Microbial-inspired self-healing of concrete cracks by sodium silicate-coated recycled concrete aggregates served as bacterial carrier

Microbially induced carbonate precipitation (MICP) is a promising technique for the autonomous healing of concrete cracks. In this study, the effect of pH on MICP was investigated. The results indicate that the MICP process was inhibited when the pH was higher than 11. Both vaterite and calcite were produced when the pH was < 8, whereas only calcite was produced when the pH was > 8. Recycled concrete aggregates (RCA) coated with sodium silicate have been proposed as protective carriers for microbial healing agents. Although the presence of the coated RCA resulted in a loss of the splitting tension strength of the concrete, the loaded healing agents were highly efficient in self-healing cracks. Concrete incorporated with 20% RCA loaded with healing agents exhibited the best self-healing performance. When the initial crack widths were between 0.3 and 0.4 mm, the 7-d mean healing rate was approximately 90%. At 28 d, the crack area filling ratio was 86.4%, while its water tightness recovery ratio was 74.4% and 29.8%, respectively, for rapid and slow absorption. This study suggests that RCA coated with sodium silicate is an effective method for packaging microbial healing agents and has great potential for developing cost-effective self-healing concrete.