Yang et al. [5] investigated the physical behavior of granite from room temperature to 800 °C. It was observed that from 25 °C to 300 °C, the porosity decreases 0.828% to 0.685%. Then, porosity increases from 0.685% to 3.460% up to a temperature of 800 °C due to the rapid formation of micro-cracks. During the opening of micro-cracks and reproduction of new cracks between temperatures from 100 °C to 500 °C, some structural changes are induced, and as a result, the porosity increases. The increasing rate is noticeable after 500 °C with a large increase in cracks [9]. Moreover, a high temperature results in the evaporation of water molecules from the minerals [12]. Generally, the porosity of granite ranges from 0.2% to 0.8% at normal temperatures. However, it increases up to 2.85% at 600 °C [13]. Vagnon et al. [14] established an exponential relationship between porosity and temperature from experimental data and pointed out that the porosity increases up to 3% at 600 °C. The crack propagation and the rate of increase in porosity are effective at 500 °C to 600 °C [15,16]. The heterogeneity of minerals generates new cracks due to thermal expansion at high temperatures and hence an increase in porosity [17]. Guangsheng Du et al. have analyzed the temperature generation and the effect of the temperature on rock microstructure changes which are basically granite rocks, as indicated by an analysis of the micro-inhomogeneity. Denature of crystal takes place when the temperature rises above 400 °C [53]. 

The permeability of rocks depends on void space, grain size, and the cementation of mineral constituents. However, if the rock pores are isolated from one another, then the rock would be impermeable. A triaxial compression experiment was conducted on Beishan granite [18] to measure the permeability changes in crack effected region. A permeability changes model was established and was presented with the help of a numerical simulation technique. The heat treatment process on the Beishan Granite up to 800 °C [19] concluded that the cracks developed due to the phase transformation of quartz and hence changed in permeability under unconfined conditions. Moore et al. [20] examined the rate of decrease of permeability from 300 °C to 500 °C and observed that after 400 °C decreasing rate of permeability is high due to greater reactivity of the material. The permeability of the rapidly cooled sample shows increases in porosity than the slowly cooled samples [21] and is directly dependent on crack formation.

Thermal effects on Jalore granite to examine the mechanical and physical properties were performed up to 600 °C [12], and the results were compared to granites of other countries. The authors [12] also observed the changes in the water content and mineral in the granite specimen with the temperature. Isaka et al. [13] analyzed the micro-structure distribution and the basic difference of crack propagation of slow cooling and rapid cooling of the Harcourt Granite up to 1000 °C. The pore connectivity model and shock induced during cooling were also observed. An experiment on the Stripa Granite up to a temperature range of 600 °C [22], with the help of an optical microscope, pointed to the distribution of elastic and fractural properties of rocks. Homend and R. Houpert [15] predicted the thermal crack propagation and estimation of crack porosity under tensile as well as compressive loading of a granite sample at a heating range between 20 °C to 600 °C. Hewze [24] presented a review article on the high-temperature treatment of granite and an analysis of the different thermo-mechanical properties of rocks. Liu and Xu [25] conducted a study on the Qinling Biotite granite under high-temperature treatment to assess the rock stability and protection for constructional progress at underground technology. Nasseri et al. [16] presented a study on the Westerly Granite for analysis of crack density and porosity with an increase in temperature, and they predicted a relation between the fractural length and crack density of the sample. Xu et al. [17] conducted an experiment on granite up to 1200 °C to predict the tensile fractural stress and microstructure analysis to determine the chemical characteristic of rocks. Yin et al. [26] analyzed the failure made of granite under different temperature limits, especially the splitting failure and shear failure. Chen et al. [27] presented a study on heat treatment of granite up to 800 °C to observe the microstructural mineral changes in granite with the help of scanning electron microscopy while analyzing such rocks for different mechanical properties changes under the temperature. Wu et al. [28] analyzed the effect of nitrogen cooling on heat-treated granite specimens and observed the mechanical and physical properties changes in medium- and fine-grained granite. Yang et al. [29] conducted a simulation method of failure of granite material containing preexisting holes under different temperatures to observe the meso-mechanics of granite material and distribution of crack propagation. Zhao et al. [30] presented a study on the thermally treated Beishan Granite up to 400 °C for rough fracture and micro-crack generation. Zuo et al. [31] carried out an experiment on Beishan Granite under high-temperature treatment with the help of a Scanning Electron Microscope. They observed that the direction of micro-crack generation depends on the distribution of the mineral grains. They also determine the elastic modulus and stress intensity factors. Dong Zhu et al. [54] conducted a Brazilian splitting test on granite material to investigate the effect of heating and cooling on the mechanical properties of granite. They also observed the plasticity increases with an increase in temperature. Xiangxi Meng et al. [55] have discussed the thermal cracking and permeability changes under the uniaxial compressive test of granite at a temperature of 100 °C to 650 °C. They have observed that the permeability of granite increases above the critical temperature.

