Materials Performance

OCT 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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OCTOBER 2018 MATERIALSPERFORMANCE: VOL. 57, NO. 10 11 T he United States currently has one of the most complete highway sys- tems in the world. Known as the National Highway System (NHS), it is comprised of roadways and bridges that are crucial to the nation's economy, mobility, and defense. The NHS currently encompasses ~230,000 mi (370,070 km) of roadways. While the NHS only includes 4 percent of the nation's roads, it carries more than 40 percent of all highway traffic, 75 per- cent of heavy truck traffic, and 90 percent of tourist traffic. 1 Included in this highway network is the ~47,000-mil (75,623-km) Dwight D. Eisenhower National System of Interstate and Defense Highways (referred to as the Interstate System) that spans the United States. The beginning of this interstate highway network became a reality more than 60 years ago through the Federal-Aid Highway Act of 1956 championed by President Dwight D. Eisenhower. Although it comprises about 1.1 percent of the nation's total public road mileage, the Interstate System carries 24 percent of all highway traffic. Funding to construct the Interstate System became avail- able in the 1950s; however, the system incorporated some existing freeways and toll roads rather than build new routes. The oldest interstate segments date back to the late 1930s. Needless to say, the roads and bridges that make up the nation's highway system are aging. The number of highway bridges in the United States that were built in 1960 and earlier is 263,671, which is ~43 percent of the total number of bridges in the country today. 2 The U.S. Department of Transportation's Federal Highway Administration (FHWA) tracks the structural health of the majority of the country's highway bridge structures—both in the NHS as well as those not included in the NHS. Bridge condition is determined based on the National Bridge Inventory (NBI) condition rating for the deck, superstructure, substructure, and culvert. If the lowest rating is greater than or equal to 7, the bridge is classified as "good." Bridges rated 5 or 6 are classified as "fair." If the lowest rating is less than or equal to 4, the bridge's classification is "poor." The NBI also classifies a bridge as "structurally deficient" if it has any component (deck, superstructure, sub- structure, or culvert) in poor or worse condition—a rating of 4 or less. 3 Out of a total of 615,002 highway bridges in the United States, 47,619 (~8 percent) have a rating of "poor." Of those poor-rated bridges, 4,842 are part of the NHS. 2 The total number of bridges rated as structurally deficient is 54,560 (~9 percent); and 5,010 of them are part of the NHS. 4 Of the 263,671 U.S. bridges that are 58 years old or older, 64,493 (~24 percent) are in good condition, while 161,906 (~61 percent) are in fair condition and 37,221 (14 percent) are in poor condition. 2 The U.S. Congress, as evidenced by the Moving Ahead for Progress in the 21st Century (MAP-21) Act and the Fixing America's Surface Transportation (FAST) Act, recognizes bridge preservation as a vital component of achieving and sustaining a desired "good" rating of highway facilities. Dealing with aging U.S. infrastructure, however, brings significant chal- lenges to state departments of transportation (DOTs), local agencies (such as counties and municipalities), and other bridge owners. Due to limited funds and increased competition for funds among highway assets, bridge owners must cost-effectively preserve and maintain their bridges to support overall highway mobility. Having an "address the worst first" approach to bridge management by focusing only on poor-rated bridges, while ignoring the maintenance needs of good- and fair-rated bridges, is inefficient and cost-prohibitive in the long term. The Rainbow Bridge, a reinforced concrete arch bridge built in the early 1930s on the Payette River National Scenic Byway near Boise, Idaho, USA, was rehabilitated in 2006. The corrosion mitigation strategy utilized electrochemical chloride extraction for the concrete arch substructure and galvanic anodes around the perimeter of concrete patch repairs in the areas that did not receive the electrochemi- cal treatment. Photo by Andre Hudon, Vector Corrosion Technologies.

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