GALVANIC ANODE SYSTEM FOR THE CORROSION PROTECTION OF STEEL IN CONCRETE

Abstract

A galvanic anode system for the corrosion protection of steel in concrete includes a galvanic anode material, which includes of zinc and alloys thereof, embedded in a solid electrolyte, and is characterized in that the galvanically available surface is larger, preferably at least twice as large, as the total geometrical surface of the metal anode. The galvanic anode system is also characterized in that, during operation, during which the anode disintegrates as a sacrificial anode, the galvanically active anode surface is reduced only slightly, preferably is not reduced up to at least 50%, in particular 75%, of the time during use.

Claims

1-18. (canceled)

19. A galvanic anode system for corrosion protection of steel in concrete, wherein it comprises a galvanic stacked anode composed of layered galvanic sub-anodes selected from perforated plate, perforated sheet, grid and mesh, composed of zinc and alloys thereof, wherein the galvanic stacked anode is embedded into an ion-conductive matrix, and wherein the thickness of the respective sub-anode is 5 twice the hole diameter, wherein the geometric total volume of the stacked anode is at least 2.3 times as high as the volume of the zinc or alloys thereof, such that the galvanically available surface area of the galvanic stacked anode is greater than its geometric total surface area.

20. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the galvanically available surface area of the galvanic stacked anode is greater than the galvanically active surface area of the galvanic stacked anode.

21. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 20, wherein the galvanically active surface area of the galvanic stacked anode does not decrease significantly.

22. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the galvanically available surface area of the galvanic stacked anode is at least 1.7 times as high as its total surface area.

23. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the diameter of the holes in the sub-anode is greater than the distance between the holes.

24. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the ion-conductive matrix hardens.

25. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the ion-conductive matrix has a pH of 7.

26. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the ion-conductive matrix surrounds the galvanic stacked anode on all sides.

27. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the volume of the ion-conductive matrix is greater than the galvanically available volume of the galvanic stacked anode.

28. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the volume of the ion-conductive matrix is 1.5 times as high as the galvanically available volume of the galvanic stacked anode.

29. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the galvanic stacked anode consists of at least 2.

30. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 19, wherein the orifices and/or mesh sizes in the galvanic sub-anodes and the thickness of the plate or the wire thickness are chosen such that the galvanic stacked anode can be galvanically active on all sides.

31. A galvanic anode system for corrosion protection of steel in concrete, wherein the galvanic anode consists of a metal sponge filled with ion-conductive matrix.

32. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 31, wherein the metal sponge has been produced from zinc and alloys thereof.

33. The galvanic anode system for corrosion protection of steel in concrete as claimed in claim 32, wherein the pore volume of the metal sponge is large enough to be able to accommodate the galvanically formed degradation products formed from zinc and alloys thereof.

34. A process for producing a galvanic anode system as claimed in claim 19, wherein it is produced by the embedding of the galvanic anode material into an ion-conductive matrix.

35. The process as claimed in claim 34, wherein the galvanic anode system is prefabricated.

36. The process as claimed in claim 35, wherein the prefabricated galvanic anode system is bonded onto the concrete and/or embedded into the concrete.

Description

EXAMPLE 1

[0106] An anode of the invention was produced as follows: Strips of width 3 cm and length 10 cm were cut out of a zinc grid (zinc content>99.2% by weight) with an inner mesh size (s) of 5 mm (see s in FIG. 3), a land width (t) of 2.6 mm (see t in FIG. 3) and a thickness (u) (wire thickness) of 1.2 mm (see u in FIG. 3).

[0107] Each zinc grid strip has a geometric total surface area of 30 cm.sup.2 and a galvanically available surface area of 50 cm.sup.2 and a weight of 13 g.

[0108] Eight zinc grids of this kind were placed one on top of another to give a stack, such that the grid holes lay one on top of another and formed a continuous cylindrical orifice. A galvanized steel wire (wire thickness 1 mm) was conducted through the cylindrical orifice at one end, laid diagonally along the underside of the anode to the other end of the anode and thence conducted back through the cylindrical orifice in the upward direction, such that the wire projected out by about 30 cm at either endthe wire serves as connecting wire for the electrical connection of the galvanic anode of the invention to the reinforcement steel to be protected. The individual grid strips and the galvanized wire were bonded to one another with a tin-zinc solder.

