Direct Measurement of Traction–Separation Law of Concrete–Epoxy Interfaces Subjected to Moisture Attack under Mode-I Loading

Abstract

A proper traction–separation law based on the physical behaviors of the concrete–epoxy interface is needed to simulate the debonding behavior of fiber-reinforced polymers–strengthened concrete structures. However, no method is available to measure the traction–separation law of the concrete–epoxy interface under mode-I loading. To address this gap, this study proposes a novel testing method to directly measure the traction–separation law of the concrete–epoxy interface. This method uses a wedge-splitting test specimen that not only requires simple testing setups but also produces stable crack propagation in the specimen. By adopting a rigid body moment assumption, the traction in the concrete–epoxy interface is expressed as a function of the applied load and the crack opening displacement. As a result, this method can directly calculate the relationship between the traction and the separation of the concrete–epoxy interface by simply recording the crack opening displacement and the applied load during the test. The success of the new method has been confirmed through experimental study. Testing results show the traction–separation law of the concrete–epoxy interface under mode-I loading can be approximated by a tri-linear law. The new method is also used to evaluate the long-term durability of concrete–epoxy interface subjected to moisture attack. It has been found that conditioning the interface specimens in water can significantly reduce the tensile strength and fracture toughness of the interface. The effectiveness of applying silane coupling agent to enhance the durability of the concrete–epoxy interface has also been confirmed by this new testing method.