Effect of curing procedure on strength development of microbial induced calcite precipitate treated lateritic soil

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4. Effect of curing procedure on strength development of microbial induced calcite precipitate treated lateritic soil

The study investigated the effect of different curing procedures (i.e., wax-cured, oven-cured at 30^o C and air-cured at ambient temperature of 25 ± 2^o C) on the strength development of compacted lateritic soil treated with Bacillus thuringiensis (Bt). Five different Bt suspension densities (i.e., 0, 1.5 x 10⁸, 6.0 x 10⁸, 12 x 10⁸, 18 x 10⁸ and 24 x 10⁸ cells/ml) were pre-mixed in the soil with four stepwise concentrations of cementation solutions (C_s) (i.e., 0.25, 0.5, 0.75 and 1 M) in the ratio of 50 % Bt : 50 % C_s of the soil optimum moisture content (OMC) and compacted using  British Standard light (BSL), West African Standard (WAS) and British Standard heavy (BSH) energies. The experimental results indicate that the strength of specimens are in the order: curing at ambient condition > oven-curing > wax-curing. Peak strength value of 1,239.38 kN/m² for specimens compacted with BSL energy and air-cured at ambient condition for treatment with mix ratio of 24 x 10⁸ cells/ml (Bt) : 1 M (C_s). Also, peak values of 524.61 kN/m² for mix ratios 24 x 10⁸ cells/ml : 1 M and 1,208.75 kN/m² for 24 x 10⁸ cells/ml : 0.75 M were recorded for specimens wax-cured and oven-cured, respectively. Higher strength values were recorded at higher compactive effort regardless of the curing method used. Microanalysis results showed that calcite crystals precipitated bridged the soil particles. Based on the findings recorded, the lateritic soil treated with Bacillus thuringiensis (24 x10⁸ cells/ml) : 0.75 M (C_s) mix ratio and exposed to ambient conditions could be used to improve the strength of lateritic soil.

9th International Congress on Environmental Geotechnics (ICEG2023)

Biogeotechnics and Bioremediation