Abstract: Mechanical behaviors and acoustic emission (AE) characteristics of mixed mode I-II fractures at rock-concrete interfaces are studied through three-point bending tests and four-point shear fracture tests on composite rock-concrete specimens. The results show the failure modes can be divided into three categories. A higher modal ratio or a rougher interface results in higher possibility of the occurrence of non-interfacial complex failure modes. Incipient cracking and unstable failure can be identified by abrupt changes in AE parameters; microcracks be classified into tensile and shear cracks byaverage frequency (AF) and the ratio of rising time to amplitude (RA value). Fracture damage evolution can be revealed by predicting the propagation direction of interface cracks using the space distribution of AE events. When the final overall destruction of the specimens is imminent, the dominant frequencies of AE signals change significantly, manifesting a sharp increase in both the number and amplitude of low-amplitude, low-frequency AE signals and sudden emergence of a few low-amplitude, high-frequency AE signals. Meanwhile, the dominant frequencies are shifting from discrete to continuous and their distributions span a relatively large range under the condition of high modal ratios.

Key words: fracture, concrete, rock, acoustic emission, interface