Bio-cementation of tropical lateritic soil via microbially induced calcite precipitation: Strength enhancement and microstructural mechanisms

This study investigates the effectiveness of Microbially Induced Calcite Precipitation (MICP) using Bacillus subtilis as a sustainable technique for biochemically stabilizing laterite soil. Lateritic soils, common in tropical regions, are problematic in construction due to high porosity, low strength, and brittle stress–strain responses. The main objectives were to characterize the physical properties of untreated laterite soil, evaluate the effect of MICP treatment on its stress–strain behaviour, and correlate mechanical improvements with microstructural changes using scanning electron microscopy (SEM) and quantitative image analysis. Results showed that untreated soil exhibited low peak stress (52 kN/m2) and brittle failure dominated by splitting cracks. Following MICP treatment, peak stresses improved markedly to 235 kN/m2 at 7 days, 296 kN/m2 at 14 days, and 420 kN/m2 at 30 days of curing. This shows that the strength exceeds commonly reported minimum requirements for stabilized subgrades in tropical pavement systems. Stress–strain curves showed higher stiffness, improved ductility, and more stable post-peak behaviour, while failure shifted toward cleaner shear cracking. The morphological analysis by SEM and image analyses confirmed progressive calcite precipitation, void filling, and stronger particle bonding over curing time. This study advances current knowledge by systematically integrating mechanical testing with microstructural quantification to elucidate the mechanics governing bio-cementation in laterite soils. These findings establish MICP as a low-carbon, environmentally friendly alternative to conventional chemical stabilizers, offering promising applications for subgrades and foundations in tropical geotechnical engineering.