars containing equal parts of clay and cement show sufficient 
 strength to meet specifications for other types and uses. 
 
 There are evidences of some relationship between the char- 
 acteristics of the clay materials and the properties of the mortars 
 in which they are incorporated. These are not sufficiently well de- 
 fined to discuss at this time. It is hoped that some correlations 
 may be possible when the remainder of the experimental data has been 
 (Obtained. 
 
"WASCHER'S" 
 
 507 S. Goodwin 
 Urbana, I1L 
 
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