Properties of Tropical Black Clay Treated with Selected Admixtures

The properties of tropical black clay (also known as black cotton soil, BCS) treated with cement kiln dust (CKD) and locust bean waste ash (LBWA) was studied. Tests performed include index and compaction using British Standard light (BSL); West African Standard (WAS) (or Intermediate) and British Standard heavy (BSH) energies. Statistical analysis was performed using two-way analysis of variance (ANOVA) incorporated in Microsoft excel software. Results obtained show that the specific gravity value of the natural BCS (2.4) reduced to a minimum value of 2.33 at 2% CKD/10% LBWA treatment. Peak liquid limit (LL) value of 55.6% was recorded at 3% CKD/6% LBWA treatment, minimum plastic limit (PL) value of 15.6% recorded for 3% CKD/6% LBWA treatment, while plasticity index (PI) value recorded a peak value of 40.0% at 3% CKD/6% LBWA treatment. The compaction characteristics, that is, maximum dry density (MDD and optimum moisture content (OMC) decreased and increased, respectively, with higher CKD/LBWA treatment. Generally, ANOVA results show that CKD and LBWA had significant effects on BCS. Although CKD/LBWA treatment improved the properties of BCS; however, the Nigerian General Specifications requirements of LL ≤ 35.0% and PI ≤ 12.0% for sub-base material in road construction were not met. It is recommended that BCS be minimally treated with 1% CKD/10% LBWA for use as subgrade material for the construction of low-volume roads.