Review on two crack-repair strategies for reinforced concrete: Microbially induced self-healing concrete (MISC) and enzyme-mediated self-healing concrete (EMSC)

Abstract

This review surveys the experimental frameworks used in two bio-based crack-repair strategies for reinforced concrete: microbially induced self-healing concrete (MISC) and enzyme-mediated self-healing concrete (EMSC). In MISC, ureolytic or denitrifying bacterial spores, typically Bacillus species, are encapsulated in carriers such as lightweight aggregates or hydrogel beads together with nutrient sources; upon crack formation, spore germination and metabolic activity precipitate calcium carbonate within fissures. Key investigations address bacterial viability in high-pH pore solutions, spore germination thresholds, nutrient transport kinetics, and the morphology and distribution of crack-filling precipitates. EMSC research focuses on the use of free or immobilized enzymes, principally urease and alkaline phosphatase, co-delivered with biodegradable substrates like urea or organic phosphates. Studies explore methods for enzyme immobilization, controlled substrate release, retention of enzymatic activity under alkaline conditions, and the spatial patterning of calcium carbonate deposition. Both approaches are evaluated through standardized corrosion assessments including chloride migration testing, electrochemical impedance spectroscopy on steel-reinforced specimens, and accelerated wet–dry cycling to simulate marine exposure as well as crack-width characterization by optical profilometry or micro-CT and mechanical recovery via flexural strength regain tests. By compiling these methodologies, this paper delineates the current investigative landscape for biologically driven corrosion mitigation in reinforced concrete