Galvanic Anode Cathodic protection (GACP)
A system utilizes anodes which generate a natural DC current to suppress the corrosion of the steel in concrete.
The anodes are typically embedded within the concrete or repair mortar and are electrically connected to the using galvanized ties.
As zinc is less noble than steel it means that the anode has a more electronegative potential than the reinforcement steel. This makes the zinc the anode and the steel reinforcement the cathode. Current will flow from anode to cathode inhibiting rebar corrosion thus avoiding concrete cracking and spalling in the presence of chloride salts within the concrete.
The zinc anode will generate an electrical field whilst immersed in the electrolyte allowing protective current to be discharged to the steel within the anode area of influence.
This allows a relatively small amount of anodes to be distributed within the structure thereby reducing manpower requirements and costs if desired, performance can be monitored by on-site personnel, according to the European standard EN 12696 “Cathodic protection of steel in concrete”.
In existing reinforced structures, CP is an integral part of the rehabilitation concept and is aimed to decrease the corrosion rate of the steel reinforcement from significant to negligible values.
CP can be used independently irrespective of the chloride concentrations and in fact the electric field will inhibit chloride ion migration towards the steel.
The re-passivation of the steel due to the different electrochemical reactions forced by the electric field will make also positive contribution to the structures life span.
New structures within aggressive environments can be provided with a CP system using a small amount of DC current that is applied early in its service life.
This type of protection is called cathodic prevention and can be used for new reinforced concrete structures, or existing structures in which the corrosion process is not yet initiated but corrosion will most probably occur due to progressive ingress of aggressive electrolytes over time.
For new constructions cathodic prevention can be applied in an easy and simple way as the current demand will be relatively low and therefore will be a low cost solution to achieve the design life span of the structure.
RESIDENTIAL STRUCTURE APPLICATION
ZLA is provided in rolls (250mm wide by 25 meters long). After application ZLA should be finished with an approved cementitious based coating of the specified texture and colour, ensuring edges and seam are properly over coated to avoid moisture ingress. System monitoring can be performed according to EN 12696.
Effectiveness:ZLA stops corrosion by placing steel in concrete in a protected cathodic state. Stopping corrosion helps prevent concrete deterioration. Unlike impressed current systems, the ZLA is fully self-powered and self-regulating, providing the proper current to maintain steel polarization. It requires no external power source, no costly electrical work and minimal monitoring.
Versatility: ZLA can be applied to the top, sides. Or bottom surfaces of concrete structures of various shapes and any sizes.
Economics: 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 of 40 years plus.
Rollanodes anodes are designed for installation in pre-drilled holes in an existing concrete structure. The electrolyte is sandwiched between the zinc layer rolls to give sufficient current capacity with additional electrolytic paste added around the anode to maintain electrical continuity within the concrete (the anode diameter is 25mm and available in lengths from 100mm to 1m).
Rollanodes are utilized in those areas where a high expectancy of corrosion is likely. They guarantee a strong reduction of corrosion and prevent new locations from corroding the future.
Bridge or viaduct beam supports and columns
Zones of newly cast concrete on an existing structure
Balcony facings and concrete facades
Rollanodes anodes are specifically designed for application in pre-drilled 30mm (minimum diameter holes to depth corresponding to the anode length + 4-5cm)