Effects of cement-lime mixes on lateritic soils for use in highway construction

Building andEneironment, Vol. 22, No. 2, pp. 141-145, 1987.

0360-1323/87 $3.00+0.00 ~ 1987 Pergamon Journals Ltd.

Printed in Great Britain.

Effects of Cement-Lime Mixes on Lateritic Soils for use in Highway Construction M. A. R A H M A N * This study describes the effects of cement-lime mixes on the geotechnical properties o f lateritic soils and recommends the optimum mix proportions of cement and lime for use in highway construction. The following 9eotechnical properties of the stabilized lateritic soils were measured: Atterberg limits, compaction characteristics, unconfined compressive strength and CBR characteristics. The test results show that cement-lime mixes can be utilized for base materials in highway construction.

cheap local material in the building industry and highway construction. Ola [5] found that less than 50% of the cement requirement for a temperate zone soil is required for efficient stabilization of a lateritic soil. Lasisi [6] reported that about 10% of cement will be needed to stabilize lateritic soils to produce blocks of the same order of magnitude of strength as for sandcrete blocks for use as masonry units in building construction. Ola [7] also worked with cement, lime and bitumen-stabilized lateritic soils and found that these stabilized soils could be used as base and sub-base materials in highway construction. Akinmusuru [8] investigated the crushing strength of fiber-reinforced earth blocks made from lateritic soil with pieces of locally available fiber. Lasisi [9] worked on cement-stabilized lateritic soils to further classify the usefulness and limitations of lateritic soils. All these studies have been trying to find practical results for the appropriate utilization of these locally available lateritic soils.

INTRODUCTION

MOST DEVELOPING countries suffer from an acute shortage of construction materials for new housing units and roads created by a growing population. There is a continuous increase in the demand for traditional construction materials. The use of concrete and reinforced concrete for low-cost housing and roads in the rural areas of the country is not often necessary. The shortage of construction materials calls for an urgent investigation into the possibility of using cheap materials for lowincome people that are locally available. One type of such materials, that is abundant supply all over the tropical and sub-tropical countries, is lateritic soil. Many people in the rural areas of West African and Southeast Asian countries are using lateritic soils as building materials but there is still a lack of adequate data for effective utilization. The knowledge of the practical usefulness of lateritic soils will benefit the house building industry and other engineering works such as construction of roads, highways, airports, earth dams, etc. The main purpose of this study is to examine the effects of different cement-lime mixes on the compressive strength and CBR (California bearing ratio) characteristics of lateritic soils and thus to find the suitability of these stabilized lateritic soils for highway construction materials. This investigation deals with lateritic soils. The word 'laterite' was first used by Buchanan [1] in 1807 to describe a ferruginous, vesicular, unstratified and porous material with yellow ochres caused by its high iron content, occurring abundantly in Malabar (India). It was locally used as bricks for buildings, and hence the name 'laterite' from the Latin word 'later' meaning brick. During the past two decades significant research work has been carried out on lateritic soils and detailed reviews of available literature have already been presented by Maignien [2], Little [3] and Gidigasu [4]. In the recent past, some investigations have also been made on Nigerian lateritic soils in order to utilize this

TEST MATERIALS The materials used in this investigation were lateritic soil, ordinary Portland cement and white hydrated lime. The soil samples were collected from University of Ire campus, Ile-Ife (Nigeria). Soil samples were reddishbrown in colour. The soil was selected for economical stabilization according to the suggestions given by the Highway Research Board of America [10]. These criteria include soils with: (a) liquid limit less than 40%; (b) plasticity index less then 18% ; and (c) percentage passing 0.074 mm size sieve less than 50%. The properties of the investigated soil are shown in Table 1. It can be seen from the table that this selected soil satisfies the criteria for economical stabilization. The grain size distribution curve of the soil is shown in Fig. 1 and it indicates that the soil was well graded. All these properties classify the soil in group A-2-6 of the American Association of State Highway Officials soil group. EXPERIMENTAL PROCEDURES

A number of laboratory tests were carried out on the lateritic soil. These laboratory tests were natural moisture

* Department of Civil Engineering, University of Ife, Nigeria. 141 BAE 22:2-D

M. A. Rahman

142 Table 1. Properties of original soils Properties

Results

Natural moisture content (%) Liquid limit (%) Plastic limit (%) Plasticity index (%) Maximum dry density (mg/m 3) Optimum moisture content (%) % passing No. 200 BS sieve (0.075 mm) Specific gravity Unsoaked CBR value (%) Soaked CBR value (%) Free swell (%) Unconfined compressive strength (MPa) Group index Soil classification (after AASHO)

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TEST RESULTS AND DISCUSSION

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height and 105 mm in diameter. Specimens were air-cured at room temperature for 7 days, 14 days and 28 days before being loaded in compression. The room temperature was low (about 10C) and humidity was very high (above 95%). Sixteen batches of nine specimens each, i.e. 144 specimens were tested. All these cylindrical specimens were tested using a 600kN Avery-Denision Universal Testing Machine. Specimens for both soaked and unsoaked CBR tests were compacted in the CBR mould. All specimens for soaked CBR were cured under water for 96 hours and percentages of swelling were determined at the end of the curing periods. Penetration testing was carried out in the CBR test with the help of a 28 kN capacity compression machine and a plunger of cross-sectional area of 19.35cm 2. The rate of penetration was 1.27mm/min. The CBR value was calculated corresponding to 2.54 mm penetration.

