Effects of thermal treatment on physico-morphological properties of Indian fine-grained sandstone

The physical, mechanical and morphological properties of a rock undergo substantial change when exposed to the extreme temperatures that are encountered in processes such as nuclear waste disposal, underground coal gasification (UCG) and building fires. An attempt has been made in this article to study the different physical and morphological changes that occur within Indian sandstone due to thermal treatment. Tests were performed on a thermally treated air-cooled and non-cooled set of samples in order to observe the change in the physico-morphological properties. Heating has a profound effect on the physical properties such as density, porosity and compression wave velocity (V_P), which have been further explained by thin-section, X-ray diffraction (XRD) and scanning electron microscope (SEM) studies. Thermal analyses such as thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed to observe the chemical changes occurring in the specimen. Since Dholpur sandstone is a quartz-dominant rock, the thermally induced chemical degradation is minimal in nature. DTA studies revealed the quartz inversion to occur at 579.19 °C. Structural changes that are caused due to the random alignment and the thermal anisotropic behaviour of different minerals lead to microcracking, thereby affecting the physical properties. This study will provide an understanding of the thermal behaviour of rocks and the relationship of the thermal behaviour with physico-mechanical behaviour. The study can prove useful while designing structures in processes such as UCG, nuclear waste disposal, deep mining and geothermal energy; the study can also enable the formation of a protocol to restore the structural integrity and aesthetic value of fire-damaged buildings.