ROAD RESEARCH LABORATORY Ministry of Transport RRL REPORT LR 365 THE MEASUREMENT OF THE TENSILE PROPERTIES OF SOIL-CEMENT by H. E. Bofinger Tropical Section Road Research Laboratory Crotihorne, Berkshire 1970 Abstract 1. 2. 3. 4. s. 6. 7. 8. Introduction Discussion of tensile tests 2.1 The direct tensile test 2.2 The indirect tensile test 2.3 The flexural test Experimental details 3.1 Preparation of specimens 3.2 Method ofmoulding 3.3 Metbod obtesting 3.3.1 Briquettes 3.3.2 Tensile tests on304.8mm x76.2 mmx76.2mm blocks 3.3.3 Indirect-tension cylinders 3.3.4 Compression tests on304.8mm x76.2 mmx76.2mm blocks 3.3.5 Flexural tests Results 4.1 Properties ofl+armondsworth brickeartb 4.2 The effect of side plates 4.3 Stress-strain relationships for soil-cement 4.4 Comparison of tensile failure stresses Discussion of results Conclusions Acknowledgements References oC CROWN COPYRIGIIT 1970 Page 1 1 2 2 2 3 4 4 5 5 5 5 5, 6 6 6 6 6 7 9 10 11 11 11 Extracts from the text may be reproduced provided the source is acknowledged THE MEASUREMENT OF THE TENSILE PROPERTIES OF SOIL-CEMENT ARSTRACT As part of an investigation of the design of soil-cement pavements, laboratory tests were carried out using Harmondsworth brickearth to examine the tensile properties of soil-cement and their relation to its compressive properties. The Report discusses three methods used for determining the tensile strength, the direct and indirect tests and the flexural test, and suggests explanations for the differences in the results obtained. Soil-cement was found to have a much higher elastic modulus when subjected to compressive stresses than when the same average tensile stresses were applied. Because of the complex behaviour of soil-cement under stress, estimates of its tensile strength from the cylinder splitting or flexural tests are uncertain. The direct tensile test which is independent of the strain characteristics provides a more reliable indication of tensile strength of soil-cement at slow rates of strain. 1. INTRODUCTION Cement or lime-stabilised soil is widely used for road bases in the tropics and whilst the great majority of roads constructed in this way give good service a significant minority are unsatisfactory because of excessive cracking in the base which reflects through the surfacing. This cracking, which occurs most frequently with the finer-grained stabilised soils, is not related to the thickness of construction and is commonly attributed to ‘shrinkage’. In order to understand how and why this cracking occurs it is necessary to find out more about the stress-strain properties of stabilised soil in tension and compression, its shrinkage properties, and the rate which it gains strength with age. With information on these lines it is possible to examine both the validity of the assumption of elastic behaviour in the case of soil cement and tbe mechanism of ‘shrinkage’ cracking. Most previous investigations of stabilised soil have been concerned chiefly with the compressive properties of the material. This Report describes a laboratory investiagtion of the tensile I properties of a soil cement and their relation to its compressive properties. The work is part of a wider research programme in which the cracking of full-sized soil-cement slabs is being investigated under various loading and curing conditions. Three laboratory methods were used to determine the tensile strength of the soil-cement; the direct tensile test, the indirect tensile test and the flexural test. Each method gave different values for the tensile strength of the material and an explanation of this is that the assumptions that form the basis for calculations of stress in the indirect and flexural tests are invalid for soil-cement. A major assumption in the elastic theory is that the elastic ‘stiffnesses’ of the material in tension and compression are equal. However it has been demonstrated that the tensile and compressive stress-strain properties of one clay-cement mixture are significantly different. In this previous study it was found that under tensile loads the stress-strain graph was slightly concave in shape and the failure was typical of brittle fracture, whereas in compression the stress-strain curve was markedly non-linear and at stresses approaching the ultimate definite plastic behaviour was indicated. However the most important difference between the two stress-strain curves was the difference between their slopes. The slope of the compressive stress-strain curve was much greater than the slope of the corresponding tensile curve, indicating that the compressive ‘stiffness’ is much higher than the tensile ‘stiffness’. The work described in this Report is an extension of this previous study. 