KTC researchers studied the use of unpainted weathering steel on bridges, using findings of inspections performed on Kentucky Transportation Cabinet (KYTC) bridges constructed with both painted and unpainted weathering steel as well as laboratory testing. Laboratory tests were conducted on test panels of conventional and weathering grades of steel to determine the performance of barrier and zinc-based coatings over abrasive-blasted substrates of those steel types in both the new and corroded conditions. The report provides the following recommendations for the use of painted and unpainted weathering steel on Kentucky bridges based upon both the field and laboratory findings: KYTC should develop a consistent policy on the use of painted and UWS bridges. The use of UWS bridges should be restricted to deck girder types using jointless designs or the current KYTC detail that incorporates concrete diaphragms. KYTC should use the FHWA T5240.22 guidelines to determine where to use unpainted weathering steel. The use of UWS bridges with fracture-critical members is discouraged. KYTC should investigate the performance of existing UWS bridges. As part of this work, the Cabinet should determine the most effective means of assessing patina performance. Baseline inspections should be performed on all KYTC UWS bridges to identify locations where patinas are not performing correctly. Based on these observations, recommendations could be advanced for remedial measures (including zone and total painting). Special emphasis should be placed on the two UWS truss bridges (KY 81 and KY 90). Guidelines should be prepared for bridge inspectors so they may properly evaluate patinas. Additional guidance should be provided to KYTC maintenance personnel to properly maintain UWS bridges