[0109] The height of the stacked anode was 18 mm, such that the mean distance (v) (see v in FIG. 3) between the zinc grid strips was about 1 mm.

[0110] The geometric total surface area of the galvanic stacked anode was 106 cm.sup.2; the galvanically available surface area was 403 cm.sup.2; the galvanically active surface area was 101 cm.sup.2. The weight of the stacked anode was 100 g.

[0111] The galvanic stacked anode was embedded into an ion-conducting matrix of the invention as follows:

[0112] 250 g of a binder as described in EP 2313352 B1 were prepared: 100 g of component A, 50 g of component B and 130 g of filler (inert marble sand 0.2-0.5 mm) were mixed with one another.

[0113] 250 g of binder were introduced into a mold having the internal dimensions L=12 cm, B=4.5 cm, H=3.5 cm. The mold filled with the binder was placed onto a vibrating table, and the stacked anode was placed onto the binder and embedded fully with vibration, in such a way that the sides and edges of the stacked anode were at least 5 mm away from the walls of the mold. After the binder had cured completely (2 weeks at 35 C.), the galvanic anode was ready for operation.

[0114] The galvanic anode of the invention was placed onto a reinforcement steel grid (8 steel rods, 10 mm, length 10 cm, bonded to one another by a welded-on 8 mm steel rod) in a plastic vessel (3 L). The reinforcement steel grid rested on an aquarium ventilation plate. The galvanic anode of the invention was electrically connected to the reinforcement steel grid via a shunt resistance of 1 ohm. The bucket was filled with about 2 liters of 3% sodium chloride solution, such that the entire arrangement was covered with at least 1 cm of salt solution. After the ventilation had been switched on, the galvanic current was measured by on-line recording of the voltage drop across the shunt resistance.

[0115] The following current values over time (after the electrical anode-cathode connection) were registered:

TABLE-US-00001 Time Galvanic current 1 hour 20 mA 1 day 14 mA 7 days 8 mA 14 days 5 mA 28 days 3 mA 3 months 2.5 mA 6 months 2.3 mA 12 months 2.4 mA 2 years 2.2 mA 3 years 2.1 mA 5 years 1.5 mA

[0116] The results show that, immediately after switch-on, a high switch-on current flows (14-20 mA), which stabilizes after about 1-3 months at 2.5-3 mA. Until about of the useful life of the galvanic anode, the galvanic current remains virtually constant; after the consumption of about of the zinc (after about 4.2 years), the galvanic current flow decreases.

EXAMPLE 2

[0117] A galvanic anode which was produced as described in example 1 was used in a concrete repair of a chloride-contaminated (up to 3.5% by weight of chloride/cement weight of the concrete) bridge longitudinal beam:

[0118] The bridge longitudinal beam had, at a point close to the longitudinal beam head, visible damageflaking concrete, cracks, rust stains. The concrete was removed from the damaged site by high-pressure water jetting over an area of about 12 m down to beyond the steel reinforcement. At the edges of the repair site toward the old concrete, by means of the galvanic wire which was wound around the respective reinforcement steel, a total of 12 anodes of the invention were secured to the reinforcement steel and embedded in repair mortar. The repair mortar contained max. 1% polymer dispersion and was specified with conductivity of 18 kohm.Math.cm.

[0119] 3 randomly selected anodes were connected to the steel reinforcement via a shunt resistance of 1 ohm, such that the voltage drop across the shunt resistance was measurable on-line: two 3.5 mm.sup.2 copper braids were soldered on upstream and downstream of the shunt resistor and the braids were connected to a current/voltage converter at a distance of about 1 m. The converter was connected via an analog/digital converter unit to a digital data recording system.

[0120] The galvanic currents measured were in the range of 0.7-0.9 mA/anode over an observation period of 5 years. This gives a current flow of 4.2-5.4 mA/m.sup.2 of reinforcement steel surface area. These data can be used to estimate a useful life of about 15-20 years. The reinforcement steel was polarized up to max. 0.665 mV, such that there was no risk of hydrogen embrittlement of the steel. There was no observation of incipient anodesnew corrosion sites in the edge region of the repair siteeven after 5 years. Potential field measurements of the reinforcement steel did not give any hint of a corrosion risk.