Effect of Compactive Effort on Properties of Cement Stabilized Black Cotton Soil Admixed with Groundnut Shell Ash 1
Ijimdiya, T. S. 1Sani L. 1Isaac, A.L 2Sani J. E. and 1Osinubi, K. J. 1 Department of Civil Engineering, Ahmadu Bello University, Zaria 2 Department of Civil Engineering, Nigeria Defence Academy, Kaduna
Abstract The results of a laboratory study on the effect of compactive effort on the strength characteristics of black cotton soil treated with a maximum 8 % ordinary Portland cement (OPC) / 10 % groundnut shell ash (GSA) blend by dry weight of soil is presented. Test results show that the strength properties of the treated soil generally increased with higher compactive effort. At optimal 8 % OPC /8 % GSA blend for samples compacted with British Standard light (BSL) and West African Standard (WAS) compaction energies, the minimum unconfined compressive strength (UCS) requirement of 1710 kN/m2 was not satisfied. However, for samples compacted using British Standard heavy (BSH) energy the minimum requirement was met. Based on UCS and durability assessment criterion, an optimal 6 % OPC /6 % GSA is recommended for the treatment of black cotton soil compacted using BSH energy for use as sub-base material in road construction.
Keywords: California bearing ratio, Cement, Compactive effort, Groundnut shell ash, Unconfined compressive strength Introduction Black cotton soil also known as tropical black clay is a type of expansive soil whose geotechnical and index properties reveal its unsuitability for use as sub-grade materials (Nelson and Miller, 1992). Black cotton soils are formed under conditions of poor drainage from basic rock or limestone under alternate wet or dry climatic conditions (Ijimdiya and Abbas, 2012). Black cotton soils (BCS) are expansive soils that swells excessively when wet and shrink when dry resulting in serious cracks without any warning due to large volume change with respect to variation of moisture content. Such soils are common product of tropical weathering and are encountered in several parts of the world. In Nigeria, these soils are found predominantly in northern region of the country lying within the Chad Basin and partly within the Benue Trough. These soils are usually unsaturated throughout most of the year and pose many problems to soil engineers (Oluwapelumi, 2012). Although poor and undesirable for engineering purposes, its properties could be improved to meet standard specification by modification/stabilization processes. Stabilization of the soil with chemical admixtures is a common method of reducing the swell – shrink tendencies of the soil and also makes the soil less plastic (Osinubi et al., 2012). Cement is one of the most effective in reducing the swelling properties of these soils (Osinubi et al., 2011). The cost of blending these soil with cement for construction is usually high, therefore the need to mix the cement-soil blend with requisite quantity of cheap admixture (like groundnut shell ash). Since the potential of GSA as a stabilizer has been established there is a need to therefore assess its effects as an admixture in cement stabilization of the soil. This is with the view to reduce the amount of cement to be used for stabilization and consequently to reduce the cost of stabilization.
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MATERIALS AND METHODS Materials Black Cotton Soils:The disturbed soil samples used for the investigation was obtained from a borrow pit at Cham a community in Balanga Local Government Area (Latitude 09043.686’N and longitude 11043.686’E) of Gombe State which is located 50 km Northwest of Adamawa State, Nigeria. The top soil was removed to a depth of 0.5 m before the soil samples were taken, sealed in plastic bags and put in sacks to avoid loss of moisture during transportation. The soil samples were then air – dried before pulverizing to obtain particles passing BS No. 4 sieve (4.76mm aperture). The soil was subjected to tests in accordance with British Standard Code of practice BSI 1377 (1990), for the natural soil and BSI 1924 (1990) for the treated soil samples, respectively. The soil belongs to the CH group in the Unified Soil Classification System (ASTM, 1992) or A-7-6(13) soil group of the ASHTO soil classification system (AASHTO, 1986) as shown in Table 1. Groundnut Shell Ash:The groundnut shell ash (GSA) used was obtained from the burning of groundnut shell sourced from Giwa local government area of Kaduna State. The groundnut shells were completely burnt under atmospheric condition within a temperature range of 500 – 700 0C measured with a thermocouple, sealed up in plastic bags and transported to the laboratory. The ash was then passed through BS No 200 sieve (75 µm aperture) and kept to be mixed with the soil – cement in the appropriate percentages. The oxide composition of GSA was determined using Neutron Activation Analysis (NAA). A summary of the properties of the GSA is shown in Table 2. Cement:cement used for the study was obtained from deport of Dangote Portland Cement in Kaduna State. The oxide composition of cement is shown in Table 2. Table 1: 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, % Colour Dominant clay mineral
