Abstract
The sustainability of reinforced concrete is critical, particularly for structures exposed to marine environments. Chlorides are implicated in causing or accelerating reinforcement corrosion and potentially earlier expensive repairs, yet there are many older reinforced concrete structures in good condition for many decades despite very high chloride levels at the reinforcement. The reasons for this are reviewed briefly, together with recent experimental work that better defines the role of chlorides. One is initiation of reinforcement corrosion but only through localized pitting at air-voids in concrete at the interface with the steel reinforcement. These tend to be small or negligible for high quality well-compacted concretes. The other role for chlorides has been shown, in experimental work, to accelerate the long-term loss of concrete alkali material. On the other hand, a review of practical experience shows that what has been termed chloride-induced reinforcement corrosion often is not that at all, but is the end-product of factors that impair the protective nature of the concrete. As reviewed herein, these include poor compaction, physical damage to concrete cover, concrete shrinkage, and alkali-aggregate reactions. The various observations presented are important for the proper understanding, analysis, and design of durable reinforced concrete structures exposed to chloride-rich environments.
Highlights
Premature or early failure of reinforced concrete (RC) infrastructure located in marine environments potentially has significant economic, environmental, and sustainability implications and should be avoided, if possible
The immediate question from the above is why there seems to be a mismatch between the current criteria about reinforcement corrosion and actual field observations for high quality concrete structures, that is, those that are of high strength, low permeability, and high remaining alkalinity but that have very high chloride concentrations
A detailed German study [40] showed that reinforcement corrosion was often attributable to damage of the concrete cover caused by vehicle loading and impact, from heavy goods vehicles
Summary
Premature or early failure of reinforced concrete (RC) infrastructure located in marine environments potentially has significant economic, environmental, and sustainability implications and should be avoided, if possible. The immediate question from the above is why there seems to be a mismatch between the current criteria (and the current thinking) about reinforcement corrosion and actual field observations for high quality concrete structures, that is, those that are of high strength, low permeability, and high remaining alkalinity but that have very high chloride concentrations This question is reviewed below, using recent experimental observations, and some classical results that have been forgotten or ignored, but which are crucial to providing new insight into the mechanisms involved in chloride-related reinforcement corrosion. While crack width is usually observed to be a critical parameter, these observations suggest that crack depth can be much more critical, as explained below They can be interpreted as examples of a wider potential problem, namely structural damage that permits, in certain cases, early corrosion initiation and potentially progressive loss of alkalinity that permits consequent corrosion aided by the presence of chlorides. Taken together with the new insights about pitting corrosion-induced initiation and eventual loss of concrete alkalis, these interpretations provide a more comprehensive view of what is conventionally thought of as ‘chloride-induced’ corrosion
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