Corrosion of structural steelwork in bridge enclosures, box sections, and anchorage chambers

Abstract

Some designs of highway bridge have structural steelwork exposed to the air within closed spaces such as box sections. Observations have shown that mild steel does not corrode in these enclosures, even though the relative humidity is normally higher than 70%. The environmental conditions within enclosures were characterized by measuring air temperature and relative humidity, steel surface temperature, time of wetness, and the concentration of sulphur dioxide. Corrosion rates of clean and prerustedmild steel were measured using electrical resistance probes. An explanation for the significantly lower corrosion rates found inside an enclosure is given on the basis of the low incidence of condensation and the low concentration of particulate matter in the atmosphere of an enclosure. Furthermore, it is suggested the critical relative humidity for corrosion in natural environments is close to 100%.