Thermal damage effect on the thermal conductivity inhomogeneity of granite

In this work, thermal damage effect on the thermal conductivity inhomogeneity of granite was experimentally investigated. To study the influence of different cooling methods, granite samples were heated at different temperature levels (from 100°C to 1000 °C), then cooled in air and water, respectively. Distributed thermal conductivity of granite samples were measured using optical scanning method before and after thermal damage treatment. Besides, some non-destructive tests (open porosity and P-wave velocity) were performed. The results indicate that thermal damage will lead to the decrease of thermal conductivity and the increase of thermal inhomogeneity degree. The decrease degree of thermal conductivity values increases with the treatment temperature. The maximum decrease can be 54.0% (after heated at 1000 °C). When the treatment temperature is higher than the phase transition temperature of quartz (573 °C), the thermal inhomogeneity degree of the damaged samples increased obviously. After heated at each temperature level, the water cooled samples exhibit greater thermal conductivity decrease and greater thermal inhomogeneity factor increase than air cooled samples. This may be attributed to the fact that rapid cooling has extra effects on the damage evolution of rock, which is induced by the high temperature gradient generated when temperature changes occur in a very short time. A thermal damage model was proposed to describe the evolution characteristics of thermal conductivity with treatment temperature. Research results in this work can provide better knowledge to the evolution mechanism of distributed thermal conductivity of engineering rock masses experienced high temperature environment, and the influence of different cooling methods.