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Tuesday, July 17, 2018 - 15:30

This report presents corrosion study findings related to corrosion resistance of eight types of metallic dowel bars. The accelerated laboratory corrosion testing was performed using seven small-scale concrete slabs that simulated typical concrete pavements for 452 d of a modified Southern Exposure followed by a detailed autopsy of the extracted bar samples. The weekly Southern Exposure cycles consisted of a 4-d wetting cycle in 15 weight percent chloride solution at 75°F and a 3-d drying cycle at 100°F. The best corrosion performance was achieved by type 316L solid stainless steel (SS) dowel bars. Three types of stainless steel–clad (SC) bars also exhibited superior corrosion resistance. The epoxy-coated (EC) dowel bars performed well and behaved similarly to the SS bar types. However, the autopsied EC dowel bars revealed varying degrees of coating delamination, and localized corrosion originated from some of the artificial coating defects. Despite this problem, EC dowel bars were able to suppress corrosion activities because of the shielding role of the coating, even disbonded EC dowel bars, against corrosion current. As expected, the worst corrosion performance was observed with the uncoated carbon steel dowel bars. Most of them produced the corrosion-induced concrete cracks. The hot-dip galvanized and zinc-clad dowel bars are classified as the second worst performance group. Even though the zinc-coating layers performed well as the sacrificial cathodic protection systems for the bare steel exposed at the artificial defect sites, the consumption rates of the zinc mass were too excessive, leading to the premature depletion of the zinc layers in the areas with elevated chloride concentration. Therefore, these zinc-based dowel bars are recommended only for infrequently salted roadways and mild service conditions. For major roadways, where repairs and/or traffic disruption are not feasible, high grades of solid SS dowel bars are recommended, even though this means very high initial costs. Considering the unavailability of the SC bars and the good performance of EC dowel bars at a much lower price, it is recommended that high-quality EC dowel bars be continuously used in the majority of the major roadways subject to heavy deicing salts provided that damage touchups and stringent quality assurance/quality control practices are implemented in the field to minimize initial coating defects until they are buried in concrete.  The full report is available from the US Federal Highway Adminsitration at https://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/15079/index.cfm