Insights into the effects of microbial consortia-enhanced recycled concrete aggregates on crack self-healing in concrete

Immobilization is used to protect incorporated bacteria to maintain its high efficiency on the microbially induced carbonate precipitation (MICP) capacity in self-healing concrete over a period of time. However, several unfa-vorable characteristics of current bacterial carriers, such as poor compatibility with the cementitious matrix, relatively high cost, and potential decrease in mechanical properties of concrete, may limit their potential implementation in reinforced concrete (RC) construction. The objective of this study was to demonstrate the feasibility of microbial consortia-enhanced recycled concrete aggregates (RCAs), immobilizing bacteria to form self-healing cracks. The effectiveness of two other immobilization techniques (RCAs and ceramsite particle -immobilized bacteria) on the self-healing efficiency of concrete was also investigated. Experimental results showed that the physical and mechanical properties of RCAs could be markedly enhanced with extension of the biodeposition enhancement time. Concrete specimens incorporated with enhanced RCA-immobilized mixed cultures exhibited a 0.47-mm-wide crack that healed after 56 days of curing, which was equal to the 0.48-mm -wide crack that healed for specimens with ceramsite particle-immobilized mixed cultures. Mineral precipitations at the crack surfaces of self-healing concrete were calcite crystals and had regular cubic shapes. Results from this study provide a promising potential of mixed culture-enhanced RCAs for a wide range of engineering applications.