Calcium carbonate formation mechanism in MSHC revealed by molecular simulation

Microbial self-healing concrete (MSHC) is an eco-friendly material that supports low-carbon development. However, the formation mechanism of calcium carbonate (CaCO3) in MSHC remains unclear. This study investigated the formation process of CaCO3 clusters in MSHC using molecular simulation. The hydroxide ion and carbonate ion (CO32-) would compete for association with calcium ion in MSHC. The formation process of CaCO3 clusters could be summarised as follows: free ions first associated to form ion pairs, then ion pairs aggregated into small clusters through ion-dipole interactions, and finally, small clusters overcame the surface charge effect by high-frequency aggregation-separation behaviour to transform into large clusters and further densify themselves. The reaction rate of CaCO3 cluster formation decreased significantly with the decrease of CO32- concentration, and the association between calcium ion and hydroxide ion would dominate when the CO32- concentration was low.