Analytical model to predict the lifetime of concrete members externally reinforced with FRP

This paper presents a multiscale analytical model that predicts the lifetime of concrete members with externally bonded FRP reinforcement. The lifetime is dictated by the debonding of external reinforcement, which takes place within the concrete cover, where microcracks (initial flaws) propagate due to the shear stresses that the bond subjects the concrete cover to. The lifetime is estimated from the propagation of such cracks until a critical crack length is eventually reached, which causes the external FRP reinforcement to lose the bond (delayed debonding). The model provides a closed form-solution for the life-through estimation of the external reinforcement, which consists of the interaction between bond shear stresses and lifetime (maximum bond shear stress versus delayed time, i.e. the ultimate domain). Crack growth is modeled at the mesoscale, where the velocity of the cracks depends on the mode II stress intensity factor, but not on the microstructure. The model assumes that the carbonation process has reduced the plasticity and cohesion of the concrete cover to zero; thus, the predictions are slightly conservative (lower bound model). Some experimental results on real scale beams are presented to corroborate the theoretical findings. A practical application of the model shows that delayed debonding significantly reduces the service life of concrete members with externally bonded FRP reinforcement.