Sand improvement by microbial-induced carbonate precipitation with casein micelles

Abstract

This study explores the incorporation of casein micelles to improve the conventional microbial-induced carbonate precipitation technique used for soil improvement. With a single application of the proposed biocementing agent containing casein micelles, a mixed slurry of natural sand solidified to self-sustaining strength within 48 h at 37°C was obtained. The stress–strain curves of the biocemented specimens obtained from a consolidated drained triaxial compression test exhibited sharp peaks at less than 1% strain. Under effective confining pressures of 30, 50 and 100 kPa, the peak deviatoric stress registered 415, 479 and 536 kPa, respectively – representing 1·8–4·1 times the maximum strength of the original sand. Vaterite calcium carbonate crystals formed by the biocementing agent ensured bridging between sand particles, resulting in the improved cohesion. The cohesion-derived residual strength tended to increase at the critical state in biocemented sand under the lowest confining stress. The localised shear band formed by the crystals may control the movement of sand particles, resulting in a change in volumetric strain behaviour. The formation of casein micelles induced the nucleation and growth of spherical crystals, acting as a casein-mediated vaterite. This formation likely contributed to the improved cohesion of sand observed in this study.