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14 Figure 2. Theoretical average crack widths for tension zone having 0.02 (Soltani 2010). interest of completeness and because enhanced corrosion 1.4 Survey of Use of High-Strength resistance is a major factor behind the drive to adopt A1035 Steel Reinforcement reinforcing steel. A1035 steel is a microcomposite Fe-C-Cr- in Bridge Structures Mn alloy that has an average chromium content of approxi- mately 9%, which is too low to be referred to as "stainless A written survey intended to assess the current practice and steel" (Cr > 10.5%) but sufficiently high to impart a degree the use of high-strength reinforcing steel was disseminated in of corrosion resistance when compared to "black steel" as June 2007. In all, 65 surveys were distributed to U.S. state represented by A615 or A706. A large number of studies have DOTs, Canadian Ministries of Transportation (MOTs), and a compared the corrosion resistance of A1035 steel with that few other agencies. A copy of the survey instrument and "raw" responses are provided in Appendix J. of A615 and A706 black steel and A955 austenitic (304 and Thirty-two surveys were returned--a response rate of 316), duplex (2101), and ferritic stainless steels. Generally, 49%. Of these, 27 (84% of those returned) report no use of the relative performance of these materials in terms of their "steel reinforcement (not prestressing rods or tendons) with corrosion resistance is ranked from most to least susceptible specified yield strengths greater than 60 ksi" (Question #1). to corrosion in the order indicated in Table 2. Thus, micro- The primary reason for not utilizing high-strength reinforce- composite alloys tend to be 2 to 10 times more corrosion ment (Question #1a) was not that it was not permitted per se resistant than black steel while austenitic stainless steel may but simply has not been used (15 of 27 respondents answer- be a few orders of magnitude improved. A summary of cor- ing "no" to Question #1). Despite this response, some rosion performance of reinforcing steel is presented in respondents went on to cite the prohibition by AASHTO on Appendix A and provides quantitative data available in the reinforcing steel having strengths greater than 60 ksi (9 of literature. 27 respondents). Additionally, five responding jurisdictions stated their specifications specifically "prohibit yield strengths above 60 ksi." It is not clear whether the prohibition cited by Table 2. Relative corrosion performance of reinforcing these latter respondents is a specific prohibition or simply a pro- steel grades. hibition by exclusion (such as, reinforcing steel strength not to Material Performance, where A615 = 1.0 exceed 60 ksi . . . ). In one case, the jurisdiction specifically A706 black steel 0.5 0.8 requires the use of ASTM A706 Grade 60 reinforcing steel. A615 black steel 1.0 Eleven of 27 respondents identified the lack of "data on per- A1035 microcomposite alloy 2 10 A955 2101 duplex stainless steel 2 10 formance to satisfy our performance requirements." One such A955 304 austenitic stainless steel >10 response specifically cited concerns about "strength, ductility A955 316 austenitic stainless steel >20 for seismic [loading] and, to a lesser extent, weldability."