Effects of Varying Cementation Reagent Concentrations on the Index and Physico-chemical Properties of Lateritic Soil Treated with Bacillus sphaericus

This study evaluated the index and physico-chemical characteristics of lateritic soil classified as A-2-6 (1) in the American Association of State Highway and Transportation Officials (AASHTO) system and SC in the Unified Soil Classification System (USCS) treated with stepped Bacillus sphaericus (Bs) suspension densities (i.e., 0, 1.5 × 108, 6.0 × 108, 1.2 × 109, 1.8 × 109, 2.4 × 109 cells/mL) for varying cementation reagent (Cr) concentrations (i.e., 0.25, 0.5, 0.75 and 1.0 M), using 25 Bs:75 Cr, 50 Bs:50 Cr, and 75 Bs:25 Cr mix ratios, respectively. The results obtained show that the optimum calcium carbonate contents were 9.0%, 8.7%, and 6.5% for the mix ratios stated above, respectively, for Bs (1.2 × 109 cells/mL) and Cr (0.5 M) with urease activity of 80.8 ms/cm and an optimum pH of 8.99. The bio-treatment of soil with 25% bacteria (1.2 × 109 cells/mL) and 75% Cr (0.5 M) mix ratio reduced the liquid limit (LL) of the natural soil from 36.5 to 34.2%, and the plasticity index (PI) from 16.4 to 11.6%. A microanalysis of specimens showed that the treated soil appeared more uniform and aggregated. The findings of the study show that bio-treatment with 25 Bs (1.2 × 109 cells/mL):75 Cr (0.5 M) mix ratio improved the index and physico-chemical properties of the lateritic soil considered in the study.