Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
  • C04B20/10—Coating or impregnating
  • C04B20/1055—Coating or impregnating with inorganic materials
  • C04B20/1066—Oxides, Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
  • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/20—Resistance against chemical, physical or biological attack
  • C04B2111/26—Corrosion of reinforcement resistance
  • C04B2111/265—Cathodic protection of reinforced concrete structures
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F2201/00—Type of materials to be protected by cathodic protection
  • C23F2201/02—Concrete, e.g. reinforced

Definitions

• This invention generally relates to the field of galvanic cathodic protection of steel embedded in concrete structures, and is particularly concerned with the performance of embedded sacrificial anodes, such as zinc, aluminum, and alloys thereof.
• cathodic protection is capable of controlling corrosion of reinforcing steel over an extended period of time without complete removal of the salt-contaminated concrete.
• Cathodic protection reduces or eliminates corrosion of the steel by making it the cathode of an electrochemical cell. This results in cathodic polarization of the steel, which tends to suppress oxidation reactions (such as corrosion) in favor of reduction reactions (such as oxygen reduction).
• Cathodic protection was first applied to a reinforced concrete bridge deck in 1973. Since then, understanding and techniques have improved, and today cathodic protection has been applied to over one million square meters of concrete structure worldwide. Anodes, in particular, have been the subject of much attention, and several different types of anodes have evolved for specific circumstances and different types of structures.
• ICCP impressed current cathodic protection
• inert anodes such as carbon, titanium suboxide, and most commonly, catalyzed titanium.
• ICCP also requires the use of an auxiliary power supply to cause protective current to flow through the circuit, along with attendant wiring and electrical conduit.
• This type of cathodic protection has been generally successful, but problems have been reported with reliability and maintenance of the power supply. Problems have also been reported related to the durability of the anode itself, as well as the concrete immediately adjacent to the anode, since one of the products of reaction at an inert anode is acid (H + ). Acid attacks the integrity of the cement paste phase within concrete.
• GCP galvanic cathodic protection
• Bartholomew et al discloses a method of patching an eroded area of concrete comprising the use of a metal anode having an ionically conductive hydrogel attached to at least a portion of the anode.
• the anode and the hydrogel are flexible and are conformed within the eroded area, the anode being in elongated foil form.
• Whitmore discloses the use of a deliquescent material bound into a porous anode body, which acts to maintain the anode electrochemically active, while providing room for the expansive products of corrosion.
• the same patent discloses several mechanical means of making electrical connection to the reinforcing steel within a hole drilled into the concrete covering material. Many of these means involve driven pins, impact tools, and other specialized techniques. These techniques are all relatively complex and difficult to perform.
• the anodes described above and the means of connection disclosed have become the basis for commercial products designed to extend the life of patch repair and to cathodically protect reinforced concrete structures from corrosion. But some embodiments, such as the use of high pH to maintain the anode in an electrochemically active state as described by Page, result in protective current that is small and often inadequate to mitigate corrosion. Use of the chemicals such as lithium nitrate and lithium bromide, result in a higher current, but even this current is sometimes inadequate in cases of high chloride contamination and the presence of strong corrosion of the reinforcing steel. Also, some of the chemicals used to maintain the zinc anode in an electrochemically active state render the corrosion products of zinc largely insoluble.
• the present invention relates to an apparatus and a composite anode for cathodic protection of reinforced concrete, and more particularly, to a method and apparatus for improving the performance and service life of embedded anodes prepared from sacrificial metals such as zinc, aluminum, and alloys thereof.
• the present invention more specifically relates to an apparatus and a composite anode for cathodic protection wherein the performance of the sacrificial anode is enhanced by the use of a combination of chemicals and a compressible, water retaining phyllosilicate such as vermiculite in an ionically conductive material such as a cementitious grout, thereby forming an activating matrix surrounding the sacrificial anode.
