METHOD FOR LAYING AN ANODE SYSTEM FOR CATHODIC CORROSION PROTECTION

Abstract

An anode system for cathodic corrosion protection should be able to be laid in a simple, quick and cost-effective manner. For this purpose, a method comprising the following steps is provided: laying a carbon fibre multifilaments in a planar and meandering or strip-shaped manner;laying at least two primary anode ribbons, which are arranged so as to be spaced apart from one another, such that the carbon fibre multifilament is arranged between the primary anode ribbons and the primary anode ribbons are connected to the carbon fibre multifilament in an electrically conductive manner in a number of contact regions.

Description

TECHNICAL FIELD

The invention relates to a method for laying an anode system for cathodic corrosion protection and to the use of a non-metal ribbon anode in a planar anode system for cathodic corrosion protection.

BACKGROUND

Structures made of reinforced concrete are integral components of the infrastructure in almost all countries in the world. In addition to residential and work buildings, many reinforced concrete structures that are driven on are also constructed, e.g. multi-storey car parks, garages, motorways, bridges, tunnels, etc. A large number of these structures have been used for 50 to 100 years (and sometimes even longer). However, said reinforced concrete structures are exposed not only to mechanical stress but in particular to de-icing salts. De-icing salts generally contain chloride, which, in conjunction with water, produces solutions that trigger corrosion in the structures. Substantial, cost-intensive repair work of the reinforcement must therefore be carried out for many structures after only 20-25 years.

For this purpose, the contaminated covering concrete is usually removed, the reinforcement steel is cleaned and provided with new corrosion protection (e.g. based on a polymer or cement). However, the repaired region often lasts only a few years (on account of mechanical, thermal and/or hygric incompatibilities), and therefore timely further repair is required precisely when the covering concrete is put under heavy stress. This incurs high costs, entails significant intervention in the structure and not least results in usage restrictions during repair work.

One option for reducing, and ideally preventing, corrosion is to use cathodic corrosion protection (CCP) in structures. As a largely destruction-free repair method, cathodic corrosion protection is gaining importance as an economical repair process for components that are at risk of or have been damaged by corrosion.

The principle of the electrochemical protection method (cathodic corrosion protection) involves electrically influencing the corrosion process in unalloyed or low-alloy steels (e.g. concrete reinforcement steel) in an extensive electrolyte (floors, seawater, when used in reinforced concrete: concrete) by introducing a direct current. Applying said direct current (protective current) causes a shift in the electrochemical potential of the metal to be protected in the negative direction, as a result of which the metal surface is cathodically polarised and damaging corrosion is prevented.

In order to impress a protective current, a durable and corrosion-resistant anode must firstly be coupled to the concrete and fitted to the positive terminal of a rectifier that serves as the voltage source. The negative pole of the direct current is connected to the steel to be protected (in reinforced concrete, to the reinforcement). After switching on the direct current, the steel to be protected is cathodically polarised and steel corrosion is largely prevented.

By using an incorporated reference electrode, the state of the building, structure or piping and/or the corrosion of the steel can furthermore be monitored remotely.

For corrosion protection that is as uniform as possible and also safe, it is desirable for the anode system to be laid out over as large an area as possible in the vicinity of the steel element functioning as the cathode, for example the reinforcement steel. However, this is hardly possible with anode systems used to date, for example when using rod anodes or titanium ribbon anodes, or is very hard to install, for example when using a reticular titanium anode. In particular, applying a reticular titanium anode to the concrete in order to protect a reinforced concrete structure is particularly work-intensive and time-consuming on account of the inflexibility of the material.

CCP-Systems are known from the publications WO 92/11399 A1, WO 99/19540 A1, EP 1 318 247 A1 and US 2014/251793 A1, for example.

The object of the invention is therefore to provide a method for laying an anode system for cathodic corrosion protection that can be carried out in a particularly simple, quick and cost-effective manner.

