Improvement of Black Cotton Soil with Ordinary Portland Cement ...

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(OPC) / locust bean waste ash (LBWA) blend in stepped concentration of 0, .... The results of the index tests conducted on the natural soil are summarized in Table 3. .... Performance Studies in Developing Acceptance specification for Laterite ...
Improvement of Black Cotton Soil with Ordinary Portland Cement - Locust Bean Waste Ash Blend K. J. Osinubi1, M. A. Oyelakin2 and A. O. Eberemu1 1 Department of Civil Engineering, Ahmadu Bello University, Zaria 2 Post Graduate Student, Department of Civil Engineering, Ahmadu Bello University, Zaria.

ABSTRACT The preliminary investigation of the Nigerian expansive clay, also known as black cotton soil, collected from New Marte, Borno State, shows that it belongs to A-7-6 (13) in the AASHTO Soil Classification. This group of soils is usually very poor for engineering use. Ordinary Portland cement (OPC) / locust bean waste ash (LBWA) blend in stepped concentration of 0, 2, 4, 6 and 8% each by dry weight of soil, was used to treat the soil. Compaction was carried out using British Standard light (BSL) energy and the three criteria for the evaluation of strength (i.e., UCS, CBR and Durability) were considered. The UCS values of specimens treated with 6% OPC / 6% LBWA increased from 178, 381 and 760kN/m2 for the natural soil to 986, 1326 and 1348kN/m2 when cured for 7, 14 and 28 days, respectively. The CBR value of 5% of the natural soil increased and peaked at 42% for 6% OPC / 6% LBWA treatment, while the durability in terms of resistance to loss in strength increased from 13% for the natural soil to 58%. The strength and durability values also increased with curing ages, thus indicating that the blend has potential for time-dependent increase in strength that will reduce the quantity of cement needed for the construction of low volume roads over the expansive soil.

KEYWORDS: California bearing ratio, Compaction, Durability, Locust bean waste ash, Ordinary Portland cement, Unconfined compressive strength.

INTRODUCTION Black cotton soils are expansive clays with potential for shrinking or swelling under changing moisture condition1. These soils cause more damage to structures, particularly light buildings and pavements, than any other natural hazard, including earthquakes and floods2. They are produced from the breakdown of basic igneous rocks where seasonal variation of weather is extreme. The soils are formed under conditions of poor drainage from basic rocks or limestones under alternating wet or dry climatic conditions. They usually exhibit high shrink-swell characteristics with surface cracks, opening during the dry seasons which are more than 50mm or more wide and several mm deep. These cracks close during the wet season and an uneven soil surface is produced by irregular swelling and heaving. Such soils are especially troublesome as pavement sub-grades. The soils are the major problem soils in Nigeria where they occupy an estimated area of 104,000km2 in the north eastern part [3]. The Nigerian black cotton soils are formed from the weathering of shaly and clayey sediments - 619 -

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and basaltic rocks. They contain more of montmorillonite with subsequent manifestation of swell properties and expansive tendencies [3]. Cement is one of the most effective in reducing the swelling properties of these soils4. Stabilization of soils with ordinary Portland cement (OPC) produces hardened materials which are capable of bearing loads for engineering purposes. TRRL5 and CEBTP6 recommended a minimum of 15% for soil fraction passing 0.425mm sieve and plasticity index greater or equal to 10. Generally, gravels require about 10% by dry weight of cement, sand requires about 7–10%, silt about 12 to 15% and clays, 12 to 20% cement by dry weight of soil [7]. The increasing cost of energy and waste disposal has made soil improvement with the abundant local available materials considered to be waste [8, 9, 10, 11, 12, 13, 14 and 15]. Locust bean waste ash (LBWA) is the product of combustion of the waste husk of locust bean pod. The locust bean tree is common in the Nigerian environment and it grows to about 15m in height and has dark, evergreen, pinnate leaves. The small, red flowers have no petals. The fruit, which is a brown, leathery pod about 10 – 30cm long contains a gummy pulp of an agreeable sweet taste in which lie a number of seeds. The seeds are edible but the wastes litter our communities with corresponding negative environmental impact. Once the seed is used for local food seasoning, the waste husk from it when burnt produces the locust bean waste ash (LBWA). The LBWA - a pozzolana - has been reported to have a good potential for improving some of the geotechnical properties of black cotton soils16. Being pozzolanic in nature, LBWA is capable of reacting with free lime, released during hydration of cement at ordinary temperatures to produce cementitious compounds.

AIM OF STUDY The aim of this research was to establish the effect of locust bean waste ash on the geotechnical properties of cement stabilized black cotton soil.

