Studying shear behavior and failure mechanism of concrete–rock interfaces between concrete structures and rock mass is highly important. To this end, laboratory direct shear tests were conducted on several bonded interfaces. The effect of normal stress, displacement rate, and bonding percentage on shear behavior of bonded joints were also evaluated. The results showed that the adhesive bond between concrete and rock has the most important effect on shear mechanism of concrete–rock interfaces. When the normal load is low, the asperities do not contribute in shear process, so the shear strength of the joints is governed by adhesive bond. The only contribution of the asperities is that they show a small peak after bond breaking peak. When the normal load is high, the asperities break simultaneously with adhesive bond and they show their contribution in the whole shear process. In a constant normal load, by decreasing bonding percentage, the brittle failure of the bonded joints is changed into softening failure because of less contribution of the adhesive bond and more contribution of the rough asperities in joint failure. Acoustic emission (AE) monitoring of bonded joints showed that for all different tested samples under various loading conditions, there has been no or very few AE activities before adhesive bond breaking point, indicating that other parameters (roughness, normal load, displacement rate) are impressed by adhesive bond and maximum shear strength is determined by this parameter.
Applicability of acoustic emission (AE) for localizing asperity damaged zones and damage intensity in joint surfaces was evaluated in this paper. With this attempt, rock joint samples obtained from tension splitting of the rock cores were tested under constant normal load condition. The locations of the AE sources were determined from propagation velocity of acoustic waves and by measuring the transferring time from event source to AE sensor. These sources correspond to asperity damaged zones. The AE signals generated from asperity degradation of joint surfaces were detected during shear testing. The energy of the generated signals was also measured to assess the intensity of the asperity failure. The results of this study showed that the AE method has a good capability in localizing the asperities’ failure points and the intensity (energy) of the asperities’ failure.
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