Temperature-induced deformational responses and microstructural alteration of sandstone

Abstract

The high-temperature response of rock is quite useful for successful exploration and exploitation of various conventional as well as unconventional energy systems such as underground coal gasification, and geothermal energy, where the associated rocks are exposed to various temperature and pressure conditions. In this study, we have investigated the effect of temperature and thermal alteration of an Indian sandstone. An investigation using acoustic emission, digital image correlation through ARAMIS, micro-computed tomography (CT) techniques and thermogravimetric analysis was performed to study the mechanical responses of the sandstone with increasing temperatures. The results indicate that uniaxial compressive strength (UCS), tensile strength and elastic modulus of sandstone reduced significantly and aligned in an overall decreasing trend with increasing temperatures. The maximum and minimum UCS of sandstone were obtained at 400 °C and 700 °C, respectively. Acoustic emission (AE) responses of the sandstone indicated an early crack initiation and crack damage for high-temperature treated specimens. The deformation was further analysed using the ARAMIS digital image correlation technique, and strain levels were visually quantified that exhibited a widespread distribution of higher strain for thermally-treated specimens at 700 °C. Microstructural thermal damage and different pore-characteristics were studied using micro-CT techniques that provided valuable information about the connected and non-connected pores of the sandstone and their evolution with increasing temperatures. The outcomes suggest a heat-induced increment in porosity by nearly 40 percent upon heating the samples from 25 °C to 600 °C, which can be attributed due to the opening of new cracks that stimulated structural damage.