Long-term observations of reinforcement corrosion for the concrete elements exposed to the north sea

There are some 1000 reinforced concrete pre-cast beam elements that have been exposed since 1943 to a harsh sea-spray environment immediately adjacent the North Sea at Arbroath, Scotland. Most (>90%) show no obvious signs of reinforcement corrosion. However, the few elements that were replaced, in about 1968 and in 1993, have nearly all resulted in severe longitudinal cracking and extensive reinforcement corrosion, despite the later concretes being superficially of better quality than the original 1943 concrete. This paper will report statistics for maximum crack width for each of the three concrete populations, based on measurements made in 2004 and in 2006, as well as in-situ and laboratory measurements that indicate the 1943 concrete shows contradictory properties, having both high permeability and high electrical resistivity. Also, the 1943 and 1993 concretes were found to have similar chloride profiles and similar chloride concentrations at the reinforcement bars, which, again, is inconsistent with the 1943 elements showing much less reinforcement corrosion than their later replacements. These observations, and some other un-reported cases in the literature, cast doubt on the conventional notion that durable reinforced concrete structures requires reduced concrete permeability, denser concretes or greater cover.