Macroscopic and microscopic research on Egyptian granodiorite behavior exposed to the various heating and cooling strategies

Thermal treatments and cooling strategies deteriorate the physical and mechanical characteristics of rocks. Hence, this study examines the cooling processes' impacts on "rapid cooling (R–C) by water and slow cooling by the oven (O–C)" after high temperatures "up to 800 °C" on the destruction of Egyptian granodiorite's physico-mechanical characteristics. Macroscopic properties such as discoloration, mass losses, volume expansion, density reduction, P-wave velocity, uniaxial compressive strength, and elastic modulus were studied as a function of microscopical evolution. The experimental results indicated that the temperature led to a progressive decrease in density and wave velocity at 200 °C, with greater values for R–C samples than for O–C. On the other hand, the UCS and E were higher for R–C specimens, demonstrating that the cooling method had an unobvious impact at lower temperatures. At 400 °C, the S–C method continued to improve mechanical parameters; however, the R–C technique showed a decline in mechanical properties and higher degradations of physical parameters and microstructure. A noticeable transition zone between 400 and 600 °C was marked by sharp growth in crack density in conjunction with a dramatic drop in all studied parameters "with greater worth for water-cooled samples." At 800 °C, regardless of the cooling strategy, the granodiorite structure thermally deteriorated, physical characteristics deteriorated, and the rock strength parameters were negligible. According to this analysis, granodiorite has a turning point after 200 °C for its properties for rapid cooling way compared to 400 °C for the slow cooling approach. Above these threshold temperatures, its microstructure, physical, and mechanical properties worsen, and the material becomes slightly brittle and more ductile. Article highlights The compressive strength of granodiorite exhibits thermal hardening at 200 °C for both slow and rapid cooling samples but still only at 400 °C for slow cooling samples. A distinct transition zone from 400 to 600 °C was identified by a significant increase in crack density and a sharp decline in all measured parameters, “with a more substantial value for water-cooled samples”. Egyptian granodiorite properties have a turning point after 200 °C for rapid cooling as opposed to 400 °C for slow cooling. The microstructure, physical, and mechanical characteristics of granodiorite deteriorate above the threshold temperatures.