Research Progress on Sodium Alginate-Assisted Microbially Induced Carbonate Precipitation for Concrete Crack Repair

Abstract

Microbially induced carbonate precipitation (MICP) can seal concrete cracks through the formation of calcium carbonate by ureolytic microorganisms. Conventional immersion and low-viscosity grouting, however, are limited by bacterial washout, inefficient calcium utilization and erosion of mineral deposits under hydraulic flow. Sodium alginate (SA) improves MICP repair through viscosity enhancement, cell immobilization, Ca2+ adsorption and in situ formation of calcium alginate gels. This review summarizes the reaction mechanism, material systems, construction routes, concentration effects, crack-scale effects, hydraulic-head effects and durability of SA-assisted MICP for concrete crack repair. Surface coating, single-shot grouting, composite biogrout and externally crosslinked hydrogel layers are compared. Reported evidence indicates that approximately 1.5% SA with an SA-solution/bacterial-suspension ratio near 7:3 is favorable for surface coating, whereas approximately 0.67% (w/v) SA balances sedimentation resistance and injectability for 0.2–0.5 mm cracks. Composite slurries containing bacteria, preformed CaCO3 particles and SA provide enhanced permeability reduction and erosion resistance under hydraulic heads. The optimum SA content depends on crack aperture, solids content, injection equipment and hydraulic pressure. Future research should clarify the coupled SA–cell–CaCO3 mechanism, long-term interfacial stability and field applicability in complex crack networks.