The National Academies

NCHRP 12-117 [Final]

Guidelines for Corrosion Protection of Steel Bridges Using Duplex Coating Systems

  Project Data
Funds: $397,854
Research Agency: Elzly Technology Corporation
Principal Investigator: Mr. J. Peter Ault
Effective Date: 5/16/2019
Completion Date: 10/30/2022
Comments: The Final Report is published as NCHRP Report 1048. The Guidelines have been forwarded to AASHTO COBS Technical Committee on Bridge Preservation



Bridge coatings greatly contribute to the longevity of steel bridges 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), otherwise the bridge may have to be completely overcoated or the coating be removed and replaced prematurely. This approach has proven to be a maintenance challenge for bridge owners. While efforts are ongoing to improve the service life of traditional coating systems another approach would be the use of “duplex systems” (hot dip galvanized or metallized with a coating system) to provide long-term protection against corrosion. Research indicates that the synergetic life of duplex coatings will extend the bridge service life beyond the traditional coating systems. Unfortunately, bridge owners have had mixed experience with duplex coatings. Some state departments of transportation (DOTs) have had great success with the duplex coating systems 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 coating systems sooner than anticipated. The processes are currently reliant on the experience of the galvanizers, metalizers, and coating applicators with lack of guidelines. As a result and in order to be consistent, there is an immediate need to develop guidelines for bridge owners on the use of duplex coating systems for corrosion protection of steel bridges.




The objectives of this research were to (1) develop AASHTO guidelines for corrosion protection of using duplex coating systems for extending the service life of steel bridges that can be adopted by AASHTO and (2) plan and conduct a workshop to demonstrate the use of proposed guidelines to an audience of DOT staff and other stakeholders. The guidelines cover the selection and application of duplex coating systems during the new design, and maintenance and rehabilitation of existing steel bridges. 


STATUS: The Final Report is published as NCHRP Report 1048. The Guidelines have been forwarded to AASHTO COBS Technical Committee on Bridge Preservation

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