2. DISCUSSION OF TENSILE TESTS 2. I The direct tensile test Researchers have used two types of direct tensile test. In the first, the specimen has enlarged ends which are gripped by a jaw. In the second, the load is applied through plates which are cemented to the ends of the specimen. When specimens of the first type are used (Fig. 1), there is some danger that stress concentrations at the grips will cause premature failure. A second disadvantage is that it is difficult to measure strain during the test. If plates are cemented to the ends of the specimen (Fig 2), it will usually fail in shear near the junction between the specimen and the resin cement. The ultimate stress will then be lower than for the ~lrst type of specimen. Alternatively, if plates are cemented to the sides of the specimen (Fig 3), it will withstand a stress as high as the enlarged-end type of specimen. 2.2 The indirect tensi Ie test In this test, which was originally developed for evaluating concrete, a vertical compressive load is applied to a cylinder of the test material which lies with its axis horizontal between the platens of the test machine (Fig 4)7. The load is applied through two packing strips positioned so that their axes lie in the same vertical plane as the cylinder axis. The purpose of these packing strips, which are of some relatively soft material, is to distribute the applied load evenly over any irregularities on the surface of the specimen. 2 The cylinder fails by splitting along its vertical axial plane and hence the test is also known as the ‘cylinder splitting test’. The tensile stress at failure is estimated from the elastic formula, ft = where ft = P= d= L= —2P ~dL ultimate tensile stress applied load diameter of cylinder thickness of cylinder The formula assumes that the vertical compressive stress does not contribute to the failure of the cylinder. In a cylinder-splitting test, if a maximum strain criterion of failure applies to the material, the orthogonal compressive stress must be taken into account in determining the tensile strength of linear elasto-brittle materials 2. Consequently the elastic formula above should underestimate the tensile strength of materials which conform to the maximum strain criterion of failure. Tests on concrete7 have shown that the indirect tensile strength is higher than the direct tensile strength. No attempt has yet been made to analyse the true stresses in the cylinder when the elastic modulus in compression (Ec) differs from the elastic modulus in tension (Et). While an anaylsis is not attempted in this paper, one would expect that the lower value of Et would reduce the tensile stress which is produced by a given load P. Therefore, the formula should overestimate the tensile strength of soil-cement. The curve relating tensile stress to strain cannot be obtained readily from an indirect tensile test. Up to the present time, the test has not been standardised for soil-ceme~ and various sizes of cylinders are employed. It has been suggested3 that packing strips are unnecessary for soilcement cylinders and that some flattening of the cylinder is not deleterious provided that a brittle failure occurs. 2.3 The flexural test For convenience, the flexural test is often used It is normal practice to use third-point loading and to equation: f= where f = M= y= 1= to estimate the tensile strength of soil-cement. calculate the extreme fibre stresses from the MY I extreme fibre stress applied moment distance from the centroid of the section to the extreme fibre moment of inertia of the section about the centroid This the theory equation assumes similar elastic behaviour in tension and compression and derives from of simple bending. 3 However, if Ec is not e~al to Et, the neu~al axis is displaced from the centroid of the section and the above equation does not apply. Laboratory tests 4 J 1 have shown that this can occur in soil5 cement beams, in which case Herbert’ s equation , which allows for different E values in tension and compression and for plastic behaviour, should be used to estimate the extreme fibre tensile stress: bh, q 02 01+ 02 where b = h= q and ff2 = += M= The position = ~ d(M~~ 4 d+ breadth of the beam depth of the beam extreme fibre stresses slope of the curved beam applied moment of the neutral axis may be obtained from the equation: q.h 71=— ‘1 + 62 where ~ = distance from extreme tensile fibre to the neutral axis q = strain in the extreme tensile fibre f2 = strain in the extreme compressive fibre The strains q and (2, may be found graphically by equating the areas under the curves relating tensile and compressive stress to strain and by plotting the area under each curve against the strain. When the tensile and compressive stress-strain curves are known, the relationship between M and ~ may be determined. The extreme fibre tensile stress at failure can be calculated for the measured failure moment. 