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Quantity 91.4 17.2 59.0 36.0 23.0 13.7 37.5 2.50 A-7-6 (13) CH High swell potential 1.51 20.1 170 3.1 Greyish black Montmoril lonite
Table 2: Chemical composition of cement and groundnut shell ash Oxide GSA (%) Cement (%) CaO 14.05 73.05 SiO2 38.88 14.42 Al2O3 10.28 3.48 Fe2O3 MgO Mn2O3 Na2O K2O SO3
4.28 7.48 0.50 0.28 12.72 2.73
3.38 1.30 0.03 0.00 2.99
P2O5 Cr203 SrO ZnO Cl TiO2 Loss on Ignition
6.53 0.003 0.108 0.101 0.37 1.71 4.20
0.11 0.01 0.46 0.00 0.15 0.21 -
Methods Atterberg Limits:the Atterberg limits consisting of liquid limit, plastic limit, plasticity index and shrinkage limit were determined in accordance with the British Standards (BSI, 1377: 1990) and BS (1924:1990) for the natural and treated soil respectively. Compaction:Tests involving moisture-density relationships carried out using three energy levels BSL, WAS and BSH. 3 kg of the soil/soil-admixtures sample was mixed thoroughly with 4 % of water (and the water was added at 4 % for each of the compaction). The sample was then compacted into the 1000 cm3 (of mass m1); in three layers of approximately equal mass with each layer receiving 27 blows of 2.5 kg rammer falling through a height of 300 mm, for the British Standard light compaction; 10 blows of 4.5 kg rammer in five layers for West African Standard compaction and 27 blows of 4.5 kg rammer in five layers for the British Standard Heavy. The blows were uniformly distributed over the surface of each layer. The collar was then removed and the compacted sample leveled off at the top of the mould with a straight edge. The mould containing the leveled sample was then weighed to the nearest 1 g, m2. Unconfined Compressive Strength:the unconfined compressive strength (UCS) was determined in accordance with British Standards (BSI, 1377, 1924: 1990). Thoroughly mixed air dried soil – GSA – Cement mixtures were compacted at optimum moisture contents (OMC) using the Standard Proctor (SP) compaction energy. The compacted soil – GSA – Cement mixtures were prepared at step concentrations of 0, 2, 4, 6, 8 and 10 % for the GSA and 2, 4, 6 and 8 % for the Cement respectively. The compacted samples were extruded from the mould using a cylindrical steel measuring 76 mm by 38 mm diameter. The samples were sealed in polythene bags and kept in the humidity room at a constant temperature of 25 ± 20 C for 7, 14 and 28 days curing period. The samples were then placed in a load frame driven at a 394
constant strain of 0.10 %/min until failure occurred. Three specimens were used for each test and the average result was taken. California Bearing Ratio: The California bearing ratio (CBR) test was conducted in accordance with BS 1377(1990) and BS 1924 (1990) for the natural and treated soils. The CBR is expressed by the force exerted by the plunger and the depth of its penetration into the specimen; it is aimed at determining the relationship between force and penetration. 5.0 kg of the soil sample/soil-admixture sample were mixed at their respective optimum moisture contents in 2360 cm3 mould. The compaction was in three layers each receiving 62 blows from the 2.5 kg rammer. The base plates were removed (after compaction) and the compacted specimens placed in sealed plastic bags for curing (for 6 days) and after the sixth day, the specimens were immersed in water for 24 hours before testing according to Nigerian General Specifications (1997). The base plates were later replaced and the specimens transferred to the CBR testing machine and positioned on the lower plate of the machine. The plunger was then made to penetrate the specimen at a rate 1.3 mm/min until the specimen failed. The mould was then inverted, base plate removed and the procedure repeated for the base of the specimens. From the values of the penetration and force recorded, a curve of force against penetration was obtained. The CBR value was calculated at penetration 2.5 mm or 5.0 mm; the greater of the two values and as their means where the value are within 10 % of each other. Results and Discussion Atterberg Limits: