Influence of thermal damage on physical properties of a granite rock: Porosity, permeability and ultrasonic wave evolutions

In this paper, parameters for characterization of connected porosity and overall damage in the thermally-cracked rock of granite in order to assess, respectively, its transport properties and its mechanical strength are identified and quantified. Samples were heated to a range of peak temperatures up to 600 °C at ambient pressure. Characterizations were made by measurement of porosity, gas permeability, velocity and attenuation of ultrasonic waves. Our study confirms the strong influence of thermal damage on physical properties, and shows clearly the potential of the above techniques in connection with this type of damage. Typically, we show that the porosity measurement only informs about open porosity, which is distributed and available at rock surface, whereas the gas permeability measurement characterizes the connected porosity. As for the ultrasonic wave propagation, it is sensitive to overall damage in the material. Nevertheless, we observed that the three techniques are complementary and similarly describe the rock behavior in each stage of heat treatment; they show a good consistency between them.