ABSTRACT
There is universal recognition that corrosion of reinforcement due to chloride penetration is the most significant threat to the existing reinforced concrete infrastructure of developed countries. Structures such as road bridges and harbour facilities are exposed to chloride-rich environments through application of de-icing salts or from the natural environment. Evidence of corrosion initiated by de-icing salts in post-tensioned grouted duct bridges caused major concern in the 1980s and 1990s leading to a four-year moratorium on such techniques by the Highways Agency in the United Kingdom. In the marine environment the tidal and splash zones are recognised as high corrosion risk areas as illustrated in Figure 6.1. Inland structures near coastal regions can also deteriorate through corrosion induced by windblown salts. Concrete permanently submerged in seawater may allow significant chloride penetration but significant corrosion may not occur due to the low level of oxygen supply. Structures such as tunnels for rail and road traffic may be exposed to saline groundwaters of similar characteristics to seawater. In highway structures drainage paths or leaking joints may channel runoff in a manner that exposes localised areas to high concentrations of chloride. Chloride-induced damage has also affected building structures. Car park ramps and decks have deteriorated due to water, laden with de-icing salts, dripping from cars. Building façades have prematurely deteriorated due to corrosion induced by calcium chloride used as an accelerator in precast work. Kropp (1995) notes that chlorides may also be introduced in fire-damaged structures through exposure to thermally decomposed polyvinyl chloride fittings and furnishings. Many buildings contain PVC and it liberates hydrochloric gas at temperatures in excess of 80°C. Structures subject to wetting and drying cycles created by weather or tidal patterns are particularly vulnerable to high chloride uptake.
