The potentials of some stabilizers for the use of lateritic soil in construction

Buildin9 and Environment, Vol. 21, No. 1, pp. 57~61, 1986 Printed in Great Britain.

0360-1323/86 $3.00+ 0.00 Pergamon Journals Ltd.

The Potentials of Some Stabilizers for the Use of Lateritic Soil in Construction MD. ANISUR RAHMAN* Lateritic soil was stabilized with various percentages of rice husk ash (RHA), lime and cement. Atterberff limits, standard Proctor compaction, unconfined compression and California bearin9 ratio tests were carried out on lateritic soil with various percentaoes of these stabilizers in order to examine their influence. The required amounts of ash, lime and cement were determined for economical stabilization. This paper presents the potentials of rice husk ash compared to lime and cement in lateritic soil stabilization. For road construction, it recommends 7% cementfor base materials, 5% lime for sub-base materials and 18% rice husk ash for sub-base materials.

from the Latin word 'later' meaning brick. Much research work has been carried out on lateritic soils in many different countries over the years and detailed reviews of available literature have already been presented by Bawa [2], Maignien [3], Little [4], Lyon Associates [5] and Gidigasu [6]. In the recent past, investigations have been carried out with some Nigerian lateritic soils in order to determine their usefulness in the building industry and highway construction and some encouraging results have been obtained. Ola [7] has reported that less than 50% of the cement requirement for the temperate zone soils is required for effective stabilization of lateritic soils. It has also been reported by Ola [8] that Nigerian lateritic soils could be potentially stabilized with lime. For use as masonry units in building construction, approximately 10% of cement will be needed to stabilize lateritic soils to produce blocks of the same order of compressive strength as for sandcrete blocks. This fact was reported by Lasisi [9]. Nigerian lateritic soils were stabilized with lime, cement and bitumen by Ola [10] and he pointed out that these stabilized soils could be used for highway construction and low-cost housing. Mesida [11-1 has established that soils in Okitipupa areas of Ondo State need only 10-12% cement for stabilization to become reliable for building purposes in that area. Korisa [12], and Lazaro and Moh [13] have given the chemical composition of RHA shown in Table 1. It is to be

INTRODUCTION LATERITIC soils have been one of the maj or highway and building materials in all the tropical and sub-tropical countries of the world for a long time. Base and sub-base materials for most of the highways, and walls of a large percentage of residential houses in rural areas have been built and continue to be built with lateritic soils that use different types of stabilizer. Many types of stabilizer have been used in different parts of the world in soil stabilization for various civil engineering works. Some of these materials are not available in some parts and some are uneconomical to produce for local construction purposes. This problem calls for urgent research in order to use local waste materials as substitutes. Two such materials are lateritic soils and rice husk ash which are abundant all over the tropical and sub-tropical regions of the world. Rice is grown in more than 75 countries and each has the problem of utilization or disposal of this low-value by-product. The main purpose of this research work is to investigate the influences of rice husk ash (RHA), lime and cement on Atterberg limits, compaction characteristics, unconfined compressive strength and California bearing ratio of lateritic soils. This paper also compares the potentials of RHA with lime and cement in lateritic soil stabilization. This investigation will help in appropriate utilization of lateritic soils in highway construction works. The knowledge of practical usefulness of RHA as an alternative to cement and lime in lateritic soil will not only benefit the highway works but also other civil engineeringworks such as the construction of airfields, earthdams, rendering of walls, low-cost housing, etc.

Table 1. Chemical composition of rice husk ash Chemical composition (%) Silicon dioxide (SiO2) Calcium oxide (CaO) Magnesium oxide (MgO) Sodium oxide (Na20) Potassium oxide (K20) Ferric oxide (Fe2Os) Phosphorus oxide (P2Os) Aluminium oxide (A12Os) Manganese oxide (MnO2) Carbon dioxide (CO 2) Loss on ignition

PREVIOUS WORKS The term 'lateritic' was first used by Buchanan [1] to describe 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' * Department of Civil Engineering, University of Ife, Ile-Ife, Nigeria. 57

Korisa [ 1 2 ] Lazaro and Sample 1 Sample2 Moh [13] 94.50 0.25 0.23 0.78 1.10 traces 0.53 traces traces ---

