238 / 2024-03-14 09:10:49

Thermal Treatment Impact on Microstructural Degradation and Macroscopic Properties of Egyptian Granodiorite

Egyptian granodiorite; thermal treatments; physical and mechanical properties; microstructure; cooling techniques

Abstract: Rock's macroscopic properties are characteristically linked to the microstructure's degradation during thermal treatment procedures. Hence, this study aimed to look at how rapid cooling (R-C) by water and slow cooling by the air (A-C) after high temperatures (up to 800 °C) change the microstructure and physico-mechanical properties of Egyptian granodiorite. Porosity, P-wave velocity, uniaxial compressive strength, and elastic modulus were examined as the microstructure evolved. Based on the experimental results, three distinct temperature zones were identified: (up to 200 °C), (200–400 °C), and (400–800 °C). At the first zone, the temperature gradually reduced wave velocity and porosity, with larger values for R-C samples than for A-C samples. Microstructural analysis showed intragranular microcracks in the R-C method samples. Furthermore, granodiorite gained thermal hardening, leading to an increase in uniaxial compressive strength. Still, the UCS and E were higher for R-C specimens, which suggests that the cooling method had a more negligible impact at lower temperatures. At the second zone, there were no considerable changes in porosity, while P-wave velocity and elastic modulus dropped due to transgranular cracks as temperature rose. Moreover, granodiorite thermal hardening was observed only for slow-cooling samples when the heating temperature reached 400 °C. The third zone had a clear degradation zone because of complicated factors like the α-β phase shift in quartz and excessive mineral expansion, which worsened the granodiorite features. As a result, transgranular cracks had fusion, and longitudinal waves failed to penetrate rock samples over 600 °C. Hence, the granodiorite structure thermally deteriorated, the physical qualities dropped, and the rock strength measures were minimal, regardless of the two cooling techniques.