Dissolution Behavior of Ureolytic Biocementation: Physical Experiments and Reactive Transport Modeling

Abstract

Microbially induced calcite precipitation (MICP) is a promising bio-mediated cementation process that can improve the engineering properties of granular soils through the precipitation of calcium carbonate on soil particle surfaces and contacts. The process offers an environmentally conscious alternative to conventional soil improvement technologies which primarily rely on the use of portland cement and high mechanical energy. As the technology transitions towards field-scale application, an improved understanding of the chemical permanence of MICP will be critical towards identifying favorable applications, predicting long-term engineering behaviors, and evaluating life-cycle environmental impacts. In this study, a series of soil column and batch reaction experiments were performed in tandem with reactive transport numerical modeling to investigate the dissolution behavior of biocementation generated via microbial ureolysis. Five soil column experiments containing a poorly graded sand were treated identically to achieve average CaCO3 contents near 5% by mass and were then subjected to either 0, 5, 10, 20, or 50 identical acidic dissolution injections. A dissolution kinetic model was calibrated independently to batch experiments involving similar solutions and was incorporated into a reactive transport model to forward predict degradation expected during soil column experiments. Spatial and temporal changes in biocementation dissolution were assessed using geophysical and geochemical measurements and observations were compared to those obtained from reactive transport simulations. Results indicate that existing kinetic models can successfully capture the dissolution behavior of ureolytic biocementation; however, model parameters may require site-specific calibration using soil column experiments. Outcomes are expected to significantly improve our understanding of the dissolution kinetics of biocementation, its effects on soil mechanical properties, and provide approaches through which the chemical resilience of MICP soil improvement can be evaluated.