Compaction and CBR Behaviour of Cement-Stabilised Sand–Black Cotton Soil Mixtures

Abstract

AbstractBlack cotton soil admixed with 0–50% sand was subjected to laboratory tests to determine the index properties, as well as compaction, and CBR behaviour when stabilised with ordinary Portland cement in the range of 0–10%. The results show that by adding sand to black cotton soil, the free swell and plasticity properties reduced with increasing sand content. Three compaction energies were employed, namely BS Light, West African Standard, and BS Heavy. The maximum dry unit weight of the soil mixture increased with sand and cement contents, and the highest value of 21.6 kN/m3 was obtained at 40% sand and 8% cement contents using the BS Heavy compaction energy. The optimum moisture content reduced appreciably on the addition of cement and sand, decreasing from 27.4 to 10.4% on addition of 30% sand and 6% cement using the BS Heavy compaction energy. The soil mixture of 30% sand and 6% cement gave the lowest optimum moisture content for all the compaction energies. Using the BS Light compaction energy, the unsoaked CBR increased from 17 to 56% at 8% cement and 40% sand contents, while for BS Heavy compaction energy, unsoaked CBR increased from 23.5 to 60% at 6% cement and 40% sand contents. At 40–50% sand content alone, the unsoaked CBR of the soil increased to 52.5%. This shows that black cotton soils can be improved upon using sand and cement to meet the requirements for subgrade, sub-base, and base material for highway construction in Nigeria. The analysis of variance shows that at 95% confidence level, sand content, cement content, and compaction energy positively affected maximum dry unit weight of black cotton soils (p-value < 0.05). On the other hand, the effect of compaction energy on optimum moisture content was found not to be statistically significant at 5% level of significance. Compaction energy was found to influence the unsoaked CBR value more than cement and sand contents.KeywordsSand–black cotton soil mixturePortland cementCompactionCBR