Choosing the proper maintenance strategy when scoping a coatings project is difficult, and potentially costly if incorrect procedures are utilized. This is especially true for steel bridges with millions of square feet of coated surface to be repaired and coated. For the last 30 years, bridge coating maintenance has been dominated by the desire to remove lead coatings from existing structures, followed by the application of Zinc/Epoxy/Urethane or other modern coatings systems. These modern coating systems are now reaching the age where major maintenance is required, and the decision must be made regarding how much coating to retain, and what methods will be used to clean and paint. This paper presents results of field and laboratory testing of alternative approaches to maintaining an Organic Zinc/Epoxy/Urethane bridge coatings system.
Maintenance alternatives evaluated during this project include degrees of power tool cleaning (e.g., SSPC-SP 3, SSPC-SP-15, and SSPC-SP-11), spot/sweep blasting (SSPC-SP 18) and a near white metal blast (SSPC-SP 10). In addition to alternative surface preparation techniques, the relative value of spot zinc versus spot epoxy priming during maintenance painting were evaluated. (Spot zinc refers to painting of zinc primer to areas of localized bare steel).
Data and knowledge presented in this paper will allow for other maintainers and owners of steel structures decide proper maintenance strategies for their bridges.
When it comes to a bridge structure with a serviceable Organic Zinc / Epoxy / Urethane (OZ/E/U) coating system, there is no golden answer on the most cost-effective maintenance painting strategy. Depending on the severity and amount of corrosion and coating breakdown on the structure, planned maintenance surface preparations range from spot power tool cleaning and spot painting to a full SSPC-SP 10 media blast and full recoating operation.
The testing completed under this program took a closer look at how various levels of surface preparations perform on differing levels of corrosion. A field study occurred concurrently conducted on the Verrazano Narrows Bridge, while laboratory testing exposed the surface preparations to an accelerated corrosion environment to gain a better understanding of the systems performance in a shorter timeframe. Data and knowledge gathered from the testing will intend to help provide necessary guidance on surface preparation procedures to be used during maintenance bridge coating projects.
