Reinforcement Corrosion in Marine Concretes—1: Initiation

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Title: Reinforcement Corrosion in Marine Concretes—1: Initiation

Author(s): Robert E. Melchers and Igor A. Chaves

Publication: Materials Journal

Volume: 116

Issue: 5

Appears on pages(s): 57-66

Keywords: alkalinity; chloride-induced; corrosion; reinforcement

Date: 9/1/2019

Abstract:
Many cases of high-quality reinforced concrete structures in marine environments show little or no corrosion despite very high chloride contents in the concrete. To explain this, it is necessary to separate initiation from active corrosion because they are governed by different mechanisms. The present paper considers corrosion initiation. It reports observations for realistic model concrete specimens at intervals for up to 12 years of exposure in a high-humidity environment. Initiation of reinforcement corrosion occurred soon after first exposure and was predominantly localized (pitting) on the side away from the casting direction. The localized corrosion was consistent with air voids at the concrete steel interface. After 2 to 3 years, the rate of corrosion declined very considerably owing to oxygen depletion within the concrete. To explain these observations, a model involving electrochemical differential aeration at the air voids at the concrete-steel interface is proposed. Numerous practical implications are discussed.