Cathodic Protection for Reinforced Concrete

Why Concrete CP Matters

Reinforcing steel in concrete is normally protected by the high-alkalinity concrete environment. Corrosion can begin when chloride contamination, carbonation, cracking, moisture, oxygen, or other conditions break down the passive layer.

Rebar corrosion creates expansive corrosion products that can crack, delaminate, and spall concrete. CP can reduce corrosion activity when properly designed and monitored.

Concrete CP differs from soil or seawater CP. The electrolyte is concrete pore solution, and current distribution depends on concrete resistivity, moisture, cover depth, rebar continuity, and anode layout.

Core Concept

Protected steel

The protected structure is the embedded reinforcing steel. Electrical continuity between rebar sections is important for current distribution and monitoring.

Concrete as electrolyte

Concrete contains pore solution that can conduct ionic current. Concrete resistivity, moisture content, cracking, and contamination affect CP performance.

Anode systems

Concrete CP may use surface-applied anodes, embedded anodes, discrete anodes, mesh anodes, conductive coatings, or other specialty systems.

Monitoring

Concrete CP systems may use embedded reference electrodes, decay measurements, current output monitoring, and periodic inspections to evaluate performance.

Current distribution

Current must reach the steel reinforcement. Dense concrete, dry areas, discontinuous reinforcement, delamination, or poor anode contact can limit protection.

Field Application

Concrete CP is used on bridge decks, parking structures, piers, wharves, balconies, columns, beams, and other reinforced concrete assets affected by corrosion.

Field evaluation may include half-cell potential mapping, concrete resistivity, chloride testing, delamination surveys, continuity testing, CP current output checks, and depolarization testing.

Concrete repair and CP design must be coordinated. Patch repairs, overlays, membranes, moisture conditions, and rebar continuity all affect CP system performance.

Common Mistakes

1. Treating concrete CP like pipeline CP.
   Why it is wrong: The electrolyte, geometry, reference electrodes, criteria, and current distribution conditions are different.
2. Ignoring rebar continuity.
   Why it is wrong: Discontinuous reinforcement may not receive protective current uniformly.
3. Ignoring concrete resistivity and moisture.
   Why it is wrong: These conditions strongly affect current flow through concrete.
4. Assuming patch repair alone solves corrosion.
   Why it is wrong: Corrosion can continue near patch boundaries or in chloride-contaminated concrete.
5. Ignoring anode-to-concrete contact.
   Why it is wrong: Poor contact limits current discharge and current distribution.

Field Example

A parking garage deck has chloride-contaminated concrete and active rebar corrosion. Patch repairs remove delaminated concrete, but adjacent chloride-contaminated areas remain.

CP may be considered to reduce ongoing corrosion activity in the remaining reinforced concrete, but the design must evaluate rebar continuity, concrete resistivity, moisture, anode layout, and monitoring requirements.

Practice Questions

1. What metal is normally protected in reinforced concrete CP?
2. Why does chloride contamination matter in reinforced concrete corrosion?
3. Why is rebar continuity important?
4. How does concrete moisture affect CP performance?
5. Why should concrete CP not be treated exactly like buried pipeline CP?

Related Pages

• Corrosion Fundamentals
• Cathodic Protection Criteria
• Reference Electrodes
• Anodes
• CP Survey Methods