Microbially induced calcite precipitation (MICP): mechanisms, engineering applications, and pathway to field-scale...

Over the last twenty years, there has been a great amount of multidisciplinary interest in Microbially Induced Calcite Precipitation (MICP) as a truly sustainable solution to ground treatment using Portland cement. The process utilizes the urease activity of ureolytic bacteria, most commonly Sporosarcina pasteurii to convert soluble urea and calcium to solid calcite in the pore space of granular media, providing cementation, impermeability reduction and contaminant sequestration without excavation or heat. This review compiles over sixty publications covering all aspects of MICP research, ranging from the enzymological chemistry of urease to the documented field trials of over 100 m³ of treated volume, to the thermodynamics of calcium carbonate polymorphism. Unconfined compressive strengths of over 10 MPa have been reached in laboratory columns and wind erosion reduction of 95% has been observed in field tests, while the efficiency of heavy metal removal can reach up to 99% for lead in aqueous laboratory systems, though removal efficiencies in soil matrices are typically lower and highly dependent on metal concentration, soil type, and treatment conditions. The self healing concrete application is the most advanced toward commercial maturity, and there are products available from Basilisk, Evonik and BioMason. Ground improvement, liquefaction mitigation, and coastal erosion control are other geotechnical applications at Technology Readiness Levels 5 to 7, with the challenges of uniformity of treatment in heterogeneous soils, management of the by-product of ammonium, bacterial transport at depth, and competitiveness with conventional grouting. New developments such as non-ureolytic microbial pathways, fiber and biochar reinforced hybrid biocementation, 3D bio-printing of living mineral structures, and process optimization via machine learning with R² > 0,95, are also being explored. The review closes with a candid critique of the gaps in the research, especially long-term durability information, scale-specific cost analyses, and standardized monitoring protocols, which will decide whether or not MICP becomes a successful laboratory-based concept that moves into a common engineering tool.