SUMMARY

This object is achieved according to the invention in that the method comprises the following steps:

• • laying a carbon fibre multifilaments in a planar manner;
  • laying at least two primary anode ribbons, which are arranged so as to be spaced apart from one another, such that the carbon fibre multifilament is arranged between the primary anode ribbons and the primary anode ribbons are connected to the carbon fibre multifilament in an electrically conductive manner in a number of contact regions;
  • connecting the primary anode ribbons to a primary anode wire.

The invention is based on the consideration that the anode system can be laid in a particularly simple and rapid manner if the inflexible titanium ribbons or reticular titanium anodes can be largely dispensed with, or if the ribbons only need to be laid linearly. Since the anode system should in any case be laid in a planar manner, a second material that can be laid in a particularly simple and flexible manner is used along with the titanium ribbons. In this case, it was discovered that a linear bundle of a plurality of carbon fibre filaments, referred to as carbon fibre multifilament, is sufficiently flexible for planar laying and also has sufficiently high electrical conductivity to qualify as an anode system for cathodic corrosion protection. Additionally, a carbon fibre multifilament of this kind can be obtained in a simple and cost-effective manner by the yard, allowing significant cost savings in the construction of an anode system.

The carbon fibre multifilament is arranged in a meandering configuration or in individual strips that are arranged in parallel with one another and that are interconnected by the anode ribbon so as to achieve a particularly uniform distribution and to allow particularly simple contacting with the primary anode ribbon via the meanders or the ends of the strips.

In order to apply the protective current to the planarly laid bundle, said bundle is electrically connected to a (for example linearly laid) titanium anode ribbon in a plurality of contact regions and said primary anode ribbon is connected to a primary anode wire. As already explained above, said primary anode wire can be connected to the positive terminal of a voltage source.

In addition to using cathodic corrosion protection in steel constructions (for example port facilities) or piping and pipelines, it can also be used in the context of reinforced structures. In this case, the reinforced structures must be retrofitted with cathodic corrosion protection or this should be immediately considered for a new construction.

When restoring reinforced concrete structures, when portions of the concrete layer are newly applied, and also in the case of new constructions, in a preferred embodiment the carbon fibre multifilament is laid on or in the fresh concrete in order to achieve particularly simple laying. However, in order to prevent short-circuiting between the carbon fibre multifilament as the anode and the reinforcement steel as the cathode due to, for example, the carbon fibre multifilament resting on the reinforcement steel, a sufficient spacing between the carbon fibre multifilament and the reinforcement steel is provided by means of an insulating intermediate layer, for example a glass fibre composite reinforcement.

In particular when retrofitting an existing reinforced structure with cathodic corrosion protection, in an advantageous embodiment, grooves are cut or milled into the concrete, into which grooves the carbon fibre multifilament can be laid. Further raising or enlargement of the concrete layer in order to cover the anode system is thus avoided.

In an alternative or additional preferred embodiment, the carbon fibre multifilament can be adhesively bonded to the concrete in order to secure it thereto. A conductive adhesive can be used for this purpose, by means of which the carbon fibre element is secured to the concrete at individual points or over the entire region. Said method can be used in particular for restoring old concrete surfaces. The adhesive used in this case comprises, in a particularly preferred embodiment, ionic additives and water in order to itself electrolytically conduct.

In order to achieve particularly good contact between the carbon fibre multifilament and the primary anode ribbon, in a particularly advantageous embodiment the carbon fibre multifilament is wound around the primary anode ribbon in the contact regions. This produces a plurality of contact points in these regions, via which contact points the current from the primary anode ribbon can be transferred to the carbon fibre multifilament.

In order to protect the contact regions as effectively as possible and at the same time better electrically interconnect the carbon fibre multifilament and the primary anode ribbon, in a preferred embodiment the contact regions are encased in epoxy resin. On account of the shrinkage of the epoxy resin after application, the contact between the carbon fibre multifilament and the primary anode ribbon is improved even further. The shrinkage of the epoxy resin is thus used in a targeted manner to enhance the contact between the carbon fibre multifilament and the primary anode ribbon. In the case of a metal primary anode, the anode is preferably insulated such that it does not itself function as a current-supplying anode. By means of the insulation, the current is prevented from being fed directly into the electrolyte and too little thereof ending up in the actual anode. In a preferred embodiment, the epoxy resin used is therefore not conductive, i.e. it is insulating.

