Cathodic protection is an electrochemical corrosion-mitigation system applied to embedded steel — rebar and post-tension tendons — in concrete structures. It does not replace deteriorated concrete or corroded steel. It interrupts the electrochemical reaction that drives corrosion by supplying a protective electrical current to the steel surface. In South Florida's coastal environment, where chloride-induced corrosion of embedded steel is the dominant cause of concrete deterioration, cathodic protection is one of the tools a structural engineer may specify when the repair scope includes elements where chloride contamination is deep enough that conventional patch-and-coat repair is unlikely to last to the next maintenance cycle. Understanding when and why engineers reach for this tool — and what installation actually looks like in an occupied building — is useful for any board or property manager going through a Phase 2 or 40-year recertification repair scope.
How corrosion of embedded steel works
Concrete is naturally alkaline — a freshly cast slab has a pH above 12, and that alkalinity forms a passive oxide layer on the surface of embedded steel that protects it from corrosion. Chloride ions — from seawater, ocean air, or deicing salts — penetrate the concrete over time and disrupt that passive layer when they reach sufficient concentration at the steel surface. Once the passive layer is broken, the steel corrodes in the presence of oxygen and moisture. The corrosion products (iron oxides) occupy a larger volume than the original steel, generating expansive pressure that fractures the concrete cover — producing the spalling and delamination that building engineers find during milestone inspections and recertification assessments. The chloride that triggered the corrosion is still in the concrete after the spall is patched. Patching alone removes the symptom; it does not remove the cause.
Galvanic (sacrificial anode) systems
Galvanic cathodic protection uses a sacrificial anode — typically zinc or aluminum — that is electrically connected to the steel reinforcement. The anode corrodes preferentially, supplying electrons to the steel and maintaining the protective current. In concrete restoration applications, galvanic anodes are typically discrete units embedded in the patch material at repair perimeters, or distributed across the deck surface in a regular grid. They require no external power source and no ongoing electrical infrastructure — the electrochemical reaction is self-sustaining as long as the anode material remains. The tradeoff is current density: galvanic systems supply lower current than impressed-current systems, which limits their effectiveness in high-chloride environments or on large structures. Engineers specify galvanic systems when the repair area is localized and the chloride level at the steel is moderate — typically at repair perimeters where the risk of incipient anode effect is highest.
Impressed current cathodic protection (ICCP)
Impressed current cathodic protection supplies protective current from an external DC power source through a distributed anode system installed on or near the concrete surface. The anode system — typically a conductive coating, a titanium mesh, or a discrete probe grid — is installed across the deck or structural element surface and connected to a transformer-rectifier unit. The rectifier converts AC power to the DC current required by the system and allows the engineer to adjust the current output to match the chloride level and surface area of the protected element. ICCP systems require an electrical connection, a permanent monitoring system, and annual maintenance inspections. They deliver higher and more controllable current than galvanic systems and are the appropriate specification for large deck areas with high chloride penetration. In South Florida's parking deck and balcony applications, ICCP is most commonly specified when chloride sampling confirms that chloride levels at the steel significantly exceed the corrosion threshold across a large area.
When engineers specify cathodic protection in a repair scope
The decision to include cathodic protection in a structural repair scope belongs to the engineer of record. The typical trigger is a chloride profile — sampling at multiple depths to determine how far chloride has penetrated — that shows chloride concentrations well above the corrosion threshold at the steel depth, across an area large enough that the engineer cannot reasonably conclude that removing all the contaminated concrete and replacing it is practical. In that condition, patching the visible spalls and coating the surface will not prevent the chloride that is already in the concrete from eventually reaching the steel in the unpatched areas and reinitiating corrosion. Cathodic protection addresses the chloride that cannot be removed. The engineer sizes the system — anode type, spacing, current output — based on the chloride profile, the steel surface area, and the targeted protection life.
Installation in an occupied South Florida building
Cathodic protection installation on an occupied condominium or commercial building in South Florida follows the same sequencing discipline as any other restoration trade: section-by-section, with resident notification, access coordination, and dust containment at every work front. Galvanic anode installation at patch perimeters adds minimal complexity to a standard concrete repair sequence — the anodes are installed when the rebar is exposed, before the patch is placed. ICCP installation is more involved: the anode system must be installed across the finished concrete surface, the cabling must be run to a central rectifier location, and the monitoring probes must be embedded before the topcoat or membrane is applied. The electrical infrastructure is concealed in the finished surface and requires access only for the annual inspection of the rectifier unit. From the resident's perspective, the installation looks like a concrete repair project with an additional step before the topcoat goes down.
- Cathodic protection is specified by the engineer of record based on chloride sampling data — it is not a product decision contractors make independently
- Galvanic (sacrificial anode) systems are appropriate for localized repair perimeters with moderate chloride levels; ICCP is appropriate for large areas with high chloride penetration
- Cathodic protection does not replace concrete repair — deteriorated concrete and corroded steel are removed and patched first; the cathodic system then protects what remains
- ICCP systems require an electrical connection, monitoring infrastructure, and annual maintenance inspection — these are ongoing obligations, not one-time installation costs
- If your Phase 2 or 40-year recertification scope includes a cathodic protection specification, ask the engineer what chloride data drove the decision — it should be quantified, not assumed