A cohesive FE model for simulating the cracking/debonding pattern of composite NSC-HPFRC/UHPFRC members

•A study about retrofitted concrete elements is presented.•The retrofitting is realized by using HPFRC or UHPFRC layers.•The interaction between the substrate and the overlay is modeled through a FE model.•An experimental bond test is performed to characterize the interfacial behavior.•Numerical and experimental results in terms of axial load vs slippage are obtained. The aim of this work is to propose to practitioners a simple cohesive Finite-Element (FE) model able to simulate the cracking/debonding pattern of retrofitted concrete elements, in particular Normal-Strength-Concrete members (slabs, bridge decks, pavements) rehabilitated by applying a layer of High-Performance or Ultra-High-Performance Fiber-Reinforced-Concrete as overlay. The interface was modeled with a proper nonlinear cohesive law which couples mode I (tension-crack) with mode II (shear-slip) behaviors. The input parameters of the FE simulation were provided by a new bond test which reproduces a realistic condition of cracking/debonding pattern. The FE simulations were accomplished by varying the overlay materials and the moisture levels of the substrate surface prior to overlay, since findings about their influence on the bond performances are still controversial. The proposed FE model proved to effectively predict the bond failure of composite NSC-HPFRC/UHPFRC members.