Linking evolution of heterogeneous microstructure and rheology of granite to 1000 °C

The study of the effects of thermal damage on the mineral components, microstructure, and macroscopic physico-mechanical properties of rocks can provide valuable references for rock engineering design and long-term safety evaluations. In this work, we systematically study the evolution of microstructure and variations in the mechanical properties of granite under high-temperature conditions. The microstructural changes and macro-mechanical properties of rocks are investigated across a temperature range of 25 °C–1000 °C through the application of characterization techniques, macro-mechanical experiments, and numerical simulations. High temperatures induce the gradual evolution of micropores and mesopores into macropores, culminating in a significant increase in porosity, with the most rapid rate of increase occurring at 400 °C. The X-ray diffraction (XRD) results indicate that the high-temperature environment (below 1000 °C) specifically affects the intensity of the maximum diffraction peaks and the half-height width (FWHM) of each mineral component in the granite. The scanning electron microscope (SEM) observation confirms the development of fracture and the reduction in cementation between mineral particles under different temperatures. Additionally, uniaxial and triaxial compression tests were conducted using the GCTS mechanical loading system. Experimental results reveal that the threshold temperature for granite damage is 400 °C, and the temperature range for the brittle-ductile transition of granite lies roughly between 600 °C and 800 °C. Numerical simulations were performed by employing non-homogeneous rock damage theory and a thermal-mechanical-damage coupling model. Simulated results align well with experimental data. Specifically, the simulations demonstrate that high-temperature treatment causes the redistribution of microstructure in granite, resulting in increased heterogeneity and a change in the failure morphology.