Tensile strength and brittleness of sandstone and granite after high-temperature treatment: a review

Abstract

High temperature may cause damage to microstructure of rock, which has a significant effect on rock behavior. In this study, the changes in tensile strength and brittleness of sandstones and granites with temperature and corresponding mechanisms are summarized and analyzed based on an extensive review of literature. The results show that as thermal treatment temperature increases to 400 °C, the tensile strength of sandstones changes with two forms: continuously increases or first decreases and then increases, while that of granites monotonically decreases at a moderate rate. In the range of 400 and 700 °C, the tensile strength of both sandstones and granites sharply decreases, indicating that 400 °C is the threshold temperature for the changes in tensile strength of them. Thereafter, it is found that the decrement rates in tensile strength of all rock samples generally become gentler. Under high-temperature environments, the dehydration and expansion of minerals, development of microdefects, and changes in mineralogical characteristics are the primary causes for the changes in tensile strength. Four brittleness indexes are calculated based on the strength properties of rocks, while only the indexes expressed by the product of compressive and tensile strength can well characterize the brittleness of thermally treated rocks. The changes in brittleness of sandstones and granites with temperature basically show a consistent trend with that of tensile strength. The reduction of rock brittleness at high temperature is attributed to the deterioration in microstructure of rocks and brittle-ductile transition of minerals.