The variation of the physical and mechanical properties of limestone after high temperature treatment has become a major issue of interest for a number of reasons, such as tunnels safety, protection of historical monuments affected by fires, and geothermal energy. Therefore, an understanding of the effects of temperature on the variation of rock properties is of paramount importance. There is no standard procedure to evaluate the effect of temperature on rocks. Different methodologies are described in the literature, and consequently, a unified procedure should be defined to evaluate the damage on rocks exposed to fire. An ideal test must mimic the real phases of a fire: heating; maximum temperature maintenance time; and cooling. The thermal gradient determines the first phase. Until now, each investigation has used a different heating velocity to reach the target temperature, varying between 2 and 120 /min. Theoretical fire curves show that thermal gradient is much higher than gradients usually used in laboratory experiments. For this reason, the effect of heating velocity must be studied in depth. This paper shows the effects of three different thermal gradients (i.e. 5, 10 and 15 C/min) on a limestone exposed to three different target temperatures (400, 600 and 800 C). To evaluate the effect of thermal gradient, samples of limestone were tested after heating to calculate porosity, density, dynamic elastic modulus, and unconfined compressive strength. The main goal of the paper is to compare the thermal damage produced by each gradient and evaluate the influence of the gradient on these properties.
The effect of the temperatures caused by fires in rocks has long been a topic of great interest for rock mechanics, since they are the main building materials for historic monuments and infrastructures such as tunnels. Fires in such cases are rare, but when they occur, they generate great social alarm and large economic losses – as well as loss of life.