Fatigue behavior of FRP–concrete bond under hygrothermal environment

•Hygrothermal environment adversely affects the bond behavior of FRP–concrete interface.•Fatigue life of the interface is significantly reduced after the environmental exposure.•Bond stiffness/strength of the interface is also apparently reduced after the exposure.•A 3-stage linear damage model was presented to describe the fatigue damage of the interface. In subtropical coastal regions, fiber reinforced polymer (FRP) strengthened concrete bridge structures are typically subject to harsh environmental attack such as temperature and humidity variations during their service (i.e. under cyclic vehicle loading). For such FRP strengthened concrete structures, fatigue performance of the FRP-to-concrete bond (referred to as interface hereafter for simplicity) is extremely important to the durability of the strengthened structures. In order to investigate the fatigue performance of the interface subjected to temperature and humidity variations, 17 double shear test specimens with carbon fiber laminate (CFL) were prepared, and experimental study was carried out on the fatigue performance of the interface in a simulated environment with constant temperature and relative humidity (RH) (60°C, 95%). The results showed that the adopted temperature and RH adversely affected the bond behavior of CFL–concrete interface. In particular, the fatigue life of specimens under the above temperature and RH is significantly less than that of reference specimens without hygrothermal pretreatment. The test results also showed that the fatigue life can be reduced by a higher stress level. Based on the analysis on the bond-slip behavior of the interface, a three-phase fatigue damage model was presented to describe the fatigue damage process of the CFL-to-concrete bond under fatigue load while exposure to a certain hygrothermal environment.