## 3 Test Results
### Changes in Microscopic Properties  
As shown in Figure 6, the morphological changes in the mineral composition and microcrack-development characteristics of the granite samples after high-temperature treatment were observed using an optical microscope, and optical microscopic images of the samples treated at different temperatures were obtained. For the convenience of statistics and resolution, intergranular cracks are marked in red, intragranular cracks in the quartz are marked in yellow, intragranular cracks in the feldspar are marked in green, and intragranular cracks in the biotite are marked in orange. The rock was mainly composed of plagioclase, potassium feldspar, quartz, biotite, and a small amount of opaque minerals. In the original state, the contact edges between minerals in the rock were straight or smooth, a small number of primary cracks were observed in the quartz and feldspar crystals, and intragranular cracks were also rare. After heating at 200 \({}^{\circ}\)C, a small number of cracks could be observed inside the plagioclase and quartz particles, and intergranular cracks were distributed at the boundaries of the plagioclase and quartz. Compared with those in the initial state, the morphology of each mineral did not change much, but some plagioclase particles were slightly fragmented. At 400 \({}^{\circ}\)C, fragmentation occurred at the contact points between various minerals in the rock, with a small number of cracks appearing inside the potassium feldspar and many light brown microcracks appearing inside the quartz particles. Compared with those of the samples at room temperature, the morphology of each mineral did not change much, with biotite showing a slight reddish-brown color, indicating oxidation and obvious fragmentation within each mineral. As the heating temperature increased to 600 \({}^{\circ}\)C, the fragmentation phenomenon at the contact points between minerals in the rock became more pronounced than that in the sample at 400 \({}^{\circ}\)C, and the number of microcracks in the feldspar minerals significantly increased. Black mica exhibits a more reddish-brown color and extensive oxidation. Due to the occurrence of quartz at the 573 \({}^{\circ}\)C \(\alpha\)-\(\beta\) phase transition, at high temperatures, (\(\beta\)) the volume of the phase quartz particles increased and recovered after cooling to room temperature. (\(\alpha\)) The process of the expansion and contraction of quartz led to an increase in the number of broken minerals at the boundaries of the quartz minerals, an increase in the crack width, and an increase in the number of intergranular and intragranular cracks. After heating at 800 \({}^{\circ}\)C, the morphology of the various minerals changed significantly, with a large number of intergranular and intragranular cracks appearing. The fragmentation phenomenon of the internal and contact parts between minerals was more obvious. After high-temperature treatment at 1000 \({}^{\circ}\)C, the surfaces of the potassium feldspar, plagioclase feldspar, and quartz all became blurred, indicating strong weathering. Black mica became redder and had a greater degree of oxidation than 800 \({}^{\circ}\)C, while the degree of fracture of black mica was also greater. The various mineral components in the rock exhibited a large number of intragranular cracks, which were interconnected. The width of the intergranular cracks reached the maximum among all temperature levels. Figure 5: Comparison of granite appearance after different temperature treatments. Figure 7 shows the optical microscopic images of granite samples treated at different temperatures at the same ratio, which clearly reveal the development of cracks within the rock. In the initial state, the granite had fewer primary cracks, and the surface of the mineral particles was relatively smooth. When the temperature rose to 200 \({}^{\circ}\)C, the granite underwent thermal damage, leading to an increase in internal cracks.