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Highway Bridges

According to a 1997 report, of the 581,862bridges in and off the U.S.A. federal-aid system, about 101,518bridges 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. 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.

According to the U.S. Department of Commerce Census Bureau, the dollar impact of corrosion on highway bridges is considerable. The annual direct cost of corrosion for highway bridges is estimated to be $6.43 billion to $10.15 billion, consisting of $3.79 billion to replace structurally deficient bridges over the next 10 years, $1.07 billion to $2.93 billion for maintenance and cost of capital for concrete bridge decks, $1.07 billion to $2.93 billion for maintenance and cost of capital for concrete substructures and superstructures (minus decks), and $0.50 billion for the maintenance painting cost for steel bridges. This gives an average annual cost of corrosion of $8.29 billion. Life-cycle analysis estimates indirect costs to the user due to traffic delays and lost productivity at more than 10 times the direct cost of corrosion. In addition, it was estimated that employing “best maintenance practices” versus “average practices” can save 46 percent of the annual corrosion cost of a black steel rebar bridge deck, or $2,000 per bridge per year.

While there is a downward trend in the percentage of structurally deficient bridges (a decrease from 18 percent to 15 percent between 1995 to 1999), the costs to replace aging bridges increased by 12 percent during the same period. In addition, there has been a significant increase in the required maintenance of the aging bridges. Although the vast majority of the approximately 108,000 prestressed concrete bridges have been built since 1960, many of these bridges will require maintenance in the next 10 to 30 years. Therefore, significant maintenance, repair, rehabilitation, and replacement activities for the nation’s highway bridge infrastructure are foreseen over the next few decades before current construction practices begin to reverse the trend. (reference)

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