Mapeshield anodes for galvanic cathodic protection
The simple concept of joining two different metals is the inspiration behind the galvanic cathodic protection technique, helping to solve problems caused by corrosion in concrete members. Mapei proposes special anodes that ensure a constant yield over time: quick and easy to apply, they may be used for both structures that are already damaged and on recent builds. We met up with our Technical Services Department to find out more about the advantages of using the MAPESHIELD line.
Galvanic cathodic protection is based on the principle of joining two metals together with different natural potential: carbon steel which is used to make the reinforcement rods and zinc in the anodes. By joining the two metals, the concrete or repair mortar acts as an electrolyte and a continuous electrical current is generated which protects the steel from corrosion. The metal with the most negative electric potential oxidises, thereby protecting the less negative of the two metals which becomes passivated.
The zinc contained in MAPESHIELD anodes oxidises over time and is sacrificed in favour of the reinforcement rods inside the concrete, thereby delaying or interrupting the corrosion process and considerably increasing the durability of the structure. Also, thanks to the electric charge in the anodes, they are able to attract chlorides and keep them away from the reinforcement rods, which in turn has a beneficial effect against corrosion.
One aspect that characterises and increases the effect of MAPESHIELD anodes is the type of electrolyte they are coated with, a material made from conductive acrylic binders and a pH regulator that ensures the zinc does not become passivated in alkaline surroundings, such as concrete, which would then prevent the anode from functioning incorrectly. This particular electrolyte also ensures the efficiency of the anodes remains constant, even in surroundings with very little moisture.
The best position for the MAPESHIELD anodes is calculated according to the density of the reinforcement rods, that is, the ratio between the surface area of the steel to be protected and the surface area of the concrete in contact with the pollutant, but also by taking into consideration the geometry of the structure and its exposure to aggressive agents.
MAPESHIELD anodes offer various advantages, they can be used on both new (prevention) and old (protection) structures and they can be placed selectively and precisely, that is, only in the areas of the structure with the highest risk of corrosion. What is more, they do not require maintenance during their normal service life and they may be monitored during operation by installing a simple control system.
MAPESHIELD I AND MAPESHIELD E ANODES
MAPESHIELD I are internal anodes with a special zinc core which, for the same volume, increase the protective surface area, a characteristic which, along with the special electrolytic material it is coated with, makes the product efficient as well as durable over time. There are four different types of internal galvanic anodes in various sizes and masses of zinc to guarantee protection for most types of reinforced concrete structures. The anodes are fastened to the metal reinforcement rods that requires protection before pouring the concrete or before applying the repair mortar.
MAPESHIELD E are self-adhesive zinc plates that are applied directly to the surface of the concrete. This type of anode can be applied easily and quickly by simply removing the protective film from the conductive gel and pressing the plate onto the surface of the concrete. The plates are then connected to the reinforcement rods inside the concrete with electrical connections previously attached to the rods.
MAPESHIELD anodes comply with ISO 12696 “Cathodic protection of steel in concrete” according to the principle of depolarising the steel reinforcement.
