The effect of long-term atmospheric aging and temperature on the electrochemical behaviour of steel rebars in mortar

[Display omitted] •Reinforced mortar samples exposed to natural atmosphere were studied during 15 years.•The 28 μm thick passive layer was submitted to a thermal cycle.•Thermal cycles degrade the passive layer lowering the barrier properties.•The cathodic reaction occurs at the electrochemically active oxide’s pore walls. This study describes changes in the electrochemical properties of carbon steel reinforcement bars embedded in mortar after their exposure to a mild atmosphere for 15 years. The development of an oxide layer was followed using electrochemical impedance spectroscopy. The samples were also subjected to a temperature cycle that allowed an electrical equivalent model to be developed in order to understand the electrochemical behaviour. This study concluded that the oxides layer plays a key role in the corrosion process by supporting the cathodic reaction. The oxide layer was identified in the frequency range of 10 kHz―1 Hz, and it grew rapidly during years 3―10 of atmospheric exposure. The aged oxide layer was also damaged by temperature cycling, which decreased the barrier effect.