Cathodic protection of steel elements at least partly embedded in a surrounding layer is well known and one method for this purpose is described in PCT Application CA00/00101 filed 2 Feb. 2000 and published as WO 00/46422 by the present inventor.
In PCT Published Application WO94/29496 of Aston Material Services Limited is provided a method for cathodically protecting reinforcing members in concrete using a sacrificial anode such as zinc or zinc alloy. In this published application and in the commercially available product arising from the application, there is provided a puck-shaped anode body which has a coupling wire attached thereto. In the commercially available product there are in fact two such wires arranged diametrically opposed on the puck and extending outwardly therefrom as a flexible connection wire for attachment to an exposed steel reinforcement member.
The puck is surrounded by an encapsulating material such as mortar which holds an electrolyte that will sustain the activity of the anode. The mortar is compatible with the concrete so that electrolytic action can occur through the mortar into and through the concrete between the anode and the steel reinforcing member.
The main feature of the published application relates to the incorporation into the mortar of a component which will maintain the pH of the electrolyte in the area surrounding the anode at a high level of the order of 12 to 14.
In use of the device, a series of the anodes is provided with the anodes connected at spaced locations to the reinforcing members. The attachment by the coupling wire is a simple wrapping of the wire around the reinforcing bar. The anodes are placed in locations adjacent to the reinforcing bars and re-covered with concrete to the required amount.
Generally this protection system is used for concrete structures which have been in place for some years sufficient for corrosion to start. In general, areas of damage where restoration is required are excavated to expose the reinforcing bars whereupon the protection devices in the form of the mortar-covered pucks are inserted into the concrete as described above and the concrete refilled.
These devices are beginning to achieve some commercial success and are presently being used in restoration processes. However improvements in operation and ergonomics are required to improve success of this product in the field.
U.S. Pat. No. 6,193,857 (Davison) assigned to Foseco discloses an anode body in the form of a puck coated with a mortar in which the puck is attached by ductile wires to the rebar within an excavation in the concrete.
During cathodic protection using a sacrificial anode material, it is well known that the anode must corrode in order to provide the protection thus generating corrosion products. Many potentially suitable anode materials such as magnesium are difficult to use in view of the significant increase in volume which occurs as the material corrodes which thus applies significant forces to the surrounding material generally concrete with the tendency to cause cracking. Even zinc which is the most common material increases in volume and the corrosion products must be accommodated within a mortar material surrounding the anode in order to prevent cracking. As shown in the above Aston application, this mortar can be attached to the anode and is inserted therewith into the concrete as the anode is embedded. Alternatively, the anode can be embedded in a filler material which has characteristics designed to absorb the expansion. It has not been possible however up to date to directly locate or embed the anode body into the concrete so that the surface of the anode material is directly in contact with the conventional concrete, or arranged so that expansion forces from the expansion of the anode during corrosion are applied to the concrete directly or through an incompressible intermediate material, since the concrete material will not accept a significant level of expansion leading to unacceptable cracking.
This significantly increases the cost and complexity of the anode members and reduces the acceptability of the method.