Mechanical and Self-Healing Performance of Cement Composites Containing Bacteria Extracted from Waste Concrete

Cracks can reduce the durability of concrete structures. To mitigate the damage caused, self-healing technologies using bacteria and cement-based materials can be utilized. For self-healing, bacteria contained within the matrix are advantageous because they can heal cracks upon introducing oxygen and water under favorable conditions. To our knowledge, this is the first study showing that <i>Lysinibacillus fusiformis</i> isolated from waste concrete induces calcite precipitation in a cement-based material. Replacing 5-20% of the mixing water with the bacterial solution increased mortar flow, and the initial compressive strength increased with the bacterial content. After long-term aging, the compressive strength of the sample with 20% bacterial solution was ~45.6 MPa, the highest among all samples. In terms of durability, the bacterial solution reduced the carbonation depth compared with that of a control sample without added bacteria, and the 20% sample showed 53% higher carbonation resistance than the control. In terms of the self-healing performance, the bacteria-loaded samples showed higher compressive strength recovery rates than the control sample, with the 20% sample showing the highest rate of approximately 131%. Therefore, <i>L. fusiformis</i> derived from waste concrete is a promising candidate bacterium for enhancing the durability and self-healing efficiency of cement composites.