93.50 2.28 --3.15 1.01 -traces traces ---

88.66 0.75 3.53 --0.36 -1.48 -0.51 3.80

Md. A. Rahman

58

noted that silicon dioxide is somewhat more than 93% of the fully burnt RHA. The properties of RHA depend greatly on whether the husks had undergone complete destructive distillation or had only been partially burnt. This was reported by Houstin [14] who also classified RHA into : (1) high-carbon char, (2) low-carbon (gray) ash and (3) carbon-free (pink or white) ash. Grist [15] reported that rice husks had been used in building materials in India. These included light-weight concrete briquettes made partly from husks. Insulating bricks were also made with cement and RHA and these resisted very high temperatures and were suitable for use in furnaces. Korisa [12] remarked that treated husks act as an inert and suitable aggregate which has been used in pressed insulating boards, high quality cement tiles and cement blocks. These blocks are rat proof and not damaged by water nor subject to shrinkage or warping. Lazaro and Moh [-13] studied lime-RHA mixtures as a stabilizer with deltaic clays and found that considerable improvement of the deltaic clays could be obtained by the addition of RHA. MATERIALS AND METHODS The materials used in this research work are lateritic soil, RHA, lime and ordinary Portland cement.

- - R i c e husk ash

gouze 3.0ram 1

Air

Fig. 1. Combustion chamber for preparation of rice husk ash.

the gauze which was fixed 50 mm above the circular pipe. The rice husk was ignited by a match and compressed air was supplied until the combustion was finished. The percentage of whitish gray ash was about 19.3. Ignition of the ash at 800°C showed that the remaining organic content was less than 3%. Specific gravity of the ash was determined as 2.35.

Experimental procedures Description of soil samples The lateritic soil samples were collected from the Universityoflfe campus, Ile-Ife, Nigeria, at a depth of 1.5 m below the ground surface in order to avoid vegetable matter. The general properties of the original lateritic soil were determined by various laboratory tests and are shown in Table 2. These laboratory tests were performed in accordance with British Standards. This lateritic soil was classified into A-7-6 group in accordance with the AASHO [16] method of classification.

Preparation of rice husk ash Rice husks were collected from Ekpoma, Bendel State, Nigeria, Their natural moisture content was 6~o. Rice husks were burnt with the help of a simple combustion chamber shown in Fig. 1. This chamber was designed by Williams and Sompong [17] and consisted of a drum, a circular pipe and a gauze. The size of drum was 0.6 m in diameter and 0.8 m in height. Compressed air was fed into a circular pipe (with 3-mm-diameter holes) which was fixed in the lower part of the drum. The rice husk was placed on

Table 2. Properties of original lateritic soil Tests Natural moisture content (%) Liquid limit (~) Plastic limit (~) Plasticity index (~) Specific gravity passing No. 200 BS sieve Unconfined compressive strength (kPa) California bearing ratio (~) Cohesion (kPa) Angle of internal friction (degrees) Group index

Results 8.02 49.80 22.60 27.20 2.64 45.30 211.20 7.73 123.00 12.80 7.73

A series of laboratory tests were carried out on A-7-6 group lateritic soil with various percentages of RHA, lime and cement. The percentages of RHA were 0, 4, 8, 12, 16, 20 and 24. The percentages of both lime and cement were 0, 2, 4, 6, 8, 10 and 12. The tests were Atterberg limits, grain size analysis, specific gravity, standard Proctor compaction, unconfined compression and California bearing ratio. All tests were performed in accordance with British Standard Specifications [18]. It is to be noted that the wet sieving method and the hydrometer method were carried out on the soil for the grain size analysis. The wet sieving method was used in order to avoid false larger size of soil grains and obtain an accurate grain size analysis. Each stabilizer was thoroughly mixed with soil in a large tray. Mixing was carried out by hand. All soil-stabilizer samples used in unconfined compression and California bearing ratio tests were compacted at optimum moisture content. Different optimum moisture contents for different percentages of stabilizers were determined by the standard Proctor compaction test. Larger specimens for the unconfined compression test were moulded with the same compactive effort and mould used in the compaction test. Smaller cylindrical specimens were prepared from the moulded sample with the help of a wire saw and soil lathe. A length~tiameter ratio of 2.0 was utilized for all test specimens in compression tests. The dimensions of every specimen were 78 mm in length and 39 mm in diameter. Specimens were air-cured at room temperature for one day and seven days before being loaded in compression. The room temperature was low and humidity was very high. Samples were sheared under strain-controlled test and the rate of strain was 1.14 mm m i n - 1. The specimens for the California bearing ratio test were moulded in the CBR mould with the same compactive