Figures 1 – 4 show the variation of the consistency limits of soil/Cement mixtures with increasing GSA content. From the plots, it was observed that the liquid limit and plasticity index increased with increase in the Cement content. With the inclusion of GSA into the soil – Cement matrix, the consistency limits increased to a peak value at 6 % GSA. Beyond 6 % GSA, the liquid limit and plasticity index values decreased. The liquid limit of the soil increased from 59 % containing 2 % Cement / 0 % GSA to a peak value of 74 % at 8 % Cement / 6 % GSA. Further increase in GSA led to a decrease in the liquid limit. The plasticity index of the treated soil sample increased from a value of 33.4 % at 2 % Cement / 0 % GSA to a peak value of 48.1 % at 8 % Cement / 6 % GSA treatment. However, the plastic limits and the linear shrinkage decreased with the inclusion of both Cement and GSA. Plastic limit decreased from a value of 25.6 % containing 2 % Cement / 0 % GSA to a value of 22.0 % at 2 % Cement / 6 % GSA, while linear shrinkage decreased from a value 17.86 % containing 2 % Cement / 0 % GSA to 12.86 % at 8 % Cement / 0 % GSA content . The reduction in Plastic limit and Linear shrinkage is in agreement with the findings of Ijimdiya and Abass (2012). The reduction could be due to the cation exchange reaction whereby the more active and higher valent cations (i.e. Ca2+) in the admixtures replaced the weakly bonded ions in the clay structure; thereby leading to the flocculation and liberation of water bonded at the outer layers (Osinubi, 1999).
395
75
65
2% Cement 4% Cement
60
6% Cement
55
8% Cement
0
2
4
6
8
10
Groundnut shell content (%)
Fig. 1: Variation of liquid limit of soil - cement mixtures admixed with Groundnut shell ash contents 29 28 27 26
2% Cement
25 4% Cement
24 23
6% Cement
22 21 0
2
4
6
8
10
8% Cement
Groundnut shell content (%) Fig. 2: Variation of plastic limit of soil - cement mixtures admixed with Groundnut shell ash content
Plasticity Index (%)
Plastic Limit (%)
Liquid Limit (%)
70
50 48 46 44 42 40 38 36 34 32 30
2% Cement 4% Cement 6% Cement 8% Cement
0
5
10
Groundnut shell content (%) Fig. 3: Variation of plasticity index of soil - cement mixtures admixed with Groundnut shell content
396
Linear Shrinkage (%)
19 18 17 2% Cement
16 15
4% Cement
14 6% Cement
13 12
8% Cement
0
2
4
6
8
10
Groundnut shell ash content (%) Fig. 4: Variation of linear shrinkage of soil - cement mixtures admixed with Groundnut shell content
Compaction Characteristics The effect of GSA content on the maximum dry density (MDD) and optimum moisture content (OMC) of the soil-Cement mixtures are shown in Figs. 5 and 6, respectively. The MDD increased with increase in GSA content and also increased as the compactive effort increased. The increase in the MDD value is as a result of densification of the soil mass due to increase in compaction energy. The MDD values for BSL, WAS and BSH are 1.41, 1.49 and 1.6 Mg/m3 respectively at 0 % GSA / 2 % Cement and their peak values are 1.7, 2.2 and 1.73 Mg/m3 at 6 % Cement / 2 % GSA, 8 % Cement / 2 % GSA and 8 % Cement / 6 % GSA.Stephen (2005) and Akinmade (2008) also reported the same trend of increasing MDD to peak values before falling at higher admixture contents where further additives had no significant impact on the MDD values. The OMC also increased with increase in GSA content but decreased as the compactive effort increased. The decrease in OMC as compactive effort increasedcould be as a result of decrease in the voids present in the soildue to more densification of the soil particles. Research works of Osinubi (1999), Stephen (2005), George (2006), Akinmade (2008) and (Ijimdiya et al., 2012) agree with the trend of increasing OMC with increase in admixture contents. This trend could be attributed to an increased desire for water which commensurates with the higher amount of the additive because more water was required for the dissociation of admixture with Ca2+ and OH- ions to supply more Ca2+ for the cation exchange reaction. It could also be due to increasing surface area cause by the higher amount of additives, which required more water for the lubrication of the entire mixture. The OMC for BSL, WAS and BSH compaction increased from 27.5, 21.0 and 20.5 % for 2 % Cement / 0 % GSA to 28, 24 and 27 % at 2 % Cement / 2 % GSA, 2 % Cement / 2 % GSA and 8 % Cement / 4 % GSA respectively. The increase in OMC as a result of increase in GSA could be due to the requirement for more water commensurate with the increasing surface area, and because more water was required to dissociate Ca2+ with OH- ions to supply more Ca2+ needed for the cation exchange reaction.
