EP2431496A1

EP2431496A1 - Composite anode for a cathodic protection system

Info

Publication number: EP2431496A1
Application number: EP10305998A
Authority: EP
Inventors: Brian Mills; Christian Tourneur; Erik Mellier
Original assignee: Soletanche Freyssinet SA
Current assignee: Soletanche Freyssinet SA
Priority date: 2010-09-17
Filing date: 2010-09-17
Publication date: 2012-03-21
Also published as: WO2012035167A2; WO2012035167A3

Abstract

The cathodic protection device (1) for a structure including metallic reinforcement comprises an electrically conducting anode member (2) extending along a longitudinal direction and a spacer element (3) having an electrical conductivity lower than the anode member. The spacer element extends along the longitudinal direction to support the anode member, and is arranged to hold the anode member apart from the metallic reinforcement of the structure.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the field of cathodic protection of reinforced structures.
Metallic components, usually made of steel, are used to reinforce structures in many applications. Reinforced concrete is a typical application, in which steel bars are embedded into concrete in order to combine the compressive strength of concrete and the tensile strength of steel. The cathodic protection system described below can be used to protect from corrosion steel bars of reinforced concrete or other kinds of metallic reinforcements, for example, cables or bars used in tie rod applications.
A cathodic protection system can be referred to as a cathodic prevention system if it is incorporated into the structure at the time of construction, which is the situation addressed by the present invention.
In an impressed current cathodic protection system, an anode is embedded within the concrete to distribute current to the metallic elements to be protected. An ionic charge through the electrolyte, for example concrete, mortar or cement grout, results between the anode and metallic elements arising from current supplied from a DC power source. This charge results in cathodic polarisation of the metallic elements thereby preventing corrosion.
Of course, any short-circuit between the cathode and the anode member prevents current flow and causes malfunction of the cathodic protection system.
In the case of reinforced concrete, the metallic elements to be protected are usually in the form of a rebar cage and an array of anode members, such as titanium ribbons, are distributed in the concrete, particularly in the concrete cover between the rebar cage and the surface of the concrete structure. The concrete cover is often relatively thin, resulting that the anode members can be close to the reinforcement (e.g. within 30 mm). Small discrete plastic clips fixed to the rebar cage are used to hold the anode members a certain distance from the rebar cage. However, such clips lack robustness. Flexibility of the anode member may cause it to touch the rebar cage between adjacent clips. Also, the clips cannot maintain the anode strongly enough when concrete is vibrated after pouring.
The present document addresses the need to safely hold an anode member of a cathodic protection system in the vicinity of, but separated from the metallic element to be protected.
A cathodic protection device for a structure including metallic reinforcement is proposed. The device comprises an electrically conducting anode member extending along a longitudinal direction and a spacer element having an electrical conductivity lower than the anode member. The spacer element extends along the longitudinal direction to support the anode member, and is arranged to hold the anode member apart from the metallic reinforcement of the structure.
The spacer element has a primary function of preventing electrical contact between the anode and the reinforcement located in the vicinity of the device. By stiffening the device, it avoids undesired contacts due to bending of the anode when the device is handled, when the filler material, for example concrete or hardened mortar or cement grout is poured, vibrated, etc. The stiffening also facilitates and speeds up the installation. Furthermore, the spacer element restricts other objects (for example tie wires) to come into contact with the anode. It is preferentially designed to permit the current flow between the anode and the reinforcement to be protected.
The spacer element may be in the form of a plastic profile having apertures to permit current flow in material between the anode member and the metallic reinforcement. Such plastic profile may have U-shaped, H-shaped, T-shaped or cylindrical cross-section.
Alternatively, the spacer element may be in the form of a matrix cast around the anode member, the matrix having an electrical conductivity of the same order as a material in which at least part of the metallic reinforcement and the cathodic protection device are embedded.
The spacer element may comprise a cement material, with or without fibres, surrounding the anode member.
Another includes a screw-shaped spacer element, and an anode member in the form of a wire, ribbon or strip helically wound into the thread of the screw-shaped spacer element.
Another aspect of the invention relates to a reinforced structure, comprising metallic reinforcement, at least one cathodic protection device as defined above, structural material in which at least part of the metallic reinforcement and the cathodic protection device are embedded, and a DC power source having terminals electrically connected to the metallic reinforcement and to the anode member of the cathodic protection device.
Electrically insulating ties may be provided for fixing the cathodic protection device to a metallic reinforcement. At least one electrical conductor may be used for connecting a terminal of the DC power source to the anode member of the cathodic protection device, and an insulating cover is mounted around an intersection area where the electrical conductor is secured in electrical contact with the anode member. The electrical conductor has an insulating coating interrupted in the intersection area, wherein the spacer element of the cathodic protection device is interrupted in the intersection area. The insulating cover is arranged to prevent contact of the anode member or the electrical conductor with the metallic reinforcement.
Other features and advantages of the cathodic protection device disclosed herein will become apparent from the following description of nonlimiting embodiments, with reference to the appended drawings.

