Effects of thermal treatment on the fracture behavior of rock-concrete bi-material specimens containing an interface crack

The study of the fracture characteristics of rock-concrete structure containing an interface crack under high temperature is vitally significant for the durability and stability assessment of concrete construction projects on rock foundations. Brazilian splitting tests were performed on rock-concrete cracked straight-through Brazilian disc (CSTBD) specimens after different heat treatment temperatures. The crack extension process of the specimen was analyzed using digital image correlation (DIC) technique. The effects of temperature, interface crack inclination and concrete strength on fracture characteristics were investigated. The results indicate that at high temperatures, free water and structural water escape from rock and concrete, and crystal structure of the mineral composition is altered, which induces the development of internal pores and microcracks in the material and weakens the mechanical properties. The specimen displays brittle fracture behavior at 25 degrees C-300 degrees C, and plastic fracture behavior at 500 degrees C-700 degrees C. The wing crack extension in concrete (weak material) occurs preferentially, and this phenomenon becomes more apparent with raising temperature. When alpha <= 45 degrees, the length of crack extension along the interface increases with increasing temperature, while when alpha > 45 degrees, the increase in temperature makes the crack initiation closer to the disc center. The fracture energy and the difference in fracture energy between varying inclinations decrease with raising temperature. Furthermore, temperature has an essential impact on fracture toughness. As temperature increases, the fracture toughness generally decreases, the difference in mixed fracture toughness between different inclination angles gradually increases, and the fracture propagation resistance weakens.