ZLA eliminates corrosion by operating as a galvanic anode
- Metalnastri Anticorrosion Systems
- Via Padova, 3, 20063 Cernusco sul Naviglio (Milano)
- +39 02 92592060
Zinc Layer Anode o ZLA
Zinc Layer Anode or simply ZLA is a high purity zinc foil (> 99.95%) coated with an ionically conductive adhesive.
ZLA is a product used in the protection of reinforced concrete constructions against rebar-corrosion. ZLA is a sacrificial galvanic anode specifically designed for giving electrochemical protection, known as cathodic protection, for the prevention of corrosion of the concrete steel reinforcement. The current required for cathodic protection is provided by the galvanic link of the steel reinforcement and the zinc layer being part of the ZLA. No external power source or what so ever is necessary.
The presence of chloride based salts within the concrete can be a threat to the passivation layer (protective oxyde-layer) on the carbon steel reinforcement of the concrete. Also variations in the concrete cover on top of the reinforcement, the quality of the concrete cover and the content of the chlorides around the reinforcement will cause similar corrosive circumstances. These circumstances will cause local corrosion cells. These places are called anodes. Other locations of the reinforcement, where the circumstances are relatively less corrosive and aggressive, remain passivated (passive oxyde-layer). These locations are called cathodes.
The combination of anodic and cathodic locations result in electrochemical reactions (redox-reactions) if the distance between the anode and cathode will be relatively small . These electrochemical reactions will convert the steel of the reinforcement into iron-oxydes (rust) at the anodic locations. Those corrosion products (rust) formed, can be 5 to 10 times the volume of the original steel reinforcement. For this reason the tension in the concrete will eventually lead to crack and spall the concrete cover. The loss of steel and concrete will eventually weaken the construction and be a threat to the safety.
The ZLA has been therefore designed to function as an additional anode replacing all the anodic locations of the reinforced concrete construction. It is applied upon the concrete surface.
The Zinc-layer is electrically linked with the steel reinforcement.
In this way the electric-circuit is completed because electric current flows through the adhesive layer and concrete by means of ionic conductance (both materials are so-called electrolytes).
Since Zinc has a natural potential which is more electronegative than the steel reinforcement, the Zinc becomes the anode after installation and forms a new corrosion cell in which the reinforcement is forced to be the cathode.
In this way the corrosion process within the concrete is transferred to the Zinc-layer avoiding futural spalling and cracking of the concrete.
ZLA is applied directly onto the outer concrete surface. The Zinc-layer is electrically connected to the steel reinforcement. In this way the electrical-circuit is completed as the electric current flows through the adhesive layer and concrete by means of ionic conductance. As soon as the electrical connection is established, the current will flow and ZLA will begin to consume and sacrifice itself.
The high conductivity of the zinc foil ensures a uniform distribution of CP current and simplifies any localised current distribution requirements.
It is supplied with a polypropylene top-liner to protect the adhesive against clogging. Before application the top-liner is removed manually and the ZLA is adhered onto a cleaned concrete surface. The ZLA is provided in rolls (250 mm wide and 25 meters long).
After application ZLA should be finished with an approved cementitious based coating of the specified texture and colour, ensuring edges and seams are properly over coated to avoid moisture ingress. System monitoring can be performed according to the standard ISO 12696.
INFRASTRUCTURE APPLICATION
ZLA can be applied to the top, sides, or bottom surfaces of concrete structures of various shapes and any sizes.
ZLA requires minimal maintenance over its long life. If desired, performance can be monitored easily by on-site personnel. With a 250 micron zinc layer the calculated life expectancy will be 21 years. Upon request the anodes can be modified to achieve a life span of 40 years plus.