Enhancement of rebar (smooth surface)-concrete bond properties by matrix modification and surface coatings

Abstract

The interface between reinforcing steel (rebar) and cement-based matrices plays an important role in determining the behaviour of reinforced concrete. Enhancement of rebar–concrete bond properties can improve the performance of reinforced concrete structures as whole. In this study, several methods, including matrix modification and surface modifications, have been investigated on their effects in improving the bond properties. The matrix modification was achieved by incorporation of polyvinyl alcohol (PVA) powder into the matrix. The surface modification were achieved by coating the cement, cement plus PVA, and cement plus silica fume powders on to the rebar surface. The enhancement of the mechanical properties of the interface by these modifications was evaluated by the pushout test, in which a closed loop controlled set-up was used to continuously measure force and displacement during loading. The experimental data were analysed by using a simplified theoretical model. The interfacial properties of the transition zone, including the stiffness, strength, friction and fracture energy of the interface, were obtained by using this model. It was found that the mechanical interfacial properties can be improved by the above-mentioned treatment methods. The interface mechanical behaviour was also investigated by microhardness measurement and scanning electron microscopy (SEM). The experimental results showed that the matrix and surface modification did increase the interfacial microhardness and reduce the porous region of interface, which were consistent with macromechanical property measurements.