Flat-face epoxy-bonded concrete joints loaded in torsion: Physical modelling

Joints in concrete structures must perform under various complex loads including torsion. This paper reports the results of an experimental programme investigating the static torsional performance of epoxy-bonded concrete joints. Torsion tests were performed using a custom experimental setup able to apply torque on a hollow concrete prism with an epoxy joint in the middle. The tested specimens failed in both cohesive and mixed modes. The cohesive failure mode was characterised by cracking in the body of concrete, while the mixed mode also included partial debonding of the joint. The cohesive mode was dominant, more ductile and exhibited higher torsional strength. The cracking behaviour of the jointed specimens was typical of concrete prisms under torsion except that in the mixed mode a crack developed along the joint on two or three specimen sides. Digital Image Correlation, applied for monitoring surface strain, showed that inclined bands of high shear strain passed across the joint during the tests. The mechanism of concrete-epoxy debonding was investigated using two standard testing methods. The low shear strength of concrete near the epoxy joint was identified as the source for the weaker, stiffer and more brittle response of the mixed failure mode in the torsion tests.