Crack Healing and Structural Recovery of Concrete Using Cytobacillus horneckiae-Induced Carbonate Precipitation

Concrete cracking poses a major durability challenge, accelerating reinforcement corrosion and reducing service life. Conventional repair methods such as epoxy injection and cementitious grouting are costly, unsustainable, and often ineffective for microcracks. This study evaluates the potential of Cytobacillus horneckiae, a resilient ureolytic bacterium, to promote microbially induced calcium carbonate precipitation (MICP) for sustainable crack remediation. Laboratory experiments assessed carbonate precipitation efficiency under varying conditions of pH, urea concentration, and temperature, alongside controlled crack-healing trials using a combined injection–diffusion method (CIDM). Results showed optimal CaCO₃ formation at pH 9, 0.75 M urea, and 35 °C, conditions consistent with concrete pore environments. Image analysis revealed a 90% reduction in surface crack area within 12 days, demonstrating accelerated healing compared with conventional injection methods. Mechanical testing indicated 75% recovery of tensile strength and ultimate load capacity, confirming partial restoration of structural integrity. FTIR spectra identified carbonate functional groups and calcite polymorphs, while SEM–EDX analyses confirmed the presence of Ca and O as dominant elements, validating biogenic CaCO₃ deposition within crack voids. Silicon traces reflected interactions with the concrete matrix, while negligible carbon detection was attributed to EDX limitations for light elements. Collectively, the findings highlight the effectiveness of C. horneckiae-mediated MICP in sealing cracks and restoring mechanical performance, offering an environmentally friendly alternative to chemical repair agents. However, incomplete depth sealing suggests that further optimization of bacterial delivery strategies is required to achieve long-term durability. This work expands the scope of MICP research beyond the conventional Sporosarcina pasteurii, providing new insights into the application of native bacterial strains for sustainable concrete self-healing technologies.