Oxygen Availability and Corrosion Propagation in RC Structures in the Marine Environment—Inferences from Field and Laboratory Studies

The splash and spray and tidal zones are generally assumed to be the most severe marine exposure environments with respect to steel reinforcement corrosion in concrete structures. However, it has been observed in several aged marine structures along the Southern African coastlines, that there is usually relatively insignificant reinforcement corrosion damage in the tidal zone, despite very high (above-threshold) chloride contents. To develop a full understanding of the severity of marine exposure conditions with regard to the actual deterioration, it is imperative that other factors that directly affect corrosion, such as oxygen availability at the steel surface (which is influenced by concrete quality, cover thickness and moisture condition), are carefully considered. The laboratory experimental work in the study presented in this paper comprised of different cover depths (10, 20 and 30 mm) and w/b ratios (0.5 and 0.8) and simulated marine tidal, splash and submerged environments. The results show that for any give exposure environment, the relative influence of each of the various factors considered should be considered in conjunction with the other factors; this finding can be generalized to include all relevant factors that can affect corrosion in a given exposure environment including ambient temperature. For example, a cover depth of 30 mm in the tidal zone with a simulated intertidal duration of 6 h effectively resulted in similar corrosion behavior to that in the submerged zone. The paper concludes that engineers should consider these factors when applying standard exposure classes in the design for durability of marine structures.