Enhancing self-healing in bio-mineralized concrete with steel slag aggregates and Bacillus subtilis

This study investigates the impact of incorporating steel slag aggregates (SSAs) into bio-mineralized concrete to enhance its SH properties. Bacillus subtilis vegetative cells are integrated to improve the concrete's healing efficacy. The effects of microbes were evaluated through damage healing measurements and the restoration of compressive strength (COS) over different durations. Characterization techniques, including x-ray fluorescence, x-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and field-emission scanning electron microscopy (FE-SEM), were used to analyze the SH process in concrete using carbonated SSA as carrier media. The results demonstrated that SSA serves as an effective carrier for microbial proliferation, significantly improving damage-healing performance. The immobilization of microbes (107 cells/mL) via SSA showed the highest fracture healing efficiency of 1.023 mm. The inclusion of microbes (107 cells/mL) in SSA aggregate concrete resulted in notable COS restoration after pre-damage by 32.29%, 31.53%, and 18.97% at 3, 7, and 28 days, respectively. FE-SEM, XRD, and EDS spot analysis identified calcite as SH precipitates, crucial for enhancing self-healed concrete performance. The cost of microbial concrete is 115.25% higher than traditional concrete due to the additional expense of calcium lactate and microbial culture, but its SH properties can prevent early damage, extend the life of structures, reduce repair costs, and mitigate carbon emissions.