Corrosion characteristics of vanadium micro-alloyed steel reinforcement bars exposed in concrete environments and industrially polluted atmosphere

Corrosion resistance performance of rebars rolled from vanadium micro-alloyed (VMA) steel was evaluated vis-a-vis rebars rolled from steel having similar chemistry to the (VMA) steel without vanadium and subjected to thermomechanical treatment after hot rolling (TMT). Three test environments namely simulated concrete pore solution, mortars, and industrially polluted atmosphere were used to assess the performance of these rebars. Mass loss, electrochemical impedance spectroscopy, DC polarization and potential-time studies were employed to acquire quantitative data and explain the observed results. Raman spectroscopy was used to identify the corrosion products formed on the surface of the exposed rebars in different environments. The corrosion resistance of VMA rebars was better than TMT especially with increased duration of exposure in chloride contaminated concrete environments. However, under the industrially polluted atmosphere, both rebars exhibited comparative corrosion rates. Lesser detrimental effect of chloride present in concrete environment on the VMA steel rebars is attributed to the higher grain boundary per unit area in these rebars than in the TMT rebars. It is suggested that owing to the stronger tendency of the higher-grain-boundary- material to interact with oxygen and moisture, a thicker film of Fe(OH)(3) was formed on its surface than on the surface of the TMT rebar, prior to their exposure to the test environments. This hydroxide film dissolved in alkaline environment of concrete, nucleated and grew as a protective FeOOH film on the surface of the rebars.