Maintenance Painting for Steel Bridges: Evaluation of Coating Systems Over Minimally Prepared Surfaces to Delay Rehabilitation

Image
3201-Thumbnail Image.png
Creator
Wolfgram, Christopher
Zienty, Daniel
Date Created
2019
Report Number
2019-37
Description
The purpose of this project was to identify efficient and cost-effective methodologies for maintenance painting of steel bridges for MnDOT bridge crews to extend the service life of the coating system by at least five years before complete coating rehabilitation would be warranted. Five generic coating systems, chosen for their compatibility with existing MnDOT coating systems and minimal requirements for surface preparation and application, were applied over minimally prepared surfaces on two St. Paul bridges. Coating performance was evaluated annually over a three-year period through visual field observation following the MnDOT Steel Bridge Coating Condition Assessment Photographic Field Guide and MnDOT Bridge and Structure Inspection Program Manual. Adhesion testing was performed in accordance with ASTM D3359 in conjunction with the third-year evaluation. The results were photographed and documented in a matrix; identifying key performance characteristics. The predominant failure affecting two of the coating systems was delamination due to application over an anti-graffiti finish coat. Otherwise, each system performed to a standard aligning with the pre-established project goal for expanded serviceability of five years. Because developing a Bridge Maintenance Coating Program requires critical timing in the inspection process to identify existing coating condition; a Bridge Coating Repair Reference Table was developed to assist MnDOT crews with determining the appropriate preventive maintenance painting strategy based on condition and existing coating system. This work also determined that surface conditions demonstrating pitting with rusting; or surfaces with an anti-graffiti coating should not be addressed through maintenance painting but instead should be considered for coating removal and replacement.