BRIEF DESCRIPTION THE DRAWINGS

Figure 1 is a perspective view of an embodiment of a cathodic protection device.
Figure 2 illustrates a cross section of another embodiment of a cathodic protection device.
Figures 3 and 4 are perspective views of a cathodic protection device mounted on a rebar cage of a reinforced concrete structure, at different stages of the assembly.
Figure 5 is a perspective view of another embodiment of a cathodic protection device.
Figure 6A is a perspective view of another embodiment of a cathodic protection device.
Figure 6B is an axial sectional view of an assembly of two cathodic protection devices as shown in figure 6A.
Figure 7A is a perspective view of yet another embodiment of a cathodic protection device.
Figure 7B is a cross-sectional view of the cathodic protection device of figure 7A, along plane A-A.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figures 1, 2 and 3 show three embodiments of a cathodic protection device 1 according to the invention, including a spacer element 3 and an electrically conductive anode member 2. In these embodiments, the spacer element 3 is in the form of a plastic profile extending along a longitudinal direction y. The anode member 2 is typically in the form of a flat ribbon of expanded metal, for example made of coated titanium. However it may also be non-expanded, corrugated, cylindrical or other shape.
The illustrated cathodic protection device 1 is prefabricated. It can be manufactured remote from construction sites.
The plastic profile 3 which has a stiffening function is made of an electrically insulating material, e.g. high density polyethylene (HDPE), crosslinked polyethylene (XLPE), polypropylene (PP), polyvinyl chloride (PVC) or recycled or reconstituted plastic. It has a central part 4 for holding the anode member 2 along the direction y and a transverse direction x, and two wing parts 5 perpendicular to the direction x on both sides of the central part 4 to rigidify the device 1. In the embodiment of figure 1, the cross-section of the spacer member 3 is H-shaped, while it is U-shaped in the embodiments of figures 2 and 3.
The central part 4 and/or the wing parts of the plastic profile have apertures 6 whose function is to let an ionic current flow between the anode member 3 and a cathode located nearby, while keeping a sufficient rigidity of the device 1. The above-mentioned ionic current flows in a filler material in which both the cathode and the protection device 1 are embedded, for example concrete or hardened mortar or cement grout. The rigidity of the device is considered sufficient if the spacer element 3 keeps the anode member 2 safely separated from the cathode when the device is installed and when the filler material is injected and/or vibrated to embed the cathode and the device. The apertures 6 are also useful to let the filler material encapsulate the anode member 2 when it is injected.
In the embodiment of figure 1, the apertures 6 are formed in the central part 4 of the H-shaped plastic profile 3. In the embodiment of figures 3-4, the apertures 6 are formed both in the central part 4 and in the wing parts 5 of the U-shaped plastic profile 3. The length of the apertures 6 provided in the central part 4 and the intervals between them along the longitudinal direction y are selected to achieve the above function of letting current flow while ensuring rigidity of the device.
The anode member 2 can be fixed to the spacer element 3 by welding on the bridges 7 located between the apertures 6 on the central part 4 of the plastic profile 3. For example, the metallic ribbon 2 is heated above the melting point of the plastic material and pressed onto the central part 4 of the profile, thus melting the plastic at the bridges 7 and welding the ribbon in place.
Figure 2 illustrates an alternative way of fixing the anode member 2 to the spacer element 3 using a snap fit assembly. In this embodiment, the ribbon forming the anode member 2 has a width (along direction x) slightly smaller than the gap between the inner faces 8 of the wing parts 5 of the plastic profile. Each of these inner faces 8 has a projection 9 near the central part 4 such that the anode member 2 can be held between the central part 4 and the projections 9. The shape of the projections 9 is defined when extruding the plastic profile 3. For mounting the device, the anode member is forced into place using the elasticity of the expanded metal and/or by pulling apart the two wing parts 5.
Figures 3 and 4 show, in their bottom part, one way of fixing the protection device 1 to a reinforcement consisting of a steel bar 10 of a reinforced concrete structure, before pouring the concrete material. In this example, insulating ties consisting of plastic collars 11 are inserted in the apertures 6 provided in the wing parts 5 of the spacer element 3, looped around the steel bar 10 and tightened. A plastic pad 12 may be inserted between the spacer element 2 and the steel bar at the position of each plastic collar 11 if it is needed to have a desired distance between the anode and the cathode. Between two fixing points (pad 12 + collar 11), the rigidity of the spacer element 3 eliminates the risks of contact between anode and cathode. It will be appreciated that many different ways can be used alternatively to hold the cathodic protection device 1 in position before pouring the concrete material.
A DC power source (not shown) has a positive terminal connected to the anode member 2 and a negative terminal connected to the metallic reinforcement to be protected from corrosion.
A reinforced concrete structure usually has a network of metallic reinforcement. Thus, cathode protection devices 1 will be distributed in the volume to be constructed with concrete so as to efficiently protect the reinforcement. The spatial distribution of the anodes is determined by conventional methods. By virtue of the spacer elements 3, the cathodic protection device 1 avoids contacts between the anodes and the cathodes even when the concrete is poured and vibrated to homogenize the reinforced concrete.
