Effects of Chloride, Humidity, and Concrete Mix on the Electrochemical Parameters of Steel Reinforcement Corrosion

Abstract

The large uncertainties of electrochemical input parameters, along with their variation with chemical environment and time, can significantly affect the accuracy of simulations and oversimplify the nonuniform corrosion distribution over time. To bridge the gap, this study investigated the effects of chloride ion concentration, humidity, and concrete mix on the electrochemical parameters through a long-term experiment of natural corrosion. The results revealed that the logarithmic anodic and cathodic exchange current density are almost constant values of −4.80 and −5.49, respectively. The cathodic equilibrium potential slightly fluctuates around 253 mV versus the saturated calomel electrode. The increase in chloride ion concentration above 0% generally leads to a reduction in the anodic Tafel slope, while the absolute cathodic Tafel slope remains almost constant when chloride ion concentration exceeds 1.214%. Due to the distinct controlling mechanisms of corrosion, the effects of chloride and water-to-cement ratio on the electrochemical parameters are susceptible to the humidity level of concrete. Interestingly, at 90% humidity, the corrosion potential may shift negatively for a lower water-to-cement ratio, resulting in a decrease in the anodic Tafel slope. Nevertheless, a lower corrosion rate can still be anticipated. Employing the Butler–Volmer equation and Nernst equation, semiempirical models were constructed by representing the effects of humidity with piecewise functions. The accuracy has been validated through experimental data from both this work and previous studies. The results and empirical models of this study provide reasonable electrochemical input parameters for simulation of nonuniform corrosion and the evolution over time.