Physical-mechanical properties and thermal-induced damage of granite after high-temperature pretreatment

This paper investigated the physical and mechanical properties of granite samples pre-treated at 25–1000 °C, and acoustic emission monitoring was conducted during uniaxial loading. The thermal damage mechanism was investigated, and the correlation between the mechanical parameters and ultrasonic wave velocity was discussed. The results indicated that the physical and mechanical properties of granite significantly become poorer with increasing temperature, but without any monotonic trend. Density decreased due to the evaporation of water at different stages after exposure to high temperature. P- and S-waves presented a linear decline before 400 °C but began to rapidly decline within the range of 400–600 °C. Static elastic modulus fluctuated slightly at low temperature (400 °C) and sharply declined (from 20.9 GPa to 3.5 GPa) at high temperature (1000 °C). Uniaxial compression strength (UCS) showed the same change characteristic as static elastic modulus, declining from 147.9 MPa at 25 °C to 35.8 MPa at 1000 °C. Peak strain continued to increase, indicating that the granite samples undergo plastic deformation after exposure to high temperature. The AE technique showed good correspondence with the failure process during loading. The initiation, propagation, and connection of micro-cracks mainly contributed to the degradation of the physical and mechanical properties. The slope change of the physical and mechanical properties at 600 °C may be attributable to the phase transition of quartz from the α phase to the β phase at 573 °C. Additionally, the static and dynamic elastic modulus exhibited good correlation with P- and S-wave velocity.