Effect of selected admixtures on the geotechnical properties of black cotton soil

Abstract

The effect locust bean waste ash (LBWA) and cement kiln dust (CKD) on black cotton soil (BCS) was studied. BCS was modified with 0, 2, 4, 6, 8 and 10 % LBWA and 0, 1, 2, 3 and 4 %CKD in relation to the soil dry weight. Test carried out include cation exchange capacity (CEC), Atterberg limits, compaction and shear strength test. Results show that a combination of LBWA and CKD have negative effect on the geotechnical properties of soil with exception in few cases. The CEC increased with increase in both the LBWA and CKD contents with deviations in few cases. Values of 21.9, 24, 34.1, 33.5, 32.1 and 33.8 Cmol/Kg were recorded at 0, 2, 4, 6, 8 and 10% LBWA content. Similar trend was observed for 1, 2, 3 and 4% CKD. Liquid limit generally increased with increase in LBWA content while plastic limit generally decreased. In the case of plasticity index, values increased with increase in LBWA content. Peak values were recorded at 6%LBWA content. Maximum dry density (MDD) decreased with increase in LBWA content. MDD values of 1.68, 1.67, 1.66, 1.65, 1.63 and 1.61 were recorded at 0, 2, 4, 6, 8 and 10% LBWA content. Similar trend was observed for 1, 2, 3 and 4% CKD. Optimum moisture content (OMC) increased with increase in LBWA content. Cohesion of soil decreased with increase in LBWA content. Values of 140, 110, 95, 60, 120 and 180 kN/m2 was recorded at 0, 2, 4, 6, 8 and 10% LBWA content, while angle of internal friction improved from its natural value up to 10% LBWA content. Statistical studies by means of two–way analysis of variance (ANOVA) reveal that LBWA and CKD have significant effect on the soil properties. Although the modified soil did not effectively improve the consistency and shear strength parameters of BCS, an optimal blend of 2% CKD/10% LBWA blend slightly improved the soil properties. The optimally modified soil could be utilised for lightly trafficked roads construction as sub-base materials.