Steel Corrosion in Submerged Concrete Structures-Part 1: Field Observations and Corrosion Distribution Modeling

Reinforcing steel in submerged marine concrete structures has generally been regarded as less susceptible to corrosion than reinforcing steel in atmospheric concrete, in part as a result of the limited availability of oxygen for the cathodic reaction at the steel surface. As durability expectations and requirements for submerged reinforced concrete (RC) structures become more ambitious, however, the need for data associated with the actual condition and fate of embedded reinforcing steel has increased. Consequently, a field assessment of decommissioned RC pilings from marine bridges was conducted. The assessment revealed multiple instances of corrosion with appreciable localized loss of steel cross section. A corrosion distribution computer model was subsequently developed for a partially submerged RC bridge pile under steady-state conditions. The model output indicated that, under oxygen diffusional limitation in the submerged region, cathodic reaction rates that might be negligible in cases of uniform corrosion can support substantial corrosion rates when corrosion is localized. The model output was consistent with the results of the field assessment. Model output also indicated that eliminating corrosion in the evaporative/splash zone could in some cases increase corrosion vulnerability of steel in the submerged region.