United States Department of Transportation
i
Chloride Contamination Remediation of Steel Bridges
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2016-11-01
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[PDF-7.35 MB]
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TRIS Online Accession Number:01632251
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Edition:Final Report
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Abstract:Researchers evaluated 32 steel surface preparation methods to determine how effectively they remove chloride from corroded chloride-contaminated steel panels. Wet methods proved more effective than dry methods. The three most effective wet methods injected mineral slag abrasives in a water stream and resulted in less than 1% chlorides remaining. Most dry surface preparation methods left significantly more chloride contamination after surface preparation. The three most effective dry methods used multiple blast cleaning cycles. These methods approached the effectiveness of the best wet methods, with 1.6 to 2.0% chlorides remaining. The least effective surface preparation was a single abrasive blast cleaning with a 40/50 steel grit mix. This resulted in 6.5 % chlorides remaining. No surface preparation method evaluated resulted in chloride contamination less than 5 µg/cm2 . Analyses with scanning electron microscopy revealed that the remaining chloride contamination (5.3 to 23.9 µg/cm2 ) was randomly deposited in individual hot spots distributed across the steel’s surface. This contamination would probably cause premature coating failure. Wet methods are significantly more effective than a single abrasive blast cleaning, irrespective of the abrasive material type or grit size used. Although, multiple iterations of blast cleaning approached the effectiveness of the best wet methods.
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