Artem Polezhaev

The effects of high temperature on the tensile strength and physical properties of rocks were investigated using furnace heating and simulated fire treatments. Four rock types—basalt, granite, limestone, and sandstone—were examined under dry, wet, and saturated conditions (0%, 50–60%, and 100% water content, respectively). Tensile strength was measured before and after heating using the Brazilian test, while changes in porosity, thermal conductivity, mass, and P- and S-wave velocities were also evaluated. Thermal measurements indicate that both heating methods reached maximum temperatures of approximately 600 °C and produced comparable effects on rock properties. Initial water content had a negligible influence on post-treatment tensile strength and physical properties. In contrast, rock lithology strongly controlled the degree of thermal damage. Basalt, characterized by high initial tensile strength, exhibited minor reductions in tensile strength and wave velocities, whereas sandstone showed greater degradation. Granite and limestone exhibited pronounced reductions in P- and S-wave velocities. Rocks with higher thermal conductivity, such as sandstone, experienced larger decreases in thermal conductivity after heating, while basalt showed the smallest change. Conversely, basalt exhibited the greatest increases in porosity and mass loss. Overall, rock lithology and initial mechanical strength are the primary factors governing rock degradation under high-temperature exposure.

Temperature fluctuations can influence the internal stress field of a rock mass, especially in its surficial layer. Inherent properties (mineral composition, porosity, and fracturing) and external forcing (air temperature, humidity, and solar radiation) control the heat flux and temperature within the rock. Long-term thermal forcing, particularly when combined with wetting-drying cycles, can exacerbate rock deterioration and weathering, leading to progressive changes in mechanical properties, as shown by laboratory experiments.In this study, granodiorite samples from the Požáry field laboratory (Central Czechia) were subjected to thermal cycling in a controlled environment of a climate chamber, with repeated and increasing cycles reaching 80°C, a temperature that was most probably never reached after the rock´s formation. During the cycling, repeated UPV measurements were made (P and S waves) to observe the changes in their velocity and the inferred dynamic elastic moduli.The results showed slow but progressive decrease in the P and S wave velocities, suggesting rock damage after only a few cycles. This indicates possible increased rock wear in case of an expected future temperature rise.