Shear bond between existing concrete and high-strength fiber reinforced overlay: Influence of substrate strength and interface roughness

Bonded concrete overlays are widely used for strengthening and repair of concrete members. The aim of a concrete repair is to restore the load-carrying capacity and stiffness of a concrete member, and to extend the service life of a structure. The bond between substrate and overlay is one of the main factors concerning the serviceability of a composite member consisting of concrete of different ages. This paper aims at better evaluating, through an extensive experimental program, the shear bond strength between existing concrete and a subsequently applied fiber reinforced overlay. The main purposes of this test program are to study the influence of the substrate strength and of the substrate surface roughness on the interface bond strength between a substrate and overlay concrete. A refinement of a novel bond test, proposed by some of the authors of this paper, is also implemented. Results indicate that there is an increase in the bond strength with an increase in the substrate compressive strength. On the other hand, the results suggest that, for the substrate strength classes investigated, the surface roughness does not influence the interface bond strength.