MATERIALS AND METHODS Materials Soil: The black cotton used in this study was soil obtained, from Chad Basin Development Authority (CDMA) reserved site, at New Marte (Latitude 130 27’N and longitude 130 50’E) along the Maiduguri – Gamboru Road in Borno State, was used for the study. The top soil was removed to a depth of 0.5m before the soil samples were taken by disturbed sampling, sealed in plastic bags and put in sack to avoid loss of moisture during transportation. The soil samples were air dried before pulverizing to obtain particles passing sieve BS No. 4, (4.75mm aperture). The oxide compositions of the soil were determined using the method of Energy Dispersive X – Ray Flourescence. Locust bean waste ash: The used for this study were obtain locally from the burning of locust bean husks sourced from Doko village around Bida in Niger State and Malali village in Kaduna State. The husks were completely burnt under atmospheric condition, sealed up in plastic bags and transported to the laboratory. The ash was then passed through British Standard No 200 sieve, with 0.75mm aperture, and kept to be mixed with the ‘soil-cement’ in the appropriate percentages. The oxide composition of the ash was determined at the Centre for Energy Research and Training (CERT), A.B.U, Zaria, by method of Energy Dispersive X-Ray Fluorescence. - 620 -

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Cement: The ordinary Portland cement (OPC) used for the study was purchased in the open market in Zaria.

Methods The laboratory tests carried out on the natural and stabilized soils include particle size distribution, Atterberg limits, compaction, California bearing ratio, (CBR), unconfined compressive strength (UCS) for 7, 14 and 28 days curing periods, and durability. The tests were carried out in accordance with BSI17 and BSI18 for the natural and treated soils respectively. The CBR tests were also conducted as recommended by Nigerian General Specifications19 (1997) with a CBR value of 180% to be attained in the laboratory for cement stabilized materials to be constructed by the mix-in-place method. The UCS and CBR tests were prepared at the optimum moisture content (OMC) and compacted with the BSL energy. Durability was determined as the ratio of the UCS of the specimen wax cured for 7 days, de-waxed top and bottom and then immersed in water for another 7 days to the UCS of specimen wax-cured for 14 days.

RESULTS AND DISCUSSION Chemical Properties of Materials Used The oxide composition of the soil is given in Table 1 while Table 2 gives the oxide compositions of locust bean waste ash and cement.

Index Properties of the Natural Soil The results of the index tests conducted on the natural soil are summarized in Table 3. The soil belongs to the A-7-6 (13) subgroup of AASHTO Soil Classification System20. Its particle size distribution curve is shown in Figure 1. The soil has high natural moisture content because it was collected during the rainy season. Its strength characteristics are low thereby rendering it unsuitable for engineering construction. Table 1: Oxide Composition of Black Cotton Soil Oxide

Concentration (%)

CaO SiO2 Fe2O3 Al2O3 MnO TiO2 LOI Others

31.01 4.74 16.19 0.13 1.34 ≤ 52

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Figure 1: Particle size distribution curve of the natural soil

Table 2: Oxide Composition of LBWA and Typical OPC Oxide

LBWA (%)

*OPC (%)

CaO SiO2 Al2O3 Fe2O3 MnO Na2O K 2O SO3 P 2O 5 Loss on Ignition

1.08 55.38 14.93 0.278 0.09 0.18 2.00

63 20 6 3 1 2 2

0.23 10.63

*After Czernin, 1962

Effect of Treatment with Cement - Locust Bean Waste Ash Blend Unconfined compressive strength The various of unconfined compressive strength (UCS) with locust bean waste ash (LBWA) content for various soil – cement mixtures are shown in Figures 2, 3 and 4 for 7, 14 and 28 days curing, respectively. Generally, strength of the black cotton soil increased with higher ordinary Portland cement (OMC) / locust bean waste ash (LBWA) blend and curing period. The increase can be attributed primarily - 622 -

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to the formation of various compounds such as calcium silicate hydrates (CSH) and calcium aluminates hydrates (CAH) and micro fabric changes, which are responsible for strength development21. Peak UCS values recorded from 178, 381 and 760kN/m2, for the natural soil, to 986, 1326 and 1348kN/m2 for treatment with 6% OPC / 6% LBWA when curing was for 7, 14 and 28 days respectively. However beyond 6% LBWA treatment, the strength of the soil decreased for all cement contents; probably because of insufficient water needed to bring the pozzolanic reaction to completion11. Although, the UCS values increased with higher curing period, the 7 day UCS value fell short of 1710kN/m2 specified by TRRL5 as criterion for adequate stabilization using OPC. The strength of 1348kN/m2 at 28 days however, showed that the strength development of OPC/LBWA treated soil is a slow process and a longer period is required to attain the specified strength.

