Corrosion Performance of Poorly Pickled Stainless Steel Reinforcement

XM-28 (UNS S24100) and 2304 (UNS S32304) stainless steel reinforcing bars with different levels of pickling were evaluated for corrosion resistance using the rapid macrocell and cracked beam tests outlined in ASTM A955. Two heats of XM-28 from the same producer were evaluated using the rapid macrocell test. A single heat of 2304 was evaluated in two conditions; as-received from the manufacturer and re-pickled using both ASTM A955 tests. The poorly pickled heat of XM-28 reinforcement failed the rapid macrocell test with a peak individual corrosion rate exceeding 16 µm/y, while the properly pickled heat passed with no significant corrosion measured. The poorly pickled 2304 reinforcing steel failed the macrocell and cracked beam tests, with peak corrosion rates of 1.07 and 6.48 µm/y, respectively, while upon re-pickling, the same heat of steel passed both tests. These results suggest the need for a method to verify that the pickling process has been performed properly. Performance during the first week of the rapid macrocell tests or requiring that the bars exhibit a bright, shiny, uniformly light surface represent two potential methods for establishing the adequacy of pickling

Stainless Steel Reinforcement as a Replacement for Epoxy Coasted Steel in Bridge Decks

The use of deicing salts in the United States has resulted in the steady deterioration of roadway bridge decks due to the corrosion of reinforcing steel. Since the middle 1970s, the principal corrosion protection techniques for bridge decks have involved the use of epoxy-coated reinforcement (ECR) and increased cover over the reinforcing bars. The combination has greatly lengthened the life of bridge decks, but does not represent a perfect solution. The higher cover increases the bridge dead load and the cost of construction. Epoxy-coated reinforcement adds only slightly to the cost of bridge construction, but there are a number of well-documented cases in both the field and laboratory in which poorly adhering epoxy coatings have actually increased corrosion problems, and there is evidence that all epoxy coatings will eventually be susceptible to those shortcomings. As a result of these concerns, a number of other protective measures have been developed or are under development. These include the use of denser concretes, corrosion inhibitors, and corrosion-resistant steel alloys. Among the latter are various types of stainless steel, including 2304 duplex stainless steel and stainless steel clad reinforcing bars. Based on earlier studies, stainless steel reinforcement is generally less susceptible to corrosion than conventional and epoxy-coated reinforcement, but all stainless steels do not provide the same level of protection and their superiority to ECR has not been clearly demonstrated in all cases. 2304 duplex reinforcing bars and NX-SCR™ stainless steel clad bars (the only stainless steel clad reinforcement that was commercially available in the U.S. at the initiation of this study) have not undergone the same level of testing as other solid stainless steels and prototype clad bars in environments similar to those found in bridge decks. Combined with the additional initial cost of stainless steel compared to epoxy-coated reinforcement, there is a need to quantify the costs and benefits of using stainless steel reinforcement as a replacement for epoxy-coated steel in bridge decks

STAINLESS STEEL REINFORCEMENT AS A REPLACEMENT FOR EPOXY COATED STEEL IN BRIDGE DECKS (FHWA-OK-13-08 2231)

The corrosion resistance of 2304 stainless steel reinforcement and stainless steel clad reinforcement was compared to conventional and epoxy-coated reinforcement (ECR). 2304 stainless steel was tested in both the as-received condition (dark mottled finish) and repickled to a bright finish. Specimens were evaluated using rapid macrocell, Southern Exposure, and cracked beam tests. ECR and stainless steel clad specimens were evaluated with the coating having no intentional damage and with the coating or cladding penetrated. ECR with the coating penetrated is used to represent ECR that has undergone damage during construction. Clad bars were also bent to evaluate the corrosion resistance of the cladding after fabrication. Bars were tested for corrosion loss and chloride content at corrosion initiation. The critical chloride corrosion threshold for each system was established, as was an average corrosion rate after initiation. Results obtained from the southern exposure and cracked beam tests are used to the estimate cost effectiveness for each system under a 75-year and 100-year service life. Epoxy-coated reinforcement and stainless steel clad bars with and without intentional penetrations in the coating, as well as 2304 stainless steel in the as-received and repickled conditions exhibit a significant increase in corrosion resistance and critical chloride corrosion threshold compared to conventional steel, with undamaged epoxy-coated specimens exhibiting the lowest corrosion rate. In the as-received condition, 2304 stainless steel did not satisfy the requirements of ASTM A955, while repickled 2304 did. The undamaged stainless steel clad bars satisfied the requirements of the rapid macrocell test in ASTM A955; however, some cracked beam specimens containing stainless steel clad bars exhibited corrosion rates greater than the maximum allowable value permitted by ASTM A955. Conventional reinforcing steel is the least cost-effective form of reinforcement, with 2304 stainless steel in the as-received condition, ECR with penetrations through the epoxy, correctly pickled 2304 stainless steel, and stainless steel clad reinforcement representing progressively more cost-effective materials. Stainless steel clad reinforcement, however, is not currently available, and its failure to pass ASTM A955 calls its long-term performance into question. Increasing the cover over the top mat of steel and considering partial-deck replacements, where applicable, are methods that should be considered to decrease life cycle costs.Final Report, October 2010-July 2013N