EP1899502B1 - Method for the cathodic protection of the reinforcements of ferroconcrete edifices against corrosion - Google Patents

Description

The present invention relates to a method for cathodic corrosion protection of the reinforcements of reinforced concrete structures, in the field of construction joints had expansion and expansion joints.

Stability and service life of reinforced concrete structures depend significantly on the corrosion protection of the reinforcing steel used. Normally, the natural alkalinity of the concrete leads to the passivation of steel surfaces, so that corrosion is usually excluded. However, due to the influence of carbon dioxide in the air, so-called carbonation can occur, with carbon dioxide being released from the atmosphere in the wet cementstone and forming carbonic acid. This reduces the alkalinity of the concrete because calcium hydroxide is converted into calcium carbonate.

As soon as this advancing process reaches the reinforcing steel (this happens relatively quickly with low reinforcement coverage), the rust-protective corrosion-protective passivation film of the reinforcing steel is destroyed. In the presence of water and oxygen, oxidation products of the reinforcing steel are formed. This destroys the structure of the steel; due to the larger volume of the oxidation products, cracking and flaking also occur in the concrete.

In addition to carbon dioxide, the passivation layer of the reinforcing steel in concrete can also be destroyed by the presence of chlorides. Chlorides, as z. B. be used as de-icing salts, can penetrate into concrete and corrosion of reinforcing steel even under cause highly alkaline conditions. The probability of corrosion increases with the amount of chloride. Chloride corrosion can only occur if there is sufficient water and oxygen in the vicinity of the reinforcing steel.

For corrosion prevention of reinforced concrete structures, there are therefore various methods, eg. B. by subsequent coating of the reinforcing steel with corrosion-protective coatings or by impregnation with rust-inhibiting chemicals.

Another possibility to prevent / minimize reinforcement corrosion is to protect the structure from moisture ingress. This can be done by waterproof paints or impregnations. In particular, the application of so-called. Hydrophobierungsmitteln (silane / polysiloxane solutions) on the concrete surface is state of the art. The disadvantage here is that these are not -dicht steam / CO ₂ and thus the described processes of carbonation only slow, but can not completely prevent. Also, these paints / impregnations must be renewed time and again to ensure the long-term effectiveness.

As an electrochemical method, the so-called cathodic corrosion protection (PPS) has been established for more than 30 years. As already described, the presence of unfavorable parameters (chloride loading, carbonation) leads to partial corrosion of the steel reinforcement. Here, the corrosion hearth forms the anode and the adjacent not yet corroded steel forms the cathode, that is, a corrosion current flows in the concrete. This leads to further accelerated corrosion of the reinforcing steel. The metal dissolution is the anodic and the oxygen reduction is the cathodic partial reaction.

The principle of the KKS is based on the fact that the anodic partial reaction, namely the dissolution of iron, is prevented by an oppositely directed direct current. By applying a protective current while the reinforcing steel is polarized, d. H. the steel / concrete potential is shifted in the negative direction. Therefore, this type of corrosion protection is also referred to as cathodic corrosion protection.

The necessary protection current can be implied by various systems at the KKS. One possibility is the use of so-called discrete anodes. These are placed in the vicinity of the steel reinforcements in the concrete. By applying an external DC power source, the steel / concrete potential is shifted in the required negative direction.

For the functioning of the method, it is important that the anodes are mounted in close proximity to all reinforcing bars. This is relatively easy to achieve in the areas in which the reinforcing steel is placed close to the concrete surface (eg on road surfaces).

However, in the areas where the steel reinforcements are placed deeper into the concrete parts, this is associated with considerable effort. This is the case especially in areas of concrete support parts, since these are usually separated by so-called construction joints. These construction joints are closed by sealing materials on the surface to prevent the ingress of moisture and salts (road salt in road surfaces). Due to leaks in these seals, however, it is very common in practice for water and salts to penetrate, which leads to corrosion of the reinforcement in the supports. In order to achieve reliable protection with the help of KKS corrosion protection, it is state of the art to provide deep boreholes on both sides of the construction joints and to introduce the corresponding anodes here. To accommodate the anodes or rod anodes, drill holes must be made on both sides, usually every 20 to 30 cm. It is particularly important to note that the borehole is mounted in the immediate vicinity of the reinforcement and the reinforcement is not injured thereby, otherwise it comes to a short circuit and ineffectiveness of the method.

The reinforcement itself acts as a cathode in the cathodic corrosion protection method and must therefore not come into direct contact with the rod anode. This process is very labor-intensive and thus expensive.

According to the GB 2 389 591 A It has been proposed to connect the anodes to a deformable, preferably plastic, polymeric material (eg, PU-based) and then to force the anodes with the deformable material into the structural joint of concrete structural parts to thereby make electrical contact with the concrete surface.

