United States Department of Transportation
i
Structural steel coatings for corrosion mitigation.
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2010-10-01
[PDF-74.22 MB]
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Abstract:Task 1 of this project was to survey the performance of coating systems for steel bridges in Missouri and to evaluate coating and
recoating practices. Task 1 was led under the direction of Dr. Glenn Washer from the University of Missouri located in Columbia,
MO. A specific literature review focused on current state-of-the-practice for overcoatings, bridge coating assessment and rating,
deterioration rate modeling as well as the risk assessment for overcoating. A new coating evaluation guideline was created to meet the
needs of bridge maintenance in Missouri. Finally a field survey was carried out onto the existing bridge coatings across 10 Missouri
Department of Transportation (MoDOT) districts and 26 counties. It was found that system S and G perform very well in many of the
situations observed. The survey indicated that in many cases system S overcoatings are providing service life extension for the coating
system, with some early failures resulting from severe exposure to deck drainage and corrosion. Deck condition, drainage, and joint
conditions were found to be the dominate factor in deterioration of the coating system, regardless of the age of the coating. Task 2 of
this project investigated the performance of new types of coating technologies on bridge corrosion mitigation and was led under the
direction of Dr. John Myers from the Missouri University of Science and Technology located in Rolla, MO. Twelve coating systems
including MoDOT system G were evaluated through several laboratory tests to study and predict the field performance and durability
of new coating technologies. The new coating systems investigated in this study involved polyurea, polyaspartic polyurea,
polysiloxane polymers and fluoropolymer. To date, these coating system technologies have not been used as a steel structural coatings
system in the State of Missouri by MoDOT. The laboratory tests consist of freeze-thaw stability, salt fog resistance, QUV weathering
and electrochemical tests. The comparison study was carried out to benchmark and understand the pros and cons of these new coating
systems. In addition, two coating systems served as overcoating studies for lead-based paint systems representative of older existing
bridges in the state of Missouri. These overcoating systems were evaluated using an accelerated lab test method and electrochemical
test. The performance of the existing MoDOT calcium sulfonate (CSA) overcoating system (system S) was also studied within the test
matrix for comparative purposes. The test results show that moisture cured urethane micaceous iron oxide zinc/polyurea polyasp
is a promising coating system for recoating of new steel
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bridges and that aliphatic polyaspartic polyurea can also be applied on
existing coatings after the surface is properly prepared.
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