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Corrosion Durability of Three-Coat and Epoxy Mastic Coating Systems after Adverse Environmental Exposures during Coating Repair

Coatings are widely used for highway steel bridges exposed to aggressive environments to extend their service life. Even with the continuous development of coating technologies, steel bridges remain susceptible to corrosion deterioration. Periodic maintenance, that may include coating repair, is required for long term bridge serviceability. Selection of compatible repair coating materials and appropriate preparation of the steel surface are critical parameters for corrosion protection. 

Product Number: 51218-145-SG
Author: Md Ahsan Sabbir, Saiada Fuadi Fancy, Kingsley Lau, Dale DeFord
Publication Date: 2018
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Coatings are widely used for highway steel bridges exposed to aggressive environments to extend their service life. Even with the continuous development of coating technologies, steel bridges remain susceptible to corrosion deterioration. Periodic maintenance, that may include coating repair, is required for long term bridge serviceability. Selection of compatible repair coating materials and appropriate preparation of the steel surface are critical parameters for corrosion protection. Environmental contaminants such as soluble salts and adverse environmental conditions including temperatures and moisture presence should be properly controlled; however, in the practical senses for field conditions, control of environmental exposure conditions are challenging. The purpose of this study was to evaluate the effect of surface preparation with varying environmental conditioning on the durability of repair coating. Adverse environments during coating repair application included exposure to different levels of humidity (5%, 75%, and 100% RH) and salt contamination was considered. After exposure to adverse conditioning, coating degradation and corrosion development on three-coat zinc-rich primer and aluminum epoxy mastic repair coatings were analyzed by cyclic salt wet/dry exposure cycles. The three-coat system appeared to have better performance during the course of the test exposure. Inadequate surface preparation (abraded steel) and salt contamination can cause reduced adhesion for the epoxy mastic and result in degraded coating barrier properties. Pull-off strength testing of samples with conditioning of the steel surface at 5-100% humidity prior to repair, did not show clear differentiation in performance.

Coatings are widely used for highway steel bridges exposed to aggressive environments to extend their service life. Even with the continuous development of coating technologies, steel bridges remain susceptible to corrosion deterioration. Periodic maintenance, that may include coating repair, is required for long term bridge serviceability. Selection of compatible repair coating materials and appropriate preparation of the steel surface are critical parameters for corrosion protection. Environmental contaminants such as soluble salts and adverse environmental conditions including temperatures and moisture presence should be properly controlled; however, in the practical senses for field conditions, control of environmental exposure conditions are challenging. The purpose of this study was to evaluate the effect of surface preparation with varying environmental conditioning on the durability of repair coating. Adverse environments during coating repair application included exposure to different levels of humidity (5%, 75%, and 100% RH) and salt contamination was considered. After exposure to adverse conditioning, coating degradation and corrosion development on three-coat zinc-rich primer and aluminum epoxy mastic repair coatings were analyzed by cyclic salt wet/dry exposure cycles. The three-coat system appeared to have better performance during the course of the test exposure. Inadequate surface preparation (abraded steel) and salt contamination can cause reduced adhesion for the epoxy mastic and result in degraded coating barrier properties. Pull-off strength testing of samples with conditioning of the steel surface at 5-100% humidity prior to repair, did not show clear differentiation in performance.

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