Quadriga - Brookes Civils Specialists

Cathodic Protection

Cathodic Protection is an engineered electro-chemical solution used for the protection of concrete; concrete encased steel frames and masonry clad steel frame structures.

The beneficial effects of the technique have been recognised since the middle of the eighteenth century, it is only during the second half of this century that the technique has been seriously employed, predominantly in the protection of pipelines, ships and oilfield structures.

Brookes have completed some of the largest and most prestigious Cathodic Protection projects on buildings and structures in the United Kingdom and have over 15 years experience and knowledge in the design, installation, power, monitoring and control of this technique.

Impressed Current Annode Types (ICC)

• Ribbon Anodes

• Mesh & Overlays

• Conductive Overlays

• Conductive Coatings

• Discrete Anodes

• Metal/Thermal Spray

Galvanic Protection Types (GCP)

Metal/Thermal Spray Technology

For many years organisations have fought to protect their assets from corrosion. The prime causes of corrosion in concrete include salt, chloride and de-icing treatments. The salt seeps into the concrete and erodes the steel reinforcing bar (rebar) causing cracks and spalling in the concrete and eventually the potential failure of the structure. One very effective, long-term solution is metal or thermal spraying the concrete with a specially activated alloy of aluminium. This is a technology that protects or extends the life of a wide variety of assets in the most hostile environments.

The majority of applications are operated in galvanic or sacrificial mode; however it can also be operated in impressed current mode. The specially activated alloy of aluminium is connected to one pole of a DC power supply. The steel rebar is connected to the other pole of the power supply. The electrical circuit is completed between the rebar and the alloy by the presence of moisture in the concrete. The action of the corrosion cell causes the alloy to corrode in preference to the steel rebar, therefore protecting the rebar from corrosion.

The process of metal/thermal spraying alloy onto the substrate ensures that there is a good, even connection path between the coating and the rebar through the concrete. Prior to spraying, damaged sections of concrete need to be repaired with rebar also repaired or replaced. The surface needs to be lightly blasted to remove any surface dirt and provide a good key to enable the coating to bond. Alloy is then applied the structure. Typical bond strength is in the region of 3n/mm2 with a coating thickness between 250 and 500 microns.

The costs to metal/thermal spray large concrete structures is not insignificant, particularly when many structures are difficult to access, such as bridges, however, the long-term benefits make the process extremely commercially attractive. Performed by experienced licensed applicators metal/thermal spray technology provides corrosion protection up to 25 years and beyond before the next significant maintenance operation is required. The protection provided can greatly prolong the life of the structure and also prevent costly accidents from cracked sections falling from the structure. Once applied, the alloy requires minimal maintenance. If required for aesthetic purposes, the alloy can also be painted.

ZLA/ISOZIN

THE PRODUCT

• Acts in the same way as hot dip galvanising.

• 99.99% Pure Zinc thickness 80µ

• Electro conductive adhesive thickness 25µ

• Operating temperature 80°C

• Normal dissipation of 4µ per year

THE PROCESS

• Galvanic action between zinc tape and structure renders the zinc tape a sacrificial anode in the

• presence of moisture.

• Electro conductive adhesive ensures electrical continuity between zinc tape and substrate

• Passive barrier coating as first line of defence formats

TECHNICAL FEATURES

1. Acts in the same way as hot dip galvanising

2. Electro-conductive adhesive

3. Constant thickness - from 80µ to 500µ

4. Supplied in rolls and gaskets

ADVANTAGES

• Minimum surface preparation required

• No Primer required

• Environmentally friendly

• Easily applied

• Can be over painted

• Economical on long life structure

• No maintenance during the structure life

• Ideal for difficult access & dangerous structures

• Many "onsite" applications

• Protection as passive barrier coating and galvanic action lamp posts

TYPICAL APPLICATIONS

• Above ground pipework

• Tanks and vessels

• Auto and trains

• Lamp posts and street furniture

• Specialised industrial applications Etc….etc

USED BY

• TRANSCO, UK

• PETRONAS, Malaysia

• SHELL, Italy

• PEMEX, Mexico

• MERCEDES BENZ, Germany

• ALSTOM, Transport division (World-wide)

• EON, UK

BENEFITS

• Reduced maintenance cost

• Reduced plant down time

• Increases the life of the structure

• No environment clean up costs

• Application is cheaper than conventional paint systems on long life structures

 

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