Synergistic mineralization and long-term viability of a multi-component microbial system for crack self-healing in cementitious materials

Microbial mineralization promotes the self-healing of concrete cracks, extending structural service life. However, harsh conditions within concrete hinder the long-term viability and self-healing potential of microorganisms. While Bacillus strains are commonly used to deposit calcium carbonate on crack surfaces, their aerobic nature presents challenges in complex environments. This study assesses the long-term survival and mineralization performance of four composite microbial systems designed according to mineralization-pathway complementarity, alkaline tolerance, oxygen-gradient adaptability, and long-term viability in cementitious environments. At pH 9 after 180 days, survival rates of composite systems increased by 2.75% to 33.15% compared with single bacteria, with mineral precipitation rising by 2.44% to 3.24%. The Bacillus subtilis and Pseudomonas aeruginosa combination exhibited superior crack self-healing, achieving a maximum healing width of 1.07 mm at 270 days, with over 80% healing for cracks up to 0.7 mm. These results underscore the potential of composite microbial systems for engineering applications.