Evaluation of Corrosion Resistance of Type 304 Stainless Steel Clad Reinforcing Bars

Abstract

The corrosion performance of a prototype 304 stainless steel clad reinforcing bar and conventional reinforcing steel is compared based on corrosion potential and macrocell corrosion tests. Tests are conducted on bare bars and bars symmetrically embedded in a mortar cylinder. Test specimens consist of bars with ends protected with epoxy or with plastic caps filled with epoxy, and clad bars with a hole drilled · through the cladding. Specimens are exposed to a simulated concrete pore solution with a 1.6 molal ion concentration of sodium chloride. Additional corrosion potential tests include specimens exposed to simulated concrete pore solution with and without pressurized air pumped into the solution and a conventional bar with a reduced thickness of mortar cover. Additional macrocell corrosion tests include sandblasted stainless steel clad bars, damaged stainless steel · specimens connected to conventional steel cathodes, mortar covered conventional bars connected to bare conventional bars, and specimens with a reduced thickness of mortar. The thickness and uniformity of the stainless steel cladding is evaluated using a scanning electron microscope. The results indicate the prototype 304 stainless steel clad reinforcement exhibits superior corrosion resistance compared to conventional reinforcing steel, but requires adequate protection at cut ends, where the mild steel core is not covered by cladding. For bare stainless steel clad bars, the macrocell corrosion rate varies between 0.0 to 0.3 μm/yr (0.0 to 0.012 mpy), about 1/ioo of the value observed for conventional bars. Stainless steel bars embedded in mortar exhibit corrosion rates between 0.0 and 0.2 μm/yr (0.0 and 0.008 mpy), averaging 1/io to 1/ 50 of the value exhibited by conventional bars. The corrosion rates for clad bars with a drilled hole through the cladding range between 0.0 and 0.75 μm/yr (0.0 and 0.03 mpy), averaging about 1 / 70 of the value exhibited by conventional steel bars. The thickness of the stainless steel cladding on bars in the current study varies between 0.196 to 0.894 mm (7.7 to 35 mils). Imperfections in the form of an indentation in the base material and a crack in the cladding material filling the indention were observed. The crack did not penetrate the stainless steel cladding and cladding is of adequate thickness to protect the mild steel core. Longer-term tests are recommended, as is use of the bar in demonstration bridge decks.