Corrosion-Resistant Steel Reinforcing Bars

Abstract

The corrosion of reinforcing steel in highway structures results in maintenance and replacement costs in the United States that are measured in billions of dollars. These costs would be greatly reduced and the durability and design life of reinforced concrete structures would be greatly enhanced if the corrosion resistance of reinforcing steel were improved. This study involves the evaluation of a concrete reinforcing steel with superior corrosion resistant properties. Previous evaluations have concentrated on the corrosion resistance of the steel in the atmosphere, which can be quite different than obtained for steel in contact with concrete. Emphasis in this study is placed on the corrosion resistance of the new steel in concrete structures. During Stage 1 of the project, this has been accomplished through the use of short-term tests tD rapidly determine the corrosion potential and time-to-corrosion of the steel using small specimens, and through the design and initiation of long-term time-to·corrosion tests on larger specimens. The study involves the evaluation of four types of steel, representing combinations of alloying elements and heat treatment. One form of conventional steel is hot rolled (H) and the other is subjected tD a heat treatment immediately following the hot·rolling operation (T). The corrosion resistant steels are obtained through the addition of alloying elements. One form of the steel is hot rolled (CRSH), and the other is subjected to a quenching and tempering heat treatment process (CRST). The key observations obtained during Stage 1 are provided by the short-term macrocell tests that indicate significant variation in the performance of the H, T, and CRSH steels, but consistently superior performance by the CRST steel when the steels are subjected to sodium chloride at molal ion concentrations ranging from 0.4 to 6.4. The longer term time-to-corrosion tests are under way, but as expected, no significant differences in the performance of the steels have been exhibited during the first 16 weeks of the test program. While the short·term tests are no~ in the themselves, adequate to justify the immediate application of the new corrosion resistant heat-treated steel in fullscale structures, they provide justification for continuing the study, with emphasis on the results of the long-term tests, and proceeding with the other tests planned for Stage 2.