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This was discussed in the Concrete Society Technical Report 44 (2015). It is important that this question is answered because cracks in concrete structures are unavoidable and reinforcement corrosion is a worldwide, trillion pound problem. It is generally acknowledged that cracks can hasten the penetration of carbon dioxide from the atmosphere and/or chloride ions from sea water (in the case of coastal structures or salt used as a de-icing agent during winter maintenance on land based structures). Eventually this results in embedded reinforcing bars losing passivity and becoming susceptible to corrosion.

Although cracks undoubtedly reduce the initiation time for corrosion, the effect on the subsequent rate of corrosion is controversial. The commonly-held view is that a large number of narrow cracks is the most desirable option, yet the results of more recent research contradict this assessment. Both views are based on the analysis of test results obtained from specimens where the cracks occur transverse to steel reinforcing bars.

ButÌýgiven that steel reinforcement in virtually all members is present in two orthogonal directions, in practice cracks which are transverse to one set of bars will inevitably be parallel to the other. If any of these cracks lie over steel bars, termed coincident cracks (see illustration), they could give rise to significant corrosion. However, very little work has been carried out on the risk of coincident cracks to corrosion. We believe that our research on this risk aspect will help resolve the debate on the significance of cracks to corrosion and provide the necessary guidance for designers to design sustainable reinforced concrete structures which remain durable during their service life.

This research aims to help resolve the debate on the significance of cracks to corrosion and to provide the necessary guidance for designers to design sustainable reinforced concrete structures which will remain durable during their service life.