Transformation mechanism of carbamic acid elimination and hydrolysis reaction in microbial self-healing concrete

Carbamic acid (NH₂COOH) plays an important role in microbial induced carbonate precipitation. However, investigations on the reaction mechanisms of NH₂COOH elimination and hydrolysis are still lacking. In this work, the transformation mechanism of NH₂COOH elimination and hydrolysis in neutral and basic conditions was investigated by quantum chemical calculation. The results showed that NH₂COOH mainly existed in the form of trans-NH₂COOH configuration in the liquid phase at room temperature. In the neutral condition, the catalysis of NH₃ or H₂O could reduce the reaction energy barrier of NH₂COOH elimination and hydrolysis, and NH₂COOH tended to carry out the elimination reaction catalysed by NH₃ to generate NH₃ and CO₂. In the basic condition, reaction energy barriers of NH₂COOH elimination and hydrolysis increased and decreased significantly, respectively, indicating that the basic condition was unfavourable for the NH₂COOH elimination reaction but rather favourable for the NH₂COOH hydrolysis reaction. NH₂COOH in the basic condition tended to carry out the hydrolysis reaction to generate NH₃ and H₂CO₃. The transformation mechanism of NH₂COOH elimination and hydrolysis in different conditions was examined in this work, which would provide the theoretical guidance for the better healing ability of microbial self-healing concrete in practical engineering.