Westerly granite (WG) is a well-known rock, believed to be isotropic. We studied WG samples heated between 100°C and 800°C, by ultrasonic sounding (US), mercury intrusion porosimetry (MIP). Thermal treatment studies are important for localities like nuclear waste storages, geothermal projects, rocks and earthquake mechanics. All measurements were done at room temperature. It was found that P and S US wave velocity, amplitude, frequency and elastic modulus decreased more than 60% as a result of thermal rock material disintegration due to the increased temperature treatment. Image analyses showed that there is also a preferred orientation of microcracks regardless of their size and thermal treatment level. MIP showed that the pore size distributions vary with different heating temperatures in depending on the thermal WG treatment.
Granite can be important rock for nuclear waste disposal or in other engineering and industrial applications where the knowledge of granite thermal degradation can be very important due to the changes of original low native porosity/permeability and high integrity. In the past, high temperature treatment has been demonstrated as having a great effect on the mechanical behaviour of some rocks (Lokajíček et al., 2012; Lokajíček et al., 2020, etc.). Increasing temperature mostly causes the changes of pore network of the rock by the formation of new microcracks and enlargement of them. Porosity and pore size distribution is the main factor influencing the associated mechanical properties as strength, elasticity, permeability and ultrasonic wave propagation. There was found that poroelastic properties of hard rocks can be affected by microstructural evolution such as porosity change and micro-cracks growth. High temperatures may induce microcrack formation and propagation and result in elastic properties change of rocks and increase of porosity. To investigate the effect of thermal degradation on granite, slow heating thermal treatments were carried out on WG granite samples in this study. The mechanical properties (e.g. elastic properties, elastic modulus, ultrasonic waves propagation, textural properties pore network, pore surface area and volume etc.), and thermal dependence of all studied parameters were investigated.
