Why does reinforcement corrosion occur in reinforced concrete?

Concrete, thanks to its highly alkaline environment, forms a protective passive film around the steel reinforcement within it, protecting the reinforcement from corrosion under normal conditions. However, this protective environment can be disrupted by two main mechanisms: chloride ions reaching the reinforcement surface and carbonation.

Chloride ions from seawater, saline environments, or de-icing salts penetrate the concrete cover, locally disrupting the passive film on the reinforcement surface and initiating pitting corrosion. In carbonation, atmospheric carbon dioxide gradually reduces the alkalinity of the concrete; as the pH decreases, the passive film becomes unstable across the entire surface.

Steel that corrodes expands in volume. This expansion creates tensile stresses within the concrete, leading to cracking, bulging (delamination) of the concrete cover, and spalling. As a result, both the load-bearing section and the service life of the structure are negatively affected.

Scope of ISO 12696

The ISO 12696 standard (applied in Türkiye as TS EN ISO 12696) defines the performance requirements for cathodic protection of steel in cement-based concrete. The standard covers both new and existing structures; it is applicable to carbon steel reinforcement and prestressed reinforcement.

The standard covers the parts of reinforced concrete structural elements that are exposed to the atmosphere, buried, submerged in water, and located in tidal zones. In this respect, it is applicable to a wide range of reinforced concrete structures such as bridges, viaducts, port and pier structures, parking lots, water tanks, and buildings near the sea.

This page focuses solely on cathodic protection of steel reinforcement in concrete. Cathodic protection of steel pipelines buried in the ground is a separate topic and is covered on our dedicated page.

The Principle of Cathodic Protection in Concrete

Cathodic protection is an electrochemical method that controls the corrosion rate by altering the potential of the steel reinforcement to be protected. A cathodic current is applied to the reinforcement from the outside; thus, the anodic (metal dissolution) reactions of the steel are suppressed.

In reinforced concrete structures, externally sourced cathodic protection, known internationally as ICCP, is commonly used. In this system, an anode system powered by a direct current source is placed on or within the concrete surface, and the protective current is distributed to the reinforcement. ICCP is preferred in chloride-contaminated and large-surface structures because the current is controllable.

Alternatively, galvanic (sacrificial anode) systems that do not require an external power supply can also be used in certain applications; however, they differ from ICCP in terms of current capacity and control.

ICCP Anode Systems

The anode system is the component that transmits the protective current through the concrete to the reinforcement, and its selection depends on the geometry of the structure, the exposure conditions, and aesthetic requirements. Various anode types can be used within the framework of ISO 12696.

  • Mixed metal oxide coated activated titanium mesh or strip: embedded in concrete coating or mortar layer to distribute current evenly over widespread surfaces.
  • Conductive coatings: conductive paint or coating containing carbon is applied to the concrete surface along with current-dissipating conductors.
  • Thermal spray zinc: a zinc-based anode layer applied to a prepared concrete surface using a spray method.
  • Discrete anodes: discrete anode elements placed in holes drilled into the concrete, used especially in repair areas.

Protection Criteria and Monitoring

The adequacy of cathodic protection is assessed not by bringing the absolute potential to a single constant value, but on the basis of potential shift (depolarization/decay). The amount of shift observed in the reinforcement potential over a certain period after the applied protective current is cut off is a conceptual criterion for determining whether the protection is adequate.

In this approach, the commonly cited concept in practice is the potential shift of approximately 100 mV observed within a certain period after the current is interrupted (100 mV decay criterion). This value is a conceptual reference; the applicable criteria, conditions, and limitations for a specific structure are determined according to the relevant clauses of the standard and the assessment of a qualified engineer.

The evaluation is performed via reference electrodes embedded in the concrete. These electrodes allow monitoring of reinforcement potential and taking depolarization measurements. Commissioning the system, current settings, and continuous monitoring are the implementation steps stipulated by the standard to ensure the protection remains effective over time.

In which structures is it applied?

Cathodic protection of steel within concrete becomes relevant in reinforced concrete structures where the risk of corrosion is high and the service life of the structure is critical.

  • Seaside and overwater bridges and viaducts
  • Highway structures and multi-story car parks exposed to de-icing salt.
  • Ports, piers, docks, and marine structures.
  • Reinforced concrete structures that come into contact with water, such as water tanks, treatment plants, and similar structures.
  • Buildings and infrastructure elements in coastal areas

Distinction Between Cathodic Prevention and Cathodic Protection

Within the framework of ISO 12696, two different purposes are distinguished. Cathodic protection is generally applied to control the rate of corrosion in existing structures where corrosion has already begun.

Cathodic prevention, on the other hand, is typically planned during the construction phase for new structures expected to be exposed to chloride contamination in the future, in order to delay the onset of corrosion and extend their service life. The selection of an appropriate approach for a structure is an engineering decision that must be evaluated by a qualified engineer, taking into account the exposure conditions, reinforcement type, and design objectives.

AES's Location and Scope of Accreditation

AES (aesinn.com) is a Type A electrical inspection organization accredited by TÜRKAK. AES's accreditation scope only covers the "6.1 Electrical Installation" inspection area.

Cathodic protection in reinforced concrete structures is a specialized field requiring expertise at the intersection of electrochemistry, corrosion, and structural engineering. AES provides technical information in this area; however, this content does not constitute a declaration of conformity on matters outside the scope of AES's accreditation.

Information Note

AES is NOT an accredited inspection/certification body in this context.

The content on this page is for informational purposes only and is subject to the technical assessment of a qualified engineer. The design, selection of criteria, and application of cathodic protection for a specific structure should be handled by a qualified engineer, taking into account relevant standards and site conditions.

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Frequently Asked Questions

What structures does ISO 12696 cover?

The standard covers cathodic protection of steel in cement-based concrete, in both new and existing structures. It applies to elements of reinforced concrete structures such as bridges, viaducts, ports, parking lots, water tanks, and buildings that are exposed to the atmosphere, buried, submerged in water, and in tidal zones. Cathodic protection of buried steel pipelines is a separate issue.

Why does reinforcement corrosion occur in reinforced concrete?

The alkaline environment of the concrete, which protects the reinforcement, is disrupted by chloride ions reaching the reinforcement level or by carbonation. In this case, the passive film of the steel becomes unstable, corrosion begins, and the expanding steel in the concrete leads to cracking, blistering, and spalling.

What is ICCP and how does it work in concrete?

ICCP is an externally sourced current cathodic protection system. An anode system powered by a direct current source is placed on or within the concrete surface; the protective current applied to the reinforcement suppresses the corrosion-causing anodic reactions of the steel, thereby controlling the corrosion rate.

What does the 100 mV decay criterion mean?

The adequacy of protection in concrete is evaluated based on potential shift rather than an absolute potential value. In practical application, a shift of approximately 100 mV observed over a certain period after the protective current is cut off is considered a conceptual reference. The criteria applicable to a specific structure are determined according to the relevant clauses of the standard and the assessment of a qualified engineer.

What is the difference between cathodic protection and cathodic prevention?

Cathodic protection is generally applied to control the rate of corrosion in existing structures where corrosion has already begun. Cathodic prevention, on the other hand, is typically planned during the construction phase for new structures where chloride contamination is expected in the future, in order to delay the onset of corrosion.

Does AES conduct inspections or certifications within the scope of cathodic protection for reinforced concrete?

No. AES's TÜRKAK accreditation scope only includes the 6.1 Electrical Installation area. AES is not an accredited inspection/certification body in this area; this content is for informational purposes only and is within the framework of authorized engineer technical evaluation.