Biomineralization Analysis and Hydration Acceleration Effect in Self-healing Concrete using Bacillus subtilis natto

Since concrete with bacteria incorporated in the matrix shows promising results in initial studies, more research has focused on using bacteria for the strength and durability enhancement of concrete. Bacterial concentrations varying from different positions on the crack surface were recorded and evaluated in conjunction with the amount of self-healing product formed. The change in bacteria concentration with the survival time in concrete was investigated and lasted for two years. The degree of mineralization of calcium carbonate from the microbial activity is also closely related to the level of survival and reduction of bacterial concentrations in concrete compared to the initial amount. These processes were tracked and analyzed through phase composition analysis and microstructure analysis. The role of nucleation sites of bacteria for accelerating mineral deposition was also investigated. The change in the content of hydrated cementitious minerals can be seen in groups of samples with different bacteria regarding cracking age (7-90 days). The increase in C-S-H content in the bacterial samples at early cracking age was significant compared with the control group. The effect on healed crack parameters through microscopic observation contributed to supporting and demonstrating the hypothesis of the combination of the formation of the calcium carbonate crystals around the bacterial cell as crystallization nuclei and the promotion of hydration for C-S-H formation.