Improved Corrosion-Resistant Steel for Highway Bridge Construction

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Improved Corrosion-Resistant Steel for Highway Bridge Construction

Author: Fletcher, Fred B | Size: 2.63 MB | Format: PDF | Quality: Original preprint | Publisher: Federal Highway Administration | Year: 2011 | pages: 94

Alloy steels with 9, 7, and 5 percent chromium (Cr) were designed to reduce the cost of ASTM A1010 steel containing 11 percent Cr. Additions of 2 percent silicon (Si) and/or 2 percent aluminum (Al) were made. The experimental steels could be heat treated to achieve the strength needed for bridges. However, only the ASTM A1010 steel exhibited sufficient impact toughness to be a candidate for bridge construction. The mechanical properties of the experimental steels are not suitable for bridge construction, although they are substantially more corrosion resistant than the conventional weathering steel, ASTM A588. When studied in the laboratory using cyclic corrosion tests, all of the steels exhibited a relatively linear rate of corrosion with increasing cycle number. As the Cr content decreased, the corrosion rate increased. The corrosion rate of the ASTM A1010 steel was one-tenth of the rate of the ASTM A588 steel. Si was detrimental to corrosion resistance, while Al was beneficial. The corrosion behavior was not a function of the steel yield strength. As the cyclic corrosion cycles increased, the proportion of oxyhydroxide corrosion product akaganeite declined and was replaced by maghemite, goethite, and lepidocrocite. However, the 11 percent Cr steels contained significantly less maghemite than the steels with lower Cr content. The 9 percent Cr, 7 percent Cr plus 2 percent Si, and 7 percent Cr plus 2 percent Al steels were exposed for 1 year on the heavily salted Moore Drive Bridge in Rochester, NY. Their corrosion rates were approximately one-half the rate of ASTM A588 weathering steel. The rust composition was similar for all three experimental steels. Life-cycle cost analyses examined the benefits of using a maintenance-free corrosion-resistant steel instead of regularly repainting a conventional steel bridge girder. By the 20th year of service, the probability is over 90 percent that the ASTM A1010 steel girder is less expensive. After 40 years, it becomes certain that the ASTM A1010 steel girder is cheaper than the painted conventional steel.

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