3. EXPERIMENTAL DETAILS Within this project one parent soil was used, namely, Hamondsworth Brickearth. The classification test results are given in Section 4 below. As some of the tension specimens were moulded with a cross section of 25.4 mm square, the soil was crushed until its maximum particle size was 3.2 mm. Additions of 6, 8 and 10 per cent of cement were included and the specimens were moulded at moisture contents of 15 and 17 per cent. 3. I Preparation of specimens The soil was moistened to 14 per cent moisture content and was allowed to stand in sealed containers for at least 3 days prior to use. The cement and the moistened soil were mixed and the required moulding water was added. Specimens were moulded, extruded, sealed in wax and cured at a temperature of 200C for 14 days before being tested. The types of specimens prepared are listed in Table 1. 4 TABLE I Summary of specimen types used in the testing programme I I Test I Investigation I Type of specimen I I Direct tension Ultimate strength Briquette with 25.4 mm x 25.4 mm cross-section Stress-strain 304.8 mm x 76.2 mm x 76.2 mm behaviour block with plates cemented to the sides at each end 1 1 Indirect tension Ultimate strength 101.6 mm x 50.8 mm diameter cylinders I I Unconfined Stress-strain 304.8 mm x 76.2 mm x 76.2 mm compression behaviour blocks Flexure Ultimate failure 304.8 mm x 76.2 mm x 76.2 mm beams moment I 1 3.2 Method of moulding Plates 1, 2 and 3 show the apparatus which was used to mould the briquettes, 304.8 mm x 76.2 mm x 76.2 mm blocks and beams, and 101.6 mm x 50.8 mm diameter cylinders respectively. The briquettes and cylinders were statically compacted to a predetermined density. To help reduce the density gradient in the cylinders, the material was rodded by hand prior to final compaction. The blocks and beams were moulded in three equal layers under a pressure of 1560 kN/m2. Under this pressure the specimens were compacted to BS maximum dry density, 2.5 kg (5.5 lb) rammer mefiod. 3.3 Method of testing 3.3. I Briquettes The load was applied to the direct~ensile briquettes through a pair of jaws which were separated at 0.76 mm/min. Because the jaws penetrate into the specimen, the deflection was not recorded and only the ultimate load was noted. 3.3.2 Tensile tests on 304.8 mm x 76.2 mm x 76.2 mm blocks Side plates were glued to each end of these blocks with a quick-setting polyester resin. End caps which incorporated a spherical seat reduced any moment in the specimens to a negligible amount. Plate 4 shows a specimen in position in the testing machine. A stressing rate of approximately 138 kN/m2/min was used. Dial gauges were attached to the top and bottom platens and the deflection was recorded. 3.3.3., Indirect-tension cylinders The cylinders were placed horizontally between the platens and loaded to failure. Two sets of specimens were tested, one without packing strips and one with 6.4 mm x 3.2 mm rubber strips inserted at the top and bottom. Packing strips are used to minimise 5 the uneven distribution of load along the length of cylinders and they must be much softer than the specimen to accomplish this. Although hardboard is recommended as packing material for the indirect tensile testing of concrete, it is unsuitable for the softer soil-cement specimens. Therefore rubber strips were used in this investigation. 3.3.4 Compression tests on 304.8 mm x 76.2 mm x 76.2 mm blocks The blocks were tested in compression to determine the stress-strain relationship. The stress was applied parallel to the direction of compaction at a rate of approximately 1040 kN/m2/min. Deflections of the top and bottom platens were noted. A group of blocks was tested to determine the effect of applying the load through side plates glued to the ends of the specimen. The stress-strain curves of these specimens were compared with the stress-strain curves of specimens loaded through the ends in the usual way. 3.3.5 Flexural tests A third-point loading system with a span of 228.6 mm was used to stress the flexural beams, The load at failure was recorded. 