The influence of nano-SiO₂ emulsion on sulfate resistance of cement-based grouts

Sulfate attack is one of the most significant durability issues for cement-based grouts, which are widely used to repair concrete structures in sulfate-rich environments. The purpose of this study was to investigate the impact of nano-SiO₂ emulsion on the sulfate resistance of cement-based grouts. The durability of the mixes was evaluated on the basis of weight loss and compressive strength. X-ray diffraction (XRD) and scanning electron microscopy (SEM) of hardened grout matrix were used to analyze the hydration products and microstructure of the hardened grout matrix. The results indicate that the hydration degree of nano-SiO₂-modified samples is higher than that of the control sample. The compressive strength from highest to lowest was 16 NSE, 10 NSE, NSP, and the control sample. The XRD and SEM results suggest that the deterioration of properties may be attributed to the formation and growth of ettringite (AFt) crystals, which may result in crack generation and extension and in the corrosion of gypsum, leading to exfoliation. The addition of nano-SiO₂ to cement-based grouts through a preprepared emulsion, which facilitates dispersion within the cement matrix, has the potential to reduce AFt and gypsum contents, enhance microstructure density, decrease the migration channels of SO42−\[\text{SO}_{4}^{2-}\], and ultimately improve the resistance to sulfate attack. This work will provide a novel route to enhance the sulfate resistance of cement-based grouts, which may be serviced in a sulfate-rich environment.