The bond behaviour of CFRP-to-concrete bonded joints under fatigue cyclic loading: An experimental study

•CFRP-to-concrete bonded joints exhibit different failure modes when subjected to fatigue cyclic loading.•Bond-slip relation of CFRP-to-concrete bonded joints under fatigue loading was obtained.•The fatigue damage starts to accumulate when the interfacial shear stress is 0.8 of the maximum interfacial shear stress. Carbon fibre reinforced polymer (CFRP) has been accepted by the construction industry as an excellent material for strengthening reinforced concrete (RC) structures against flexural and shear loads. Behaviour of such CFRP strengthened RC structures under quasi-static loading conditions is well understood. Most of the existing studies on CFRP strengthened RC structures under fatigue cyclic loading are focused on demonstrating the effectiveness of the CFRP strengthening on enhancing the fatigue life. However, bond-slip behaviour, a key behaviour governing the performance of flexural/shear strengthened RC structures using externally bonded CFRP, under fatigue cyclic loading remain largely unknown. This paper presents an experimental study aimed at investigating the behaviour of CFRP-to-concrete bonded joints under fatigue cyclic loading. A novel data acquisition system was developed to obtain the strain distribution along the bond length at required force intervals. Experimental results revealed that CFRP-to-concrete bonded joints under fatigue cyclic loading could fail in many different failure modes including, cohesion failure within concrete, cohesion failure within adhesive, and interlaminar failure within CFRP laminate. Failure mode was found to be dependent on the strength of concrete, type of the CFRP laminate, and loading amplitude. Bond-slip relations under fatigue cyclic loading showed that the fatigue damage initiates when the interfacial shear stress is above 80% of the interfacial shear strength.