Performance of bitumen protective coatings for buried concrete

Following the discovery in the late 1990s of seriously damaged M5 motorway bridge foundations due to thaumasite formation, the standards for buried concrete were changed. Binder types and mix designs to resist aggressive ground conditions are specified; however, in highly aggressive conditions it may be necessary to utilise additional protective measures including surface coatings to ensure the survival of buried concrete structures. Such measures may also be used to prevent deterioration of concrete of lesser specification than would be required for a particular ground aggressivity. The paper presents results from a long-term laboratory-based study in which concrete cubes of high susceptibility to thaumasite attack, with and without bitumen coatings, were exposed to sulfate-rich solutions at 4·5°C for 5 years. Moreover, concrete prisms of the same concrete and three others of different susceptibilities to attack, each with one bitumen-coated face, were buried in pyrite-bearing clay for 9 years, at 4·5°C. All types of concrete tested suffered significant attack, whereas the bitumen coating, even if damaged, proved successful in preventing deterioration of even the most vulnerable concretes. The paper concludes with a brief discussion of the potential benefits of using coatings for the protection of buried concrete.