Biomineralization Process of CaCO Precipitation Induced by Bacillus mucilaginous and Its Potential Application in Microbial Self-healing Concrete.

Microbial induced calcium carbonate precipitation (MICP) is widely common in nature, which belongs to biomineralization and has been explored carefully in recent decades. The paper studied the effect of temperature, initial pH value and Ca concentration on bacterial growth and carbonic anhydrase activity, and then revealed the biomineralization process through the changes of Ca concentration and calcification rate in alkali environment. Meanwhile, microbial healing agent containing spores and calcium nitrate was prepared and used for the early age concrete cracks repair. The self-healing efficiency was assessed by crack closure rate and water permeability repair rate. The experimental results showed that when the optimal temperature was 30 °C, the pH was 8.0-11.0, and the optimal Ca concentration was 0-90 mM, the bacteria could grow better and the carbonic anhydrase activity was higher. Compared with reference, the crack closure rate with the crack width up to 0.339 mm could reach 95.62% and the water permeability repair rate was 87.54% after 28 d healing time of dry-wet cycles. XRD analysis showed that the precipitates at the crack mouth were calcite CaCO. Meanwhile, the self-healing mechanism of mortar cracks was discussed in detail. In particular, there is no other pollution in the whole mineralization process, and the self-healing system is environmentally friendly, which provides a novel idea and method for the application of microbial self-healing concrete.