Overall, connecting a carbon anode to a primary anode and the following copper cabling have so far been very difficult to implement and have represented a big problem. In contrast to other anode materials, carbon cannot be welded or soldered to the primary anode or to the copper cabling. However, by using linear and flexible bundles of carbon fibres, it is possible to wind the primary anode ribbon in order to increase the contact surface area. Additionally, there is the possibility of mechanical connection or adhesive bonding using a conductive adhesive.

In order to secure the entire anode system, or merely portions thereof, to the reinforced concrete, said anode system is advantageously covered with a conductive mortar. As a result, it is optimally protected against external influences.

In addition to using cathodic corrosion protection of this kind in reinforced concrete structures, it is also possible to protect steel structures, such as piping and port facilities, from corrosion.

The advantages achieved by this invention consist in particular in allowing a particularly simple and cost-effective planar application of an anode system by using a carbon fibre multifilament. Use of a fabric that is less flexible during laying or of a mat as the anode system can therefore be avoided. The current is thereby fed through linearly laid primary anodes, for example made of titanium ribbon, and then via the contact regions into the carbon fibre multifilament and thus is planarly distributed.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will be described in greater detail with reference to the drawings, in which:

FIG. 1 shows a detail of reinforced concrete comprising cathodic corrosion protection,

FIG. 2 is a cross-section through the primary anode ribbon in a contact region in various embodiment variants,

FIG. 3 shows carbon fibre multifilaments being laid with glass fibre composite reinforcement,

FIG. 4 schematically shows the sequence of the method for laying an anode system.

DETAILED DESCRIPTION

Identical parts are provided with the same reference signs in all figures.

In the embodiment according to FIG. 1, a reinforced concrete structure 1 is shown, the steel reinforcement or reinforcement steel 2 being protected from corrosion by means of an applied voltage 4. Cathodic corrosion protection of this kind is necessary, since, due to various processes, such as carbonation, and in particular due to the effect of chlorides, the passivation of the reinforcement steel 2 can locally be reversed. As a result, anodic regions, which result in metal dissolution, and cathodic regions, in which O2 is formed, are produced, which overall leads to the formation of local corrosion sites. During cathodic corrosion protection, an electrical voltage is applied between the corroding reinforcement and an anode connected to the component.

The primary protective effect is based on the electrochemical reaction equilibria being shifted on account of the polarisation until the material dissolution in the anodic regions is suppressed in favour of the cathodic partial reaction.

Another primary protective effect arises from the passive regions of the corroding reinforcement also being cathodically polarised, such that the driving force for the corrosion process is absent. While the primary protective effects materialise very quickly, the secondary protective effects, such as the rise in OH— concentration on the reinforcement surface or the depletion of oxygen in the vicinity of the reinforcement as a result of the cathodic reaction and the migration of negatively charged Cl— ions towards the anode, come into effect later, but then lead to a reduction in the protective current density.

In the embodiment according to FIG. 1, an anode system 8 is applied onto the existing concrete 6 comprising reinforcement steel 2. The anode system 8 in this case comprises a bundle of carbon fibre filaments, referred to as a carbon fibre multifilament 10, which is arranged in a meandering configuration on the concrete 6. In the edge region of said carbon fibre multifilament 10, i.e. in the region of the meanders, two primary anode ribbons 12 in the form of titanium ribbons are arranged. The meanders 14 of the carbon fibre multifilament 10 wind around the titanium ribbons 12 so as to make an electrical connection possible. The titanium ribbons 12 are connected to the positive terminal of the voltage source 4 via a primary anode wire (not shown). In this case, said voltage can be checked by a remote monitoring system (not shown), such that the state of the structure or reinforced concrete construction can be detected and continuously monitored. In the embodiment shown, the anode system 8 arranged on the concrete is covered by a conductive mortar 16 in order to protect it from external influences and access.

