Optimizing the self-healing of concrete cracks under actual service oxygen conditions via mineralization of facultatively aerobic microbial consortia

Microbially induced carbonate precipitation (MICP) offers a promising solution to reduce the maintenance costs of concrete structures by enabling self-healing of cracks. However, the availability of oxygen in the actual service environment may markedly impair the microbial mineralization efficiency, especially for aerobic bacteria. Moreover, axenic cultures exhibit lower adaptability to variable environments and higher costs in the isolation and cultivation process than nonaxenic cultures do. Facultatively aerobic microbial consortia (i.e., facultative nonaxenic cultures), which exhibit stable mineralization under both aerobic and anoxic conditions, were proposed in this study to improve the crack-healing capacity in an actual service environment. The self-healing ability of concrete cracks under ambient oxygen was tested via comparisons with axenic cultures such as urease-producing bacteria and denitrifying bacteria. Furthermore, the cooperative effects of fibers and the immobilization of preenhanced recycled concrete aggregates (RCAs) were evaluated to further optimize the self-healing capacity and mechanical properties of the concrete. The test results revealed that the facultative nonaxenic cultures exhibited stable and efficient healing performance, achieving a crack surface area healing percentage of 76.7 % and an average healing depth of 33.08 mm after 56 days of healing. The incorporation of fibers further enhanced surface area and depth healing by 12.3 % and 13.4 %, respectively. Moreover, preenhanced RCAs as carriers improved the interfacial transition zones (ITZs) of the concrete, contributing to an increase in compressive strength of up to 12.7 %. The stable mineralization and high oxygen adaptability of facultative nonaxenic cultures enabled reliable crack healing under actual service oxygen conditions.