The Effects of Loading Rates on the Tensile Fracture Characteristics of Heat-treated Granite, Sandstone and Marble Based on Brazilian Splitting Tests

Elevated temperatures pose a significant challenge in deep rock engineering, where excavation rates critically impact construction progress and safety. This study investigates the effects of loading rates (0.05–0.4 mm/min) and 400°C thermal treatment on the tensile fracture characteristics of granite, marble, and sandstone using Brazilian splitting tests. Test results indicate that at 25°C, tensile strength increases with loading rates for all three rock types. Sandstone exhibits the highest sensitivity to loading rates variation, followed by granite, while marble shows the least responsiveness. After thermal treatment at 400°C, tensile strength decreased significantly in all samples. Marble demonstrated the greatest reduction (average decrease: 62.24%), followed by sandstone (37.14%) and granite (33.57%). Furthermore, post-treatment tensile strength decreased with increasing loading rates in marble and sandstone, but continued to increase in granite. High-precision scanning electron microscopy (SEM) revealed the underlying mechanisms: as loading rates increase, microfractures transition from intergranular (IG) to trans-crystalline (TC) patterns; concurrently, elevated temperatures alter mineral composition and microstructure. These findings provide a theoretical basis for safety protocols in deep rock engineering.