Abstract
Reinforcing steel in submerged concrete structures has generally been regarded as immune from corrosion given the limited availability of oxygen at the rebar surface for the cathodic reaction. As durability expectations and requirements for submerged reinforced concrete (RC) structures have increased however, the need for data associated with the actual condition and fate of the embedded reinforcing steel has increased. Autopsies were conducted on actual bridge piles decommissioned after a 60 year service life, and a predictive computer model was developed for a partially submerged RC bridge pile. The corrosion rate of the reinforcing steel in the pile model was evaluated under varying degrees of depassivation. The rate was found to be small given uniform depassivation of the steel but substantial in cases that involved highly localized anodes even if the overall cathodic reaction rates were small. Additional predictive modeling indicated that the implementation of corrosion control measures in the splash/evaporation zone could in some instances increase vulnerability to corrosion of steel in the submerged zone. While subject to some uncertainty due to the delay between pile extraction and autopsy, there were indications of significant localized steel corrosion in the decommissioned piles. The estimated corrosion rate was found to be substantial based an estimate of the initiation period derived from empirical and historical data. The traditional view that submerged concrete reinforcement corrosion is of little consequence merits revisiting, especially with increasingly ambitious durability goals.