For connecting the anode member(s) 2 to the positive terminal of the DC power source, electrical conductors 20 of the type shown in figures 3 and 4 can be used. These conductors 20 consist of metallic strips having an insulating coating in the form of a plastic sheath 21 to isolate them electrically from the filler material. In the illustrated embodiment, the strips 20 extend transversely to the anode members 2 of adjacent cathodic protection devices, and in the intersection area, their plastic sheath is removed to permit electrical contact with the anode members 2. One or two metallic strips 20 and one or two anode members 2 are overlapped in the intersection area and secured together in electrical contact by welding and/or other methods. The spacer element 3 of each device 1 is also interrupted in the intersection area so as to facilitate the assembly of the metallic components.
As can be seen in figure 3, a metallic reinforcement 10 may be located in the vicinity of the intersection area where the metallic strips 20 and anode members 2 are exposed. In order to eliminate risks of contact of the anode members 2 or the metallic strips 20 with the reinforcement, an insulating cover 25 as shown in figure 4 can be used.
The cover 25 surrounds the intersection area so as to protect the metallic strips 20 and the anode members 2 in the intersection area where the plastic sheath 21 and the spacer element 3 are absent, such that the strips 20 and anode members 2 are prevented from contacting the reinforcement 10. For example, the cover 25 may include a plastic plate 26 to be installed between the device 1 and the rebar cage 10 and a U-shaped profile 27 whose internal cross-section matches the external cross-section of the spacer elements 3. The lateral parts of the U-shaped profile 27 have notches 28 to leave a passage for the strips 20 and their sheaths 21 on both sides of the intersection area. The U-shaped profile 27 can then be engaged with the two ends of the spacer elements 3 and attached to the plate 26 by means of clips (not shown) provided at the ends of the lateral parts of the U-shaped profile 27.
Figure 5 illustrates an alternative embodiment of the cathodic protection device 1, in which the plastic profile 3 has two lateral parts 3A, 3B directly extruded on the metallic ribbon forming the anode member 2 by means of a suitably shaped extrusion die. If it is necessary to further stiffen the device, bridge elements 30 can be welded to the lateral parts 3A, 3B so as to maintain the distance between them.
Another embodiment of a cathodic protection device 1 is illustrated in figures 6A-B. In this embodiment, the spacer element 3 has the shape of a screw made of plastic or another insulating material. A wire, ribbon or strip forming the anode member 2 (shown in figure 6B but not in figure 6A) is helically wound at the bottom of the thread 34 of the screw-shaped spacer element 3. The helical rib 35 of the spacer element 3 has a sufficient height to accommodate the wire 2 and to maintain a minimum distance between the wire and the periphery of the screw-shaped spacer element 3, in order to safely avoid contact of the wire with a reinforcement or other metallic part which may come close to or against the screw-shaped spacer element 3. Such spacer element 3 has a length L of about one meter for instance. It can be assembled end-to-end with another similar spacer element prior to winding the anode member 2. For this, one end of the spacer element has an axial plug 36 and the other end has a recess 37 for receiving the plug 36 of a similar spacer element 3 assembled next to it as shown in figure 6B.
The winding of the wire 2 onto a plurality of screw-shaped spacer elements 3 dimensioned and assembled end-to-end according to the needs can be performed on the construction site. The diameter of the wire 2 may be of about 2 millimeters, for example.
It the embodiments described above with reference to figures 1-6, the spacer element 3 is made of an electrically insulating material. It has an open structure (e.g. U-shaped or H-shaped profile, apertures 6, thread 34) in order to prevent shielding between the anode members 2 and the metallic reinforcement 10 to be protected.
Alternatively, the spacer element may be made of a material having some electrical conductivity, for example an electrical conductivity of the same order of magnitude as the filler material (e.g. concrete) in which the reinforcement is embedded.
Such an embodiment is illustrated in figures 7A-B. The spacer element 3 can be in the form of a cylindrical matrix cast around a wire-shaped anode member 2.
A convenient material for forming the matrix is hardened cement grout, possibly incorporating some fibres. The spacer member 3 is then formed in a cylindrical mold in which the wire, ribbon or strip is centrally located to be surrounded by the grout. After hardening of the cement grout, a cathodic protection device 1 is obtained which is suitable for embedding into concrete or another structural material. For example, its length L' is about 3 meters and its diameter D about 25 millimeters. The anode member 2 may be a rigid wire having a diameter d of about 4 millimeters. Prior to injecting the grout into the mold, a flexible connection wire 40 may be soldered at the end of the rigid wire (or one at both ends). The connection wire 40 has an insulating coating and extends beyond the cement matrix 3 for connection to the DC power supply.
An embodiment as illustrated in figure 7A-B can be applied to reinforced concrete, and it may also be useful in other applications including tie rod arrangements where it can be used to protect anchored strands or rods from corrosion.
It will be appreciated that the embodiment described above is an illustration of the invention disclosed herein and that various modifications can be made without departing from the scope as defined in the appended claims.

