Sorption release efficiency and repair effect of carriers for microbial self-healing concrete

The type of carrier and its adsorption and release characteristics of microorganisms significantly influence the self-healing efficiency of concrete cracks. In this study, the water absorption rate, cylinder compressive strength and microbial adsorption release properties of six common carriers (volcanic rock, expanded perlite, ceramsite, ceramic sand, recycled bricks and recycled concrete) were systematically investigated to identify the optimal carrier for microbial self-healing concrete. The results indicated that, under negative pressure conditions, the water absorption of all six carriers reached saturation within 15 min. After immobilising single, binary and ternary microbial cultures, the release rates from ceramic sand were 5.5%, 8.4% and 14.8%, respectively, demonstrating that the microbial release performance followed the order ternary > binary > single. When ceramic sand was loaded with the same concentration of bacterial suspension (single, binary and ternary microorganisms) and brought to a saturated surface-dry state, the microbial release rates reached 12.0%, 36.0% and 60.0%, respectively. These values represent a significant increase over the release rates observed under constant-weight conditions (5.5%, 8.4% and 14.8%). Furthermore, visible cracks in concrete specimens incorporating the bacteria-loaded ceramic sand were effectively filled with calcium carbonate precipitation.