Interface Between an Old Concrete and a Bonded Overlay: Debonding Mechanism

Abstract

The ageing of concrete structures creates the need for their repair. The thin bonded overlay technique is widely used; it is particularly suitable for the repair of large concrete areas. It is appropriate for slabs on grade (mainly industrial floors), pavements, bridge decks, walls and tunnels. Toppings and linings are similar applications. The aim of the overlay may be to smooth a damaged surface, and/or to improve the mechanical capacity of a structure by increasing its thickness, or to provide additional cover for corrosion protection. The durability of such repairs or overlays depends on the durability of their bond with the base structure; it is usually the critical aspect. Work, carried out in Laboratoire Materiaux et Durabilite des Constructions (Laboratory for building Materials and Constructions Durability) in Toulouse, France, is part of a larger programme started in 1990. The programme objective is to achieve a thorough knowledge of the debonding mechanisms of an overlay. Design rules and practical recommendations eliminating or drastically reducing durability hazards are expected to be developed. The work reported here focuses on the debonding propagation along an interface, notably the major influence of the interlocking between the two faces of the debonding interface. The study relies on finite elements modelling and on the comparison with experiments. Having evidenced the major role of interlocking in the example of a crack propagation, the paper focuses on the actual case of an interface. Debonding propagates in mixed mode, mode I combined with mode II, bringing an extra degree of complexity. Beyond the problem of the mixed mode, an important issue is how interlocking changes while debonding propagates. Indeed, mode I debonding opening damages interlocking for both mode I and mode II. A mode II slip has the same coupled effect on interlocking. A very significant problem is taking into account the coupling of mode I and II displacements to evaluate the actual value of the interlocking at any step of the propagation. The involved parameters have been identified and a method is proposed to take into account the coupling. The comparison with experimental results is promising. This research opens a new approach on the mechanism of the propagation of a debonding along an interface. The next step will consider evolution of the interlocking in the case of fatigue loading.