Effect of nanomaterial modification on mechanical properties and hydration mechanism of sulphoaluminate cement grouting materials

• The hydration mechanism of high-water-cement-ratio nano-grouting materials has been studied. • NC significantly improved the hydration process and microstructure of cement-based grouting materials. • When the NC content was 1.0%, it significantly improved the compactness of the grouting material. • NC promotes the nano-core effect hydration process of grouting materials. Cement grouting materials play a critical role in underground engineering applications, particularly for rock reinforcement and seepage control. This study investigates the performance enhancement of sulphoaluminate cement (CSA) grouting materials through nano-clay (NC) modification. Dynamic ultrasonic pulse velocity (UPV), mercury intrusion porosimeter (MIP), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the hydrated pastes. Six different NC dosages (0, 1, 2, 3, 5, and 7 wt.%) were systematically evaluated. The results demonstrate that 1 wt.% NC content provides optimal performance enhancement, UPV measurements showed strong correlations with mechanical properties and served as effective non-destructive evaluation indicators. It revealed that optimal NC content promotes ettringite and C-S-H gel formation while refining pore structure, with gel pores (<10 nm) increasing from 17.2% to 19.8%. The spatial structure of AFt and its pore-filling effect within the C-S-H gel affect the mechanical properties and refine the pore size distribution of the cement pastes. However, excessive NC content (>3 wt.%) adversely affects hydration kinetics and coarsens the pore structure. The study provides fundamental insights into NC-modified cement hydration mechanisms and offers practical guidance for underground grouting applications.