Vermont's Experience with Bridge Deck Protective Systems

Intrusion of moisture and deicing chemicals into reinforced concrete bridge decks results in premature deterioration of the concrete and corrosion of the reinforcing steel. Vermont's search for an effective waterproofing system which would seal bridge decks and thus prevent intrusion of the moisture and chlorides has resulted in the application and evaluation of 29 different membrane systems since 1971. A number of the protective membranes have been in service for sufficient time to draw conclusions on their effectiveness. The results of followup evaluations show that several systems have provided complete protection to the bridge decks while a number of other materials have prevented chloride intrusion except in areas where deicing chemicals are often trapped due to the ponding effect of curb lines and expansion dams. Such results suggest that the simple and inexpensive materials could be specified for sealing the major portion of a deck surface if a compatible and impervious membrane material is placed over poorly drained areas. Difficulties encountered with the application of sophisticated and expensive membrane systems have resulted in a theory that the search for the most effective waterproofing system should concentrate on uncomplicated and less costly materials which could be applied without difficulty. The results of laboratory tests indicate that liquid-applied membranes offer substantial protection, even when pinholes and bubbles occur in the coatings, when contrasted with the chloride intrusion which occurs in untreated concrete. The tests also show the relationship between resistivity readings and chloride penetrations and suggest that readings well below the generally accepted standard of 500 000 Ω may be acceptable.