Influence of differential thermal alteration on the physical and mechanical properties of greywacke

Elevated temperature is one of the important factors influencing rock properties. Complex thermomechanical study has to be conducted to properly evaluate its effect on the rock mass. Due to the testing equipment limitations, these studies are commonly performed with pre-fired specimens, allowing for assessment of the heat-altered rock mass retrospectively, i.e., in the cooled state. However, the fired specimens prepared for our pilot thermomechanical study of greywacke showed only partial internal alteration with commonly used heating curve parameters, possibly affecting the test results. This paper presents the results of the partial thermal alteration effect on the properties of greywacke. The conducted analyses suggest that the mechanical properties are not explicitly influenced by the partial alteration, enabling the use of standard specimens. However, the bulk density is directly linked to the progressive alteration, therefore longer firing times or smaller specimens are necessary to obtain more accurate values.