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Fig. I. Particle size distribution curve of soils. content, specific gravity, grain size analysis, Atterberg limits, standard Proctor compaction, unconfined compression and California bearing ratio (CBR). All these tests were performed in accordance with British Standards [11]. Grain size analysis was carried out by wet sieving and hydrometer methods. The wet sieving method was performed in order to avoid false larger size of soil grains and obtain an accurate grain size distribution curve. Atterberg limit tests were carried out on lateritic soil with different percentages of lime. The percentages of lime were 0, 3, 6 and 9 (by weight of dry soil). Sixteen series of standard Proctor compaction tests were performed to determine the optimum moisture contents for various mix proportions of lime and cement. The mix proportions (% lime and % cement) were 0 + 0 , 3+0, 6+0, 9 + 0 , 0 + 3 , 3+3, 6+3, 9+3, 0 + 6 , 3+6, 6 + 6, 9 + 6, 0 + 9, 3 + 9, 6 + 9 and 9 + 9 in percentages by weight of dry soil. Laboratory tests including moisture content, density, unconfined compression and California bearing ratio were performed using the standard Proctor compactive energy because this is easily achieved in the field. All specimens used in compression and CBR tests were compacted at optimum moisture contents. Cement, lime and soils were mixed thoroughly in a large tray and the required amount of water was added gradually. Mixing was carried out thoroughly and uniformly by hand. Specimens used in unconfined compression tests were compacted in the mould with the same compactive energy per volume as in the standard Proctor compaction tests. The dimensions of every specimen were l15.5mm in

General properties of the original soil are shown in Table 1. The grain size distribution curve of the soil is presented in Fig. 1. These properties show quite clearly that the soil used was ideal for economical stabilization [10]. The results of Atterherg limit tests on the soil with various percentages of lime are shown in Table 2. The trend of changes of liquid limit, plastic limit and plasticity index is also presented in Fig. 2. Both liquid and plastic limits increase linearly with lime content. The rate of increase of plastic limit is higher than that of the liquid limit. As a result, the plasticity index decreases linearly with increase in lime content. The summary of the results of standard Proctor compaction tests on the lateritic soil with different mix proportions of lime and cement is shown in Table 3. The nature of changes of optimum moisture content of the

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Plastic limit (%)

Plasticity index (%)

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38.01 39.20 39.90 40.50

22.14 28.08 32.80 37.60

15.87 11.20 7.10 2.90

Effects of Cement-Lime Mixes

143

Table 3. Effect of cement-lime mixtures on compaction characteristics, CBR characteristics and unconfined compressive strength of soil Mix description (% lime+% cement) OMC (%) 0+ 0 3+0 6+ 0 9+ 0 0+ 3 3+ 3 6+ 3 9+ 3 0+6 3+ 6 6+ 6 9+6 0+ 9 3+ 9 6+ 9 9+9

UC (MPa)

CBR (%)

yd (mg.m3)

7 days

14 days

28 days

Unsoaked

Soaked

Swell

1.82 1.76 1.75 I.74 1.81 1.75 1.74 1.73 1.84 1.78 1.77 1.76 1.88 1.82 1.81 1.80

1.028 1.850 2.261 2.114 2.343 3.065 3.577 3.429 3.042 3.764 4.276 4.128 3.700 4.422 4.934 4.786

1.028 1.910 2.425 2.317 2.631 3.513 4.029 3.920 3.288 4.170 4.686 4.577 4.316 5.198 5.714 5.605

1.028 2.050 2.631 2.466 2.857 3.879 4.459 4.295 3.740 4.762 5.343 5.178 5.261 6.320 6.864 6.699

27.2 71.3 78.3 74.5 78.7 112.8 144.3 138.6 131.7 160.6 199.5 185.6 195.2 226.7 234.5 214.5

l 1.7 45.1 69.0 62.5 52.7 82.5 102.5 90.0 109.7 135.3 158.7 132.7 178.0 188.4 202.5 179.7

0.42 0.14 0.10 0.05 0.25 0.11 0.06 0.04 0,18 0.07 0.04 0,03 0.12 0.05 0.03 0.02

14.40 16.00 16.20 16.40 15.48 17.08 17.28 17.48 15.80 17.40 17.60 17.80 16.00 17.60 17.80 18.00

OMC: optimum moisture content; yd: maximum dry density; UC: unconfined compressive strength; CBR: California beating ratio.

