Experimental investigation on mechanical properties and permeability evolution of red sandstone after heat treatments

Triaxial compression tests were carried out on red sandstone samples which had been previously subjected to heat treatments at 20, 200, 400, and 600 °C to study the change in properties and mechanical characteristics of the rock and the permeability (gas) evolution. Results show that: (1) the color of the sandstone changes from gray to brownish red with incremental change of temperature; (2) the strength of the rock increases with heat treatments from 20 to 200 °C and decreases with heat treatments from 200 to 600 °C, while the permeability of the rock after the heat treatments changes in the opposite trend; (3) from 20 to 200 °C, the primary pores and cracks close gradually, which results in the strength and elastic modulus increasing and permeability of the rock after the heat treatment decreasing; from 200 to 600 °C, the degradation of the sandstone causes the fall in strength and elastic modulus, and the rise in strain corresponding to the peak stress and permeability of the rock after the heat treatment; (4) the permeability in a stress-strain process varies with the evolution of cracks; (5) when the heating temperature is beyond 800 °C, the sandstone is seriously thermally damaged.