Microbially Induced Calcium Carbonate Precipitation in Microcracks Coupled Biochemical, Transport, and Fracture-Mechanical Analysis

Microbially induced calcium carbonate precipitation (MICP) is a bio-mediatedmineralization process with potential to seal microcracks and reduce fluid transport incementitious materials. Its effectiveness depends not on bacterial activity alone, buton the coupled evolution of bacterial viability, substrate and calcium-ion transport,aqueous speciation, mineral nucleation, crack geometry, and mechanical restraint.This paper develops a theoretical framework for analyzing precipitation withina water-accessible crack. Ureolysis is represented by enzyme-mediated kinetics;carbonate speciation and calcite saturation are described through aqueous equilibriaand an ion-activity product; and crack-scale transport is coupled to precipitationdriven changes in aperture and hydraulic conductance. A fracture-mechanicalformulation is included to distinguish geometric sealing from actual restoration ofload-bearing capacity. The framework identifies principal design trade-offs: rapidprecipitation can obstruct transport before reactants penetrate the crack, whereasslower, spatially distributed precipitation may improve sealing uniformity. It alsohighlights limitations that require experimental calibration, including bacterialsurvival in highly alkaline cementitious environments, variable crack roughness,nonuniform biofilm distribution, and competition between mineral phases. Theproposed equations constitute a modeling framework rather than a calibratedpredictive model; quantitative application requires material-specific measurementsand validation.