The Influence of Anhydrite on the Mechanical Performance of Calcium Sulfoaluminate Cement-Based Grouting Materials

Cement-based grouting reinforcement technology is an essential method to enhance the mechanical performance of fractured rock depending on the type of grouting material used. To further understand the influence of anhydrite on the calcium sulfoaluminate cement-based grouting materials, this study investigates the sample of the grouting material with (calcium sulfoaluminate cement, anhydrite, and quicklime) under different ratios with a series of experiments including compressive strength, setting time, and slurry pH test. The macro and micro mechanical characteristics of different calcium sulfoaluminate cement grouting samples were revealed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that anhydrite enriched the system with needle-like ettringite (AFt), and plume-shaped aluminum hydroxide (AH₃), which contributed to the strength improvement. The optimal dosage of anhydrite-quicklime was 80:20 with a compressive strength of 9.5 MPa, 14.7 MPa, and 18.4 MPa at (1 d, 14 d, and 28 d), making up 38.5% of the total strength, and 80% independent of the quicklime dosage (14.2 MPa, 23.2 MPa, and 24.5 MPa), making up 52.5% of the total strength. Furthermore, X-ray diffraction and scanning electron microscopy results proved that anhydrite ratios are the main factor influencing grouting material reinforcement effectiveness and are more beneficial for improving the mechanical performance of calcium sulfoaluminate cement-based grouting material.