Application of microbial precipitation in self-healing concrete: A review on the protection strategies for bacteria

• Varied protection strategies for self-healing concrete by MICP compared in detail. • Protection strategy selection concerning compatibility and effectiveness proposed. • Potential of protection strategies and prospects of MICP self-healing discussed. Exploration of microbially induced CaCO 3 precipitation (MICP) has led to the application of this phenomenon in the field of self-healing concrete in recent years. However, survival of bacteria is a concern due to the harsh environmental conditions in the concrete matrix. Protection of bacteria has been regarded as an effective way to maintain microbial activity. The improvement in self-healing performances encouraged different research groups to evaluate alternative protection strategies. The aim of this review is to provide an in-depth comparison of these different strategies, including immobilization, encapsulation, and some other novel approaches. Attention was paid especially to the guidelines for the selection of protection strategies which allows for the probability of crack hitting and the compatibility among protective carriers, healing agents, and concrete matrix. The self-healing effectiveness including crack closure efficiency and restoration of mechanical and durability performances were elaborated. Limitations of current studies, challenges in practical applications, and future investigation perspectives were shortly outlined.