Mechanical properties like Young’s modulus, Poison’s ratio, tensile strength, compressive strength, and p-wave velocity record changes with an increase in temperature. A few publications addressing such changes by various authors up to 1000 °C are reviewed here.

Young’s modulus is a measure of the stiffness of a material under tension and compression. Basically, it is a relation between stress and strain of a material. Young’s modulus is a measure of the characteristic of a material and is used in geo-mechanical engineering design [32]. Young’s modulus generally decreases due to an increase in temperature. The decreasing rate is more enhanced in the rapid cooling method than in the slow cooling method [1]. The dynamic damages basically depend on the elastic modulus and wave velocity of the material. The elastic modulus is classified into three basic categories, i.e., initial elastic modulus, tangent elastic modulus, and secant elastic modulus [2]. The slope of the linear elastic stage is represented by this equation:

The relationship between elastic modulus and wave velocity can be represented by the following equation [2]:

where E and µ represent the elastic modulus and Poisson’s ratio, respectively. The ρ and ν are the density and longitudinal wave velocity of the material.

The dynamic and static elastic modulus decrease with an increase in temperature. Young’s modulus of granite after high-temperature treatment shows a decreasing trend. The rate of decrease of static modulus is higher than the dynamic modulus for the same temperature variation rate [5]. The elastic modulus decreases rapidly after 400 °C to 800 °C, and the rate of decrease is around 10% than the room temperature [6]. It was observed that the decreasing rate is more extreme in the case of rapid quenching than in slow cooling. The decreasing rate of ‘E’ during rapid quenching and slow cooling is about 60% and 50% up to 600 °C temperature, respectively [1]. The rate of decrease in Young’s modulus creates thermal cracks, which decrease the strength of the materials [33,34]. The change of elastic modulus usually effects on elastic stages of the stress–strain curve, and it causes dynamic damage to the material [2].

In case of strain burst in the granite sample, Young’s modulus reduces with an increase in temperature. The strain distribution is due to changes in Young’s modulus and the yield point [4]. With an increase of temperature up to 800 °C, the stress–strain curve of the granite becomes non-linear, and the material reaches a yielding point. If the temperature limit is high, the materials deform slowly and with thermally deformation cracks that affect the fracture propagation [5]. If the temperature increases up to 1000 °C, the elastic modulus decreases by 20% of the normal value [6]. In the case of the Strath Bogie Granite, the rate of decrease of Young’s modulus is about 15% between temperatures 600 °C to 800 °C [7]. The constant slow-temperature heating and varying temperature rapid-heating effects on the mechanical behavior of granite, and slow cooling prevents the thermal shock after heating along with decreasing Young’s modulus [9]. The elastic modulus tends to steady state up to a temperature of 200 °C due to less dependency on the elastic property of granite. Then, between 300 °C to 800 °C decreases gradually with an increase in temperature [10]. After 400 °C, it was found that the elastic modulus is greater in the case of fine-grain granite than the medium-grain and coarse-grain granite. The crack density increases, and the thermal crack development is the main reason for such diverse nature of elastic modulus during heating [20].

Poisson’s ratio is one of the most important deformation mechanical properties indicating the brittle–ductile transition characteristic of a rock. Poisson’s ratio is the ratio of the transverse contraction strain to the longitudinal extension strain. It was observed that up to 500 °C, the Poisson’s ratio decreases by 25% for the slow cooling process but in the case of the rapid cooling process, the reduction rate of Poisson’s ratio is 20% up to 300 °C [10]. However, up to 800 °C, the Poisson’s ratio increases by 38% for slow cooling and 50% for the rapid cooling process. The reduction of Poisson’s ratio is due to micro-crack generation and an increase in transverse strain.

