Improving durability of discrete zinc sacrificial anodes for steel rebar protection: biochar incorporation into the encapsulation matrix

The cathodic protection (CP) performance of discrete Zn-based sacrificial anodes (DZSAs) embedded in reinforced concrete is conventionally enhanced by increasing the alkalinity or porosity of the encapsulation matrix. However, both strategies often accelerate initial anode depletion and undermine long-term CP effectiveness. This study introduces a third approach: incorporating inherently porous biochar particles (BCPs) into the DZSA encapsulation matrix. Laboratory investigations revealed that BCPs reduce early-stage anode consumption while sustaining CP performance across prolonged wet–dry cycles. These dual benefits—enhanced durability and environmental sustainability—are attributed to BCPs’ electrolyte-buffering capacity and their ability to mitigate the accumulation of zinc oxidation products at the anode–matrix interface. Electrochemical impedance spectroscopy (EIS) confirmed that BCPs retard barrier-layer formation by stabilizing interfacial chemistry, while energy-dispersive spectroscopy (EDS) revealed improved anodic product transport and reduced surface passivation. Collectively, these findings position BCPs as a multifunctional additives that significantly extend the service life of embedded DZSAs, offering a sustainable solution for corrosion mitigation in chloride-laden concrete infrastructure.