Mechanical properties and the mechanism of microscopic thermal damage of basalt subjected to high-temperature treatment

To explore the thermal damage deterioration characteristics of basalt, the evolution of physical parameters, mechanical properties and failure modes was investigated. Based on computed tomography image reconstruction techniques, the spatial distribution and morphological characteristics of the pores of basalt were explored. The results indicate that thermal damage leads to the phase transition of basalt mineral grains and uncoordinated expansion and deformation, increasing the thermal deterioration of rock specimens. The temperature of 800 °C is the threshold for rapidly deteriorated physical properties of basalt, which has deformation characterized by the transition from ductility to brittleness. With the increase in temperature, basalt specimens transit from shear failure to tensile-shear combined failure, and then to tensile splitting failure. Meanwhile, irregular block-shaped collapse is transformed to strip-shaped rock fragments spalling. The crack width based on CT technology and three-dimensional (3D) image reconstruction of the crack volume can quantify the structural deterioration characteristics of basalt induced by thermal damage. When the temperature increases: 25 °C → 600 °C → 1000 °C, the corresponding porosity of the rock changes from 6.86% → 7.04% → 18.02%, exhibiting an evolution from low-speed development to high-speed growth. The thermal damage sensitivity of different lithologies at high temperatures differs, among which, the thermal damage sensitivity of marble is the highest, followed by granite and then basalt, the sensitivity of sandstone is the lowest.