Investigation on fracture properties and FPZ evolution of concrete/rock bi-material interface after low-level fatigue loading.

This study investigated the fracture properties and FPZ evolution of concrete/rock bi-material interface after low-level fatigue loading. Firstly, the fatigue loading tests were performed under the frequency of 1.0 Hz with respect to two upper limits less than the initial cracking load, i.e. 60 % and 70 % of the peak loads. After 80,000 loading cycles, the quasi-static loading tests were performed to measure the fracture behavior of concrete/rock bi-material interface. Thereafter, the DIC tests were conducted to observe the crack extension process and analyze the FPZ evolution. According to the comparisons of fracture behaviors between the fatigue specimen and control specimen, the effects of the low-level fatigue loading on the fracture properties and FPZ evolution of concrete/rock bi-material interface were discussed. The results indicate that the unloading paths follow the loading paths coincidentally for each loading cycle, and this means that the mechanical response of the concrete/rock bi-material interface under low-level fatigue loading is elastically dominated. After the low-level fatigue loading, the initial cracking load and initial fracture toughness exhibit obvious increasing tendency, whereas the unstable fracture toughness decreases obviously, which is induced by the significant decrease of the critical crack length. In addition, the fully-developed FPZ length and the corresponding crack length of fatigue specimen are less than that of control specimen, indicating that the brittleness of concrete/rock bi-material interface becomes larger after low-level fatigue loading. [ABSTRACT FROM AUTHOR]