United States Department of Transportation
i
Assessing Corrosion of Extracted MSE Wall Reinforcement Coupons, Utah Phase II Study
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2020-09-01
[PDF-11.92 MB]
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Edition:Final Report May 2018 to Jan 2020
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Abstract:The purpose of this study was to extract galvanized steel wire reinforcement coupons from mechanically stabilized earth (MSE) walls along I-15 in Salt Lake Valley and determine the rate of corrosion that has taken place since Phase I, which was conducted by Gerber and Billings (2010). The galvanized steel reinforcement analyzed in this study has been in place for 19 to 20 years at the time of extraction. A total of 85 coupons were extracted and laboratory analysis was performed to determine the thickness of remaining zinc galvanization on each coupon. Soil samples were obtained from each one-stage wall extraction location to determine moisture content for correlation with corrosion. After laboratory testing was performed, the measured zinc coating thickness was compared to that determined in Phase I. An average corrosion rate of approximately 0.024 oz/ft2/year has occurred since Phase I. According to the AASHTO (2017) design corrosion rate of 0.35 oz/ft2/year for the first two years and 0.09 oz/ft2/year until the depletion of the zinc, the zinc coating would have been completely depleted after 16 years. Based on the results of laboratory testing, the initial galvanization coating was likely greater than the specified thickness of 2.0 oz/ft2 (86 μm). The zinc galvanization is corroding at a slower rate than the AASHTO design rate. The AASHTO design rate for depletion of zinc coating and subsequent corrosion of the steel reinforcement is conservative for the corrosion conditions present in the MSE wall reinforcement coupons tested. The integrity of the steel reinforcement that is currently in place is not likely to be compromised by corrosion.
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