Repairing performance and bottleneck analysis of concrete with encapsulated oxygen-dependent microbial Agent: Simulation-Aided characterization

Microbial self-healing concrete has natural advantages because of its environmental harmlessness and compatibility. Appropriate nutrients, microbial composition, and carriers are critical for microbial repairing agents to maximize restoration effectiveness in the harsh environment of concrete. However, little attention has been paid to the evolution of the healing process and the underlying mechanisms of bottlenecks. In this study, the potential of calcium lactate as the main nutrient source for Bacillus alcalophilus (B. alcalophilus), an alkali-resistant spore-producing microorganism, has been demonstrated firstly. The repairing performances and bottlenecks of oxygen-dependent microbial agent were then explored. Considering the harsh environment of concrete, calcium sulphoaluminate (CSA) cement was introduced to form a protective shell through artificial aggregate technology. Simultaneously, to reduce the influence of un-hydrated cement particles and to stabilize the continuous supply of calcium ions, the matrix has a higher maturity through 60 days of hydration. The results show that the encapsulated microbial self-healing agent had good repairing effects on cracks introduced after 60 days of hydration. Moreover, the distribution of repairing products in cracks was observed by X-CT, and the microbial remediation ability based on aerobic decomposing organic compounds was verified by simulation. The bottlenecks, shallow restoration depth and uneven distribution of restoration products, are mainly caused by gas transport and microbial biochemical activity. Finally, increasing the oxygen content in the fracture zone is an effective means to promote carbonate production and fracture filling