Anode Materials, Conductive Coatings, and Prestressing Steel in Cathodic Protection of Concrete Structures: A Critical Review of Properties, Degradation, and Safety

The durability and safety of cathodic protection (CP) in reinforced and prestressed concrete depend on interactions among electrode materials, electrochemical conditions, and structural response. This critical review examines how anode composition, microstructure, conductive layers, concrete resistivity, and current distribution affect protection performance and material degradation. Laboratory studies, numerical simulations, and field evidence are compared for titanium/mixed-metal-oxide anodes, zinc-based galvanic systems, graphite and carbon-modified cementitious materials, polymeric coatings, and contact mortars. Particular attention is paid to interfacial processes, distinguishing initial conductivity and current delivery from electrochemical stability, anode consumption, and demonstrated service life. Accelerated aging and field exposure are treated as complementary, but non-equivalent, evidence of durability. For prestressing steel, the effects of cathodic polarization, strength, stress state, and exposure on hydrogen-assisted damage are examined; meeting protection criteria alone does not establish hydrogen safety. Instant-off potentials, depolarization measurements, and electrochemical impedance spectroscopy are assessed alongside material and structural diagnostics, including their limitations. A three-dimensional P–T–B framework distinguishes local protection performance (P), technological durability (T), and material and structural safety (B). Standardized characterization and long-term validation remain necessary before laboratory findings can inform prestressed-concrete applications under realistic operating and environmental exposure conditions.