4. RESULTS 4. I Properties of Harmondsworth Brickearth Liquid limit = 53 per cent Plastic limit = 20 per cent Plasticity index = 33 per cent Specific gravity = 2.70 Particle size: 7 per cent sand 55 per cent medium & coarse silt 10 per cent fine silt 28 per cent clay (<0.002 mm) When the soil was mixed with 8 per cent of cement, the BS optimum moisture content was 17 per cent and the maximum dry density was 1778 kg/m3. In all of the experimental work, the cement used was a blended ‘Typical Ordinary Portland Cement’ to BS 12 supplied by the Associated Portland Cement Manufacturers Ltd. 4.2 The effect of side plates The techniques that are normally used to measure tie strain in a tensile specimen are either to attach some form of extensometer to the specimen or to glue resistance gauges to its surface. Both of these techniques are difficult to employ on soil-cement specimens. The sharp pins of extensometers that lightly indent the surface of metal and plastic specimens thus forming accurate gauging points, cause local failure in the relatively weak soil-cement. A pin seated in the disturbed material in this failure zone is not a reliable gauging point. Glues that are used to attach resistance strain gauges to specimens are much stiffer and stronger than hardened soil< emeriti 6 Comparative measurements 1 specimens indicated a ‘stiffness’ measurements of elongation. have shown that resistance strain gauges glued to soil-cement approximately 100 times the ‘stiffness’ calculated from mechanical Therefore, in this series of experiments side plates were glued to the ends of the specimens both for the application of load and as reference points from which to measure elongation. When side pla~s are used to @ansfer the load to a 304.8 mm x 76.2 mm x 76.2 mm specimen, tie effective length of the specimen must be estimated so that the strain can be calculated. The effective length must lie somewhere between the total length of the specimen (304.8 mm) and the clear distance between the side plates (152.4 mm). Because the tensile stress-strain specimens can be loaded only through some attachments such as side plates, the effective length problem was studied using a @oup of compression specimens. The compressive stress-strain curves for three specimens are drawn in Fig 5. Up to a stress of 1.3 and 1.1 MN/m2 respectively, specimens 912 and 914, which were loaded through side plates, had curves identical with Specimen 913 which was loaded directly through the ends of the specimen. A gauge length of 228.6 mm (midway between 152.4 and 304.8 mm) was used to calculate the strain in Specimens 912 and 914. As the tensile strength of this soil-cement is much lower than 1.1 MN/m2, it was assumed that there would be no slippage between the plates and the tensile specimens. This assumption was supported by the test results which showed brittle characteristics of the tensile stress-strain curves at the failure points and no indication of sudden slippage. Although the loads applied through the side plates to tension specimens are in the opposite direction to the compressive loads, there is no apparent reason why an effective length of 228.6 mm is not satisfactory for tensile strain calculations. 4.3 Stress-strain relationships for soil-cement Three specimens were tested at each cement and moisture content to detemine both the tensile and the compressive stress-stiain curves. For each group of specimens, the best-fitting stress- ... strain curve has been drawn. Only these average curves are included in Figs 6 and 7. -. . . .. . .. -.$ ‘$ It’can be seen that the tensile and compressive stress-strain curves have different characteristics. This confirms the previous observations 1. The tensile curves are concave upwards and there is an insignificant effect of cement and moisture content on the shape and slope of the curve. Each tensile curve shows a characteristic brittle fracture with no plasticity at failure. The compressive stress-strain curves have a distinct plastic region near failure. Listed in Table 2 are the tensile and compressive secant moduli of the best fitting curves and the confidence limits at the 95 per cent level. The tensile moduli were determined at failure and the compressive moduli at one-third of the failure stress. Because the extieme fibre compressive stress in a beam at failure is much smaller than the ultimate, the compressive modulus at one+hird -- of the ultimate stress is more representative of the properties of the material. The ratio of E c/Et varies from 7.5 to 11.1. TABLE 2 Stress-strain test results on cement-stabilised Harmondsworth brickearth Tensile Cement Moisture Et content content 95 per cent (Mo!:lus) (Modulus of percent percent Average curve) confidence MN/m2 MN/m2 limits -— —- -.