Damage Evolution of Granodiorite after Heating and Cooling Treatments

The awareness of the impact of high temperatures on rock properties is essential to the design of deep geotechnical applications. The purpose of this research is to assess the influence of heating and cooling treatments on the physical and mechanical properties of Egyptian granodiorite as a degrading factor. The samples were heated to various temperatures (200, 400, 600, and 800 degrees C) and then cooled at different rates, either slowly cooled in the oven and air or quickly cooled in water. The porosity, water absorption, P-wave velocity, tensile strength, failure mode, and associated microstructural alterations due to thermal effect have been studied. The study revealed that the granodiorite has a slight drop in tensile strength, up to 400 degrees C, for slow cooling routes and that most of the physical attributes are comparable to natural rock. Despite this, granodiorite thermal deterioration is substantially higher for quick cooling than for slow cooling. Between 400:600 degrees C is 'the transitional stage', where the physical and mechanical characteristics degraded exponentially for all cooling pathways. Independent of the cooling method, the granodiorite showed a ductile failure mode associated with reduced peak tensile strengths. Additionally, the microstructure altered from predominantly intergranular cracking to more trans-granular cracking at 600 degrees C. The integrity of the granodiorite structure was compromised at 800 degrees C, the physical parameters deteriorated, and the rock tensile strength was negligible. In this research, the temperatures of 400, 600, and 800 degrees C were remarked to be typical of three divergent phases of granodiorite mechanical and physical properties evolution. Furthermore, 400 degrees C could be considered as the threshold limit for Egyptian granodiorite physical and mechanical properties for typical thermal underground applications.

Automated summary

The research evaluates the impact of heating and cooling treatments on the physical and mechanical properties of Egyptian granodiorite, indicating that slow cooling below 400°C results in relatively stable rock properties, while quick cooling leads to more severe thermal deterioration. Between 400°C and 600°C represents a transitional stage where physical and mechanical characteristics degrade exponentially.