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2.4
MDD (Mg/m3)
2.2
2% C BSL 4% C BSL
2
6% C BSL 8% C BSL
1.8
2% C WAS 4% C WAS
1.6
6% C WAS 8% C WAS
1.4
2% C BSH 4% C BSH
1.2 0
5
6% C BSH
10
8% C BSH
Groundnut shell ash content (%) Fig. 5: Variation of maximum dry density of soil - cement mixtures admixed with Groundnut shell ash content 30
OMC (%)
28
2% C BSL
26
4% C BSL
24
6% C BSL
22
8% C BSL 2% C WAS
20
4% C WAS
18
6% C WAS
16
8% C WAS
14
2% C BSH 4% C BSH
12
6% C BSH
10
8% C BSH
0
2
4
6
8
10
Groundnut shell ash content (%) Fig. 6: Variation of optimum moisture content of soil - cement mixtures admixed with Groundnut shell content Unconfined Compressive Strength The general test recommended for use in the determination of the additive to be used in the stabilization of soil is the unconfined compressive strength (UCS) test (Singh, 1991). It is an important factor in the evaluation of the design criteria for the use of soil as a pavement material (Ola, 1983). The test results for the UCS are shown in Figs. 7 – 9. The UCS at 7 day curing increased from 78, 72.5 and 1100 kN/m2 at 2 % Cement / 0 % GSA to a peak value of 989, 1387 and 1801 kN/m2 respectively at 8 % Cement / 8 % GSA, 8 % Cement / 8 % GSA 398
and 8 % Cement / 6 % GSA treatments. The results obtained show that specimens treated with BSL and WAS did not meet the 7 day 1710 kN/m2 specified by (Osinubi et al., 2012) as criterion for adequate Cement stabilization but BSH meet the requirement. Fig.8 shows the 14-day UCS values which increased with increased admixtures and compactive efforts. The UCS values increased from 52,264 and 1289 kN/m2 to peak values of 850, 1430 and 2310 kN/m2 at 8 % Cement / 8 % GSA, 8 % Cement / 8 % GSA and 8 % Cement / 6 % GSA for BSL, WAS and BSH compaction energy levels, respectively. Fig. 9 shows the 28-day UCS values which also increased as the admixtures and the compactive efforts increased. The values increased from 157, 123 and 1389 kN/m2 to peak values of 1132, 1766 and 2893 kN/m2 at 8 % Cement / 6 % GSA, 8 % Cement / 8 % GSA and 8 % Cement / 6 % GSA for BSL, WAS and BSH compaction energy levels, respectively. 1800 1600 2% C BSL
UCS (kN/m2)
1400
4% C BSL 6% C BSL
1200
8% C BSL
1000
2% C WAS 4% C WAS
800
6% C WAS
600
8% C WAS
400
2% C BSH 4% C BSH
200
6% C BSH
0
8% C BSH
0
2
4
6
8
10
Groundnut shell ash content (%) Fig. 7: Variation of UCS (7 day curing) of soil - cement mixtures admixed with Groundnut shell content
2500
UCS (kN/m2)
2000
2% C BSL 4% C BSL 6% C BSL
1500
8% C BSL 2% C WAS
1000
4% C WAS 6% C WAS
500
8% C WAS 2% C BSH 4% C BSH
0 0
2
4
6
8
10
6% C BSH 8% C BSH
Groundnut shell content (%) Fig. 8: Variation of UCS (14 day curing) of soil - cement mixtures admixed with Groundnut shell content
399
3000 2% C BSL 4% C BSL 6% C BSL 8% C BSL 2% C WAS 4% C WAS 6% C WAS 8% C WAS 2% C BSH 4% C BSH 6% C BSH 8% C BSH
UCS (kN/m2)
2500 2000 1500 1000 500 0 0
2
4
6
8
10
Groundnut shell content (%) Fig 9: Variation of UCS (28 day curing) of soil - cement mixtures admixed with Groundnut shell content
CBR (%)
California Bearing Ratio The California bearing ratio (CBR) value of a soil/stabilized soil is an important parameter in gauging its suitability for engineering use. It gives the indication of the strength and bearing ability of the soil. The unsoaked CBR for BSL compaction gave a peak value of 50.6 % at 6 % Cement / 8 % GSA from a value of 5 % for 2 % Cement / 0 % GSA. For WAS compaction, the CBR value increased from 8 % for 2 % Cement / 0 % GSA to a peak value of 61.5 % at 6 % Cement / 8 % GSA. Unsoaked CBR value for BSH increased from 46.2 % for 2 % Cement / 0 % GSA to a peak value of 83.1 % at 6 % Cement / 8 % GSA (see Fig. 10). The unsoaked CBR also showed an increase in the CBR as the compactive efforts increased, this indicates that the denser the soil due to higher compactive effort, the greater the strength of the soil i.e. the CBR value for BSL, WAS and