• 'surrounding' is meant at least partial encapsulation of the anode. This combination is particularly effective absorbing the expansive corrosion products of the zinc anode.
• the chemical component of the activating matrix may be any one, or a combination of, the chemicals previously disclosed in the prior art. These include chemicals that are deliquescent or hygroscopic, also sometimes known as humectants. Such chemicals maintain the region near the anode moist and highly conductive. Particularly advantageous are lithium nitrate, lithium bromide, or other deliquescent or hygroscopic chemicals. Other chemicals intended to raise the pH of the matrix to a value greater than about 13.5 are also known to be effective. A water-retaining phyllosilicate mineral resembling mica has been found to be a particularly useful component of the present invention. A specific form of this mineral is vermiculite.
• Vermiculite particles in the matrix appear to serve both functions of increasing the protective current delivered by the anode, and effectively absorbing the expansive products of corrosion.
• the anode itself may be in a variety of forms, but is preferably in an elongated foil, or ribbon form.
• the anode is composed of zinc, magnesium, aluminum or their alloys, or combinations of these metals.
• the ionically conductive material that binds the phyllosilicate particles together, and to the zinc anode, may be either of a cementitious nature, or may be a hydrogel, as taught by the aforementioned prior art.
• the composite anode for cathodic protection also incorporates an elongated metallic conductor that serves to electrically connect the sacrificial anode to the reinforcing steel, or other metal to be protected, thereby providing an electrical path for the flow of protective current.
• the elongated metallic conductor may be attached to the reinforcing steel by one of several methods, such as wrapping, twisting, resistance welding, tig welding, mechanical compression and the like.
• the present invention also relates to a method of cathodic protection of reinforced concrete, and more particularly, to a method of improving the performance and service life of embedded anodes intended to apply cathodic protection to reinforcing steel and other metals embedded in concrete.
• Figure 1 illustrates one method of utilizing the anode assembly of the present invention
• Figure 2 illustrates the anode assembly of Figure 1 in cross section
• FIG. 3 illustrates the results of the tests described in Example 1 to follow.
• the drawings are not necessarily to scale but are merely schematic representations, not intended to portray specific parameters of the invention.
• the drawings are intended to depict only typical embodiments of the invention and, therefore, should not be considered as limiting the scope of the invention
• Figure 1 shows the surface of a reinforced concrete structure 1 in plan view with an excavation 2, where loose and delaminated concrete has been removed. Reinforcing bars 3, running both horizontally and vertically, are shown exposed in the excavation 2.
• a flexible, elongated anode assembly 4 is shown placed near the edge of the excavation 2.
• the anode assembly 4 is fastened to reinforcing bars 3 with metallic wire conductors 5 for the purpose of making contact and allowing protective current to flow.
• This anode assembly has a thickness of between about 0.01 inch and about 0.2 inch and a width between about 0.2 inch and about 2 inches. However, it is understood that the dimensions of the anode assembly are dictated by such parameters as the size of the excavation, and the flexibility, bend ability, and conductivity of the anode assembly, and ease of installation,
• FIG 2 illustrates a cross sectional view of the structure of Figure 1.
• the anode 6 is shown in a central configuration.
• the metal anode 6 is enclosed on both sides by an activating matrix 7 to form the anode assembly 4.
• the activating matrix 7 comprises an ionically conductive material, a phyllosilicate such as vermiculite, and at least one activating chemical designed to keep the anode metal in an electrochemically active state.
• the activating matrix 7 on each side of the anode is bound on one side by a protective plastic sheet 8, such as polyethylene, designed to protect the activating matrix 7 during shipping and handling.
• the protective plastic sheet 8 is removed prior to placing the patch material into the excavation.
• the present invention relates broadly to all reinforced concrete structures with which cathodic protection systems are useful.
• the reinforcing metal in a reinforced concrete structure is carbon steel.
• other ferrous-based metals can also be used.
