Cathodic protection basics

Cathodic protection is a primary solution for protecting reinforced concrete structures, providing a highly effective solution for corrosion prevention and significantly increasing the lifespan of structures. In this guide, we’ll be going through some cathodic protection basics:

Principles of cathodic protection
How does it work?
Why we use it
Examples of cathodic protection

Principles of cathodic protection

When discussing cathodic protection basics, it’s important to explain what we actually mean by “cathodic protection”.

Cathodic protection is a method of corrosion prevention. It works by making the encased metal surface the cathode of an electrochemical cell. This simple protection technique connects the metal to be protected to a more easily corroded “sacrificial metal” to act as the anode. There are two types of cathodic protection:

Galvanic (or “passive”)

This method works by connecting the sacrificial anode to the metal to be protected. The difference between the metals generates electricity forming an electrochemical cell which drives corrosion of the anode and protects the underlying metal. This type of cathodic protection is typically used to protect oil rigs and platforms, steel water heaters and tanks.

Impressed current cathodic protection (ICCP)

ICCP is more suitable for larger structures, where the number of sacrificial anodes required to deliver the correct level of current would make passive cathodic protection unfeasible. Instead, the anodes used in ICCP are connected to an external power source that delivers constant electrical flow and uses a metal that is more active than the base metal to create anodes with a much stronger electrochemical potential.

Why do we use cathodic protection?

Corrosion of reinforced concrete structures is one of the most common reasons for buildings requiring concrete repairs that we encounter.

Corrosion is caused by the process of carbonation – and often through contamination by sea salt. Cathodic protection offers a technically-sound solution to mitigating corrosion damage because it deals with the corrosion problem across the entire area treated. This cannot be achieved with conventional repair methods without removing all concrete where salt or carbon dioxide has penetrated. Such extensive repair is frequently prohibitive in terms of practicality and cost.

Example of cathodic protection: EDF Hartlepool Power Station

Our team installed a cathodic protection system to a corroded drumscreen, as part of a larger programme of concrete remediation works.

Corrosion of the reinforced concrete structure had been caused by carbonation and contamination of concrete by sea salt which passes through the drumscreen chamber as part of the power station’s cooling process.

Prior to installation, our team installed scaffolding, carried out hammer testing of the surfaces due for repair and undertook hydrodemolition to remove the defective areas of concrete – essential steps to ensure the area was correctly prepared. Next, we quantified and installed replacement rebar and a suitable number of anodes before finishing with R4 Dry Sprayed Micro Repair Concrete.