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Cathodic protection is an electrochemical technique that stops corrosion of steel reinforcement inside concrete structures by making the steel behave as a cathode in a controlled electrochemical cell. It is one of the most effective long-term interventions available for reinforced concrete assets suffering from chloride ingress or carbonation-driven corrosion.
This article explains what cathodic protection is, how the two main systems work, when each is appropriate, and how it compares to conventional concrete repair alone.
To understand cathodic protection, it helps to understand how reinforcement corrodes in the first place. Corrosion of steel is an electrochemical process. In a corroding structure, small differences in electrical potential across the reinforcement create anode and cathode areas. At the anode areas, iron dissolves from the steel and forms rust. At the cathode areas, the reinforcement is protected. The rust products expand, cracking and spalling the surrounding concrete, and the process continues indefinitely unless interrupted.
Cathodic protection interrupts this process by making the entire reinforcement network behave as a cathode. When the steel is uniformly cathodic, corrosion effectively stops at the anode areas because the electrochemistry that drove it no longer exists. The reinforcement remains protected for as long as the cathodic protection system continues to operate.
This approach addresses the corrosion mechanism directly rather than just repairing the visible damage. Conventional patch repair removes damaged concrete and replaces it, but leaves the surrounding contaminated concrete continuing to corrode. Cathodic protection stops corrosion across the whole structure, not just the repaired areas.
Impressed current cathodic protection, usually abbreviated to ICCP, uses an external low-voltage DC power supply to drive a small protective current through the reinforcement. Anodes are installed on or within the concrete, wired to the positive terminal of the power supply. The reinforcement is wired to the negative terminal. The power supply drives current from the anodes through the concrete to the reinforcement, and back through the wiring to complete the circuit.
The anodes are consumed slowly over time as they release the protective current, but modern anode systems are designed for design lives of 25 to 40 years or more. The power supply, cabling and monitoring provisions form the permanent installed system. Monitoring points allow operators to verify that the correct level of protection is being achieved across the structure and to adjust the driving current as conditions change over time.
ICCP is used on large-scale structures where long-term protection is needed and where the cost of an installed system is justified by the value of the asset. Bridges, multi-storey car parks, marine structures and other high-value infrastructure are typical applications. The system requires ongoing monitoring and periodic anode replacement over its design life, but delivers protection that repair alone cannot match.
Galvanic cathodic protection, also called sacrificial protection, works without any external power supply. Instead, it relies on the natural electrochemical difference between two different metals. Zinc-based anodes are installed on or within the concrete, wired to the reinforcement. Because zinc is naturally more reactive than steel, it corrodes preferentially, releasing a small protective current that keeps the steel cathodic. The zinc anode is sacrificed to protect the reinforcement, which is where the “sacrificial” name comes from.
Galvanic systems are simpler and lower-cost than ICCP because there is no external power supply, no permanent monitoring installation, and no ongoing electrical adjustment. However, protection levels are lower than ICCP and the design life is typically shorter, usually 10 to 20 years depending on anode size and environmental conditions.
Galvanic protection is particularly useful for smaller structures, for localised protection around concrete repair patches (where it prevents the incipient anode effect that would otherwise cause corrosion to accelerate in the concrete surrounding the patch), and for situations where an external power supply is impractical or where the client prefers a lower-maintenance solution.
Cathodic protection is not always the right answer. On structures where corrosion has not yet reached a significant extent, protective coatings and physical repair alone may be sufficient. On structures where deterioration is very advanced or where the structural capacity has been compromised, replacement may be more cost-effective than protection. Cathodic protection sits in the substantial middle ground where corrosion is established but the structure remains fundamentally sound and where extending its service life is worth the investment.
The specific decision depends on several factors. How advanced is the corrosion, established through half-cell potential mapping and chloride profiling. What is the intended remaining service life of the structure. How does the cost of cathodic protection compare against continued cycles of reactive repair over that remaining life. What is the client’s asset management strategy for the structure. Where these factors align, cathodic protection is often the most cost-effective long-term intervention available.
The specification decision requires proper corrosion assessment and technical input. This is not a decision to make from visible damage alone. A corrosion condition survey combining half-cell potential mapping, chloride profiling, cover surveys and structural assessment provides the technical basis for whether cathodic protection is warranted and, if so, whether an impressed current or galvanic system is the right approach.
Design life varies by system type and installation. Impressed current systems are typically designed for 25 to 40 years or more of protection, with periodic anode replacement extending life further. Galvanic anode systems typically provide 10 to 20 years of protection, depending on anode size, exposure environment and the level of protection required. Both require monitoring to verify performance and adjust to changing conditions.
For context, the initial cost of a cathodic protection system on a large asset such as a multi-storey car park is often comparable to two or three cycles of reactive repair over the same period. Over the full design life, the cost comparison typically favours cathodic protection, sometimes substantially, because the underlying corrosion mechanism is addressed rather than repeatedly patched.
No. Cathodic protection stops future corrosion but does not reinstate concrete that has already spalled or delaminated. The typical approach combines concrete repair to address existing damage with cathodic protection to prevent further deterioration.
Delivered together, they form a durable solution. The repair restores the visible condition and structural integrity of damaged elements. The cathodic protection stops the underlying corrosion mechanism across the whole structure, including the areas surrounding the repair that would otherwise continue to corrode. Applied without the protection, patch repair often accelerates corrosion in adjacent areas through the incipient anode effect. Applied together, the combined system delivers decades of additional service life.
Cathodic protection is a specialist technical intervention that should be specified from proper corrosion assessment rather than as a default response to visible damage. If your building, car park, bridge or infrastructure asset is showing signs of reinforcement corrosion, or if a previous condition survey has identified widespread chloride contamination, cathodic protection may be worth evaluating as part of the long-term repair and protection strategy.
The starting point is a corrosion condition survey that establishes the extent and rate of deterioration, followed by a technical evaluation of whether impressed current or galvanic protection is appropriate for the structure and the intended remaining service life.
Cathodic protection is one of the most significant technical advances available in reinforced concrete asset management. Applied correctly to the right structure at the right point in its life, it converts a deteriorating asset into a stable one for decades. Applied to the wrong structure, or without proper specification, it delivers less than the client expects.
If you would like an initial conversation about whether cathodic protection is appropriate for your asset, get in touch with the CRS team.
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