Stabilizers for the Use of Lateritic Soil in Construction Table 3. Effects of stabilizers on Atterberg limits of lateritic soil RHA (%) 0 4 8 12 16 20 24

LL (%)

PL (%)

PI (%)

Lime (%)

49.8 51.4 52.2 52.6 53.4 54.3

22.6 26.1 29.5 31.9 35.2 38.6

27.2 25.3 22.7 20.7 18.2 15.7

--

--

--

0 2 4 6 8 10 12

LL (%) 50.2 50.9 51.7 52.3 53.3 54.0 54.1

PL (%)

60 50

PI (%)

24.9 29.9 33.8 38.3 42.9 47.7 51.3

0~o : 30

25.3 21.0 17.9 14.0 10.4 6.3 2.8

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energy per volume as in the standard Proctor compaction test. Penetration testing was carried out in the California bearing ratio test with the help of a plunger of crosssectional area of 19.35 cm 2. The rate of penetration was 1.27 m m min-1. The CBR value was calculated corresponding to 2.54 m m penetration, since this was always higher than the value obtained at a penetration of 5.08 mm.

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RESULTS AND DISCUSSION

26

Atterberg limits test

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The results of Atterberg limits tests on A-7-6 group lateritic soil with various percentages of R H A and lime are shown in Table 3. The trend of changes of liquid limits, plastic limits and plasticity indices with various percentages of R H A and lime are also presented in Fig. 2(a). Atterberg limits change linearly with increase in stabilizer contents for both R H A and lime. Liquid and plastic limits increase directly with increase in stabilizer contents. But, the plasticity index decreases linearly as the percentage of R H A and lime increases. It is the opinion of the author that when R H A and lime are mixed with finegrained cohesive soils, these cause flocculation of the soil which decreases the plasticity index.

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e : Rice husk osh lime • : Cement 8:

~" 22 E $21 I

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Fig. 2. Variation of Atterberg limits, maximum dry density and optimum moisture content with stabilizer contents.

tested. In the case of RHA-stabilized lateritic soil, the maximum dry density decreases steeply up to 16% R H A and then remains almost constant. It is to be noted that these compaction characteristics occur as a result of both the grain size distribution and specific gravities of the soil and stabilizer. The stabilizers initially coat the soils to form large aggregates which consequently occupy larger spaces. Therefore, the tendency is for the fine-grained soils to initially decrease in dry density until the stabilizer which tends to increase the dry density compensates for the larger spaces. Only cement with high specific gravity is able to produce this effect (the specific gravities of cement, lime and R H A are 3.15, 2.2 and 2.35, respectively).

Standard Proctor compaction test A summary of results of compaction tests on lateritic soil stabilized with various percentages of RHA, lime and cement are shown in Table 4. The changes of maximum dry density and optimum moisture content with increase in stabilizer contents are presented in Figs 2(b) and (c), respectively. M a x i m u m dry density of cement-stabilized lateritic soil decreases very slightly up to 4%/0cement and then begins to increase. M a x i m u m dry density of lime-stabilized soil decreases at a reducing rate over the range of contents

Table 4. Effects of stabilizers on compaction characteristics of lateritic soil RHA (%)

Yd(max) (mg m - 3)

OMC (%)

Lime (%)

Yd(max) (mg m - 3)

OMC (%)

Cement (%)

Yd(max) (mg m - 3)

OMC (%)

0 4 8 12 16 20 24

1.563 1.490 1.440 1.410 1.390 1.385 1.386

22.00 25.20 25.60 25.67 25.70 25.70 25.60

0 2 4 6 8 10 12

1.560 1.540 1.520 1.505 1.490 1.480 1.475

21.75 22.30 23.04 23.50 24.02 24.40 24.80

0 2 4 6 8 10 12

1.567 1.550 1.545 1.547 1.585 1.615 --

21.40 22.10 22.50 22.50 22.40 22.40 --

OMC : optimum moisture content; Yd(max) : maximum dry density.

