Synergistic effects of microencapsulated bacterial spores and superabsorbent polymer on self-healing performance in mortar

This study explores the feasibility of utilizing a superabsorbent polymer (SAP) to improve the self-healing performance of microbial-induced calcium carbonate precipitation (MICP) in cement-based materials. The amount of microencapsulated bacterial spores was varied from 0.25-1 % by cement weight. The SAP content was set to either 0 or 4 % by cement weight. As additives, the impact of SAP and MICP bacteria on mortar properties, including flowability and compressive strength, was assessed. The self-healing performance was evaluated based on crack-healing percentage and water permeability recovery. Microstructural analyses, including thermogravimetry/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), were performed to investigate the microstructural and chemical changes during the healing process. The findings revealed that specimens exclusively mixed with 4 % SAP exhibited a slightly lower crack-closure efficiency compared to those mixed exclusively with 1 % MICP bacteria. However, the SAP-containing specimens exhibited a higher degree of permeability recovery. Meanwhile, in the binary additive system with 0.5 % MICP bacteria and 4 % SAP, the specimens exhibited the highest crack-closure percentage of 91 % and a final water discharge rate of 15 mL/min after 45 days of healing. In contrast, specimens mixed exclusively with 1 % MICP bacteria showed a crack-closure percentage of 76 % and a final water discharge rate of 59 mL/min. These results suggest that incorporating SAP into the MICP system enables a reduction in MICP bacterial content without compromising self-healing performance.