Abstract
•EIS for protective properties of oxide films on reinforcement steel.•Passive films grown in chloride contaminated SPS.•Thermo-mechanically treated mild steel and low-alloy steel.
Electrochemical studies (AC impedance and DC polarization) have been used to study the protective properties of passive films that form on reinforced steel embedded in concrete as a function of time and space. Experiments have been performed on passive/oxide films grown on the surface of steel reinforcement bars exposed to chloride-contaminated simulated concrete pore solution (SPS) prepared by dissolving a representative amount of sodium hydroxide and potassium hydroxide in distilled water and saturated with lime. A common type of locally available concrete reinforcement TMT (thermo-mechanically treated) mild steel with TM (tempered martensitic) and PF (pearlite ferrite) rings (source “A”) was investigated in comparison to a type of hot rolled low-alloy steel without thermo-mechanical treatment (source “B”). The results of the elemental analysis and metallographic microstructure coupled with electrochemical studies indicate that the coupled surface and sub-surface composition of TMT rebar has a time-dependent reversing effect on the protective properties of the passive oxide films that provide durability and protection to the steel rebars against corrosion in concrete. Steel with TM–PF rings has a better initial corrosion resistance in comparison to low alloyed steel. However, with the passage of time, its corrosion resistance decreases, and alloyed steel finally dominates over the TMT rebar.