A Critical Review of Ureolytic and Non-Ureolytic Bacterial Efficacy in Self-Healing Concrete

Concrete's inherent susceptibility to cracking compromises structural longevity and drives carbon-intensive repair practices. Microbial self-healing concrete offers a sustainable alternative by exploiting bacterial biomineralization to autonomously restore structural integrity. This critical review synthesizes the current understanding of two principal microbial strategies: the rapid, urease-driven ureolytic pathway of Sporosarcina pasteurii and the slower, biofilm-mediated non-ureolytic pathway of Bacillus subtilis. The underlying biochemical mechanisms—ureolysis-based Microbially Induced Calcite Precipitation (MICP), carbonic anhydrase catalysis, and Extracellular Polymeric Substance (EPS) formation—are compared to elucidate their respective roles in crack sealing. Incorporation strategies, including direct mixing and encapsulation, are evaluated for their trade-offs between process simplicity, bacterial viability, and long-term performance. A quantitative synthesis of the literature reveals that both approaches can enhance compressive strength by up to 100%, heal cracks up to 1.7 mm wide, and reduce permeability by over 70%. However, the ureolytic pathway's rapid healing advantage is offset by ammonia-induced corrosion risks, whereas non-ureolytic systems ensure safer, longer-term resilience at slower rates. Persistent challenges include the absence of standardized evaluation protocols, limited long-term field data, and high production costs. Addressing these gaps through unified testing standards, scalable encapsulation methods, and integration with low-carbon binders remains pivotal for translating microbial self-healing concrete from laboratory innovation to reliable infrastructure technology.