Self-healing of Concrete Cracks by Immobilizing Microorganisms in Recycled Aggregate

Self-healing technology based on microbial induced carbonate precipitation can achieve cracks-healing of concrete. As concrete cracks appear, dormant bacterial spores introduced into concrete are activated, and calcium lactate is used as substrate to form calcium carbonate for healing crack. Due to the harsh environment in concrete, bacterial spores directly introduced become inactivated. Therefore, the introduction of good protective carrier is critical, and the mechanical properties and economy of the carriers are also the keys to improving self-healing technology. In this study, recycled aggregate was used as a protective carrier for Bacillus pasteurii to enhance the self-healing capacity. The effects of this technique were investigated by comparing with three other incorporation techniques, i.e., direct introduction of bacteria, diatomaceous earth-immobilized bacteria, and expanded perlite-immobilized bacteria. The healed crack width value of specimens incorporated with recycled aggregate-immobilized bacteria was close to that of specimens incorporated with expanded perlite-immobilized bacteria (the healed widths were 0.28 mm and 0.32 mm, respectively), which was larger than that of specimens incorporated with diatomaceous earth-immobilized bacteria (the healed width was 0.14 mm) and specimens directly introduced bacteria. Scanning electron microscope and electronic data switching analysis confirmed that precipitation formed at cracks was calcium carbonate.