Chloride-Induced Corrosion Behavior of Stainless Steel and Carbon Steel Reinforcing Bars in Sound and Cracked Concrete

A comparative evaluation has been made of the corrosion resistance of four stainless steel grades and two carbon (black) steel grades of reinforcing bars. The stainless steel grades were UNS S31653, UNS S24100, UNS S32101, and UNS S32304. The black steel bars were 400 grade and the weldable 400W. Linear polarization resistance measurements were made of the bars in sound concrete in which chloride had migrated under a 500 mV potential gradient. The black steel bars were actively corroding after only two weeks' exposure, while the stainless steel bars all remained passive over the 139 week test period. In concrete with artificial cracks in the cover, above and parallel to the bars, macrocell corrosion was observed in the black steel within the first two weeks of exposure and was initiated in the UNS S24100 bars over a period of 21 weeks to 57 weeks. The other grades of stainless steel remained passive for the 128 week test period.