Chloride ion distribution in twenty-year-old prestressed bridge girders

The distribution of chloride ions was determined for three prestressed concrete bridge girders that had been exposed to deicing salts over a period of 20 years. The girders became available for testing when they were removed from an interstate overpass in the Minneapolis-St. Paul metropolitan area because of bridge realignment. Chloride ion samples were taken from an interior girder and two facia girders. The amount of chlorides present in the deck slab was also investigated. The level of chlorides in the bridge girders at the depth of the prestressing strands did not generally exceed 120 ppm by weight of concrete, which is less than the threshold level to initiate corrosion (250 to 510 ppm). There were no visible signs of corrosion evident on the strands that were subsequently removed from the girders. Samples obtained from the bridge deck contained chloride ion levels on the order of 1000 to 2000 ppm by weight of concrete at the depth of the reinforcement.