Mechanism of CaCO ₃ Nucleation during Microbially Induced Carbonate Precipitation Reinforcement of Siliceous Sand Considering Surface Chemistry and Calcium Concentration

Microbially induced carbonate precipitation (MICP) has emerged as a globally innovative biotechnology with broad applications across various engineering disciplines. Despite its widespread use, the fundamental mechanisms governing calcium carbonate (CaCO 3 ) nucleation during the MICP process are inadequately understood. In this study, we employ molecular dynamics simulations to explore the effects of surface properties and Ca 2+ ion concentration on the nucleation behavior and morphology of CaCO 3 during MICP-based reinforcement of siliceous sand. Our results reveal that quartz surfaces with specific hydroxyl group densities promote a distinct dispersed deposition of CaCO 3, whereas higher Ca 2+ ion concentrations induce rapid homogeneous nucleation, producing large, loosely packed CaCO 3 clusters. These simulation results align well with scanning electron microscopy observations, which reveal irregularly shaped and loosely packed CaCO 3 formations. Overall, our findings underscore the critical role of surface chemistry and the ionic environment in controlling the outcomes of MICP treatment, offering valuable microscopic insights to enhance its effectiveness in geotechnical and civil engineering applications.