Mechanism and application of a coating-free microbial self-healing agent in cement-based composites

Over the past two decades, the use of Microbially induced carbonate precipitation (MICP) technology for self-healing concrete cracks has emerged as a feasible and environmentally friendly approach. In microbial self-healing concrete, microorganisms and nutrients are immobilized within suitable carriers to protect the microorganisms, thereby enabling concrete self-repair. The choice of carriers and preparation methods significantly influences the self-healing performance of concrete. Expanded perlite (EP), a porous carrier widely studied in microbial self-healing concrete, has shown great potential. Building on previous EP-based self-healing agent preparation methods, this study simplifies and improves the process by proposing an uncoated multi-species microbial self-healing agent to enhance healing efficacy. The results demonstrate that the coating-free EP self-healing agent exhibits excellent crack healing performance. When 1200 mL of healing agent was added to the basic mix ratio of the mortar sample, the healing rate for cracks measuring 1.4–1.6 mm reaches 70.9 %, with a maximum average water-tight crack width of 0.86 mm. The maximum healed crack width achieved is 1.772 mm. Additionally, the study reveals that the coating-free EP self-healing agent improves the compressive strength of mortar at lower dosages compared to traditional EP agents. By optimizing the preparation process, the cost of the coating-free EP self-healing agent is reduced, while the self-healing capability of concrete is significantly enhanced.