It was recognized by the mid 1970s that the corrosion of concrete structures was caused by the corrosion of the reinforcing steel in the concrete which, in turns, was induced by the intrusion of even a small amount of chloride from the deicing salts into the concrete. It is difficult to estimate the cost of these corrosion-related damages to conventionally reinforced and prestressed concrete bridge components in the nation. According to a 1997 report, of the 581,862 bridges in and off the U.S.A. federal-aid system, about 101,518 bridges were rated as structurally deficient. Most of these bridges were not in danger of collapse, but they were likely to be load posted so that overweight trucks will be required to take a longer alternative route. (reference)
The estimated cost to eliminate all backlog bridge deficiencies (including structurally and functionally) was approximately $78 billions, and it could increase to as much as $112 billions, depending on the number of years it takes to meet the objective. The average annual cost, through year 2011, for just maintaining the overall bridge conditions, i.e., the total number and the distribution of structurally and functionally deficient bridges, was estimated to be $5.2 billions. While corrosion of the reinforcing steel was not the sole cause of all structural deficiencies, it was a significant contributor and has therefore becomes a matter of major concern.
The magnitude of this corrosion problem in the transportation infrastructure has increased significantly in the last three decades and is likely to keep increasing. Even though the cost of maintaining bridge decks is becoming prohibitively expensive, the benefits provided by deicing salts are too great, however, that it's use is not likely to decrease in the future. In fact, the use of road deicing salts, which are extremely corrosive due to the disruptive effects of its chloride ions on protective films on metals, has actually increased in the first half of the 1990s-after a leveling off during the 1980s.