Figure 2: Variation of UCS (7 days curing) of soil-cement mixtures with LBWA contents

Figure 3: Variation of UCS (14 days curing) of soil-cement mixtures with LBWA contents

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Figure 4: Variation of UCS (28 days curing) of soil-cement mixtures with LBWA contents Table 3: Geotechnical Properties of the Natural Soil Property Percentage passing BS No 200 sieve, % Natural Moisture Content, % Liquid Limit, % Plastic Limit, % Plasticity Index, % Linear Shrinkage, % Free Swell, % Specific Gravity AASHTO Classification USCS NBRRI Classification Maximum Dry Density, Mg/m3 Optimum Moisture Content, % Unconfined Compressive Strength, kN/m2 California Bearing Ratio, % Color Dominant clay mineral

Quantity 71.0 35.0 63.0 27.0 36.0 17.0 75.0 1.94 A-7-6 (13) CH High swell potential 1.34 24.0 220 5 Grayish black Montmorillonite

California bearing ratio The California bearing ratio (CBR) value is an indicator of soil strength and bearing capacity and it is used in the design of base and sub-base of pavements. The variation of CBR with OPC / LBWA blend is shown in Figure 5. Generally, CBR values increased with higher OPC / LBWA content. A peak CBR value of 42% was recorded for 6% OPC/ 6% LBWA treatment of the soil from a value of 5% for the natural soil. The formation of secondary cementitious materials that resulted from the reaction between the lime librated from the hydration of cement and the pozzolanic LBWA could be responsible for the - 624 -

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increase11. The recorded peak value is low when compared with the CBR value of 180% which, the Nigerian General Specification19 recommends should be attained in the laboratory for cement stabilized material to be constructed by the mix-in-place method. However, the value met the requirement for subbase courses proposed by22 for a superior residual soil with values of 60 – 80% for bases and 20 – 30% for sub-bases.

Figure 5: Variation of CBR of soil-cement mixtures with LBWA contents

Durability A stabilized soil can only be used as pavement material when it meets the strength (UCS or CBR) and durability requirements. It was proposed by Ola [23] that an allowable 20% loss in strength (i.e. 80% resistance to loss in strength) should be recommended for a specimen cured for 7 day and immersed in water for 4 days. The variation of resistance to loss in strength of soil-cement with LBWA content is shown in Figure 6. The resistance to loss in strength for the black cotton soil from New Marte, Nigeria, increased from 13% for the natural soil to a peak value of 58% at 6% OPC/ 6% LBWA treatment. This is low compared to the allowable value, but considering the harsher condition these samples were subjected to, the treated soil may be acceptable as a sub base material.

CONCLUSION A study was conducted to assess the effect of OPC / LBWA blend on black cotton soil. The natural soil was treated with the additives in stepped concentration of 0, 2, 4, 6 and 8% by dry weight of the soil. The results obtained indicate that: 1. There was a general increase in the UCS values with OPC / LBWA content and curing period. The soil treated with 6% OPC / 6% LBWA recorded the peak UCS values of 986, 1326 and 1348kN/m2 from 178, 381 and 760kN/m2, for the natural soil, when cured for 7, 14 and 28 days, respectively. Although, the 7 day UCS value fell short of 1710kN/m2 specified by TRRL5 as criterion for adequate stabilization using OPC, the strength at 28 days, showed that the strength development of OPC/LBWA treated soil is a slow process and a longer period is required to attain the specified strength.

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2. The CBR values of the treated soil also showed a general increase with increase in OPC/LBWA treatment. The CBR achieved a peak value of 42% at 6% OPC / 6% LBWA, from a value of 5% for the natural soil. This value is low when compared with the CBR value of 180% recommended by the Nigerian General Specification19; the value, however, met the requirement for sub-base courses proposed by22 for a superior residual soil. Durability assessment of the treated soil recorded a peak value 58% resistance to loss in strength (42% loss in strength) at 6% OPC/ 6% LBWA treatment. This fell short of the recommended value of 80% resistance to loss in strength, but it could be acceptable since the limiting value proposed by Ola23 is based on 4 day soaking and not the 7 days soaking which the specimens for this research were subjected to. Based on these results, it is recommended that about 50% replacement of cement by the ash could be used for the treatment of the soil to achieve a sub base material, thereby reducing the quantity (and cost) of cement needed for stabilization and the environmental menace cause by the waste.

