Theoretical investigation on the formation mechanism of carbonate ion in microbial self-healing concrete: Combined QC calculation and MD simulation

[Display omitted] •A method for discovering low-energy cluster configurations was proposed.•H2CO3 tended to decompose through a concerted mechanism in the neutral condition.•H2CO3 tended to form CO32– by a two-step reaction in the basic condition of MSHC.•Increasing temperature promoted the CO32– formation rate in the basic condition. Carbonate ion (CO32–) is essential to the formation of calcium carbonate in microbial self-healing concrete (MSHC). The self-healing effect of MSHC can be improved in practical engineering by exploring the control parameters affecting the CO32– formation. However, investigations on the formation mechanism of CO32– in MSHC are lacking. In this work, the formation mechanism of CO32– in MSHC was investigated by quantum chemical calculation and molecular dynamics simulation. The results showed that carbonic acid (H2CO3) tended to decompose through the concerted mechanism rather than the stepwise mechanism in the neutral condition, and the calculated reaction energy barrier and reaction rate constant were in good agreement with experimental values reported in the literature. In the basic condition of MSHC, H2CO3 was highly prone to react with hydroxyl ion to form CO32– by a two-step reaction rather than react with water to form carbon dioxide, with a rate-determining step energy barrier of 11.56 kcal/mol. The increased temperature could promote the formation rate of CO32–, which was as high as 6.72×104 s−1 at room temperature. The investigation on the formation mechanism of CO32– in this work would provide the theoretical guidance for the better healing ability of MSHC in practical engineering.