Claims

A cathodic protection device for a structure including metallic reinforcement (10), the device comprising an electrically conducting anode member (2) extending along a longitudinal direction and a spacer element (3) having an electrical conductivity lower than the anode member (2), characterized in that the spacer element extends along the longitudinal direction to support the anode member and is arranged to hold the anode member apart from the metallic reinforcement of the structure.
The device as claimed in claim 1, wherein the spacer element is a plastic profile (3) having apertures (6) to permit current flow in material between the anode member (2) and the metallic reinforcement (10).
The device as claimed in claim 2, wherein the plastic profile (3) has U-shaped, H-shaped, T-shape or cylindrical cross-section.
The device as claimed in claim 2 or 3, wherein the anode member (2) is welded to the plastic profile (3).
The device as claimed in claim 2 or 3, wherein the anode member (2) is in the form of a ribbon snap fit into the plastic profile (3).
The device as claimed in any one of the preceding claims, wherein the spacer element (3) is in the form of a matrix cast around the anode member (2), the matrix having an electrical conductivity of the same order as a material in which at least part of the metallic reinforcement and the cathodic protection device are embedded.
The device as claimed in any one of the preceding claims, wherein the spacer element (3) comprises a cement material surrounding the anode member (2).
The device as claimed in claim 6 or 7, wherein the anode member (2) is in the form of a wire.
The device as claimed in claim 1, wherein the spacer element (3) is screw-shaped, and wherein the anode member (2) is in the form of a wire, strip or ribbon helically wound into the thread (34) of the screw-shaped spacer element.
A reinforced structure, comprising metallic reinforcement (10), at least one cathodic protection device (1) as claimed in any one of the preceding claims, structural material in which at least part of the metallic reinforcement and the cathodic protection device are embedded, and a DC power source having terminals electrically connected to the metallic reinforcement and to the anode member (2) of the cathodic protection device.
The reinforced structure as claimed in claim 10, further comprising electrically insulating ties (11) fixing the cathodic protection device (1) to a metallic reinforcement (10).
The reinforced structure as claimed in claim 10 or 11, further comprising at least one electrical conductor (20) for connecting a terminal of the DC power source to the anode member (2) of the cathodic protection device (1), and an insulating cover (25) mounted around an intersection area where said electrical conductor is secured in electrical contact with the anode member, wherein said electrical conductor has an insulating coating (21) interrupted in the intersection area, wherein the spacer element (3) of the cathodic protection device is interrupted in the intersection area, and wherein the insulating cover is arranged to prevent contact of the anode member or the electrical conductor with the metallic reinforcement (10).