Thermal effect on the physical properties of carbonate rocks

The effect of thermal damage on the physical properties of five carbonate rocks has been investigated. The tests were conducted on two marbles and three limestones, mainly composed of calcite but with different grain sizes, porosities, structural and textural characteristics. Cubic samples prepared from these rocks were gradually heated to a specific temperature level of 100, 200, 300, 400 and 500 °C, and gradually cooled down to room temperature without causing thermal shock in order to investigate the effect of heating temperature on physical properties such as microstructure, bulk density, effective porosity and P-wave velocity. Microscopic investigations from thin sections showed that damage in rocks at elevated temperatures was induced in different severity depending on grain size, porosity, structural and textural characteristics. Colour changes were also observed in porous limestones (Lymra and Travertine) due to organic material. In accordance with the degree of calcite dilation depending on heating temperature and in turn new microcrack occurrence, separation along intragrain and/or intergrain boundaries and widening of existing cracks, P-wave velocity decreased to various levels of the initial value, whereas porosity increased. Microscopic analyses and P-wave velocity measurements indicate that compaction of rock structure up to 150 °C occurred and induced calcite dilation had no significant damage effect on the rock material. Compaction of rock structure led to an increase in P-wave velocity and slight decrease in porosity. Most of the damage occurred within 24 h of heating time and further heating treatments brought relatively minor changes in physical properties. Damage intensity was well explained with P-wave velocity and effective porosity values depending on temperature increase.