Synergistic optimization of nanosilica sol-calcium aluminate cement composite grout by silica micropowder: Effects on microstructure and sealing performance

This study investigates the influence of silica micropowder, used as a partial replacement for calcium aluminate cement (CAC), on the rheology, early strength, sealing performance, and pore-structure evolution of nanosilica sol-CAC composite grout. Results showed that a significant increase in silica micropowder content delayed the hydration process and postponed the rapid-rise viscosity point, thereby extending the workable time window. An appropriate dosage (10%) enhanced compressive strength by approximately 7%, whereas excessive amounts decreased strength due to insufficient reactive components. Grouting substantially reduced rock-core permeability by more than three orders of magnitude, and the lowest post-grouting porosity was achieved at a 20% silica micropowder dosage. Nuclear magnetic resonance revealed that silica micropowder markedly reduced large pores while increasing small and moderately sized pores, leading to refined pore-size distribution and overall improved matrix compactness. These findings demonstrate that the dilution and micro-filling effects of silica micropowder synergistically optimize the multiscale microstructure of the composite grout, improving its injectability, strength development, and sealing efficiency.