Modelling of debonding between old concrete and overlay: fatigue loading and delayed effects

Abstract

The paper focuses on the propagation of debonding along an interface between a substrate simulating old concrete and a cement-based thin bonded overlay. The aim of the study was to obtain the data necessary for relevant and efficient debonding modelling. The work combined experiment and simulation. Two types of overlay materials were investigated, fibre reinforced mortar (FRM) and plain mortar. Tensile tests were performed to obtain the residual normal stress–crack opening relationship. The shrinkage of the overlay material was characterized by tests on prismatic specimens that showed the evolution of both drying shrinkage and autogenous shrinkage versus time. The substrate—overlay interface was investigated by static tensile tests to provide the relationship between debonding opening and residual normal tensile stress. Its evolution under fatigue loading was assumed to follow a cyclic bridging law for plain concrete. Three-point flexural fatigue tests were then performed on repaired substrate to obtain information on the structural behaviour of the interface. The debonding propagation was monitored by a video-microscope with a magnification of 175× . Relying on the identified and quantified parameters, the above mentioned fatigue tests were modelled by the finite element method using the CAST3M code developed in France by Atomic Energy Commission (CEA). A comparison between model and experimental results shows good agreement and proves the important role of interlocking in the debonding mechanism.