soil with various mix proportions of lime and cement is presented in Fig. 3. It can be seen from the figure that the optimum moisture content increases with increase in both lime and cement. This increase in optimum moisture content is due to the pozzolanic reaction of lime with the soil constituents and also due to extra water required for hydration of cement. The trend of changes of maximum dry density for various combinations of lime and cement is presented in Fig. 4. The figure shows clearly that the maximum dry density decreases with increase in lime content but in the ease of cement, the dry density increases almost linearly. It is the opinion of the author that these changes of maximum dry density occur as a result of both the grain size distribution and specific gravities of the soil grains and stabilizers. It is to be noted that the specific gravities of soil grain, lime and cement are 2.70, 2.20 and 3.15 respectively. The results of unconfined compression tests on the soil with various mix proportions of lime and cement are shown in Table 3. The changes of compressive strength for different combinations of lime and cement are also presented in Figs 5(a), 5(b) and 5(c). The results show I

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clearly that the compressive strength increases with increase in both lime and cement. In the case of cement, the increase of compressive strength is relatively higher and more linear. The compressive strength remains sensibly constant after 6% lime contents. Maximum compressive strengths are attained at a mix proportion of 6% l i m e + 9 % cement. These strengths are 4.934, 5.714 and 6.864 MPa for 7 days, 14 days and 28 days respectively. The summary of the results of both soaked and unsoaked CBR tests is shown in Table 3. The changes of CBR values and percentages of swelling for various mix proportions of lime and cement are presented in Fig. 6. The CBR values increase almost linearly with increase in both lime and cement contents. CBR values are relatively higher for cement compared to lime. Maximum soaked and unsoaked CBR values are attained at a mix proportion of 6% lime + 9% cement. The percentage of swell decreases with increase in both lime and cement contents. The rate of decrease of swell is higher in lime compared to cement. Most of the specimens made from various mix proportions of lime and cement satisfy CBR criterion

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(80%) for base materials in highway construction. F r o m the point of view of both economy and CBR values, a mix proportion of 3% l i m e + 3% cement can be used for base materials.

S U M M A R Y AND C O N C L U S I O N S Based u p o n the test results, the following conclusions can be drawn : (a) On the basis of compressive strength, California bearing ratio and percentage of swelling, the lateritic

Fig. 6. Effect of cement-lime mixtures on CBR characteristics of soil.

soil investigated can be stabilized with lime-cement mixes for highway construction materials. (b) F r o m the point of view of economy, compressive strength and CBR value, a combination of 3% lime and 3% cement can be used for base materials in highway construction. (c) Since lateritic soil is abundantly available all over the tropical and sub-tropical countries of the world, it has potential for reducing construction costs, especially in the rural areas of the country. Acimowledgement~--The author would like to thank Mr. E. O. Aremu, Mr. K. I. Adetunmbi and Mr. R. I. Ogbuo for their assistance in the testing.

REFERENCES

1. F. Buchanan, A Journal from Madras through the countries of Mysore, Canara and Malabar (India). London, The East India Company (1807). 2. R. Maignien, Reviews of Research on Laterites. Natural Resources Research IV, UNESCO, Paris (1966). 3. A.L. Little, Definition, formation and classification, In: Z. C. Moh (ed.), Proc. Special Session on Engineering Properties of Lateritic Soils, 7th ICSMFE, Mexico, 2, Asian Institute of Technology, Bangkok, Thailand (1969). 4. M.D. Gidigasu, Laterite Soil Engineering, Pedogenesis and Engineerimd Principles, Developments in Geotechnical En#ineeriny 9. Elsevier, Amsterdam (1976).

Effects o f C e m e n t - L i m e M i x e s 5. S.A. Ola, Need for estimated cement requirements for stabilizing lateritic soils. J. Transportation Engng Division, Am. Soc. Cir. Engrs. 100, TE2, 379-388 (1974). 6. F. Lasisi, Masonry units for low-income housing from cement-stabilized lateritic soils. Proc. Int. Conf. on Low-Income Housing Technology and Policy, Thailand, 2, 1037-1046 (1977). 7. S.A. Ola, Geotechnical properties and behaviour of some stabilized Nigerian lateritic soils. Q. J. Engng Geol. 11, 145-160 (1978). 8. J . O . Akinmusuru, Fiber-reinforced earth blocks. J. Construction Div., Am. Soc. Cir. Engrs. 107, CO3,487-496 (1981). 9. F. Lasisi and A. M. Ogunjide, Effect of grain size on the strength characteristics of cement-stabilized lateritic soils. Bdg Envir. 19, 49-54 0984). 10. Use of soil-eement mixture for base courses. Wartime Road Problems No. 7, Highway Research Board, National Research Council, Division of Engineering and Industrial Research, Washington, D.C. (1943). 11. British Standards, Methods of Testing Soils for Civil Engineering Purposes, B.S. 1377, British Standards Institution, London (1975).

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