BSH are 50.6, 61.5 and 83.1 % respectively at 6 % Cement / 8 % GSA. The Soaked CBR values also showed an increase with higher doses of the admixture and with increased compactive efforts.Peak CBR values of 18.3, 23 and 64.3 % for BSL, WAS and BSH compactive effortswere recorded at 6 % Cement / 8 % GSA for all the three compactive efforts. The reduction in the CBR value of soaked samples when comparedwith the unsoaked CBR valuecould be was due to the ingress of water into the specimen which weakened it and reduced its strength. (see Fig. 11). The 83.1 % recorded met the Nigerian General Specification (1997) requirement of 30 % for sub base materials. 90 80 70 60 50 40 30 20 10 0
2% C BSL 4% C BSL 6% C BSL 2% C WAS 4% C WAS 6% C WAS 2% C BSH 4% C BSH 6% C BSH
0 2 4 6 Groundnut shell ash content (%)
8
Fig. 10: Variation of CBR (Unsoaked) of soil - cement mixtures admixed with Groundnut shell content
400
70 60
CBR (%)
50
2% C BSL 4% C BSL
40
6% C BSL
30
2% C WAS
20
6% C WAS
4% C WAS
2% C BSH 4% C BSH
10
6% C BSH
0 0
2
4
6
8
Groundnut shell ash content (%)
Fig. 11: Variation of CBR (Soaked) of soil - cement mixtures admixed with Groundnut shell content
Conclusions Based on the results obtained from the investigation carried out, the following conclusions can be made: 1. The black cotton soil used is an A-7-6 (13) or CH soil in AASHTO (1986) and USCS (ASTM, 1992) Classification Systems respectively. 2. The liquid limit of the soil increased from 59 % for 2 % Cement / 0 % GSA to a peak value of 74 % at 8 % Cement / 6 % GSA. 3. The plasticity index of the soil increased from 33.4 % for 2 % Cement / 0 % GSA to a peak value of 48.1 % at 8 % Cement / 6 % GSA. 4. The plastic limit decreased from 25.6 % for 2 % Cement / 0 % GSA to 22 % at 2 % Cement / 6 % GSA. 5. The linear shrinkage decreased from 17.86 % for 2 % Cement / 0 % GSA to 12.86 % at 8 % Cement / 0 % GSA. 6. The plasticity index values for all the concentration of the additive exceeded the 30 % value prescribed for sub grade soil by the Nigerian General Specifications (1997). 7. MDD increases with increase in admixture and also increases as the compactive effort increases. 8. OMC increases as the admixture increase but decreases with increase in compactive effort. 9. The UCS at 7 day curing increase from 78, 72.5 and 1100 kN/m2 at 2 % Cement / 0 % GSA to a peak value of 989, 1387 and 1801 kN/m2 respectively at 8 % Cement / 8 % GSA, 8 % Cement / 8 % GSA and 8 % Cement / 6 % GSA treatment. 10. The results obtained show that specimens treated with BSL and WAS did not meet the 7 day 1710 kN/m2 specified by (TRRL, 1977) as criterion for adequate Cement stabilization but BSH meet the requirement. 11. Curing period of 14 and 28 days also show an increase in UCS value due to increase in the compactive effort and as the compactive effort increases a higher UCS value that met the requirement are obtained. 12. The 28 day curing period UCS values obtained showed that the Cement / GSA blend had a long term advantage in terms of strength gain. There were tremendous increments in the values of UCS. The 28 day curing period UCS recorded a peak value of 2893 kN/m2 at 8 %
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Cement / 6 % GSA for BSH compaction, showing that the soil treated with this blend can be used (at BSH compaction) as base course of pavement material. 13. The unsoaked CBR also shows an increase in the CBR as the compactive efforts increases, these indicates that the denser the soil due to higher effort the greater the strength of the soil i.e. the CBR value for BSL, WAS and BSH are 50.6, 61.5 and 83.1 % respectively at 6 % Cement / 8 % GSA. 14. The Soaked CBR also shows an increase in its value as the admixture increases and also as the compactive effort increases. CBR values peak at 18.3, 23 and 64.3 % for BSL, WAS and BSH compactive efforts respectively at 6 % Cement / 8 % GSA for all the compactive effort.
