Strengthening effect of nano-SiO2 on microbial induced carbonate precipitation (MICP) solidified sediment: Macro- and micro-analysis

Sediment consolidation via microbial induced carbonate precipitation (MICP) aligns with the principles of sustainable development in resource utilization. This study aimed to explore the solidification potential and mechanisms of integrating nano-SiO2 as a supplementary material in MICP-treated sediment under various conditions, employing permeability, unconfined compression strength (UCS), X-ray diffraction (XRD), scanning electron microscopic (SEM), and adsorption techniques. The results demonstrated a reduction in permeability and an increase in UCS in sediment treated with ≤0.1% nano-SiO2-assisted MICP. The factors contributing to solidification potential followed a specific order: Ca2+ concentration > OD600 > nano-SiO2 dosage > biochemical reaction time. When combined with MICP, nano-SiO2 at concentrations below 0.05% promoted the transformation from aragonite to calcite. Furthermore, nano-SiO2 triggered the creation of early-stage C-S-H gels, aged viscous-like silicate gels, and spurrite [Ca5(SiO4)2CO3] to cement the sediment. Additionally, the micro filling of nano-SiO2, minerals, and gel phases significantly bolstered the sediment's strength. Finally, the impressive adsorption capacity of nano-SiO2 for Ca2+ (qm = 0.26mol/g) alleviated the toxicity of excessive Ca2+ on urease activity, thereby facilitating urea hydrolysis and CaCO3 nucleation. The synergistic effect of nano-SiO2 with MICP, involving cementation, filling, nucleation, and mitigation of Ca2+ toxicity, provides valuable insights for the sediment reinforcement applications.