REFERENCES 1. Fredlund, D. G. and Rahardjo, H. (1993) Soil Mechanics for Unsaturated Soils, Wiley, New York. 2. Jones, D. and Holtz, J. (1973) “Expansive soils: Hidden Disaster.” Civil Engineering, Vol. 43 pp 54. 3. Ola, S. A. (1983) “The geotechnical properties of black cotton soils of North Eastern Nigeria.” In S. A. Ola (ed.) Tropical Soils of Nigeria in Engineering Practice. Balkama, Rotterdam, pp. 160178. 4. Matawal, D. S. and Tomarin, O. I. (1996) “Response of some tropical laterite to cement stabilization.” College of Engineering Conference Series, Kaduna Polytechnic, Vol. 3 pp 90-95 5. TRRL (1977) “A guide to the structural design of bitumen surfaced roads in tropical and subtropical countries.” Transport and Road Research Laboratory, Road Note 31, H. M. S. O., London. 6. CEBTP (1980) “Guide pratique de dimension emenldes chausses pour les pays Tropican X.” Centre Experimental de Recherchies et D’Etudes du Batiment et des Travanx, publics Paris. 7. Gilliot, J. E. (1987) Clay in Engineering Geology. Elsevier Publishing Company Amsterdam. 8. Mohammedbhai, G. T. G. and Bagant, B. T. (1990) “Possibility of using bagasse ash and other furnace residue as partial substitute for cement in Maritius.” Revne Agricole et Sulclriere de l’lle Maurice, Vol. 64, No 3 pp.1-10. 9. Osinubi, K. J. and Medubi, A. B. (1997a) “Evaluation of cement and phosphatic waste admixture on tropical black clay road foundation.” Proceedings of 4th Intn’l. Conference on Structural Engineering Analysis and Modeling (SEAM 4), Kumasi, Ghana, 9-11 July, Vol. 2, pp. 297-307. 10. Osinubi, K. J. (1998 a, b) “Stabilization of tropical black clay with cement and pulverised coal bottom ash admixture.” In: Advances in Unsaturated Geotechnics. Edited by Charles, D., Shackelford, Sandra L. Houston and Nien-Yin Cheng. ASCE Geotechnical Special Publication, No 99, pp 289-302. - 626 -

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11. Osinubi, K. J. (1999) “Evaluation of admixture stabilization of Nigerian black cotton soil.” Nigerian Society of Engineers Technical Transactions, Vol. 34, No 3, pp 88-96 12. Medjo, E. and Riskowiski, G. (2004) “A Procedure for processing mixtures of soil, cement and sugar cane bagasse.” Agricultural Engineering International Journal of Scientific Research and Development. Manuscript BC 990, Vol. III, pp 1-6. 13. Osinubi, K. J. and Mustapha, M. A. (2005) “Effect of Bagasse Ash on Cement Stabilized Laterite”. Seminar Paper Presented in the Department of Civil Engineering, Ahmadu Bello University, Zaria, Nigeria. 14. George, M. (2006) Stabilization of Black Cotton Soil with ordinary Portland Cement using Bagasse Ash as Admixture. M.Sc. Thesis, Department of Civil Engineering, Ahmadu Bello University, Zaria 15. Alhassan, M. and Mustapha, M. A. (2006) “Effect of Rice Husk Ash on Cement Stabilized Laterite”. 16. Akinmade (2008) The Effects of Locust Bean Waste Ash on the Geotechnical Properties of Black Cotton Soil. Unpublished M.Sc. Thesis, Department of Civil Engineering, Ahmadu Bello University, Zaria. 17. B.S. 1377 (1990) “Methods of testing soil for civil engineering purposes”. British Institute, London.

Standards

18. B.S. 1924 (1990) “Methods of Tests for stabilized Soils.” British Standards Institute, London. 19. Nigerian General Specification (1997) Road and Bridge Works. Federal Ministry of Works, Abuja, Nigeria. 20. AASHTO (1986) “Standard Specifications for Transport Materials and Methods of Sampling and Testing.” 14th Edition, American Association of State Highway and Transport Officials (AASHTO), Washington, D.C 21. Kedzi, A. (1979) Stabilized Earth Roads. Elsevier, Amsterdam, pp. 327. 22. Gidigasu, M. D. (1982) “Importance of Material selection, Construction Control and Field Performance Studies in Developing Acceptance specification for Laterite paving gravels.” Solos and Rocha, Rio de Janeiro, Brazil. Vol. 5 No1 23. Ola, S. A. (1974) “Need for estimated cement requirement for stabilizing lateritic soil.” J. Transport Div., ASCE, Vol. 17, No 8, pp. 379-388. 24. Czernin, W. (1962) Cement Chemistry and Physics for Civil Engineers, Crosby Lockwood, London.

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