United States Department of Transportation
i
Evaluation of surface modification methods to mitigate rusting and pitting in weathering steel bridges : final report.
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1986-09-01
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By Raman, A.
[PDF-20.64 MB]
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Abstract:Accelerated laboratory atmospheric exposure simulation tests with an acceleration factor of 50 and extending for a maximum of 2200 wet-dry cycles (6-year exposure equivalent) gave corrosion loss data that agreed fairly well with the field data derived from field coupons. The tests corresponding to sheltered location exposure showed that the rusting process does not slow down and stabilize with time in humid, tropics - equivalent conditions. Average metal losses were: 0.1-0.33 mpy in tests simulating exterior, open exposure, about 1 mpy in tests simulating sheltered location exposure, about 2.5 mpy in total immersion testing, about 40 to 64 mpy in salt fog tests and about 60 to 100 mpy corrosion rate in electrochemical tests for initial corrosion processes.
Surface modifications with rust modifier-type inhibitors are generally found to be beneficial to slow down the corrosion process and stabilize the protective AM layer or the amorphous rust phases. Phosphoric acid application is found to be very effective in the respect and fine rusting prevails on top of such phosphoric acid-treated surfaces. Based on the results obtained, several recommendations are made for treating the weathering steel in several Louisiana bridge sections with inhibitor-type chemicals.
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