Study of crack healing in Portland cement-based mixtures via enzyme-induced carbonate precipitation (EICP)

Enzyme-induced carbonate precipitation (EICP) is a method that directly utilizes enzymes to induce the formation of calcium carbonates, offering a promising alternative to microbially induced carbonate precipitation (MICP). By eliminating the need for bacteria, EICP simplifies the material preparation process, reduces costs, and avoids potential environmental concerns associated with microbial use. Accordingly, this study evaluated the feasibility of EICP-enabled crack healing in Portland cement (PC)-based mixtures. The study revealed that urease was highly sensitive to alkalinity, and urease was promptly inactivated within one day when pH reached 12. These findings suggest that the direct incorporation of urease into PC-based mixtures presents significant challenges. Accordingly, this study investigated two application methods for urease-based crack repair, which are soaking and injection. The results showed that soaking in healing medium containing urease, urea and CaCl₂ was most effective. Further analysis of the medium composition revealed that the optimal formulation was 12 U/mL urease combined with a 0.75 M urea-CaCl₂ solution. This formulation was able to fully heal cracks up to 2 cm after 15 days soaking. Overall, this study has identified the challenges of applying EICP in PC-based mixtures and proposed an efficient formulation and application method for crack healing.