GB2140456A

GB2140456A - Cathodic protection

Info

Publication number: GB2140456A
Application number: GB08234450A
Authority: GB
Inventors: Roger Drury Browne; Michael Philip Geoghegan; Sunil Chandra Das
Original assignee: TAYWOOD ENGINEERING Ltd
Current assignee: TAYWOOD ENGINEERING Ltd
Priority date: 1982-12-02
Filing date: 1982-12-02
Publication date: 1984-11-28

Abstract

Steel reinforcement (2) embedded in concrete is protected against corrosion by a cathodic protection system in which the anode serving as a ground bed is a thin film (3). As the anode is a very thin film it can be applied to the under-surface of a horizontal or near horizontal run, and also to upright surfaces, and the cathodic protection system is thus particularly suitable for upright reinforced concrete columns.

Description

SPECIFICATION Cathodic protection This invention relates to cathodic protection of steel in concrete.

Cathodic protection is a well known technique for inhibiting corrosion of metals buried in soil or immersed in water. It has also been possible, where a reinforced concrete member has been laid in a horizontal or near horizontal run carrying a top wearing surface, for example a bridge deck carrying a road surface, to utilise the top surface in a cathodic protection system. To this end, as the top surface there has been used placed asphalt/concrete serving as an electrical ground bed that is the anode in a cathodic protection system. However, such material cannot be applied to the under-surface of a horizontal or near horizontal run, nor can it be applied to an upright surface of, for example, a column or pier.

According to the present invention there is provided a method of cathodically protecting steel reinforcement embedded in concrete, comprising connecting the steel reinforcement in a cathodic protection system that has as its anode an electrically conductive film applied to the surface of the concrete. The film is very thin and hence can be applied to the under-surface of a horizontal or near horizontal run, and also to upright surfaces, and hence the present method can be utilised to obtain cathodic protection where the ground bed serving as the anode has to be carried by an under-surface or by an upright surface. Also provided is a cathodic protection system for protecting steel reinforcement embedded in concrete, comprising an electrically conductive film applied to the outer-surface of the concrete and serving as the anode of the system.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a sectional view of a steel reinforced concrete pillar, and Figure 2 is a block diagram of a cathodic protection system provided for the pillar of Figure 1.

The concrete pillar 1 of Figure lisa conventional pillar having steel reinforcement 2. To one upright face of the pillar 1 there is applied an electrically conductive paint film 3. For certain applications it may be necessary first to apply a primer to the surface in order to achieve the required bond and conduction characteristics. A top protective, or weathering, coating may also be required over the conductive paint film, designed to meet specific requirements as determined by the position of the concrete member, its exposure to the environment, possible abrasion and so on. Primer could, for example, be based on silicate. The top or weathering coat could consist of polyurethane or epoxy based paint.

The electrically conductive paint contains a suitable conductive pigment, such as graphite, carbon or cokebreeze, an organic binder such as epoxy, and a hardener in proportion to give a conventional consistency for paint so that it can be applied readily on the concrete as a thin film having high conductivity. Typically the conductive paint has a resistivity between 2 and 10 ohm-cm. The dry paint coat has a film thickness of 1-5mm with 5% voids to allow escape of gases generated due to electrochemical reaction at the anode of the cathodic protection system.

The primary anodes 4 of the cathodic protection system are made from a thin durable non-corrosive metallic strip of, for example, titanium or niobrium metal electroplated with platinum to a thickness of 5 micron. They are fixed on the concrete surface by an epoxy adhesive and then covered by the conductive paint which functions as the ground bed of the system. The primary anodes can be of strip, rod or wire, mesh or buttom formation with an inter-anode spacing of between 10 and 50 meters.

The primary anodes are connected by lines 5 to the positive terminal of a variable current DC source 6 (Figure 2) fed from a DC power source 7.

The steel reinforcement 2 is connected by lines 8 to the negative terminal of the DC current source 6 so as to constitute a cathode. Further lines 9 connect the steel reinforcement across a series of operational amplifiers 10 to which are also connected, by lines 11, reference half-cell electrodes 12 embedded in the concrete at many places close to the steel reinforcement 2. These electrodes 12 can be silver/silverchloride electrodes.

The outputs of the operational amplifiers 10 are fed, via lines 13, to a circuit 14 that automatically selects the output emanating from the electrode 12 sensing the lowest voltage and feeds this output via a line 15 to a further operational amplifier 16 to which is also fed, via a line 17, a reference voltage.

The output of the further operational amplifier 16 is fed via a line 18 to control the variable current source 6. In operation a decreasing voltage measured by the electrodes 12 results in increasing output current in the cathodic protection system, the level of the impressed current being automatically controlled in order to prevent the corrosion potential as sensed by the electrodes 12 from rising above the reference level (at line 17).

1. A method of cathodically protecting steel reinforcement embedded in concrete, comprising connecting the steel reinforcement in a cathodic protection system that has as its anode an electrically conductive film applied to the surface of the concrete.

2. A method as claimed in claim 1, wherein the film has a thickness of 1-5mm.

3. A method as claimed in claim 1 or 2, wherein the film has a resistivity of 2-10 ohm-cm.

4. A method as claimed in claim 1,2 or 3, wherein, in use, the voltage at a plurality of regions around the reinforcement is sensed and the lowest utilised, in comparison with a reference voltage, to control a variable current source of the protection system.

