Physical and mechanical properties of Beishan granite after different high temperature treatments

In China, Beishan granite is chosen as a potential host surrounding rock of a high-level radioactive waste (HLW) repository. For this research, Beishan granite specimens were heated up to 300 °C, 400 °C and 500 °C, respectively. And conventional triaxial compression tests were conducted after cooling down the samples. The results show that after 300 °C, 400 °C and 500 °C heating treatment, the diameter of samples increases by 0.066%, 0.143% and 0.409%, respectively, which is a little larger than the axial length changes. Mechanical tests show that peak strength increases slightly with increasing temperature. However, the dilatancy threshold is lower than that observed for samples which have not experienced heating treatment. Peak strain and dilatancy threshold strain show a strong temperature dependence. The higher the temperature, the greater the strain. Furthermore, increasing temperature has negative influence on threshold elastic modulus Ec and tangent elastic modulus Et. Poisson ratio decreases when temperature increases from 300 °C to 500 °C, but it is still larger than that observed for samples which have not experienced heating treatment. In addition, AE monitoring shows a quiet period in the initial loading stage, which proves that the micro cracks are closed during heating and contribute to the increase of peak strength.