Synergistic effect of composite bacteria on self-healing process of concrete crack

The calcium precipitation activity (CPA) of bacterial strains can vary in response to shifts in ambient conditions. When these conditions become unsuitable, the CPA of bacterial cells may decrease noticeably, potentially compromising the self-healing process. Nonetheless, the synergistic behavior of various bacterial strains can present additional crystallization sites for calcium precipitation and adapt to diverse ambient conditions, thus enhancing microbial-induced calcium precipitation (MICP). In this article, we delve into the interconnected mechanisms involving forty-one bacterial strains, assessing their initial spore concentration ratios and nutritional needs in relation to CPA. Based on CPA considerations, DSM6307 and B6, were selected and combined. Subsequent investigations were carried out to determine the efficacy of self-healing concrete exposed to co-cultured bacterial strains. The mineralization capacity of these combined strains was bolstered using starch and ammonium nitrate as carbon/nitrogen sources, with the ideal initial spore concentration ratio between B6 and DSM6307 established as 4:6. Through visual assessments confirmed that the synergistic effect of B6-DSM6307 can yield repair efficiencies nearing 100% for crack widths between 0.02 mm and 0.2 mm. Furthermore, water permeability and capillary absorption tests on the sample block demonstrated that the repair compound, derived from the composite spore dry powder B6-DSM6307, effectively seals cracks and binds securely. A microstructural evaluation using scanning electron microscope emphasized the prominent presence of calcite crystals, attributed to the metabolic actions of the introduced composite strains within the cracks. The findings presented in this research pave the way for subsequent studies focusing on the incorporation of co-culture bacterial strains into CPA-based engineering strategies.