Thermal Effects on Heterogeneity and Anisotropy of Spatial Distribution of Microcracks in Granite
Jingwei GAO+, Lifeng FAN#
Beijing University of Technology, China

The rock is subjected to thermal action in high-temperature rock engineering. The thermal action induces the generation of microcracks in rock due to the differences in thermal expansion properties of minerals. Quantitative characterization of microcrack characteristics is important for understanding the thermally induced deterioration mechanism of rock properties. The parameters, such as length, width, area, volume and porosity, were generally introduced to quantitatively describe the microcrack characteristics in previous studies. To further quantitatively describe the spatial distribution characteristics of the microcracks, in the present study, two indexes (heterogeneity coefficient and anisotropy coefficient) were proposed based on the micromechanics Computed Tomography (CT) experiment. The two indexes were used to quantitatively describe the heterogeneity and anisotropy of spatial distribution of microcracks. Moreover, the effects of heating temperature (from 25 to 1000 °C) and thermal cycling number (from 0 to 16 times at 500 °C) on the heterogeneity coefficient and anisotropy coefficient were further discussed. The results show that both the heterogeneity and anisotropy of thermally treated granite increase to their maximums as temperature increases to 500 °C and then significantly decrease to constants as temperature further increases. For the specimens subjected to thermally cycling treatments at 500 °C, both the heterogeneity and anisotropy increase significantly after the first thermal cycle, after which the heterogeneity and anisotropy change slightly as the cycling number further increases. The proposal of the heterogeneity coefficient and anisotropy coefficient realizes the quantitative characterization of the spatial geometric characteristics of the microcracks.