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Publication Number: FHWA-HRT-12-044
Date: November 2012
The following conclusions are based on test results of the eight coating systems collected during the initial coating characterization, 3,600 h of ALT, 10 months of NW and NWS exposure testing, and 6 months of outdoor exposure testing at GGB:
Test results from this study indicate that none of the selected coating systems, including the two three-coat control coatings, will provide maintenance-free corrosion protection to steel bridge structures for 100 years.
The two three-coat control systems, IOZ/E/PU and ZE/E/PU, and the one-coat system, HRCSA, were chosen for their good performance records in an earlier FHWA one-coat study.(22) As expected, they performed well, and they were better than the other test coating systems in every category. The remaining five coating systems, ZE/PU, Zn/PS, TSZ/LE, ZnE/LE, and HRCSA, were selected for a possibility of providing superior performance to commercially available products in the current market. However, they did not deliver desirable performance exceeding the three best coating systems.
Premature failure of two two-coat systems, TSZ/LE and ZnE/LE, was not anticipated during the coating selection process. Their performance was the worst among the eight coating systems and had a negative impact on this study, leading to early termination of the research. Three test coating systems, MCU/E/F, ZE/PU, and Zn/PS, performed satisfactorily in some categories and poorly in the others compared to the best performers. None of them showed consistently good performance.
It is apparent that cutting-edge coating technology, regardless of cost, is not ready to deliver super durable coating systems that can last more than 100 years without significant maintenance interventions.
Until future research and development efforts produce coating systems with extended service life, the main goal should be to use the proven legacy coating systems correctly by reducing human errors and improper applications. At the same time, researchers should strive to develop surface-tolerant primers against salts residue, adhered rusts, and mill scale; a simple yet reliable in situ test method for surface chloride concentration; and allowable chloride contamination(s) on the blasted steel surface. Significant advancement in these areas will allow for the creation of more durable steel bridge coatings than what is currently available.
Topics: research, infrastructure, structures
Keywords: research, structures, One-coat, Two-coat, Three-coat, Steel bridge coatings, Corrosion protection, Accelerated laboratory testing, Outdoor exposure, Coating performance evaluation
TRT Terms: research, infrastructure, Facilities, Structures