Bacteria based self-healing of later-age cracks in concrete

Monitoring and rehabilitation of cracks in concrete structures can be rather expensive, labour intensive and often presents technical difficulties. Nonetheless, it is vital for prolonging their lifespan. As an alternative to traditional repair techniques self-healing in cementitious materials has been proven a promising technology for crack remediation. The use of bacteria in self-healing relies on their ability to metabolically facilitate the precipitation of calcite, which can act as a crack sealant. Since cracking is likely to occur throughout the life of concrete it is important to investigate the long-term effectiveness of the method. In this study bacterial spores of the species B. cohnii were added in cement mortar mix, along with nutrients for the bacteria. Reference samples of plain mortar and control samples containing only nutrients were also prepared for comparison. Two sets of samples were prepared: one with samples that were cracked after 28 days of curing and one with samples cracked after 9 months. A single crack of 0.4–0.5 mm crack width was introduced to all samples. After cracking, samples were left to heal semi-submerged in water. Healing was examined at two temperatures, at 7.5 and 20 °C, for both sets of samples. Optical microscopy and water-flow tests were used for evaluating the healing. Results showed that substantial healing can be achieved in 9 months old samples containing bacteria, both at 7.5 and 20 °C, comparable to that of 28 days old samples. The long-term competence of bacteria-based self-healing technology for crack remediation in concrete is, therefore, demonstrated.