Immobilizing bacteria in pre-enhanced recycled coarse and fine aggregates for improving the self-healing efficiency of cracks in concrete

A reasonable immobilizing method can effectively increase the self-healing efficiency of bacteria-based concrete. Recycled coarse aggregates (RCAs) are highly compatible with the concrete matrix, which is a type of bacterial carrier. However, direct immobilization of bacteria into RCAs may compromise the mechanical properties of concrete. Moreover, individually immobilizing bacteria into RCAs may limit self-healing because of their large particle sizes. In this study, a method for immobilizing bacteria into both preenhanced recycled coarse and fine aggregates (RAs) was proposed to increase the healing efficiency of concrete cracks. The effectiveness of this method in increasing the crack-healing efficiency was evaluated via comparison with that of concrete individually incorporating preenhanced RCAs. Additionally, the crack-healing efficiency of the concrete with fibers was evaluated to investigate the further improvement effect of the fibers. After 14 days of healing, the average crack healing width was 0.38 mm and the percentage of complete crack healing was 68 %, which were 35.7 % and 123.7 % greater, respectively, for the samples with both preenhanced recycled coarse and fine aggregates than for the samples individually incorporating preenhanced RCAs. Moreover, the fiber incorporation can increase the healing efficiency of cracks with larger widths and mitigate the reduced self-healing efficiency caused by preenhanced RAs. Microscopic analysis revealed that the incorporation of fibers could facilitate the formation of precipitates to fill the crack zones and potentially alter the crystal morphology. These results provide a scientific basis for potential applications of RAs in bacteria-based self-healing concrete.