Bio-nano soil stabilisation using MICP and nano-silica: performance and sustainability

This study introduces a novel bio-nano soil stabilisation technique that combines microbially induced calcium carbonate precipitation (MICP) with amorphous nano-silica (NS) to improve the geotechnical properties of various sandy soils. The research aims to enhance soil strength and sustainability while evaluating the environmental trade-offs. Laboratory experiments were conducted on medium-to-fine sand, silty sand, and clayey sand, investigating the influence of bacterial concentration (10¹–10⁷ cfu/ml), cementation solution molarity (0.25–2.0 M), and NS dosage (1%–2.5% by weight). Key performance indicators included compaction characteristics, permeability, California Bearing Ratio (CBR), and ultrasonic pulse velocity (UPV). Under optimal conditions (10⁶ cfu/ml and 1.75 M solution), the treatment significantly improved CBR and UPV while reducing permeability. The addition of 2% NS further enhanced performance, increasing dry density and CBR by up to 73% and 131%, respectively, while reducing permeability by 57%. X-ray diffraction confirmed calcite formation, validating successful mineralisation. A cradle-to-gate life cycle assessment revealed a 49% increase in carbon footprint due to NS use, indicating a trade-off between performance gains and environmental impact. These findings suggest a promising, synergistic solution for sustainable ground improvement.