Study on Cover Depth for Prestressed Concrete Bridges in Airborne-Chloride Environments

Abstract

In Japan, prestressed/reinforced concrete bridges often suffer deterioration from steel corrosion in the chloride-laden air of marine environments with high concentrations of airborne chloride particles. Only a few decades after erection, several prestressed concrete bridges have already been replaced due to significant corrosion in the main girders. To develop a reasonable design policy for building more durable concrete bridges that require less maintenance, the performance of conventional concrete cover as corrosion protection in coastal environments needs to be properly evaluated. In this paper, the authors address the effectiveness of conventional concrete cover with a water-cement ratio of 0.36 and 0.43 in airborne-chloride environments and propose a realistic evaluation method based on Japanese surveys of airborne chloride distribution and deterioration in existing concrete highway bridges. The proposed evaluation method uses the chloride diffusion coefficient for uncracked concrete exposed to the choride atmosphere and the boundary chloride level based on its relationship to airborne chloride levels. The results of this research provide the basis for a cogent policy for corrosion protection in coastal areas for concrete bridges with 100-year design lives.