In the embodiments of FIG. 2, the primary anode ribbon 12 in a contact region 18 is shown in cross-section in a variety of embodiments.

In FIG. 2a, the primary anode ribbon 12 around which the carbon fibre multifilament 10 is wound is located in a previously milled or cut groove 20 in the concrete 6. Said groove 20 has been filled with a grouting mortar 16 in a further work step in order to protect the primary anode ribbon and also the carbon fibre multifilament 10.

In FIG. 2b, the primary anode ribbon 12 around which the carbon fibre multifilament 10 is wound is also arranged in a groove 20 in the concrete. However, in contrast with FIG. 2a, in this embodiment the primary anode ribbon 12 and the carbon fibre multifilament 10 are encased in an epoxy resin 22. However, in principle, the use of other resins or even mortar is also possible. This additionally protects the primary anode ribbon 12 and the carbon fibre multifilament 10 and produces particularly close contact on account of the shrinkage of the epoxy resin 22 after application. In order to fill the groove and to thus secure the primary anode ribbon 12, a grouting mortar 16 is also used in this case.

In FIG. 2c, however, the primary anode ribbon 12 around which the carbon fibre multifilament 10 is wound lies directly on the concrete 6. The anode system is in this case covered with a layer of conductive mortar 16 such that it is secured on the concrete. In contrast with FIG. 2c, in FIG. 2d, the primary anode ribbon 12 around which the carbon fibre multifilament 10 is wound is secured to the concrete by means of a conductive adhesive 24 before it is covered by the conductive mortar.

The fastening options for the primary anode ribbon shown here can also be applied to the carbon fibre multifilament. Said carbon fibre multifilament can also be inserted in grooves in the concrete, encased in epoxy resin, adhesively bonded to the concrete or covered in a layer of conductive mortar.

When laying the filaments 10 in fresh concrete, care must be taken to ensure that the filaments 10 do not touch the steel reinforcement 2 or lie too closely thereto, such that a short circuit between the filaments 10 as the anode and the steel reinforcement 2 as the cathode can be prevented. In the embodiment according to FIG. 3, the filaments 10 are thus arranged on an insulating glass fibre composite reinforcement 28. In this case, the filaments 10 are firstly fastened to said glass fibre composite reinforcement 28 using ties 30 and then the combination of filament and glass fibre composite reinforcement 28 is fastened to the steel reinforcement 2 using additional ties 32. In this way, sufficient spacing between the filaments 10 and the reinforcement steel 2 can also be ensured in fresh concrete, for example in new-concrete structures.

In FIG. 4, the individual method steps for applying an anode system 8 comprising a carbon fibre multifilament 10 are shown in schematic drawings.

As shown in FIG. 4a, the carbon fibre multifilament 10 is applied onto the concrete 6 in a meandering configuration. For this purpose, it is possible for grooves to be cut or milled into the concrete in a previous work step, into which grooves the carbon fibre multifilament 10 can be inserted. When laying the carbon fibre multifilament 10, the meanders 14 are intentionally broad, such that a loose loop of carbon fibre multifilament 10 is formed. The grooves can then be filled with grouting mortar in order for the carbon fibre multifilament to be secured to the concrete 6 for the additional work steps.

In a subsequent work step (FIG. 4b), the titanium ribbons 12, as the primary anode, are laid in the region of the meanders 14. On account of the planarly laid carbon fibre multifilament 10, it is possible to arrange the titanium ribbons 12 in a linear manner. In this way, costly and complicated shaping of the titanium ribbons 12 can be dispensed with. In this case, too, it is possible for grooves to be made in the concrete 6 beforehand, into which grooves the titanium ribbons 12 can be recessed.

