Thermal damage and permeability evolution in granite subjected to rapid heating and cooling: Experimental and numerical insights
摘要
As clean energy technologies advance, the engineering challenges caused by rapid thermal fluctuations are expected to become more complex. This study investigates the damage behavior of granite subjected to rapid heating and cooling, focusing on the underlying damage evolution processes. A range of experimental and computational methods, including nuclear magnetic resonance (NMR), synchronous thermal analyzer (STA), and discrete element method (DEM), were used. The results show that as temperature increases, material density, P-wave velocity, and dynamic elastic modulus decline exponentially, while the damage index and linear thermal expansion coefficient increase. Thermal damage primarily results from dehydration, thermal expansion, decarbonation, plasticization, phase changes, cracking, and decomposition. Thermal shock decreases the contribution of micropores to total porosity, while macropores grow above 200 °C. The study also improves the Schlumberger-Doll-Research (SDR) and Timur-Coates models, enhancing the accuracy of permeability predictions under different cooling conditions. High temperatures slightly reduce the fractal dimension of the pore structure, which negatively correlates with permeability. As temperature rises, pore coalescence and crack propagation increase, significantly altering permeability. DEM simulations show that cracks are mainly influenced by tensile stresses and thermal expansion and contraction stresses. Higher heating temperatures cause more extensive cracks, while crack contributions decrease during cooling at 600 °C. Thermal damage creates additional energy release paths, increasing local thermal resistance and hindering heat transfer. Finally, thermal cycling results in a more directional crack distribution and a notable decrease in contact angles at 600 °C, indicating microstructure rearrangement.