Durability of reinforced concrete bridges in marine environments

Achieving long-term durability for reinforced concrete structures particularly in marine environments remains a matter of much interest. Recent research findings based on observations from actual bridge performance and specially conducted long-term experiments for a wide variety of concretes indicate that chloride concentrations are involved only indirectly in initiating reinforcement corrosion and in serious active corrosion. For high quality concretes loss of concrete alkalinity (i.e. acid neutralizing capacity) as imparted by the cement content rather than direct corrosion attack of the steel reinforcement is the critical aspect. The rate of dissolution of calcium hydroxide, normally very low, is increased by chlorides and by greater internal surface area, such as in poor quality, porous, concretes. Only when the concrete pH drops below sufficiently will large-scale reinforcement corrosion be possible. However, cracking of concrete cover through to the reinforcing bars may cause accelerated localized loss of alkalinity, and thus severe very localized corrosion.