Performance of Bacteria-Based Non-encapsulated Self-healing Concrete

This study focuses on the mechanical performance of non-encapsulated self-healing concrete using bacteria by direct application. The influence of Bacillus subtilus bacteria on crack healing, compressive strength regains, sorptivity, water absorption, impact strength, and concrete microstructures was examined in this study. M30 grade concrete with a water-cement ratio of 0.45 was used for control specimens. For bacteria incorporated specimens, water content was fully replaced with three different percentage of healing agent. The healing agent comprises of 10, 20, 30% bacterial solution (BS) and 90, 80, 70% nutrient solution (NS) was directly mixed with concrete mixtures with bacillus subtilis bacterial concentration of 10⁵ cells/ml and the mixtures were designated as BC 1, BC 2, and BC 3. The concrete specimens were subsequently cured by two methods; wet-dry cycle and full-wet and the results were compared with the control. The cast specimens were immersed in water for 24 h, then held at room temperature for another 24 h in the wet-dry cycle, which was repeated for 28 days. Specimens were immersed in water for 28 days during full-wet curing. However, the curing water was changed every 24 h to ensure that the bacteria had enough oxygen to precipitate calcium carbonate. Results show that the addition of bacteria enhances the mechanical properties compared with control concrete. SEM and XRD results show the micro-structural morphology and the calcium carbonate precipitation.