Optimization of Enzyme-Induced Calcium Carbonate Precipitation (EICP) to Improve the Mechanical Performance of Repaired Concrete

Hydraulic concrete structures are prone to surface cracking due to sustained loads, fluctuating water levels, and environmental factors, which weaken the bearing capacity of concrete. This study investigates the repair of concrete cracks using enzyme-induced calcium carbonate precipitation (EICP) and either chitosan (CS) or sodium alginate (SA). Enzyme activity, mineralization reaction, ultrasonic, compressive strength, splitting tensile strength, XRD, FTIR, and SEM tests were conducted to assess the repaired performance of concrete. A Laplace model was developed for predicting splitting tensile strength, ultrasonic transit time and compressive strength. It was found that the optimal enzyme activity was achieved at enzyme concentration of 110 g/L, urea concentration of 0.3 mol/L, pH of 8, and a standing time of 0-10 minutes. The optimal EICP mineralization conditions were reached at enzyme concentration of 110 g/L, cementation solution concentration of 0.3 mol/L, pH of 8, skim milk powder content of 1.2%, and enzyme-cementation ratio of 1:0.75. EICP treatment significantly reduced ultrasonic transit time, and markedly enhanced the compressive and splitting tensile strengths. The optimal additive contents for CS and SA were identified as 0.2% and 0.6%, respectively. These findings offer a technical support for the effective repair of cracks in hydraulic concrete.