Thermal alterations in the poro-mechanical characteristic of an Indian sandstone - A comparative study

Knowledge of the variations caused by high temperature to the mechanical properties is a vital asset in processes such as underground coal gasification (UCG), in-situ disposal of nuclear waste and during the recovery of geothermal. The study can also provide valuable insights during the restoration of fire-damaged buildings. Due to the presence of heat, changes in rock morphology and mineralogy lead to a substantial change in the geomechanical properties of rock. Effect of high temperatures (1000 °C) on the tensile and compressive strength of a fine-grained Indian Sandstone have been analysed in this study. Induced ductility, observed at temperatures above 500 °C causes the rock to exhibit properties similar to that of a plastic material. The geomechanical properties decrease sharply beyond 500 °C, which has been referred to as the critical temperature of the rock. Beyond the critical temperature, internal structure of the rock undergoes considerable damage in the form of microcracks and fissures created due to phase transition of quartz at 573 °C and generation of thermal stress. Change in internal structure and mineralogy have been analysed by performing XRD (X-ray powder diffraction) and FDXM (Four-dimensional X-ray microscopy) studies. With the help of FDXM, change in porosity of rock has been analysed by studying the variation in connected and non-connected pores.