Comparative Effectiveness of Bacillus Subtilis and Bacillus Pasteurii in Enhancing the Self-Healing Capacity of Concrete

Concrete cracking remains one of the most pressing challenges in construction industries, leading to water ingress, corrosion of steel reinforcement, and eventual structure degradation. This research study investigates the efficacy of microbial-induced calcium carbonate precipitation (MCIP) as a self-healing mechanism by incorporating Bacillus Subtilis and Bacillus Pasteurii into the concrete mixture at proportions of 3%, 4.5%, and 6% by weight of cement. A fixed mix ratio of 1:1:2 with a water-cement ratio of 0.45 was used throughout the study. Specimens were cast, cracked using a universal testing machine, and
subjected to healing in water. Testing included in this research compressive strength and split tensile strength before and after healing, along with Scanning Electron Microscopy(SEM) analysis to confirm calcium carbonate precipitation. Key findings reveal that Bacillus Pasteurii at 3% achieved the highest compressive strength of 5834 psi, a 55.9% increase over conventional concrete, while Bacillus Subtilis at 3% showed the highest tensile strength of 379 psi, a 12.84% increase. SEM confirmed successful formation of calcium carbonate. The
research study provides a comprehensive comparison, guiding optimal bacterial
concentration selection for targeted performance in self-healing concrete.