-—. 147 6 15 121 124 ? 39 119 112 8 15 152 145 * 50 132 162 10 15 165 158 * 11 156 144 6 17 138 138 ?9 138 194 8 17 154 165 k 61 149 171 10 17 155 152 * 34 144 Ec (Modulus! MN/m2 1510 1606 1344 1100 1100 1100 2310 1910 1276 993 1103 1076 1434 1655 1153 1505 1400 1166 Compressive — I 1 Ec (Modulus of 95 per cent Ec confidence — Average curve) MN/m2 limits Et 1380 I * 330 I 11.1 1110 I — I 7.7 1580 I t1294 I 10.0 1041 I * 151. I 7.5 1310 * 700 7.9 1400 ? 449 9.2 .-,,.,,,,.,.,.,.,.,.............,,—.,.---.,.--.-,,,,-.--,-..—.-.—.”-...--—,—..-.,-..——--——, —,.,,-— —, ...,. ., ,--,.,. ., “,,,-.,—— ,—-.—,. .-. ——”—. “---- --.. —.. -..—..— .— Similar test results were obtained from specimens cut from a stabilised pavement in Malaya, as is shown in Fig 8, 9, 10 and 11. The material was a clean sand stabilised with cement, and, as before, fiere was a large difference between Ec and Et. 4.4 Comparison of tensile failure stresses The tensile stresses at failure are recorded in Table 3. TABLE 3 Comparison of tensile stresses at failure Cement content percent 6 8 10 6 8 10 Moisture content percent 15 15 15 17 17 17 Direct tensile strength Briquettes kN/m 2 269 358 418 373 398 480 Blocks kN/m2 245 360 428 332 418 400 Indirect tensile strength Vith packing kN/m 2 304 367 405 Without packing kN/m 2 271 303 366 Extreme fibre flexural stress Elastic Herbert kN/m2 , kN:/m2 404 491 664 463 630 758 278 383 485 336 432 543 The tensile stresses for the cylinder-splitting tests were calculated from the existing elastic formula, while both the simple elastic and Herbert analyses were used to estimate the tensile extreme fibre stresses in flexural specimens. Each result in the Table represents the average of five tests, except for the direct tensile blocks for which three tests were averaged. 1. 2. 3. A statistical analysis of the r~ults in Table 3 has shown that: There is no significant difference (at the 95% confidence level) between the direct tensile strengths obtained from ‘briquette’ and ‘block’ specimens. When rubber packing strips were used in the indirect test the calculated failure stresses were higher than when the packing was omitted. The failure stresses of specimens tested with rubber packing strips were 4.9 to 25.1 per cent higher (95% confidence level). It has been previously stated3 that packing strips should not affect the indirect tensile strength of soilcement. The results of the indirect test were significantly lower than those of the direct test. This is in contrast to results that have been obtained for concrete 7. With packing strips the 95% 9 confidence interval of the difference was 5.0 to 22.6 per cent. Without packing strips the interval was 17.3 to 32,7 per cent. 4. There was little difference between the measured direct tensile strength and the extreme fibre tensile stress calculated by the Herbert equation. The 95% confidence interval showed the beam strengths to be 0.6 to 12 per cent greater than the briquette strengths. When the simple elastic formula was used the extreme fibre stresses were much greater than the briquette strengths and the 95% confidence interval of the differences was 40.2 to 55.4 per cent. 5. DISCUSSION OF RESULTS In previous researchl a heavy expansive clay stabilised with 4, 6 and 8 per cent cement was stressed in compression and tension. The compressive secant modulus, Ec, at a stress of 2/3 of the ultimate was from 2.4 to 4.7 times larger than the tensile secant modulus, Et, at failure. Within this research programme a lighter, inactive clay was stabilised with 6, 8 and 10 per cent cement and the ratio of Ec to Et varied from 7.5 to 11.1, Similar tests on sand-cement specimens cut from a road pavement also showed that Ec was much greater than Et. This difference in the behaviour of soil-cement under compressive and tensile loads cannot be explained by any mechanism that is supported, at the present, by experimental results. A possible explanation derives from the macro structure of the material in which planes of weakness occur between the soil particles and the stabilised matrix. Under compressive loads these planes of weakness should be closed and the stress transmitted directly across them, Hence, almost all of the cross-section resists part