Effective Use of Duplex Coating Systems to Improve Steel Bridge Structure Durability
Steel bridge coatings greatly contribute to the
longevity of a bridge structure and reduce the total life-cycle cost by
protecting steel bridge members from corrosion. For most steel bridges across
the nation, the most popular practice is to provide a 3-coat, zinc-rich primer
system. The 3-coat system generally requires regular maintenance (touchup) and
may have to be completely overcoated or repainted after as little as 15 years.
This approach has proven to be a maintenance challenge for bridge owners. While
efforts are on-going to improve the service life of traditional paint systems
another approach would be the use of duplex systems (hot dip galvanized or
metallized with a traditional finish coat) to provide long-term protection
against corrosion. The combination of a metallic coating and a traditional
finish coat is often referred to as a “duplex coating.” Van Eijnsbergen1
suggests that the synergetic life of duplex coatings is 1.5 to 2.3 times the
sum of the individual lives – this means that may result in service lives in
excess of 75 years.
owners have had mixed experience with duplex coatings (including the
galvanizing and metalizing process and/or finish coat application). Some DOTs
have had great success with the approach while others have had issues with
galvanizing and metalizing quality, experienced adhesion problems with the
finish coating, or have had to perform maintenance painting of the duplex
system sooner than anticipated. The processes are currently reliant on the experience
of the galvanizers, metalizers, and coating applicators and as such, may be
considered more of an art than science. The proposed project will close the gap
between art and science by developing design guidelines, guide specifications,
and a state of the art report.
objective of this research is to collect technical data and develop practical
guidelines that allow bridge engineers to position duplex coating systems among
alternative corrosion control options for steel bridge structures.
SCOBS global focus:
SCOBS prioritized objective:
1 Extend Bridge Service Life
Duplex coating systems
could be an option for improved durability for a large percentage of the
nation’s bridge population. While economic considerations vary, duplex systems
are available for shop and/or field application for new bridges, maintenance
coating for existing bridges, and to protect steel components replaced during
major rehabilitation. Effective use of duplex coating systems should make steel
bridge designs more competitive by reducing service life cost through increased
performance. The use of duplex systems should more than offset any increased
application costs through the elimination costs associated with additional recoating
cycles, such as: mobilization, maintenance and protection of traffic, user
costs, surface preparation containment and disposal, as well as additional
application costs. This project directly addresses the 2013 SCOBS strategic
vision objective to “Extend Bridge Service Life.” SCOBS T-9, T-14, T-18; SCOM;
the AASHTO National Bridge Preservation Partnership’s (NBPP) Coatings Group;
TRB AHD 30, Standing Committee on Structures Maintenance, and TRB AHD30(2),
Steel Bridge Coating Subcommittee have expressed support for this project.
Synthesis 20-05, Topic 48-03, Corrosion
Protection for Extending Steel Bridge Service Life
The researcher shall use a combination of
laboratory testing and field studies to accomplish the project objectives. The
main tasks would be the development of three documents:
guideline for the use of duplex coatings. This document will provide the
designer guidance on technical and economic issues relating to duplex coating
systems and alternative systems. Issues to be addressed will include
considerations for new construction and maintenance painting and considerations
when selecting among galvanizing and metallizing.
specifications for duplex coatings. These guide specifications will be
developed in AASHTO format and will address the proper procedures for quality
application of both the metallic and the finish coatings. They will also address
testing procedures for qualification of duplex coating systems.
State of the art report.
This report will document laboratory testing and field performance of duplex
coating versus other systems on bridges. The report will identify
state-of-the-art training and qualifications for applicators and inspectors.
The report will also identify gaps in technology, training and other resources
which, if filled would improve the state-of-the-art.
Implementation would be through a combination of
This research would be relevant and useful to the bridge design, maintenance, and construction community throughout the US.
|Sponsoring Committee:||AFF20, Steel Bridges
|Research Period:||24 - 36 months|
|RNS Developer:||J. Peter Ault, P.E and Jeffrey A. Pouliotte, P.E. (FL DOT)|
|Source Info:||The TRID database was searched using terms such as “galvanizing,” ”metallizing,” and “duplex coatings.” About half of the database hits related to concrete bridges (either using galvanized rebar, or thermal zinc treatments). The other half predominately addressed comparison studies on the relative performance of traditional coatings and metallic coatings, the benefits of metallic coatings, or adhesion of paints to galvanizing. Much of the directly relevant work was anecdotal. No comprehensive study was identified that covered the design considerations, proper specifications, or performance of duplex coating systems.|
|Index Terms:||Coatings, Steel bridges, Durability, Galvanizing, Metal working, |
|Cosponsoring Committees:||AHD30, Structures Maintenance|
Maintenance and Preservation
Bridges and other structures