Enhancing fiber–matrix interface permeability resistance of natural fiber-reinforced, bio-cemented sand by CaCO3 seed pretreatment

This study explores the application of roughness pretreatment on plant-based natural fiber surfaces to enhance the sealing effectiveness of the sand-fiber interfacial. The technique roughens the reinforced material by presetting CaCO3 seeds on the fiber surface, thereby immobilizing more bacteria as nucleation sites, further increasing the interfacial bonding area by promoting bio-mineralization and achieving efficient sealing of preferential flow channels. Experimental investigation was conducted to compare the promoting effects on bio-mineralization of reinforced sand with three pretreated fibers. Results showed that the fibers pretreated with CaCO3 could fill the pores to bridge sand particles more effectively by aggregating bio-mineralized precipitates around them. The bacterial immobilization rate and calcium carbonate content of bio-cemented sands with fiber pretreatment remarkably increased with increasing fiber surface roughness characterized by fractal dimension (Fd) when compared to the samples without pretreatment, and the maximum increase was 35.66% (coir, Fd=1.390) and 152.3% (jute, Fd=1.330). The profile water-conducting rate and average hydraulic conductivity have been reduced by 46% and 86%, Among the three fibers, ramie has the lowest hydraulic conductivity of 5.396 × 10−8m/s, which is lower than that of jute and coir (1.041 × 10−7m/s and 3.885 × 10−7m/s). Furthermore, the promotion of bacteria on bio-mineralization and more even distribution (upper, middle, and lower parts are 36%, 34%, and 30%, respectively) of CaCO3 were confirmed through bacteria staining testing and dye tracer testing. Finally, the effects of average flow velocity and shear rate on bacterial immobilization and sealing of preferential flow channels are discussed.