Effects and mechanisms of mineral composition of sand on MICP process

The microbially induced calcium carbonate precipitation (MICP) is a new environmentally friendly stabilization technique for soils with broad application prospects. To investigate the effect of mineral composition of sand particles on the MICP process, the quartz sand and calcareous sand are chosen as the representative materials. The sand particles are bound with epoxy resin to create samples, which are subsequently subjected to the MICP treatment by immersing them in prepared bacterial and cementation solutions. The calcium carbonate production, mineral phases, crystal morphology and interfacial cementation characteristics are quantitatively analyzed using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultrasonic tests. The results indicate: (1) The calcareous sand particles are more conducive to the MICP, with an average calcium carbonate generation per unit area that is about 5 times that of the quartz sand particles. (2) The calcium carbonate precipitated on the surfaces of both sand particles mainly consists of vaterite and calcite, with the calcareous sand inducing a higher proportion of calcite precipitation because of its lower interfacial energy. (3) The calcium carbonate precipitated on the surface of the quartz sand is predominantly composed of larger spherical particles, while the morphology of calcium carbonate on the surface of the calcareous sand is predominantly plate-like. (4) The microbially induced calcium carbonate on the calcareous sand particles exhibits higher interfacial cementation strength. After subjecting the samples to ultrasonic agitation, the mass loss rate of the calcium carbonate on the quartz sand is about 10 times that on the calcareous sand. Based on these findings, the theories from the disciplines such as microbiology, crystal chemistry and mineralogy are employed to systematically analyze the mechanisms through which quartz sand and calcareous sand affect the MICP process and its outcomes. This study provides new insights and is of significant importance for optimizing the application of the MICP in geotechnical engineering.