Investigation of additive-assisted microbial-induced calcium carbonate precipitation in 3D printed cross fractures

Abstract

Microbially induced carbonate precipitation (MICP) with additives is a promising approach for seepage control in the field of geotechnical engineering. This study designed and fabricated four cross-fracture models using three-dimensional printing. One of the models did not include additives and was treated with a mixed injection strategy. The other three models were prepared using different types of additives such as calcium carbonate, jute fiber, and gravel particles, which were treated with a staged injection strategy to improve our understanding of the optimized MICP process. The increased mass of calcium carbonate in the model was determined by the difference in the model’s weight before and after four-cycle intervals to evaluate the effect of the three additives and two injection strategies on seepage control and precipitation patterns. The results indicated that the masses of the precipitates increased the most for the model without additive owing to gravity during the MICP process; however, the clogging effect was weakest during the seepage experiment. This may be because the smooth inner surfaces of the model and a higher flow rate prevented the floc and cementation solution from settling. The models that included plant fibers and gravel particles provided more surfaces that facilitated calcium carbonate precipitation and contributed to seepage control. The model with calcium carbonate produced a considerable amount of calcium carbonate and interacted positively with the fracture surfaces, leading to the largest decrease in seepage. In the case of calcium-carbonate additives, a layer of precipitates was formed, which increased the inner surface roughness and enhanced the boundary-layer effect. This promoted the precipitation and settling of floc and the formation of more reliable bridges within the cross-fracture model compared with those of other additives.