Corrosion Resistant Alloys for Reinforced Concrete

Deterioration of concrete bridges because of reinforcing steel corrosion has been recognized for four-plus decades as a major technical and economic challenge for the United States. As an option for addressing this problem, renewed interest has focused on corrosion resistant reinforcements, stainless steels in particular. The present research study was performed jointly by Florida Atlantic University and the Florida Department of Transportation to evaluate reinforcements of this type. These reinforcements included solid stainless steels 3Cr12 (UNS-S41003), 2101LDX (ASTM A955-98), 2304 (UNS-S32304), 2205 (UNS 31803), two 316L (UNS S31603) alloys, and two 316 stainless steel clad black bar products, and MMFX-2 (ASTM A1035). Black bar (ASTM A615) reinforcement provided a baseline for comparison purposes. Results from short term tests and preliminary results from long-term exposure of reinforced concrete slabs were presented in the first Interim Report (FHWA-HRT-07-039) for this project. This report provides longer-term data and analyses of four different types of reinforced concrete specimens, two of which were intended to simulate northern bridge decks exposed to deicing salts and the remaining two to simulate substructure elements undergoing seawater exposure. Three different concrete mix designs were employed, and specimen types included variables such as 1) a simulated concrete crack, 2) a bent top bar, 3) corrosion resistant upper bar(s) and black steel lower bars, and 4) intentional clad defects such that the carbon steel substrate was exposed. Cyclic wet-dry ponding with a sodium chloride (NaCl) solution was employed for the former two specimen types, and continuous partial submergence in either a NaCl solution or at a coastal marine site in Florida for the latter two. The exposures were for periods in excess of four years. The candidate alloys were ranked according to performance, and an analysis is provided that projects performance in actual concrete structures. A subsequent final report is to be issued at a later time.