Study on thermal crack characteristics of granite in Shandong Province, China under different temperatures and heating/cooling treatments

The qualitative and quantitative analysis of crack initiation characteristics, extended procedure, and crack network morphology of rock under different temperatures and heating/cooling paths was conducted in order to delve deeper into the mechanism of thermal cracking, and the analytical perspectives mainly include microstructure, thermodynamics, and mineral crystal properties. Research results indicate that 200–300 °C and 600 °C are two obvious mutation points of water-cooled samples, while air-cooled samples show mutation points around 600 °C. The initiation positions of thermal cracking under all temperature paths are relatively similar, with intergranular crack located between particles at the edge of the sample or intercrystalline cracks in the middle of feldspar or quartz aggregates. Slow heating and rapid cooling contribute to the complexity of the thermal crack network, and rapid heating can form larger sized thermal cracks. The process of thermal cracking can be divided into three stages: initiation of small cracks, joint development of main cracks and small cracks, and interconnection of cracks to form a network structure. The thermal cracking mechanism is attributed to differences in expansion and thermal conductivity among various crystals.