A new bacteria-based self-healing system triggered by sulfate ion for cementitious material

Concrete in complex environments is prone to cracking due to its own brittle and porous characteristics. When environmental sulfate ions intrude into concrete, the formation of gypsum and ettringite can lead to unrestricted expansion and subsequent cracking of the concrete, so a selfhealing system that responds to environmental ions is necessary. In this study, barium-doped calcium alginate gels that could be triggered by sulfate ions were used to encapsulate microbial-based repairing agents. Experimental results showed that Bacillus spores of up to 40% mass were encapsulated in a modified alginate hydrogel, which had good compatibility with bacteria and concrete. Meanwhile, the sensitivity of microcapsules to sulfate at different concentrations was also verified. The new self-healing system introduces two response modes, namely sulfate triggering and mechanical stimulation, to address concrete cracks at various ages. Even for cracks that emerge 60 days later, the crack healing ratio can still reach 80%. Additionally, the new system can provide organic-inorganic composite repairing products to maintain the stability of the repaired structures at the crack site. The repair system demonstrates good uniformity and compatibility, and the negative impact on mechanical performance can be alleviated by reducing particle size. To conclude, the new self-healing system has great potential for concrete applications in saline or marine environments.