Abstract
The interface of old to new concrete is the weakest plane during retrofitting and repairing of concrete structures, resulting in the interface or adhesive failure of the composite formed. Various surface preparation techniques and adhesives have been used and reported in the literature to improve the bond behavior of concrete-to-concrete interface. Epoxy is a commonly used adhesive to bond existing concrete with new overlay concrete, as it provides high adhesion and chemical resistance; however, inadequate roughness and low strength negatively affect the epoxied concrete joints, causing poor bonding at the concrete interface. On the other hand, the use of graphene oxide (GO) in epoxy showed significant enhancement in its mechanical properties. Hence, in the present study, GO-modified epoxy has been proposed as an adhesive to improve the bond performance of the interface between existing and new concrete by conducting split tensile, bi-surface shear, and slant shear tests. Simultaneously, a comparison has been carried out with other frequently used surface preparation techniques such as grinding wire brushing (GW), grooves, and adding carbon and glass fiber laminate over the existing concrete with and without neat (plain) epoxy. The GO-modified epoxy has been prepared using three different GO concentrations; out of them, 0.05% by weight turned out to be the optimum concentration and performed best under all bond strengths and resulted in concrete failure instead of adhesive failure. Furthermore, scanning electron microscopy (SEM) revealed homogeneous dispersion of GO at 0.05% by weight and formation of the bond between GO and cement hydrates with both concrete interfaces. As a result, GO-modified epoxy turned out to be a high-strength adhesive to join existing concrete with fresh overlay concrete for strengthening, retrofitting, and repairing concrete structures and shows an effective composite action.
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