Modulating Ureolytic Reaction in Microbially Induced Calcite Precipitation using Acetic-Acetate Buffer for Enhanced Spatial Homogeneity

Microbially Induced Calcite Precipitation (MICP) is emerging as a sustainable ground improvement technique. Its rapid ureolysis reaction kinetics cause calcium carbonate to clog the injection region, as well as spatial inhomogeneity in biocementation. Acid-based treatments were used in the past to control the reaction kinetics and potentially improve cementation distribution. However, inducing extremely low pH conditions inhibit urease activity and impede the reaction, thereby limiting its application. In contrast, buffer solutions allow variable lag time modulation by controlling buffer capacity while maintaining a constant pH, enabling regulation of precipitation onset and providing control over ureolytic activity, which previously has not been explored systematically. This study introduces a novel approach that uses an acetic-acetate buffer at pH 4, with two distinct buffer capacities, to modulate the lag time prior to the onset of biocementation. The synergetic effects of buffer capacity ( β) , biomass (B 0 ) , and cementation reagent concentrations ( C 0 ) on urea hydrolysis kinetics and the lag time were evaluated. Unconfined compressive strength (UCS) test and mercury intrusion porosimetry (MIP) were employed to investigate the influence of buffer on strength and homogeneity in terms of pore structure evolution upon biocementation. Study demonstrates that elevated buffer capacity effectively delays the MICP reaction and provides control over urease activity, enabling far-field reagent transport and promoting uniform cementation. The proposed buffer treatment promotes existing crystal growth over new nucleation, thereby increasing the relative size of the precipitated crystals and enabling control over the mineralogy of the precipitated crystals. The observed superior mechanical properties (UCS up to 3.62 MPa) are attributed to the homogeneous cementation, which altered the pore structure of the treated soil uniformly, stemming from the modulated ureolytic reaction. Overall, the research presents a first-of-its-kind, buffer-based strategy to regulate biochemical kinetics, promoting spatial uniformity and expanding the applicability of MICP for subsurface stabilization.