The microstructure of epoxy bonded steel-to-concrete joints

Exposure tests are being carried out on concrete specimens strengthened by steel plates epoxy bonded to the surface of the concrete. Visual examination has shown that corrosion of the steel plate can take place at the interface between the steel and the adhesive and the existence of chlorides in the corrosion product have been detected. Similar results have been observed on a small section of plate removed from a strengthened highway bridge. A microstructural analysis of the concrete/resin system using marker solutions and electron microscopy has revealed cracks and pores in both the concrete and the resin. It has been shown that these cracks act as routes for corrosive liquids to reach the steel plate and cause corrosion. The use of a primer on the steel plate has been generally successful in inhibiting the corrosion. (A)