Oxygen diffusion into unsaturated seawater and sea sand concrete and its effect on non-uniform corrosion of steel bars

Oxygen diffusion in reinforced concrete (RC) is a crucial factor affecting the corrosion of steel bars under a high chloride environment, while it is also controlled strongly with the saturation degree of the concrete. Therefore, the objective of this work is to elucidate the diffusion of oxygen in unsaturated concrete and its effect on the corrosion of steel bars. In this work, a self-made device is developed to study the oxygen diffusion in seawater and sea sand concrete (SSC) and the wire beam electrode (WBE) technique is innovatively used to investigate the effect of oxygen on the corrosion of steel bars. The oxygen diffusion coefficient of SSC was decreased maximum by 97.3 % with the internal relative humidity (RH) of concrete increasing from 12 % to 88 %, it was increased by 96.5 % when the water-binder ratio increased from 0.18 to 0.48. A multi-factor coupling model considering the relative humidity and strength of concrete was developed to estimate the oxygen diffusion coefficient of concrete. The corrosion process of steel bars was tracked by the WBE technique and it presented as the formation and propagation of the local anode zone. However, the electrodes were still in a passivation state after corrosion for 120 d when the water-binder ratio was lower than 0.28 or the oxygen concentration was lower than 21 % even in SSC. Therefore, the pitting anode zone will be shrunk and the corroded steel bars were re-passivated with insufficient oxygen supply during the late service process.