15. The CBR value of 83.1 % recorded for unsoaked CBR met the Nigerian General Specification (1997) requirement of 30 % for sub base materials. 16. Based on the test results an optimum 8 % Cement /6 % GSA treatment of black cotton soil is recommended for use as sub-base treatment when compacted with British Standard heavy energy. References AASHTO (1986).“Standard Specifications for Transport Materials and Methods of Sampling and Testing.” 14th Edition, American Association of State Highwayand Transport Officials (AASHTO), Washington, D.C 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, AhmaduBello University, Zaria. ASTM (1992). Annual Book of Standards Vol. 04.08, American Society for Testing and Materials, Philadelphia. B.S. 1377 (1990). “Methods of testing soil for civil engineering purposes”. British Standards Institute, London. B.S. 1924 (1990). “Methods of Tests for stabilized Soils.” British Standards Institute, London. George, M. (2006) Stabilization of black cotton soil with ordinary portland cement using bagasse ash as admixture. MSc. Thesis, Department of Civil Engineering, Ahmadu Bello University, Zaria. Ijimdiya, T. S. and Abbas L. A. (2012). “Stabilization of Black cotton soil using groundnut shell ash as an admixture” EJGE, Bund, F Nelson, D. and Miller, J. (1992). Expansive Soils: Problems and Practices in Foundation and Pavement Engineering. John Wiley and Sons, Inc. New York. Nigerian General Specification (1997). Road and Bridge Works. Federal Ministry of Works, Abuja, Nigeria. Oluwapelumi, O. O. (2012). “Effect of soil suction on the compressibility and strength of North East Nigerian Black cotton soil” EJGE Bund. Osinubi, K. J. (1995). “Lime modification of black cotton soils.” Spectrum Journal, Vol. 2, Nos 1 and 2, pp. 112 – 122. Osinubi, K. J. (1999). “Evaluation of admixture stabilization of Nigerian black cotton soil.” Nigerian Society of Engineers Technical Transactions, 34(3): 88-96 Osinubi, K.J, R. Diden, Ijimdiya, T. S., Eberemu, A.O. (2012). Effect of Elapsed Time after Mixing on the Strength properties of Black Cotton Soil Cement Blast Furnace Slag Mixtures. Journal of Engineering Research. 17, 4. Pp.
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Osinubi, K. J., Oyelakin, M. A. and Eberemu A. O. (2011). "Improvement of black cotton soil with ordinary Portland cement – locust bean waste ash blend." The Electronic Journal of Geotechnical Engineering, Vol. 16, Bund. F, pp. 785-796. Peter, G. M. (1993). “Fly Ash Stabilization of Tropical Hawai Soils.” In: Fly ash for soil improvement, K. D. Sharp (ed.) Geotechnical Engineering Division of ASCE, Geotechnical Special Publications, No 36, pp. 15–20 Singh, G. (1991): Highway Engineering, 3rd Edition, Standard Publishers Distributors. Pp.599 – 619. Stephen, A. T. (2006). Stabilization Potential of Bagasse Ash on Black cotton Soil. Unpublished M.Sc. Thesis, Department of Civil Engineering, Ahmadu Bello University, Zaria.
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