Corrosion Protection of Steel Highway Bridges: I Full scale trials of paint systems

Full scale trials of ten paint systems, applied on the plate girders of the Loudwater Viaduct, are described. The best performance during four years of exposure was given by a solvent less epoxy system, but its application requirements were stringent and may be difficult to meet in practice. For high corrosivity sites, a chlorinated rubber paint system should give a good performance with easy application, although transportation damage between fabrication shop and site may be a problem. A general conclusion is that aluminium pigment should be excluded from conventional micaceous iron oxide paints. In several instances aluminium has been leached out as aluminium salts leading to deterioration. of the paint system and rusting of the substrate.

The importance of the micro-climate to which sheltered bridge steelwork is exposed is discussed. Steel girders are not washed by rain and the combination of corrosive contaminants and long periods of wetness can be a particularly severe condition for paint coatings under a bridge deck. Further research on the characterisation of bridge sites and evaluation of priming paints has been initiated.