Bonding properties of composite interface composed of concrete/magnesium phosphate cement-based ECC/CFRP plate

To prevent premature debonding of fiber reinforced polymer (FRP) from concrete surface and achieve rapid repair of flexural members, magnesium phosphate cement-based ECC (MPC-ECC) with many advantages of early strength, multi-cracking and steady-state cracking was combined with carbon fiber reinforced polymer (CFRP) to explore the feasibility of strengthening flexural members. The bonding properties of the concrete/MPC-ECC/CFRP composite interface were investigated in this study. Results showed that the higher composite interface bearing capacity can be obtained by using the MPC-ECC as a binder compared to the use of epoxy resin adhesive, which can reach 15.9 kN. In addition, it was found that a good bonding between the high-pressure water gun treated concrete and the MPC-ECC was obtained, which could ensure that the concrete/MPC-ECC interface does not fail before the MPC-ECC/CFRP interface fails. Compared with the concrete/CFRP interface, the maximum effective bond length, slip value of CFRP, and energy consumption of the concrete/MPC-ECC/CFRP composite interface are greatly improved, all of which increase with the increase of MPC-ECC thickness. Furthermore, the composite interface has obvious residual stress in the failure stage, which can avoid the sudden failure of specimens. However, the increase of curing age from 7 days to 28 days does not significantly improve the bonding performance, which reflects that the bond strength of the composite interface mainly develops within 7 days, that is, possessing good early strength characteristics.