Microbial Precipitation of Calcium Carbonate for Crack Healing and Stabilization of Sandy Soils

Microbially induced calcium carbonate (CaCO3) precipitation (MICP) can improve the shear strength of soil via biocementation while reducing its porosity and hydraulic conductivity. The purpose of this study was to evaluate the effect of the addition of bacterial metabolites and montmorillonite on the crack healing and biocementation of sandy soil during the MICP process. Cracks were generated by drying wet soil samples in Petri dishes, after which they were sprayed with one of four treatments: deionized water, a cementation solution, bacteria mixed with the cementation solution, and bacterial metabolites mixed with the cementation solution. After five cycles of this spray treatment, the surface crack ratio was observed to decrease by about 71% when living cells were used and by about 80% when microbial metabolites were added. However, the crack reduction ratio was relatively low when treated with water (28%) and the cementation solution alone (48%). To investigate the effect of adding a phyllosilicate to improve the strength of sandy soil, MICP was induced in sand mixed with 0–30% montmorillonite (MMT). As a result, the soil strength increased with higher levels of MMT, indicating that MMT contributed to soil stabilization as a colloid for CaCO3 precipitation and via adhesion between sand grains. Therefore, for the crack healing and stabilization of sandy soil, the addition of bacterial metabolites and montmorillonite may enhance the effectiveness of the MICP process.