Md. A. Rahman

60

Table 5. Effects of stabilizers on unconfined compressive strength of lateritic soil

RHA (~)

UC strength (kPa) 1 day cured

Lime (~)

0 4 8 12 16 20 24

211.2 217.0 250.2 303.2 371.6 416.0 348.5

0 2 4 6 8 10 12

UC strength (kPa) 1 day 7 day cured cured 210.7 314.1 601.2 578.8 563.6 567.2 577.6

Cement (~)

-513.5 749.0 742.6 727.0 716.0 732.3

0 2 4 6 8 10 12

UC strength (kPa) 1 day 7 day cured cured 212.0 339.0 507.0 870.0 1051.0 1515.0

-622.0 893.0 1190.0 1703.0 2001.0 --

UC strength : unconfined compressive strength.

The optimum moisture content increases with addition of RHA. This increase in moisture content becomes constant after reaching 12% RHA. Addition of lime to the soil raises the optimum moisture content linearly. The pozzolanic reaction of R H A and lime with the soil constituents tends to increase the optimum moisture content. The optimum moisture content also increases with the addition of cement. This increase is due to extra water required for hydration of cement. It becomes constant after addition of 4% cement.

Unconfined compressive strenoth test The summary of results of unconfined compression tests on lateritic soil with various percentages of RHA, lime and

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cement are shown in Table 5. The trend of changes of unconfined compressive strength with stabilizer content are also presented in Fig. 3 (a). The unconfined compressive strength increases almost linearly with increase in RHA. M a x i m u m compressive strength is 416 kPa at 2 0 ~ R H A after which it starts to decrease. Addition of lime also increases unconfined compressive strength in specimens air-cured for both one day and seven days. M a x i m u m compressive strengths are 601.2 and 749 kPa for one-day and seven-day air-cured specimens, respectively. These increases in compressive strength become constant after addition of 4% lime. In the case of cement, the increase in unconfined compressive strength is higher and more linear compared to lime and RHA. Compressive strengths are as high as 1515 and 2001 kPa corresponding to one-day and seven-day air-cured samples. These increases in unconfined compressive strength with increase in stabilizer contents indicate that the cohesion of the lateritic soil increases due to the addition of RHA, lime and cement. The compressive strength of RHA- and lime-stabilized soils is low. The fact that the unconfined compression test is not suitable for soils having larger soil particles is why the compressive strengths are underestimated here. Ola [10] also obtained relatively low compressive strength values for lime stabilized A - l - a soil as compared to the more cohesive A-2-4 and A-7-6 soils.

California bearin 9 ratio test

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The results of California bearing ratio tests with the addition of stabilizer contents are shown in Table 6. The nature of changes of CBR value with various percentages of RHA, lime and cement are also presented in Fig. 3(b). California bearing ratio increases almost linearly for 0 -

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Table 6. Effects of stabilizers on California bearing ratio of lateritic soil

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Fig. 3. Variation of unconfined compressive strength and California bearing ratio of lateritic soil with stabilizer contents.

RHA (%)

CBR (%)

Lime (%)

CBR (%)

Cement (%)

CBR (%)

0 4 8 12 16 20 24

7.73 11.96 22.03 44.82 76.02 77.68

0 2 4 6 8 10 12

9.70 25.50 59.40 59.40 46.60 35.90 34.00

0 2 4 6 8 10 12

9.20 21.00 34.00 66.70 99.10 141.20

CBR : California bearing ratio.

Stabilizers f o r the Use o f Lateritic Soil in Construction

12% RHA contents and the maximum value is obtained at 18% RHA. After reaching 18% RHA, CBR values tends to decrease. In the case of lime, the maximum California bearing ratio is obtained at 5% lime and then starts to decrease. The California bearing ratio for cementstabilized soil increases linearly and rapidly. Cementstabilized soil has much higher CBR values than lime and RHA-stabilized soil. The results of California bearing ratio tests indicate that the appreciable improvement of this A-7-6 lateritic soil has taken place with all these three stabilizers.

