Evaluation of Stainless Steel Clad Reinforcing Bars

Abstract

The corrosion performance of stainless steel clad reinforcing bars provided by Structural Metals, Inc. is compared with that of conventional (black) reinforcement. 304 stainless steel is used as the cladding material. The No. 19 (No. 61 bars are compared using rapid corrosion potential and macrocell tests. The tests are carried out in two stages, first with bare reinforcement and then with reinforcement encased in mortar. Test spe.cimens are placed in simulated concrete pore solution with a 1.6 molal ion concentration of sodium chloride. The continuity and uniformity of the cladding is measured using a scanning ele.ctron microscope. The study indicates that the cladding provides a significant improvement in corrosion performance, if the mild steel core of the clad bars is adequately isolated from chlorides. For bars not encased in mortar, the corrosion rate of the clad bars ranges between 0 and 0.3 µm/yr, about 1 1100 of the value observed for the black bars. For bars encased in mortar, the corrosion rate averages 0.1 µm/yr, 1 I 20 to 1/50 of the value exhibited by the black steel. Cladding thickness varies between 0.196 and 0.894 mm (7.7 and 35 mils), averaging 0.467 mm (18 mils). Based on an average corrosion rate of about 0.2 µm/yr for stainless steel bars not embedded in mortar (representing the corrosion rate that would be expected at a void adjacent to a bar in concrete), the cladding appears to be satisfactory if the current minimum thickness is maintained. Tests of bars clad with 316 stainless steel and longer-term tests are recommended.