Mechanical reinforcement mechanism of nano-SiO2 in grouted consolidation bodies

This study investigates the mechanism by which nano-SiO₂ (NS) enhances the strength of grouted consolidated bodies (GCB). GCB with NS contents ranging from 0% to 2.5% by weight of the grouting material were prepared. Uniaxial compressive strength tests, scanning electron microscopy analysis, and nanoindentation tests were carried out to obtain the microstructural characteristics of the slurry–rock interface under different NS addition conditions. The mesoscopic elastic modulus and hardness distribution characteristics of GCB, as well as the influence of microstructural features on macroscopic uniaxial compression test results, were also analyzed, elucidating that the interfacial transition zone (ITZ) at the slurry–rock interface is the weakest region within the GCB. The mechanical properties of the slurry–rock interface were studied using the macroscopic, mesoscopic, and microscopic scales, revealing the modification and optimization mechanisms of NS on the interface. Results show that the peak strength of the GCB increases with the addition of NS. NS optimizes the microstructural morphology, enhances interface compactness, reduces ITZ thickness, and improves interface bonding, significantly enhancing GCB strength in macroscopic mechanical behavior. With the increase in NS content, the failure mode of the samples also improves, with surface cracks significantly reduced and no large-area spalling observed. Scanning electron microscope results at the microscopic level indicate that hydration products, such as calcium silicate hydrate (C–S–H), ettringite, and calcium hydroxide, at the slurry–rock interface interact to form a complete cementitious system, enhancing interface compactness. In addition, increasing NS content promotes secondary hydration reactions in the grouting material, generating more C–S–H gels that fill internal pores in the GCB. Nonhydrated NS particles also occupy internal pores, improving interface bonding performance. Nanoindentation test results show that the interface thickness, elastic modulus, and hardness of GCB vary with different NS contents. NS addition decreases the slurry–rock interface thickness significantly, and the interface thickness of GCB containing 2.5% NS is reduced by 24 µm compared with those without NS. © The Editorial Department of APPLIED GEOPHYSICS 2024.