Effect of different treatment of surfaces in concrete-to-concrete interface

Shear forces transferred between concrete-to-concrete contacts are a major factor in the strength of many reinforced concrete structures. In composite construction, the interface is the medium that separates the old and new concretes during the precast and cast-in-place concrete assembly. The interface must ensure the transmission of shear force as a main requirement to resist the applied loads on the structure. Under this scope, the goal of this paper is to study the behavior of connections between the old and new concretes with different surface roughness. Initially, an experimental study was conducted to investigate the transfer of horizontal shear force between two concrete layers at different times and different transmission mechanisms without the use of dowel action. The surface of the old concrete was treated with three different surface textures (smooth, epoxy, and sandblasted), then seventeen specimens were tested. The ‘‘push-off” test method was conducted to determine the relationship between the monotonous load and slip to determine the strength of connectors. The results showed that the interface surfaces treated by epoxy exhibited the maximum average shear strength and the maximum average load compared with the smooth and sandblasted surfaces. The sandblasted interface surfaces resulted in a slightly lower average of failure slip than the epoxy interface. While the smooth interfaces show nonobvious load-slip relations, the epoxy treated surfaces revealed linear shapes and the sandblasted surfaces showed nonlinear shapes.