Plasticity characteristics of lateritic soil treated with Sporosarcina pasteurii in microbial-induced calcite precipitation application

The plasticity characteristics of lateritic soil with varying Sporosarcina pasteurii (S. pasteurii) suspension density and compositional variables were evaluated in microbial-induced calcite precipitation (MICP) application. The liquid limit value of the natural lateritic soil was used to prepare samples with three mix proportions of the bacteria and cementation reagent (i.e., 25% bacteria–75% cementation reagent, 50% bacteria–50% cementation reagent and 75% bacteria–25% cementation reagent). The S. pasteurii suspension densities used to trigger the MICP process are 0, 0.5, 2.0, 4.0, 6.0 and 8.0 McFarland standards (i.e., 0, 1.50 × 108, 6.0 × 108, 1.20 × 109, 1.80 × 109 and 2.40 × 109 cells/ml, respectively). Tests carried out on the treated specimens include Atterberg limits and linear shrinkage as well as calcite content using the acid wash method. Results obtained showed a general decrease in the Atterberg limit values with higher S. pasteurii suspension density. The best improvement of plasticity index was achieved for lateritic soil prepared with 75% S. pasteurii and 25% cementation reagent at S. pasteurii suspension density of 2.40 × 109 cells/ml with a corresponding peak 6.0% calcite content. Also, a maximum 4% contaminant concentration of a synthetic leachate produced the best S. pasteurii growth pattern.