Abstract
The thin bonded cement-based overlay technique is well known nowadays for repair work on large concrete areas. However, these overlays have sometimes posed problems because of their uncertain durability: cracks and interface debonding may occur after a period in service. This paper, associating experiment and simulation approaches, focuses on some key parameters influencing debonding propagation along the concrete overlay-substrate interface. The case of monotonic loading has been treated in a previous contribution, so this work is dedicated to the case of fatigue loading, which is a more realistic representation of exploitation conditions. Based on the cohesive crack concept, a model was built and validated by comparing numerical and experimental results of fatigue tests on overlay-substrate composite specimens. Different factors having an impact on interface debonding under fatigue loading were then investigated. First, the loading level was considered. Then, for the overlay material, the parameters analysed were autogenous shrinkage, Young's modulus, tensile strength, and types of fibre-reinforcement. For the curing conditions, the relative humidity of the surroundings was taken into account. Concerning the overlay-substrate interface, its normal tensile strength and its bond defects were examined. The numerical analysis allowed the influence of each factor to be evaluated. In particular, the effect of shrinkage on the durability of the composite specimens was clarified. The importance of the capacity of fibres to control debonding by restraining crack opening was proved.