Modelling of multi-species transport in concrete under the action of external electric field: Influence of the overpotential at electrode–electrolyte interfaces

Abstract

• A model describing ionic transport with electrostatic potential effect is presented. • Overpotential at electrodes during ionic transport are examined and demonstrated. • Interaction of ionic transport and electrostatic action is described and demonstrated. • Effects of various processing parameters on ionic transport in concrete are discussed. • Transient chloride binding mechanism is discussed and illustrated. The application of external electrical field on concrete structures is widely used to protect it from chloride attack or to evaluate its resistance to chloride penetration in a short period. During these electrochemical processes, the polarization of electrodes placed inside and/or outside of concrete cannot be ignored. This study proposes a numerical model dealing with the mass transport and electrode polarizing process under an externally applied voltage, in which multi-species electromigration, time-varying overpotential and non-equilibrium binding are involved. The Tafel Equation is adopted to express the overpotential at electrode–electrolyte interfaces. The electro-potential boundary changing with overpotential is reset at each time step to obtain the accurate concentration distributions of ionic species. Additionally, benchmarks against third-party experiments are conducted to verify the reliability of the present model. The effects of externally applied voltage, Tafel parameters and initial ionic species concentration on the interaction of overpotential and chloride penetration are also quantitatively examined. The obtained results show that the potential difference between two concrete surfaces is always lower than that applied on electrodes due to the influence of polarization, which has a further impact on the temporal and spatial concentration distributions of ionic species in the pore solution of concrete.