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.
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.
This object is achieved according to the invention in that the method comprises the following steps:
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.
An embodiment of the invention will be described in greater detail with reference to the drawings, in which:
Identical parts are provided with the same reference signs in all figures.
In the embodiment according to
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
In the embodiments of
In
In
In
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
In
As shown in
In a subsequent work step (
Subsequently (
Finally (
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.
Number | Date | Country | Kind |
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10 2015 115 297.5 | Sep 2015 | DE | national |
This patent application is a 35 U.S.C. § 371 national phase filing of International Application No. PCT/EP2016/071458, filed Sep. 12, 2016, which claims priority to German Patent Application No. 10 2015 115 297.5, filed Sep. 10, 2015, the disclosures of each of which are hereby incorporated herein by reference in their entireties.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/071458 | 9/12/2016 | WO | 00 |