CORROSION PROTECTION PERFORMANCE OF BRIDGE DECKS AND MARINE SUBSTRUCTURES CONSTRUCTED WITH EPOXY COATED REINFORCING STEEL IN VIRGINIA

Corrosion protection performance of epoxy coated reinforcing steel (ECR) was assessed in three bridge decks and three marine pile structures in Virginia in 1996. The decks were all constructed with an upper mat of ECR and a lower mat of 50% bare and 50% ECR as reinforcing steel and 100% bare bars as temperature/shrinkage steel. The decks were 17 years old at the time of the investigation. Two of the marine structures were eight years old and the other was seven years old at the time of the investigation. The investigation included a visual surface crack survey of the right traffic lane and the drilling of 12 cores randomly located in the lowest 12 percentile cover depth in each deck. The marine piles were drilled at an elevation between high and low tides. A single core was taken from a total of 30 piles. Visual inspection of the concrete core and the extracted ECR was performed. Measured concrete properties included the moisture content, absorption, percent saturation, carbonation depth and effective chloride diffusion constant. The effective diffusion constants were determined for the decks only because the concrete piles had been coated with an epoxy surface coating. ECR measured properties were physical damage, coating thickness, adhesion loss and corrosion at damaged sites and undercoating corrosion at adhesion test sites. Chloride content of the concrete and carbonation of ECR trace were also determined. The results show that the epoxy coating has debonded and is debonding from the reinforcing bar. The observed debondment of the epoxy coating from the bar is in agreement with the thermodynamic instability of epoxy-ferric oxide systems in moist environments and other ECR field studies. The debondment of the epoxy occurs in concrete without the presence of chloride. The rate of debondment is related to the concrete moisture conditions (percent moisture content and annual variations), temperature, coating defects (holidays, dented and mashed areas, and holes) and other bar and coating properties. Epoxy coatings will debond from reinforcing steel in Virginia's marine environments in about six years and about 15 years in bridge decks. Since Virginia uses low permeable concrete and epoxy coats the concrete surface of marine piles, the epoxy coating on the steel will be debonded from the steel before the chlorides arrive at the depth of the ECR in piles. For bridge decks, the epoxy coating will be debonded from the steel before the chlorides reach the depth of 12 percent of the ECR for 95 percent of the bridge decks. Thus, ECR is extending the service life of only five percent of the bridge decks in Virginia. Because the epoxy is debonded from the steel when the chlorides arrive, underfilm corrosion takes place in an underfilm acidic environment. The rate of underfilm corrosion is faster than bare steel in concrete and the service life extension provided by the debonded coating is nil. The in-place cost of ECR is about five percent greater than bare steel. Based an these results, ECR appears to provide only up to five years of additional service life for only five percent of the bridge decks in Virginia; hence the use of ECR in Virginia may not be cost effective. Additional decks should be evaluated to confirm the results of this and other studies. For the covering abstract see ITRD E111699.