The Poisson’s ratio is related to the ratio of p-wave velocity and s-wave velocity. The ratio decreases as the temperature increases [14]. Aim et al. [22] observed the Poisson’s ratio changes in Stripa Granite up to 600 °C in two unconfined stress conditions. Homond-Etienne and Houpert [15] observed a negative Poisson’s ratio of granite in compression as well as in tensile stress conditions up to 600 °C. The abnormality sign of lateral strain leads negative Poisson’s ratio, which is theoretically considered for isotropic material. Yang et al. [5] tested the ratio in granite up to 800 °C. They observed that the static Poisson’s ratio decreases from 0.127 to 0.038 up to 600 °C and then increases rapidly from 0.038 to 0.367 up to 800 °C. However, the dynamic Poisson’s ratio does not depend on the temperature. Wu et al. [28] showed that the Poisson’s ratio does not show a noticeable effect on cyclic heating and cooling due to rock heterogeneity.

The compressive strength of a material is the capacity to withstand the load under compression. The compressive strength is basically performed for stress–strain analysis of a material under different loading conditions. Compressive strength [35] determined at different temperatures revealed that it decreases with an increase in temperature [1,35]. The tests were performed under different heat treatment conditions, i.e., under slow cooling–heating or rapid heating–cooling and also quenching in a different medium. In the case of slow cooling, it was observed that the compressive strength reduces by about 5%, but strength reduces when heating the sample beyond 600 °C.

From the experimental results, it was found that the compressive strength first increases slightly up to 300 °C and then decreases gradually up to 800 °C [5]. As the rocks are heterogeneous materials, the strength distribution is unequal in different positions, and the stress concentration affects the formation of cracks. The expansion of the thermally affected rock matrix reduces the distance of minerals, resulting in the enhancement of the bonding strength. So, firstly, the overall strength increases [36,37]. Further, the increase in temperature results in the weakening of grain boundaries, permanent damage to the rock due to the formation of cracks, and a decrease in compressive strength. The rapid cooling method significantly reduces the compressive strength than the slow cooling method due to the thermal shock [10]. Jinhui Xu et al. describe the typical dynamic mechanical characteristic of granite material under strain and temperature. They have discussed that the dynamic compressive strength manifests and increments when the rise of temperature is from 50 °C to about 100 °C. Dynamic compressive strength after that point becomes reduced with higher temperature. However, the elastic modulus becomes more sensitive toward the change in temperature in comparison to the strength rate. The damages related to thermal behavior appreciably decrease at a lower temperature. They recommended that 110 °C is a critical temperature that inflicts alteration in thermomechanical properties and has a relationship with the dynamic strength of granite samples [56]. Sheng-Qi Yang et al. [57] experimented on granite up to 800 °C temperature. The axial compressive test was conducted, and thermal damages, strength, and deformation were measured. Kai Chen et al. [58] have conducted the uniaxial compressive test of heat-treated granite, and the Weibull distribution damage law demonstrates the analysis of the damage behavior of granite. 

Tensile strength of granite after thermal treatment for both slow cooling and rapid quenching show decreasing trends. In the slow cooling process, the reduction rate of tensile strength is 73% up to 600 °C and about 78% for the rapid cooling process. After 400 °C, the rate of decrease of tensile strength changes sharply [1]. Gautam et al. [12] observed that the tensile strength of Jalore Granite increased gradually up to 300 °C due to the expansion of rock molecules and compact specimen, but beyond this temperature, the tensile strength decreased sharply up to 600 °C. The sharp decrease beyond 300 °C is ascribed to the loss of water molecules and minerals from the material, the expansion coefficient of minerals, and the distribution of thermal stress. In the case of the Stripa Granite, tensile strength first increased slightly up to 100 °C then decreased up to 600 °C due to the increase in the microstructure of the material [22]. The tensile strength of the Senones Granite decreased more rapidly than the Remiremont Granite up to 600 °C due to an increase in the density of micro-crack [15]. The tensile strength of Biotite Granite decreased up to 1000 °C from 25 °C with decreasing rate of 35% [25]. The tensile strength of granite decreased by about 20% when it was in cyclic heating to 600 °C and subsequent quenching in liquid nitrogen [28]. R. Tomas et al. [59] conducted an experiment on 46 cubic granite samples, heating the temperature from 105 °C to 700 °C and cooling the specimen in different conditions. They have observed that the tensile stress is different between the two adjacent particles and improved the hardening effect of granite. The elastic modulus improved due to the hardening effect when the temperature was below 500 °C. Timo Saksala [60] approaches a 3D numerical prediction model to predict the effect of the tensile strength of granite. The sample is heated up to Curie point (near 527 °C), and then the sample is cooled down with air. The simulation results are validated to predict the tensile strength analysis and induced thermal crack propagation.