How do high temperatures affect rock properties? A comprehensive review of experimental thermal effects and underlying mechanisms

Understanding how rocks behave when exposed to high temperatures is of paramount importance in various geological engineering fields. The effect of temperature in these applications is typically simulated at the laboratory scale to evaluate its impact on both the micro and macro properties of rocks. This paper presents a comprehensive literature review on the practical applications, experimental methods, changes in properties, physical and mechanical processes, and the controlling factors in rocks exposed to high temperatures. To this end, a dataset was compiled comprising of 10,000 temperature-property pairs, leading to 1360 temperature-property evolution curves. The review first examines the main motivations behind these studies to identify the practical applications of studying rocks and the thermal effects of temperature. It then highlights the experimental methods, such as heating techniques, temperature gradients, duration of heating, cooling methods, and maximum temperatures, while noting a wide disparity of procedures. Subsequently, laboratory techniques are identified for evaluating the consequences of high temperatures, including visual and microstructural characterization, as well as the assessment of physical, mechanical, thermal, and hydraulic properties of rocks. The evolution of these properties for different rock types is described. Key thermal processes are then discussed, such as chemical reactions and physical changes. Additionally, techniques for estimating microstructural thermal damage and the conditioning factors that control the evolution of rock properties are reviewed. Finally, modelling techniques used to simulate heat transfer, stress-strain distribution, and thermal cracking, as well as the prediction of mechanical properties using numerical methods, particle-based approaches, and artificial intelligence are also reviewed.