Cathodic protection works by turning the embedded reinforcing steel into the cathode of an electrochemical cell, suppressing the anodic reactions that drive rebar corrosion. The technique has been used for decades to control corrosion and extend the service life of concrete">reinforced concrete structures, and its application is codified in BS EN ISO 12696, which sets out polarisation and depolarisation-based protection criteria for both impressed current systems and galvanic (sacrificial anode) systems.

For structural engineers and asset owners managing ageing bridges, car parks and marine structures, cathodic protection offers an alternative to full concrete removal and reinstatement where chloride-induced or carbonation-induced corrosion has already begun. Rather than replacing contaminated concrete, the system modifies the electrochemical environment around the reinforcement so that the steel no longer corrodes at an unacceptable rate.

What are the two main system types?

BS EN ISO 12696 distinguishes between two fundamentally different ways of delivering protective current to the reinforcing steel:

  • Impressed current systems use an external power supply to drive current from an installed anode to the reinforcement, allowing the applied current and potential to be controlled and adjusted over the life of the structure.
  • Galvanic (sacrificial anode) systems rely on a more electrochemically active metal connected to the reinforcement; the sacrificial anode corrodes preferentially and supplies protective current without an external power source.

How is protection verified against the standard?

The standard's protection criteria are based on two complementary approaches: the measured potential value of the reinforcement, and the extent of potential decay observed during a depolarisation sequence, in which the protective current is switched off and the steel's potential is tracked as it drifts back toward its natural corrosion potential. Both impressed current and galvanic installations are assessed against these criteria, which form the specification basis used across highway, marine and building structures.

However, the academic literature raises questions about how reliably these criteria reflect actual protection performance. Research published in RILEM Technical Letters examined cathodic protection on a corroded concrete wall affected by macrocell corrosion, using six reference electrodes alongside a time-dependent finite-element model built in COMSOL Multiphysics to simulate polarisation and depolarisation behaviour. The study found that experimental and numerical results showed significant differences in the time response depending on where the reference electrode was located on the structure.

"This conclusion indicates that the concept of protection criteria defined by the standards is not suitable to assess the efficiency of cathodic protection applied to reinforced concrete structure."

— Stephane Laurens and Raoul Francois, LMDC, RILEM Technical Letters

What does this mean for specifiers?

For practitioners specifying or verifying cathodic protection systems, the research implies that a single depolarisation reading at one monitoring point may not give a representative picture of protection across an entire element, particularly where corrosion is localised in macrocell form rather than uniformly distributed. Electrode placement and the number of monitoring points become engineering decisions in their own right, not just a compliance formality against BS EN ISO 12696.

Cathodic protection sits alongside other durability strategies for reinforced concrete, including low-permeability concrete mixes, increased cover, and corrosion-resistant reinforcement. Where structures already show active corrosion, however, cathodic protection remains one of the few interventions that can arrest the process without extensive demolition. Understanding both the standard's criteria and their documented limitations is relevant background for anyone assessing durability strategies for existing concrete assets, including those exploring carbon-based reinforcement alternatives or revised exposure class assessments for refurbishment projects within the broader context of circular construction and asset life extension.