Insight into the mechanism of microbially induced carbonate precipitation treatment of bio-improved calcareous sand particles

The use of the calcareous soil as a backfill material in ocean constructions faces pervasive challenges due to the significant rate of particle fracture. To meet the requirements of marine ecological protection, a bio-cementing technique, microbially induced carbonate precipitation (MICP), has emerged as a green method for improving the soil properties of calcareous sands. This paper presents a detailed study on the effect of MICP on the fracture behaviours of calcareous particles and its treating mechanism at microscopic scale level. First, individual calcareous and dolomite particles were treated by MICP for different numbers of rounds. The increase ratio of the particle mass and the filling degree of the intra-particle pores were then measured to evaluate the treatment effect of MICP on individual sand particles. Combining with scanning electron microscopy measurements of the evolution of the particle morphology and internal microstructures of the calcareous particles, the intra-particle pore filling effect as well as the surface coating effect induced by MICP treatment were directly observed. Finally, a series of single-particle crushing tests indicated that the intra-particle pore filling effect of MICP rather than the surface coating effect played the dominant role in improving the fracture pattern and fracture strength of calcareous sand particles.