Study on the mechanism of mechanical property strengthening of Beishan granite under mild temperature condition

Abstract

Many researches found that mechanical properties of granite were strengthened under the mild temperature range (within 300 °C), which is positive for the long-term safety of the high-level radioactive waste (HLW) geological disposal engineering. To study the thermal strengthening mechanism of granite under elevated temperature by the decay heat of the HLW, a novel experiment was carried out which stress loaded firstly to cause stress damage, then thermal loaded to study the temperature effect on stress damaged granite. Results show: (1) the deformation memory effect and the Kaiser effect existed after stress loaded for non-thermal treated and 120 °C treated on granite, while the deformation memory effect (DME) was significantly faded after 250 °C treated. (2) The volume of pores/cracks in Beishan granite increased after stress loaded, then decreased significantly after 120 °C and 250 °C treated. (3) The deformation behavior, AE activity and pores/cracks closure all showed that the stress induced damage could be healed at elevated temperature, which is positive for the HLW disposal engineering. (4) A viscoelastic frictional sliding model was used to analyze the mechanism of DME fading and the mechanical property strengthening.

Keywords

• Thermal healing
• Acoustic emission
• Pore size distribution
• DME and DRA