This method is relatively complicated and expensive. In addition, the reliability of the corresponding method is not given satisfactorily over the entire period of use.

The present invention therefore an object of the invention to develop a method for cathodic corrosion protection of the reinforcements of reinforced concrete structures, which does not have the disadvantages of the prior art, but allows a cost-effective and reliable method for cathodic corrosion protection of steel reinforcements of concrete works.

1. a) eine Seite der Konstruktionsfugen der Betonträgerteile abdichtet,
2. b) die KKS-Anoden in die Konstruktionsfugen einbringt,
3. c) in die einseitig verschlossenen Fugen ein ionisch leitfähiges Gel einbringt und
4. d) ggf. die Konstruktionsfugen vollständig abdichtet.

This object has been achieved in that one

1. a) one side of the construction joints of the concrete support members seals,
2. b) introduce the KKS anodes into the construction joints,
3. c) introduces an ionically conductive gel in the joints closed at one end and
4. d) if necessary, completely seal the construction joints.

It has surprisingly been shown that it is possible with the help of the ionic conductive gel to reliably ensure the necessary electrical conductivity over the entire period of use, which is a prerequisite for effective and reliable corrosion protection of steel reinforcements of concrete works.

The method according to the present invention thus comprises at least three stages. In the first step a) one side of the construction joints of the concrete support members is sealed, wherein this sealing of the joints is preferably carried out with the aid of chemical-resistant sealants, a specially adapted joint profile or a glued-on joint tape.

The chemical-resistant sealants can be based on silicone, polyurethane, acrylate, silyl-modified polymers (SMP), bitumen, MS polymer, epoxy and polysulfide. The joint tapes, which are preferably used in the form of fabric tapes, may consist of the same materials as the sealants. However, preference is given to rubber mixtures, such as silicone rubber, acrylic rubber and bituminous rubber. In this way, the construction joints are sealed watertight on one side, so that a liquid-tight gap for receiving the anodes is formed.

In the following step b) the KKS anodes are then introduced into the construction joints. The corresponding anodes can in this case consist of the usual materials, such as. B. so-called. MMO (Mixed Metal Oxide) anodes, activated titanium metal anodes, platinized niobium metal anodes or conductive ceramic anodes based on titanium oxide. The shape of the corresponding KKS anodes is largely uncritical. Thus, band-shaped anodes can readily be resorted to, but in the method according to the invention the PPS anodes are preferably used in the form of rod anodes.

It is to be regarded as essential to the invention that in stage c) an ionically conductive gel is introduced into the gap closed on one side. The ionic conductive gel here has the task to reliably ensure the necessary electrical conductivity over the entire period of use. This must u. a. have a high water retention capacity to prevent dehydration and thus loss of effectiveness.

The ionically conductive gel, which can be used both in (semi) liquid and in pasty form, preferably consists of 10 to 90 wt .-% of a polyhydric alcohol, 0.1 to 20 wt .-% stabilizers, 0.01 to 5% by weight of electrolyte, 0 to 50% by weight of inert fillers and the remainder water and optionally further additives in the form of thickening and preservatives or defoamers.

The polyhydric alcohol used is preferably ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 2,3-butanediol or glycerol.

Particularly suitable stabilizers are water-soluble, ionic or nonionic cellulose derivatives, such as methylcellulose (MC), hydroxyethylcellulose (HEC), methylhydroxyethylcellulose (MHEC), methylhydroxypropylcellulose (MHPC), microbially produced polysaccharides, such as welan gum, naturally occurring extractively isolated polysaccharides ( Hydrocolloids) such as alginates, xanthans, carrageenans, galactomannans.

In the case of the electrolytes, one or more slightly water-soluble salts selected from the group of hydroxides, nitrites and nitrates of sodium, potassium, lithium, calcium and aluminum are preferably used.

The inert fillers having a preferred particle size of 0.1 to 3 mm consist in particular of calcium carbonate, quartz, aluminum oxide, barium sulfate and slate.

After introduction of the ionic conductive gel in the joints closed at one end, the construction joints are possibly completely sealed in the last step d), wherein one can resort to the already described in step a) chemical resistant sealants, the specially adapted joint profiles or the glued joint tapes. According to this preferred embodiment is to be prevented that subsequently water can penetrate into the construction joints.

The method according to the invention has the advantage that both sides of the reinforced concrete structure can be protected in the joint area with only one anode and that the risk of a short circuit due to unintentional contact of the anode with the steel reinforcement of the concrete plants is ruled out from the outset.

In addition, with the aid of the method according to the invention, a very cost-effective and effective method for cathodic corrosion protection of the steel reinforcements of concrete works is provided, which also works reliably over a longer period of use.

