Objective and Methods  This study aims to reduce the economic cost of sulfoaluminate cement-based grouting materials while also achieving excellent grouting reinforcement effects. To this end, it investigated the variation patterns of the compressive strength, setting time, and fluidity of the ultrafine fly ash (UFA)-ultrafine sulfoaluminate cement (USC) system by incorporating different dosages of silica fume (SF) and nano-silica (NS). Furthermore, the mechanisms behind the hydration reactions of the system were explored. Using multiple distinct testing techniques such as X-ray diffraction (XRD) mineralogy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric-differential thermal analysis (TG-DTA), and scanning electron microscopy (SEM), this study analyzed the phase composition and microstructures of the hydration products.

Results and Conclusions  The incorporation of SF into the UFA-USC system led to decreased compressive strength and setting time of the system across various ages. As NS was added, the compressive strength of the UFA-USC system at all ages showed an upward trend initially and then decreased, with the optimum NS dosage determined at 2%. As only NS was mixed into USC, the compressive strength of USC at various ages also increased initially and then decreased, with the optimum NS dosage proving to be 3%. In contrast, the setting time of the USC at various ages shortened first and then increased when the NS was added. Microscopically, the incorporation of SF or NS did not change the hydration product types of the USC but enhanced its early hydration. Notably, the incorporation of NS resulted in more compact microstructures of the hydration products, thus improving the compressive strength of the USC. The USC-based grouting materials were applied to floor grouting for water blocking at a coal mine in Shanxi Province. The field tests verified that the materials hold high value in engineering. The results of this study provide a theoretical basis for the application of nanomaterials in grouting engineering. Furthermore, they are of significant practical value in improving the grouting reinforcement technology system used for the surrounding rocks of deep roadways.