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Publication Number: FHWA-HRT-09-044
Date: October 2009

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CHAPTER 6. RESEARCH STUDY #2: HIGHWAY BRIDGE STEEL COMPONENTS SUBJECT TO SIMULATED ATMOSPHERIC EXPOSURE

OBJECTIVE

The objective of this component of the study was to expand the knowledge base of atmospheric corrosion monitoring on highway bridge steel components. The objective was accomplished in three parts. First, an accelerated cyclic method for the production of protective/nonprotective oxide layers on bare steel specimens in chloride environments (task 2.1) was validated. Next, short-term corrosion rates were monitored during accelerated laboratory cyclic exposures performed using galvanic sensors to provide a better understanding of the corrosion mechanisms on bare steel coupled to a cathodic material (task 2.2). Last, prototype galvanic sensors of uncoated high strength steel strands were developed and evaluated for suspension cable in-service performance monitoring (task 2.3).

Material

Two types of steel, A606-04 (a thin-gauge weathering steel) and SAE1010 (a common carbon steel with no weathering resistance), were used for the following experiments. Table 5 shows the respective alloying elements present in the different steels (the remainder was iron, Fe) as well as their respective Legault-Leckie (American Society for Testing and Materials (ASTM) G 101) atmospheric corrosion resistance indices.(22) A higher index (ILL)—which is based on elemental composition—indicated a higher weathering ability (corrosion resistance) of the steel. Steel with a minimum ILL of 6 is considered a weathering steel. There is a large difference between the A606-04 and SAE1010 steels used in this study.

Equation 3. Index. Uppercase I subscript uppercase LL equals 26.01 times percentage copper (Cu) plus 3.88 times percentage nickel (Ni) plus 1.20 times percentage chromium (Cr) plus 1.49 times percentage silicon (Si) plus 17.28 times percentage phosphorus (P).

Table 5. Alloying elements and Legault-Leckie corrosion index of the steels.
Material Percent Cu Percent Ni Percent Cr Percent Si Percent P ILL
SAE1010 0.02 0.01 0.03 0.008 0.008 0.73
A606-04 0.33 0.17 0.46 0.33 0.01 6.40

Note: Cu = copper, Ni = nickel, Cr = chromium, Si = silicon, and P = phosphorus.

For cable sensors, high-strength steel wire was obtained from Small Parts, Inc.©, made in accordance with ASTM A228 and supplied in straight 1,828.8-mm lengths. The ASTM A228 chemistry specifications were C = 0.700 to 1.00 percent, Fe≥98.4 percent, and Mn = 0.200 to 0.600 percent.(23) Tensile strength was at least 220,000 psi. An elemental analysis by scanning electron microscopy/energy dispersive analysis by X-ray determined that Mn was in the stated range. Casual work fabricating with this wire indicated high stiffness, although no quantitative mechanical testing was performed.

 

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