Mineralogical and microstructural study of thermally treated Egyptian limestone and the related modifications to its physico-mechanical properties
摘要
The chemical composition of rocks and sedimentation conditions vary by region, making it challenging to identify the typical evolution of rocks, even of the same type, under different temperatures. This study aimed to link the mineralogical alteration of Egyptian limestone induced by temperatures up to 800 °C with changes in its microstructure and physical and mechanical properties. The results indicated that limestone’s P-wave velocity and elastic modulus decrease linearly with increasing temperature. However, the porosity and mass loss of limestone change slowly as the temperature rises to 400 °C, followed by a noticeable increase above this threshold. Furthermore, the specimen’s mass rapidly changes between 600 and 800 °C, and the breakdown of CaCO3 is most rapid at 782 °C. Once heated to 800 °C, the surface turns pale gray or white, and the exterior surface peels off, small chunks detach, and open fractures develop. On the other hand, the uniaxial compressive strength rises to even 400 °C and then drops sharply after that temperature. All the metrics studied showed significant changes at 400 °C, leading to a dramatic increase in crack density. Hence, we identified a remarkable evolution point at 400 °C. After this temperature, the mechanical, physical, and microstructural properties of limestone worsened. Compared with limestones from other regions, the Egyptian limestone used in this study is purer and less brittle. Therefore, Egyptian limestone is ideal for applications that require high-temperature stability.