Some Insights into Aging of Embedded Zinc Anode: A Study Using Simulated Concrete Pore Solutions

Zinc (Zn) based discrete sacrificial anodes can be embedded in the repair patch of reinforced concrete structures to prevent premature failure of the patch (“the ring effect”) and to provide cathodic protection to the adjacent steel reinforcement in the concrete. However, their protective efficacy tends to degrade over time mainly due to the accumulation of Zn oxidation products on the surface of the zinc core, which forms a physical barrier that blocks the transport of ions and notably increases the interfacial resistance. To extend the service life of embedded Zn anode and reduce its electrochemical aging, innovative approaches are urgently needed to remove these products from its surface before the formation of a barrier layer. To this end, this work investigates the time-dependent electrochemical aging of Zn anode in simulated concrete pore solutions as a function of several factors, i.e., pH value of the electrolyte, concentration of supporting electrolyte, and surfactant concentration. The protection performance (indicated by the protection current density, apparent voltage difference, and depolarized potential of the rebar) and the characteristics of the Zn anode (e.g., open circuit potential and corrosion current density) served as indicators of electrochemical aging of the anode. In addition, the finite element method (FEM) served to model the transport behavior of zinc oxidization products (diffusion versus electromigration) in electrolytes under various pH values. This work reveals that the electrical field between the zinc anode and the rebar is the main reason for the accumulation of oxidization products on the surface of the zinc core.