Self-healing of concrete cracks by use of bacteria-containing low alkali cementitious material

Self-healing based on microbially-induced calcium carbonate precipitation has been proposed as a smart and environmentally friendly strategy for the repair of concrete cracks. It is advisable to incorporate bacteria-based healing agents in fresh state concrete during mixing. Although the selected bacteria are alkaliphilic spore-forming strains, they are still vulnerable to the harsh environment of concrete. In this paper, we developed a protective carrier for the bacteria by using calcium sulphoaluminate cement, which is a type of low alkali, fast hardening cementitious material. By regulating the composition of the carrier material and the content of healing agents, the compatibility of the carrier with both the healing agents and the concrete matrix was optimized. The carrier, which acted as a support for the bacteria, was effective in preserving the bacterial activity over a long period of time. After embedding this bacteria-based self-healing system in concrete, cracks up to 417 μm with a crack closure near 100% was achieved in 28 days. Compared with plain mortar, the regain ratios of the compressive strength and water tightness increased 130% and 50%, respectively. The research suggests the potential application of this novel microbial self-healing system in extending the life span of concrete.