Determination of changes in the micro-structural, physical, strength properties of limestone and marbles exposed to fire

Within the scope of this study, changes in the mineralogical, physical and strength properties of limestone and marble samples exposed to high temperatures were investigated, and the changes in the strength of the rocks were tried to be estimated using non-destructive test data. When the void ratio values of the rocks were examined, it was observed that there was a decrease in the void ratio of the limestone samples exposed to high temperatures, while an increase in the void ratio in the marble samples with high temperature. In the study, it was determined that the small changes due to the increase in temperature were not caused by heat, and high temperatures (up to 680 °C) were not effective on the physical properties of this type of carbonate rocks. Thin sections were used to determine the mineralogical and microstructural properties of the rocks. It was observed that calcite mineral was dominant in the thin sections taken from the samples. In non-destructive tests, it was observed that the longitudinal wave velocity decreased at each temperature level depending on the temperature increase. LEEB hardness values were also measured, and a decrease in the hardness values in general was recorded with the increase in temperature in marbles. Unlike marbles, limestone samples showed an increase in Leeb values. The change in uniaxial compressive strength values with increasing temperature shows a similar trend with the change in Leeb hardness values. Strength is characterized by uniaxial compression strength value. The effect of temperature increase on strength was also evaluated. While an increase was observed in the strength depending on the temperature in the limestone samples, it was observed that the strength of the marble samples decreased with the increase in temperature. This depends entirely on the clay content. In the study, the temperature curve recommended by Eurocode (2002), reaching a maximum of 680 degrees, was used as the heating method, and the samples were exposed to high temperatures at 200, 300, 400, 500, 600 and 680 °C for 2 hours. In order to prevent the development of thermal cracks, the slow cooling method was preferred, and the samples were left to cool naturally in the furnace. When all the results obtained within the scope of the study were evaluated, it was determined that the mineralogical and micro-structural properties were very effective, especially the clay content, unlike the lithological properties, in the evaluation of the effect of high temperatures on the rocks