Abstract: With the increase of temperature, macroscopic mechanical parameters of granite often experience a slight increase, a slight decrease, a substantial reduction in several stages. The nanoindentation test is carried out on the main mineral components of the heat treated granite to reveal the microscopic mechanism of the evolution of the macroscopic mechanical parameters of the granite with temperature. (1) The microstructure does not change significantly under the temperature of 300 ℃; and no microcracks are found. At the temperature between 300 ℃ and 500 ℃, microcracks begin to occur in the interior of the rock mass; when the temperature exceed 500 ℃, a large number of microcracks are generated in the rock mass and gradually expand and increase. (2) The elastic modulus and hardness of quartz increased slightly at 300 ℃. When the temperature exceeds 300 ℃, the elastic modulus and hardness begin to decrease. When the temperature exceeds 500 ℃, the crystal structure changes from phase to phase; 400-500 ℃, the elastic modulus and hardness begin to decline. When the temperature exceeds 800 ℃, the elastic modulus and hardness drop sharply, for mica, the elastic modulus and hardness increase within 800 ℃, above 800 ℃, the modulus of elasticity and hardness decrease sharply. (3) The macroscopic mechanical properties of granite are related to the mechanical properties and microstructure of the main mineral components; it is mainly controlled by the former in the range of room temperature to 300 ℃ and controlled by the combination in the range of 300-500 ℃. When it exceeds 500 ℃, it is mainly controlled by the latter. The related research results can provide experimental data and theoretical support for studying the temperature effect of granite and other rocks.

Key words: heat treatment, nano-indentation, mineral composition, elastic modulus