of the compressive load. When tensile loads are applied there can be no transference of load across the weak planes and only a reduced proportion of the gross crosssection is able to resist the load. Therefore the actual tensile stresses in parts of the material will be much larger than the average stress, especially when the concentrations of stress at the ends of cracks are considered. It follows that the tensile ‘stiffness’ calculated from the average stress should be much lower than the compressive ‘stiffness’. On a micro-scale, the possibility that there are fundamental differences between the tensile and compressive properties of the untracked material should not be discounted without experimental proof. It has been demonstrated that rubber packing strips increase the calculated failure stress in cylindersplitting tests performed on a cement-stabilised silty clay (Harmondsworth brickearth). necause Ec is greater than Et, the cylindersplitting tests should produce calculated tensile strengths which are greater than the direct test. The indirect tensile strengths in this investigation were lower than the direct strengths. Apparently the reduction in the calculated strength which is caused by neglecting the orthogonal compressive stress 2. 1s more important than the difference in the tensile and compressive stiffness. 10 The Herbert equation gives extreme fibre flexural stresses which are not markedly different from the direct strengths of the material. It appears thatthe simplified stress model which is used in the Herbert analysis applies to soil-cement beams. As the elastic flexural equation is invalid for soil-cement because Ec is not equal to Et, previous flexural test results are suspect and must be treated with discretion. As the static stiffness characteristics are so different in tension and compression the dynamic stiffnesses should be carefully studied before elastic-pavement stress analyses are applied unreservedly to untracked soil-cement pavements. The effects of variations in the rate of strain are currently being evaluated at the ~oad ~esearch Laboratory. 6. CONCLUSIONS 1. 2. Soil-cement has a much higher secant modulus when subjected to compressive stresses than when tensile stresses are applied. The ratios of Ec to Et that were obtained in this series of tests varied from 7.5 to 11 and these figures reinforce other unpublished results. ~ecause the measured failure load in a direct tensile test is independent of the strain characteristics of the specimen, it is the only method which can readily measure the tensile strength of soil-cement. Cylindersplitting and flexural tests are of little value for assessing the tensile strength of soil-cement unless the actual failure stresses can be calculated. This is much more difficult to achieve than the direct measurement of tensile strength in the simpler direct tensile test. 7. ACl(NOWLEDGEMENTS The work described herein was carried out in the Tropical Section of the ~oad qesearch T,aboratory while the author was on study leave from the lJniversitY of Queensland and temporarily attached to the Section. The author wishes to express his gratitude to the Director of ~oad ~esearch, Mr D J Lyons, for permission to work at the I,aboratory and to Dr E D Tingle, !Iead of Tropical Section, for his encouragement and assistance. GA 1. 2. 3. The author is also indebted to Messrs P R Nelson (P\VD ~ritish Solomon Islands) and Sullivan (Tropical Section) who asssited in the Research. 8, REFERENCES BOFINGER, H.E. Soil-cement as a rigid pavement material. lJnpublished Ph D thesis, University of Queensland, 1968. ORR, D.M.R. Deformation and strength of concrete in tension. Paper No 2781 presented at the Institution of Engineers Conference on the Deformation of Concrete and Concrete Structures, Brisbane, Sept 1969. FRYDMAN, S. The applicability of the ~razilian (indirect tension) test to soils. Australian ‘Journal of Applied Science, 1964, 15 (4), pp 335-43. II 4. METCALF, J.B. Flexural tests on small soil-cement beams. Proceedings of 3rd Conference of the Australian ~oad Research Board, l~66,Vol 3, Part 2, pp 1562-74. 5. NADAI, A. Theory of flow and fracture of solids. Vol 1. New York, 1950. (McGraw Hill), 2nd edition, pp 353-359. 6. WRIGHT, P.J.F. The flexural strength of plain concrete. Department of Scientific and Industrial Research, Road Research Technical Paper No 67. London, 1964 (HM Stationery Office). 7. WRIGHT, P.J.F. Comments on an indirect tensile test on concrete cylinders. Magazine of Concrete Research 1955, 7 (20), 87-96. 