CONCLUSIONS On the basis of the results obtained from the tests on these stabilized soils, the following conclusions can be drawn: (a)

F r o m the point of view of unconfined compressive strength and California bearing ratio, the A-7-6

61

lateritic soil can be stabilized with 7% of cement for base materials for highway construction. (b) Based upon California bearing ratio, this lateritic soil can be stabilized with 5% of lime for sub-base materials. (c) O n the basis of California bearing ratio, the lateritic soil A-7-6 can be stabilized with 18% RHA for subbase materials. (d) The potentials of RHA in the lateritic soil stabilization are considerable compared to lime and cement. (e) Since RHA and lateritic soils are in a b u n d a n t supply all over the tropical and sub-tropical countries of the world, RHA can be potentially utilized as a substitute for lime and cement in order to reduce the construction cost, particularly in the rural areas oft'he less-developed countries. Acknowledgements--The author would like to thank Mr. S. A. Raji, Mr. V. O. Okafor and Mr. O. M. Olatinwo for their assistance in the laboratory work.

REFERENCES 1. F. Buchanan, A Journal from Madras Through the Countries of Mysore, Canara and Malabar. The East India Company, London (1807). 2. K.S. Bawa, Lateritic soils and their engineering characteristics. J. Soil Mech. Fdns Div., Am. Soc. cir. Engrs 83, 1-15 (1957). 3. R. Maignien, Reviews of research on laterites, Natural Resources Research IV, UNESCO, Paris (1966). 4. A.L. Little, Definition, formation and classification, Proc. Special Session on Engineering Properties of Lateritic Soils (Edited by Z. C. Moh), Asian Institute of Technology, Bangkok, Thailand (1969). 5. Lyon Associates, Laterites and lateritic soil and other problem soils of Africa, An EngineeringStudy for Agency for International Development AID/csd-2164, Lyon Associates, Baltimore, MD, U.S.A. 6. M.D. Gidigasu, Laterite soil engineering, pedogenesis and Engineering Principles. Developments in Geotechnical Engineering, Vol. 9. Elsevier, Amsterdam (1976). 7. S.A. Ola, Need for estimated cement requirements for stabilizinglateritic soils, J. Transpn Div., Am. Soc. civ. Engrs TE2, 379-388 (1974). 8. S.A. Ola, The potentials of lime stabilization oflateritic soils, J. Engng Geol. 11, 305-317 (1977). 9. F. Lasisi, Masonry units for low-income housing from cement stabilized lateritic soils, Proc. Int. Conference on Low-income Housing Technology and Policy, Thailand, Vol. 2, pp. 1037-1046 (1977). 10. S.A. Ola, Geotechnical properties and behaviour of some stabilized Nigerian lateritic soils, Q. Jl Engng Geol. 11, 145-160 (1978). 11. E.A. Mesida, Soil stabilizationfor housingin Okitipupa Area, Ondo State, Nigeria. Occasional Research Papers, Department of Geology, University of Ire, Ile-Ife, Nigeria (1978). 12. J. Korisa, Rice and Its By-products, 2nd edn, pp. 426. Edward Arnold, London (1958). 13. R.C. Lazaro and Z. C. Moh, Stabilization of deltaic clays with lime--rice husk ash mixtures, Proc. 2nd Southeast Asian Conference on Soil Engineering, pp. 215-223 (1970). 14. D.F. Houstin, Rice Chemistry and Technology, pp. 301-340. American Association of Cereal Chemists, MN (1972). 15. D.H. Grist, Rice, 4th edn, pp. 548. Green, London (1965). 16. AASHO, Standard Specifications for Highway Materials and Methods of Sampling and Testing, 10th edn. American Association of State Highway Officials, Washington, DC (1970). 17. F.H.P. Williams and S. Sompong, Some properties of rice hull ash, Geotech. Engng, J. Southeast Asian geotech. Soc. 2, 75-81 (1971). 18. British Standards, Methods for Testing Soils for Civil Engineering Purposes, B.S. 1377, British Standards Institution, London (1975).