Comparative Bond Study of Stainless and High-Chromium Reinforcing Bars in Concrete

Concrete bridge decks in corrosive environments have used several methods to prevent corrosion of the reinforcing steel including the use of alternative steels as reinforcement. While research has been conducted on corrosion resistance, very little information is available about the bond strength of alternative metallic reinforcement such as solid stainless steels and high-strength, high-chromium (HSHC) alloys. Therefore, the tensile bond strengths of three alternative metallic steel reinforcements in concrete are compared with conventional A615 Grade 60 steel reinforcement. Two types of stainless steel were considered, 316LN and 2205 duplex. An HSHC microcomposite bar was also considered. A total of 250 bond tests were performed with beam-end specimens similar to the ASTM A944 specimen. Bonded lengths of 4 to 12 in. were used for No. 4 and No. 6 reinforcing bars. Concrete clear cover for all tests was 1 1/2, in. to produce cracking bond failure. No transverse reinforcement was present. The normal strength concrete was typical of that used in Michigan bridge decks. Statistical comparisons of bond test results with predicted values for bond strength of A615 reinforcement revealed there was no reason to believe the bond strength of the alternative metallic reinforcing bars was less than predicted. The conservatism of the current development-length relationships generally predicted lower bond strengths than were observed. Therefore, no modifications are suggested when estimating the development length of these reinforcements as a one-to-one replacement for A615 Grade 60 reinforcement, No. 4 to No. 6 bars, using standard development-length relationships.