Biomimetic robust self-healing of Bacillus Subtilis immobilized through sisal fiber for next-generation concrete infrastructure

Bio-healing is now believed as a promising technique for the repair of concrete cracks. However, the healing capability of bacterial mixes against repeated damage cycles is still questionable. This study aims to investigate the robustness of bio-healable concrete against two successive damage cycles using Bacillus Subtilis immobilized via sisal fiber. The formulated bio-concrete exhibited improved mechanical properties and attained a maximum of 13.96 % and 36.82 % enhancement in terms of compression strength and split tensile strength. Self-healing efficacy was assessed by quantifying the average crack healing width and the recovered strength in compression during the healing phase. Results revealed that sisal fiber efficiently preserves spores of the bacillus strain and enhances its bio-metabolic potential to precipitate calcite for sealing concrete cracks. The average crack of 0.48 mm width was successfully healed in the first damage cycle whereas the complete repair of a 0.28 mm wide crack on average was attained in the healing phase of the second damage cycle. The maximum recovered compressive strength was 82.65 % and 50.42 % in the two successive damage cycles through bio-healing. The crack-healing precipitate was identified as calcite crystals through forensic examination. Consequently, immobilizing Bacillus Subtilis with sisal fiber was proved as a viable approach for improving the mechanical properties of concrete and inducing robust self-healing in repeated damages.