The following example is intended to illustrate the invention in more detail.

example

The method according to the invention was carried out on a parking deck, consisting of precast concrete slab parts and precast concrete support parts with steel reinforcement. Here, the absence of the necessary passivation layer and thus slight corrosion on the carrier parts was suspected on the steel reinforcement in the area of the structurally determined expansion joint, in particular due to penetrating de-icing salt.

The construction joint was bonded over a length of 15 m in the region of the underside of the support with a joint tape approximately 20 cm wide (Thoroflex 200 from Masterbuilders) using an epoxy resin adhesive (Thoroflex 2000 Adhesive from Masterbuilders) to form a liquid-tight gap. Then, an ionically conductive gel was introduced into the resulting gap up to approximately ¾ of the gap height. MMO primary arrays (Duranode Fa. CPI-GK) were introduced into the gel at intervals of about 1 m along the construction joint in such a way that the Anodes in the lower third of the gel layer were.

The gel used had the following composition: 0.80% by weight Stabilizer based on xanthan gum 40.00% by weight ethylene glycol 0.03% by weight calcium nitrate 34.02% by weight water 0.15% by weight preservative 25.00% by weight filler

Subsequently, the construction joints were completely sealed from above with the previously described sealing tapes Thoroflex 200 (from Masterbuilders). The potential measurement was carried out with Ag / AgCl reference electrodes. The measuring points for this were chosen so that these formed a mesh-like measuring area at a distance of 250 and 500 mm from one another and along the 15 m long movement gap at the concrete support surfaces adjacent to the movement joint. A potential measurement prior to commissioning of the anode system showed that values of <-300 mV were measured over the entire measuring range and thus already reinforcement steel corrosion was present. To the MMO anodes was applied a DC voltage with a voltage of 3 V and a current flow of 100 mA, which corresponds approximately to the required current density of 10 to 15 mA / m 2 reinforcing steel. The current was applied to the anodes over a period of 2½ months. After switching on the anode system, a slow shift of the potential into the negative region was immediately detected.

Finally, the potential was determined with the current switched on ("ON potential") and after 4.5 h after switching off the current ("off potential") with the aid of the Ag / AgCI reference electrodes over the entire measuring range. The proof of effectiveness is given in accordance with EN 12 696, if the difference between ON potential and OFF potential is at least 100 mV. The required potential difference was reached at approx. 75% of the 52 measuring points, so that a satisfactory corrosion protection is given.

Claims (12)

1. A method for the cathodic corrosion protection (CCP) of reinforcements of ferroconcrete edifices in the region of construction joints, wherein

   a) one side of the construction joints between two concrete supporting elements is sealed,

   b) the CCP anodes are introduced into the construction joints,

   c) an ionically conductive gel is introduced into the joints closed on one side, and

   d) optionally the construction joints are sealed completely.
2. The method according to claim 1, wherein the sealing of the joints in steps a) and d) is carried out by means of chemical-resistant sealing materials, a specially adapted joint profile, or an adhered bonding tape.
3. The method according to claim 1 or 2, wherein there are used as the CCP anodes so-called MMO (mixed metal oxide) anodes, activated titanium metal anodes, platinized niobium metal anodes, or conductive ceramics anodes based on titanium oxide.
4. The method according to one of claims 1 to 3, wherein the CCP anodes are used in the form of rod anodes.
5. The method according to one of claims 1 to 4, wherein the conductive gel has a high water retention capacity.
6. The method according to one of claims 1 to 5, wherein the gel is used in liquid, semi-liquid or pasty form.
7. The method according to one of claims 1 to 6, wherein the gel comprises from 10 to 90% by weight of a polyhydric alcohol, from 0.1 to 20% by weight stabilizers, from 0.01 to 5% by weight electrolyte, from 0 to 50% by weight inert fillers and, as the remainder, water and optionally further additives in the form of thickeners and preservatives or antifoams.
8. The method according to claim 7, wherein there is used as the polyhydric alcohol ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 2,3-butanediol or glycerol.
9. The method according to either claim 7 or 8, wherein there are used as stabilizers water-soluble, ionic or non-ionic cellulose derivatives, such as methylcellulose (MC), hydroxyethylcellulose (HEC), methylhydroxyethylcellulose (MHEC), methylhydroxypropylcellulose (MHPC), microbially produced polysaccharides, such as welan gum, naturally occurring polysaccharides (hydrocolloids) produced by extraction, such as alginates, xanthans, carrageenans, galactomannans.
10. The method according to claim 7, wherein there are used as the electrolyte one or more readily water-soluble salts selected from the group comprising hydroxides, nitrites and nitrates of sodium, potassium, lithium, calcium and aluminum.
11. The method according to claim 7, wherein the inert fillers consist of calcium carbonate, quartz, aluminum oxide, barium sulfate and shale.
12. The method according to claim 11, wherein the inert fillers have a particle size of from 0.1 to 3 mm.