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The U.S. Federal Highway Administration (FHWA) has rated almost 200,000 bridges, or one of every three bridges in the U.S., as structurally deficient or functionally obsolete. Furthermore, more than one-fourth of all bridges are over 50 years old, the average design-life of a bridge. The Strategic Highway Research Program (SHRP) of the U.S. National Research Council recently estimated that the cost of damage to America's bridges currently stands at about $20 billion and is increasing at the rate of $500 million per year. SHRP concluded that the structural deterioration found in these bridges is primarily the result of corrosion.

What is Corrosion and How Do We Control It?

Corrosion is the deterioration of a material, usually a metal that results from a reaction with its environment. Over a period of time the components of a bridge may deteriorate to the extent that the bridge is no longer safe. However, using current corrosion control technology in conjunction with maintenance and monitoring guidelines, we are preventing their decay and extending the lifespan of bridges to a certain extent, but with multiple corrosion protection system strategies, the lifespan can be extended by decades.

Common strategies for corrosion control include:

(1) designing the structure with corrosion prevention in mind and selecting corrosion-resistant materials when constructing and refurbishing bridges;

(2) the application of protective coatings, membranes, and protective sealers to the bridge which can serve as a barriers to corrosive environments;

(3) the use of direct electrical current and sacrificial materials to mitigate corrosion on reinforced concrete and bridge decks, a process known as "cathodic protection" and

(4) electrochemical chloride extraction.

Why are Bridges Deteriorating?

A number of factors contribute to bridge corrosion. One of the most common is the use of deicing salts on roads and bridges, a practice which has contributed significantly to the deterioration of such structures. The salts cause corrosion of the steel reinforcing bars and other steel components supporting the bridge. This form of corrosion is the main cause of concrete bridge deterioration. Other problems that lead to corrosion include bridge designs that do not adequately consider drainage requirements, stresses, shrinkage, or expansion, and environmental factors such as frequent freezing and thawing cycles.

Compounding the effects of a corrosive environment is the lack of proper monitoring and maintenance of bridges. Technology exists that can keep bridges free from the harmful effects of corrosion, but it is only effective if it is used properly and regularly monitored.

What Can We Do?

First, persons responsible for design, maintenance, and rehabilitation of bridges must be made aware of existing corrosion control technology and related benefits. These individuals should be given the opportunity to receive specialized training or provided the necessary support to obtain input from qualified professionals. Second, the public and private sectors should encourage and promote the inclusion of lifecycle costs for new bridge construction, including maintenance and rehabilitation, for any new bridge construction project. Repair and maintenance of these structures using corrosion control technologies can extend their useful life and be much less costly than replacement. Finally, an increased commitment to fundamental and applied research on corrosion control for structures such as bridges is necessary, instead of the costly replacement option.

Conclusion

Controlling corrosion on bridge structures can prevent premature failure and lengthen their useful service life, both of which save money and natural resources, and promote public safety. America depends upon its bridges to move into the future, and paying proper attention to maintenance of these structures will help guarantee the safety of people across the country.