5. A method of cathodically protecting steel reinforcement embedded in concrete, substantially

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cathodic protection This invention relates to cathodic protection of steel in concrete. Cathodic protection is a well known technique for inhibiting corrosion of metals buried in soil or immersed in water. It has also been possible, where a reinforced concrete member has been laid in a horizontal or near horizontal run carrying a top wearing surface, for example a bridge deck carrying a road surface, to utilise the top surface in a cathodic protection system. To this end, as the top surface there has been used placed asphalt/concrete serving as an electrical ground bed that is the anode in a cathodic protection system. However, such material cannot be applied to the under-surface of a horizontal or near horizontal run, nor can it be applied to an upright surface of, for example, a column or pier. According to the present invention there is provided a method of cathodically protecting steel reinforcement embedded in concrete, comprising connecting the steel reinforcement in a cathodic protection system that has as its anode an electrically conductive film applied to the surface of the concrete. The film is very thin and hence can be applied to the under-surface of a horizontal or near horizontal run, and also to upright surfaces, and hence the present method can be utilised to obtain cathodic protection where the ground bed serving as the anode has to be carried by an under-surface or by an upright surface. Also provided is a cathodic protection system for protecting steel reinforcement embedded in concrete, comprising an electrically conductive film applied to the outer-surface of the concrete and serving as the anode of the system. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a sectional view of a steel reinforced concrete pillar, and Figure 2 is a block diagram of a cathodic protection system provided for the pillar of Figure 1. The concrete pillar 1 of Figure lisa conventional pillar having steel reinforcement 2. To one upright face of the pillar 1 there is applied an electrically conductive paint film 3. For certain applications it may be necessary first to apply a primer to the surface in order to achieve the required bond and conduction characteristics. A top protective, or weathering, coating may also be required over the conductive paint film, designed to meet specific requirements as determined by the position of the concrete member, its exposure to the environment, possible abrasion and so on. Primer could, for example, be based on silicate. The top or weathering coat could consist of polyurethane or epoxy based paint. The electrically conductive paint contains a suitable conductive pigment, such as graphite, carbon or cokebreeze, an organic binder such as epoxy, and a hardener in proportion to give a conventional consistency for paint so that it can be applied readily on the concrete as a thin film having high conductivity. Typically the conductive paint has a resistivity between 2 and 10 ohm-cm. The dry paint coat has a film thickness of 1-5mm with 5% voids to allow escape of gases generated due to electrochemical reaction at the anode of the cathodic protection system. The primary anodes 4 of the cathodic protection system are made from a thin durable non-corrosive metallic strip of, for example, titanium or niobrium metal electroplated with platinum to a thickness of 5 micron. They are fixed on the concrete surface by an epoxy adhesive and then covered by the conductive paint which functions as the ground bed of the system. The primary anodes can be of strip, rod or wire, mesh or buttom formation with an inter-anode spacing of between 10 and 50 meters. The primary anodes are connected by lines 5 to the positive terminal of a variable current DC source 6 (Figure 2) fed from a DC power source 7. The steel reinforcement 2 is connected by lines 8 to the negative terminal of the DC current source 6 so as to constitute a cathode. Further lines 9 connect the steel reinforcement across a series of operational amplifiers 10 to which are also connected, by lines 11, reference half-cell electrodes 12 embedded in the concrete at many places close to the steel reinforcement 2. These electrodes 12 can be silver/silverchloride electrodes. The outputs of the operational amplifiers 10 are fed, via lines 13, to a circuit 14 that automatically selects the output emanating from the electrode 12 sensing the lowest voltage and feeds this output via a line 15 to a further operational amplifier 16 to which is also fed, via a line 17, a reference voltage. The output of the further operational amplifier 16 is fed via a line 18 to control the variable current source 6. In operation a decreasing voltage measured by the electrodes 12 results in increasing output current in the cathodic protection system, the level of the impressed current being automatically controlled in order to prevent the corrosion potential as sensed by the electrodes 12 from rising above the reference level (at line 17). CLAIMS

2. A method as claimed in claim 1, wherein the film has a thickness of 1-5mm.

5. A method of cathodically protecting steel reinforcement embedded in concrete, substantially as hereinbefore described with reference to the accompanying drawings.

6. A cathodic protection system for protecting steel reinforcement embedded in concrete, comprising an electrically conductive film applied to the surface of the concrete and serving as the anode of the system.

7. A cathodic protection system as claimed in claim 6, wherein the film has a thickness of 1-5mm.

8. A cathodic protection system as claimed in claim 6 or 7, wherein the film has a resistivity of 2-10 ohm-cm.

9. A cathodic protection system as claimed in claim 6,7 or 8 and further comprising electrodes at a plurality of regions around the reinforcement, a circuit for obtaining an output from the electrode sensing the lowest voltage, and a variable current source, for the system, that is controlled by the output of a comparison between the first-mentioned output and a reference voltage.

10. A cathodic protection system for protecting steel reinforcement embedded in concrete, substantially as hereinbefore described with reference to the accompanying drawings.