Extrinsic influence of environment on the corrosion behaviour of enamel-coated steel dowel bars

A new type of enamel coated dowel bars for use as concrete pavements has been recently developed and implemented. A gradual deterioration of such bars can occur due to corrosion occurring at locations of the fine microscopic cracks and other defects in the coating. The results of a study aimed at evaluating and understanding the corrosion resistance of such dowel bars is presented and comparisons made with corresponding epoxy-coated dowel bars. Identical defects were introduced onto the surface of the dowel bars with the two types of coatings. The extrinsic influence of environment and resultant corrosion based on type, location and severity of the defects was carefully examined. Test results reveal the corrosion resistance of enamel-coated dowel bars to be as good as the corrosion resistance of the corresponding epoxy-coated dowel bars. The presence of corrosion products was essentially confined to locations of the defects in the test specimens when the steel was exposed to concrete and subject to induced current to accelerate corrosion thereby demonstrating the enamel coating on the surface of the dowel bars to be effective in isolating the steel from the surrounding concrete and concurrently providing enhanced resistance to corrosion. Also, the enamel-coated dowel bars did not experience peeling of the coating at the interface. The epoxy-coated dowel bars revealed peeling of the epoxy coating from the surface that eventually got stuck to the inner surface of the surrounding concrete. This demonstrated that the enamel-coated dowel bars would perform better under prevailing service conditions in concrete pavements where relative free sliding is both essential and required.