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.