The ultimate test of the coating systems durability and suitability were the field
exposure tests. These were conducted at aggressive highway bridge sites and offer the following
• The substrates include pieces of angle and plate cut from previously exposed highway bridge steel. Thus, coatings were tested on angles and T's rather than on flat plates. The specimens also contained built up corrosion products and embedded chloride exactly as they occur on the bridges. The test specimens were exposed at some of the most corrosive areas of the bridges (i.e., under leaking deck joints, exposed to traffic splash). Thus the coating systems were exposed and evaluated at the precise environments where they are required to protect against corrosion.
The test specimens consisted of small individual angles and plates. This feature allowed all the specimens to be coated under controlled and uniform circumstances, thus reducing the influence of application as a variable. In addition, because the specimens were small and numerous, a statistical design could be applied to the placement of the specimens and through the use of replicates. The coating systems were monitored and evaluated for up to 4 years. This permitted the observation and recording of coating surface and underfilm degradation that takes some time to develop. It also allowed for relatively reliable estimates of the coating effectiveness and lifetime. Based on all the above results, a set of guidelines has been prepared on how to maintain and protect weathering steel bridges. The guide provides the following type of recommendations:
• Techniques for evaluating the severity of the exposure and the extent of corrosion and surface contamination.
• Suitable techniques for preparing the surface and determining the degree of cleanliness.
• Suitable coating systems for various types of bridge exposures.
• General information about which structures or portions of structures require protective coatings.