Subsequently (FIG. 4c) or even while the titanium ribbons 12 are being laid, the loops of the carbon fibre multifilament are wound around the titanium ribbons 12 in the region of the meanders 14. This produces contact regions 18 in the region of the meanders 14 via which an electrical connection between the titanium ribbon 12 and the carbon fibre multifilament 10 is established. Said contact regions can, for example, be encased in epoxy resin such that the contact regions 18 are protected and such that, on account of the shrinkage of the epoxy resin, a stronger and more secure bond between the carbon fibre multifilament 10 and the titanium ribbon 12 is produced. If present, the grooves for the titanium ribbons 12 may subsequently also be filled with grouting mortar, as a result of which the anode system 8 is secured to the concrete 6.

Finally (FIG. 4d), the titanium ribbons are connected to the positive terminal of a voltage source (not shown) via a primary anode wire 26.

In this way, a particularly simple, quick-to-lay and cost-effective planar anode system for cathodic corrosion protection in reinforced concrete structures is achieved.

LIST OF REFERENCE SIGNS

• 1 reinforced concrete
• 2 reinforcement steel
• 4 voltage source
• 6 concrete
• 8 anode system
• 10 bundle as carbon fibre filaments
• 12 primary anode ribbon
• 14 meander
• 16 mortar
• 18 contact regions
• 20 groove
• 22 epoxy resin
• 24 adhesive
• 26 primary anode wire
• 28 glass fibre composite reinforcement
• 30 tie
• 32 tie

Claims

1. Method for laying an anode system for cathodic corrosion protection, comprising the following steps: laying a carbon fibre multifilament in a planar manner;laying at least two primary anode ribbons, which are arranged so as to be spaced apart from one another, such that the carbon fibre multifilament is arranged between the primary anode ribbons and the primary anode ribbons are connected to the carbon fibre multifilament in an electrically conductive manner in a number of contact regions, characterised in that,the carbon fibre multifilament is arranged in a meandering configuration or in individual strips that are arranged in parallel with one another and that are interconnected by the anode ribbon.

2. Method for laying the anode system according to claim 1, further comprising connecting the primary anode ribbons to a primary anode wire.

3. Method for laying the anode system according to claim 2, characterised in that, in the case of protecting reinforced concrete structures, the carbon fibre multifilament is laid in prepared grooves in concrete.

4. Method for laying the anode system according to claim 3, characterised in that the carbon fibre multifilament is fastened by means of an adhesive.

5. Method for laying the anode system according to claim 1, characterised in that, in the case of protecting reinforced concrete structures, the carbon fibre multifilament is laid in fresh concrete or mortar.

6. Method for laying the anode system according to claim 5, characterised in that the carbon fibre multifilament is wound at least in part around the primary anode ribbon in the contact regions.

7. Method for laying the anode system according to claim 6, characterised in that epoxy resin is used to connect the carbon fibre multifilament and the primary anode ribbon in the contact regions.

8. Method for laying the anode system according to claim 7, characterised in that the carbon fibre multifilament and/or the primary anode ribbon is covered with a conductive mortar.

9-10. (canceled)

11. Method for laying the anode system according to claim 1, characterised in that, in the case of protecting reinforced concrete structures, the carbon fibre multifilament is laid in prepared grooves in concrete.

12. Method for laying the anode system according to claim 1, characterised in that the carbon fibre multifilament is fastened by means of an adhesive.

13. Method for laying the anode system according to claim 1, characterised in that the carbon fibre multifilament is wound at least in part around the primary anode ribbon in the contact regions.

14. Method for laying the anode system according to claim 1, characterised in that epoxy resin is used to connect the carbon fibre multifilament and the primary anode ribbon in the contact regions.

15. Method for laying the anode system according to claim 1, characterised in that the carbon fibre multifilament and/or the primary anode ribbon is covered with a conductive mortar.

16. Method for laying the anode system according to claim 1, characterised in that the carbon fibre multifilament is arranged in the meandering configuration.