The effect of surface and loading conditions on the corrosion performance of stainless steel rebar

Deterioration of reinforced concrete structures due primarily to chloride induced corrosion of plain carbon-steel reinforcement is a widespread problem, particularly in areas close to marine environments and where de-icing salts are used to keep roadways clear of ice. Replacing plain carbon-steel rebar with highly corrosion resistant stainless steel rebar has been shown to greatly increase the lifespan of concrete structures in harsh environments, and yields favourable life-cycle costs despite high initial costs. In attempt to lower stainless steel rebar's initial cost of processing, this research compared its corrosion resistance in the pickled (mill scale removed) and as-rolled (mill scale intact) surface conditions. Rebar was embedded in highly-chloride contaminated concrete, and corrosion performance between the two surface types was compared in order to determine if conventional pickling of stainless steel rebar is necessary. A second part of this research addressed possible concern of reduced corrosion resistance of pickled stainless steel rebar in concrete exposed to chlorides when subjected to dynamic loading due to micro-motion at the concrete/crack interface.;Corrosion current densities, corrosion potentials and cyclic polarization measurements of pickled 316 and 2205 stainless steel rebar in embedded in dynamically and statically loaded OPC concrete beams and exposed to salt solution revealed no distinction in corrosion behaviour between the two loading types. However, electrochemical noise measurements taken when cyclic loading of dynamically loaded beams was on revealed much higher fluctuations than both statically loaded beams and dynamically loaded beams when cyclic loading was off. This suggests that, although the passive surface film characteristics of the dynamically loaded bars appear to be restored when cyclic loading is off, during cyclic loading the surface film is susceptible to breakdown and general corrosion.;It was concluded that as-rolled stainless steel rebar in aggressive environments would provide sufficient corrosion resistance for the 75 year lifespan currently specified by the Canadian Bridge Code (CAN/CSA-S6-06, 2006), however it is recommended that monitoring of these specimens be continued to ensure high corrosion rates and/or concrete cracking do not develop. As well, investigation into the effects crevice corrosion cells found in typical concrete structures could have on as-rolled stainless steel rebar's corrosion resistance should be undertaken. With regard to loading conditions, no significant evidence was found suggesting that pickled stainless steel rebar has reduced corrosion resistance when loaded dynamically versus statically. Therefore pickled stainless steel rebar is recommended for use in dynamically loaded concrete structures if others factors permit. However, the higher electrochemical noise measured during cyclic loading suggests that corrosion behaviour could be influenced largely by frequency of loading, and so further study should be undertaken for applications involving more extreme cyclic loading conditions than those used in this experiment. (Abstract shortened by UMI.);Microcell corrosion rates and corrosion potentials of pickled and as-rolled 304LN and 316LN, as well as pickled 2205 stainless steel rebars embedded in concrete prisms admixed with 7.5% Cl- by weight of cement remained stable during the measurement period, indicating that no significant/detectable changes in corrosion states occurred during this time. Cyclic polarization (CP) curves showed the surface film of the pickled specimens exhibiting an increase in protection from the applied anodic polarization, whereas the as-rolled bars exhibited a steady increase in current densities characteristic of uniform corrosion from applied anodic potential. Nevertheless, CP had no apparent long-term detrimental effect on the corrosion potentials, macrocell current densities or LPR measurements of either surface condition, thus initial passive surface characteristics were regained. Autopsied concrete specimens at the end of testing revealed very little rusting on the pickled stainless steel, with some superficial rusting on the top surface of the as-rolled bars, believed to have formed during the early cement hydration stages when ionic conductivity and subsequent macrocell corrosion rates were higher. Areas of significant corrosion occurred predominantly near the epoxy-covered ends of the bars where localized corrosion occurred from crevice effects as well a residual knife marks left from applying the epoxy. These "artificial" effects would have had significant contribution to the higher corrosion currents measured on the as-rolled bars.