# Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review
## 1 Introduction  
Earthen materials such as rocks have a wide range of applications in various rock-engineering related domains, including rock slope stabilization, rock drilling, tunneling and excavation, coal gasification, nuclear waste repositories, geothermal energy extraction, construction material, and foundation engineering [1; 2; 3; 4]. Rocks are heterogeneous, anisotropic, and aggregate of different minerals. They are not perfectly elastic material but rather brittle in nature. However, deep-seated rocks show ductility under high pressure and temperature conditions [5]. The rock mass exposed to the surface is found discontinuous due to its weathering. Temperature is one of the most important weathering agents that significantly alter the engineering properties of the rock mass. Construction of sensitive structures, such as skyscrapers, dams, nuclear power plants, tunnels, etc., in the thermally deteriorated rock mass is taken into account as a major challenge. These structures may experience severe damage or reduction in their service life under the adverse effects of altered engineering properties of the thermally damaged rock mass [6]. Therefore, the study of thermal effects on rock properties has been garnering attention for the last few decades.  
Carbonate rocks are a sub-class of sedimentary rocks and abundantly found on the upper Earth's crust. Limestone and dolostone are the two major types of carbonate rocks and have a wide range of applications in the construction, cement, glass, mining, and petroleum industries [7]. Several researchers have investigated the engineering behavior of carbonate rocks subjected to various temperature ranges between ambient temperature and high temperature (20-1000 \({}^{\circ}\)C) [6; 7; 8; 9; 10; 11; 12; 13]. They have noticed that limestone and dolostone under high temperatures experience mineralogical alteration, inter-granular and intra-granular cracking, reduction in dynamic-mechanical strength parameters, and appreciation in porosity and permeability.  
In high-temperature rock mechanics and geotechnics, the evaluation of the engineering characteristics of carbonate rocks is of great interest. For example, dimension stones obtained from carbonate or silicate rocks are important construction materials. In a building fire event, their temperature may rise above 800 \({}^{\circ}\)C [14]. The underground coal gasification process may increase the temperature of host carbonate rocks up to 1500 \({}^{\circ}\)C [15]. This process not only significantly damages host rocks but also releases oxides of nitrogen, carbon, sulfur, etc., in the environment. Similarly, during a plate tectonic event (at depth \(>\) 40 km and 500-850 \({}^{\circ}\)C), thick deposits of carbonate rocks at the subduction zone liberate excessive carbon dioxide, which is one of the major global warming factors [16]. Furthermore, magmatic activities, such as contact metamorphism, increase the temperature of country rocks from 300 to 800 \({}^{\circ}\)C [17]. At a shallow depth, the decay of radioactive elements in their repositories heats the host rocks from 50 to 250 \({}^{\circ}\)C [7]. The level of temperature and pressure increases with depth. Therefore, the extraction of geothermal energy and hydrocarbons from deep-seated carbonate rocks requires special attention because of their altered geomechanical characteristics [18].  
This study aims to summarize the research work on thermally treated carbonate rocks to discern their behavior against increasing temperature. In this research work, the literature review covers the experimental findings of pre-heated and post-heated carbonate rocks. Furthermore, it evaluates the damage characteristics of thermally degraded carbonate rocks in terms of mineral dilatancy, rock fabric, microstructural properties, physico-mechanical behavior, fluid transport properties, thermal transport properties, and dynamic response.