12 AA Fig. 1 TENSILE SPECIMEN LOAOED THROUGH GRIPPING JAWS — Polyester resin adhesive Fig. 2 TENSILE SPECIMEN LOAOEO THROUGH PLATES CEMENTED TO ITS [NDS I Specimen / Polyester resin adhesive Fig.3 SCHEMATIC ARRANGEMENT 0[ TENSILE SPECIMEN LOADED THROUGH PLATES CEMENTEO TO THE SIOES Of THE SPECIMEN AT EACH ENO Fig. L THE INDIRECT TfNSILE TEST — 35 3.0 25 2.0 1.5 10 05 913 ( End loading ) 912 ( Side p[ate Loading) _ 914 (Side plate loading ) 1 0 0 20 60 80 100 120 lLO Strain ( x 10-4) Fig. 5 COMPRESSIVE STRESS-STRAIN CURVES SHOWING TH[ [FFECT OF S10[ PLATES CEMENTEO TO THE ENDS OF THE SPICIMEN 0 o 10 20 30 Strain ( x 10-L) Fig. 6a AVERAGE TEN$ILE STRESS -STRAIN CURVES FOR CEMENT-STABILISEO HARMONDSWORTH BRICKEARTH MOULDEO AT 15 PER CENT MOISTURE CONTINT -- o / ,/ 0’ - 10 20 30 Strain (x 10-L) Fio. 6b AV[RAGE TENSILE STRESS. STRAIN CURV[S FOR CEMENT - STABILISED HARMONDSWORTH BRICKEARTH MOULOEO AT 17 PER CENT MOISTURE CONTENT . 3.5 3.0 2.5 2.0 N E 1.5 z x w $ L G 1.0 0.5 0 , , 111/ , ! 1 I I I o 10 20 30 Lo 50 60 70 Strain (x 10-4) Fig.70 AVERAGE COMPRESSIVE STRESS - STRAIN CURVES FOR CEMENT- STABILISED HARMONOSWORTH BRICKEARTH MOULOED AT 15 PER C[NT MOISTURE CONTENT. 0 , 10 per cent cement ,8 per cent cement 1 * ~ 6 per cent cement o 10 20 30 40 50 Strain ( x 10-4 ) Fig. 7b AVERAGE COMPRESSIVE STRESS- STRAIN CURVES FOR CEMENT -S TABILISEO HARMOHOSWORTH BRICK EARTH MOULDEO AT 17 PER CENT MOISTURE CONTENT / o 0 20 40 60 80 100 Stratn ( x 10-4 ) Fig. 8 TEHSILE STRESS-STRAIN CURVES FOR SPECIMENS SAWN FROM THE PAVEMENT AT ROMPIN ( HOLE 3), MALAVSIA. .- 0 20 Lo 60 80 100 Strain (x 10-4) Fig.9 COMPRESSIVE STR[SS-STRAIN CURVES FOR SPECIMENS SAWN IROM THE PAVEMENT AT ROMPIN (HOLE3) MALAYSIA 0 20 40 60 80 100 Strain ( x 10-4 ) Fig. 10 TENSILE STRESS-STRAIN CURVES FOR SPECIMENS SAWN FROM THE PAVEMENTAT ROMPIN(HOLE 5/6), MALAVSIA. 5.0 L.o 30 ‘E z z m : : * 2.0 1.0 0 0 20 40 60 80 100 Strain ( x 10-4) Fig.11 COMPRESSIVE STRESS-STRAIN CURV[S FOR SPICIMENS SAWN FROM THE PAVEMENT AT ROMPIN ( HOLE 5/6) MALAYSIA PLATE 1 Neg No B2437/6a Moulding apparatus for tensile briquettes PLATE 2 Neg No 02487/68 Moulding apparatus for blocks and beams 1 I PLATE 3 Neg No B2436/6a Moulding apparatus for indirect-tensi Ie-test cylinders PLATE 4 Neg No B 23&f10 “Tensile block in position in the testing machine (1S67) Dd635272 4M 10/70 H.P. Ltd. G1915 PRINTED IN ENGLAND ABSTRACT The meas[lrement of the tensile properties of soil-cement: H E BOFIN’GER: Ministry of Transport, RRL Report LR 365: Crowthorne, 1970 (Road Research Laboratory). As part of an investigation of the design of soil-cement pavements, laboratory tests were carried out using Harmondsworth brickearth to examine the tensile properties of soil-cement and their relation to its compressive properties. The Report discusses three methods used for determining the tensile strength, the direct and indirect tests and the flexural test, and suggests explanations for the differences in the results obtained. Soil-cement was found to have a much higher elastic modulus when subjected to compressive stresses than when the same average tensile stresses were applied, Because of the complex behaviour of soil-cement under stress, estimates of its tensile strength from the cylinder splitting or flexural tests are uncertain, The direct tensile test which is independent of the strain characteristics provides a more reliable indication of tensile strength of soil-cement at slow rates of strain. ABSTRACT The measurement of the tensile properties of soil-cement: H E BOFIN’GER: Ministry of Transport, RRL Report LR 365: Crowthorne, 1970 (Road Research Laboratory). As part of an investigation of the design of soil-cement pavements, laboratory tests were carried out using Harmondsworth brickearth to examine the tensile properties of soil-cement and their relation to its compressive properties. The Report discusses three methods used for determining the tensile strength, the direct and indirect tests and the flexural test, and suggests explanations for the differences in the results obtained. Soil-cement was found to have a much higher elastic modulus when subjected to compressive stresses than when the same average tensile stresses were applied. Because of the complex behaviour of soil-cement under stress, estimates of its tensile strength from the cylinder splitting or flexural tests are uncertain. The direct tensile test which is independent of the strain characteristics provides a more reliable indication of tensile strength of soil-cement at slow rates of strain.