Influence Mechanism Of Temperature And Humidity On Corrosion Control Mode And Rate Of Reinforcing Steel In Concrete

Corrosion of reinforcing steel is one of the important causes of durability degradation of reinforced concrete structures. The reinforcing steel often shows significantly different corrosion levels when the reinforced concrete structures under different environmental conditions, which largely depends on the temperature and relative humidity. The influences of temperature and relative humidity on the corrosion control mode and corrosion rate of reinforcing steel were investigated by combining with the theoretical analysis, numerical simulation and experimental data in this thesis. The main contents of this thesis are as follows:(1) The corrosion mechanism and control mode of corrosion process of reinforcing steel embedded in concrete were discussed first. In order to develop the macrocell corrosion model of reinforcing steel embedded in concrete, the corrosion potential of the anode and cathode were established by inferring the activation and concentration polarization overpotentials based on the principle of electrochemical corrosion and taking into account the influence of reverse reaction rate on the activation polarization overpotential. The analysis results show that the effect of reverse reaction rate on the activation polarization overpotential cannot be ignored when the corrosion current density is small or the exchange current density is large.(2) The influences of temperature and relative humidity on the various electrochemical parameters, such as the equilibrium potential, exchange current density, Tafel slope, limiting current density and concrete resistivity were discussed. Then, the macrocell corrosion model of reinforcing steel embedded in concrete which takes into account the temperature and relative humidity was developed. The analysis results show that the corrosion rate increases first and then decreases rapidly as the relative humidity increases; meanwhile, the control mode of corrosion process changes from the resistance control into the cathodic control gradually, as the relative humidity increases. Under both the resistance and cathodic controls, the corrosion rate increases with the temperature.(3) The influences of temperature and relative humidity on the control mode of corrosion process for the reinforcing steel embedded in concrete was analyzed based on the developed macrocell corrosion model. And then, a practical prediction model for corrosion rate which takes into account relative humidity, temperature, water-to-cement ratio, chloride content and concrete cover thickness was proposed. The applicability and efficiency of the proposed prediction model of corrosion rate were validated by comparing with the experimental data of both artificial accelerated and natural corrosion experiments.