• the anode assembly of the present invention relates to galvanic cathodic protection (GCP), that is, cathodic protection utilizing anodes consisting of sacrificial metals such as zinc, aluminum, magnesium, or alloys thereof. Of these materials, zinc or zinc alloys are preferred for reasons of efficiency, longevity, driving potential and cost. Sacrificial metals are capable of providing protective current without the use of ancillary power supplies, since the reactions that take place during their use are thermodynamically favored.
• the sacrificial metal anodes may be of various geometric configurations, such as flat plate, expanded or perforated sheet, or cast shapes of various designs.
• a preferred configuration of the anode, and anode assembly of the present invention is a flexible elongated foil, or ribbon configuration.
• the composite anode is elongated and flexible, in which case it is easily conformed to be placed around the edge of the excavated patch, thereby mitigating the anode ring effect of corrosion. It may also be useful to fix the elongated composite anode around the edge of the excavated patch with non-conductive ties.
• the ties may incorporate a non-conductive shield to prevent an excessive amount of current to pass to the reinforcing bar adjacent to the composite anode.
• the anode metal is surrounded, on at least one side, by an ionically conductive material.
• the ionically conductive material may be one of several known conductive cementitious grouts, or may be a material known as a hydrogel.
• the word "hydrogel” as used herein is meant to include any ionically conductive adhesive gel which is a coagulated colloid that typically is a viscous and tacky, jellylike product. In broad terms, water can be present in the hydrogel from about 5% to 95% by weight, and is usually present in major amount, e.g. 70-90 weight percent.
• Preferred hydrogels for the present invention are organic, polymeric structures that have a molecular weight sufficiently high for the hydrogels to be self-supporting.
• inorganic, polymeric structured hydrogels may also be used, e.g. those based on polysilicates or polyphosphates.
• the use of mixtures of organic and inorganic hydrogels is also contemplated.
• the self-supporting hydrogels are form stable under normal conditions, and have good ionic conductivity, as well as good adhesiveness or tackiness. This adhesiveness as well of the flexibility of the hydrogel allows it to securely adhere to the anode metal even when the metal is bent or twisted.
• Hydrogels useful for this invention are further specified in U.S. Patent 5,292,411, the teachings of which are incorporated herein by reference.
• the vermiculite used in the present invention is a phyllosilicate mineral resembling mica.
• Vermiculite mined in the US is a hydrated phlogopite or biotite mica that expands or delaminates to many times its volume when heated, a process called exfoliation.
• Vermiculite used in the present invention is in exfoliated form, and is incorporated essentially within the ionically conductive material.
• the particle size for the vermiculite used may range from about 0.01 to 0.1 centimeter.
• Vermiculite may be used in the present invention by incorporating into the activating matrix in the amount of between about 2% and about 15% of total weight, more particularly, between about 5% and about 12%.
• sacrificial metal anodes tend to passivate in the alkaline environment of concrete, it is necessary to provide an activating agent within the ionically conductive material to maintain the anode in an electrochemically active and conductive state.
• the use of deliquescent or hygroscopic chemicals serves to maintain a galvanic sprayed zinc anode in an active state, thereby continuing to deliver protective current.
• Two of the most effective chemicals for this purpose namely lithium nitrate and lithium bromide (LiNO 3 and LiBr), enhance the performance of sprayed zinc anodes.
• LiNO 3 and LiBr serve to improve the performance of embedded discrete anodes. It has been found that a mixture of lithium nitrate and lithium bromide in an amount of between about 1% and about 15% is particularly effective for this purpose.
• a steel reinforced 12 x 12 x 4-inch (30.5 x 30.5 x 10.2 cm) concrete test block was constructed using concrete with the following mix proportions:
• Airmix air entrainer (0.95% oz/CWT) - about 6.5% air
• the test block contained about 24 inches (60 cm) of #4 (12 mm dia.) reinforcing bar, or about 0.25 square feet (240 square centimeters) of steel surface area.
• Each test block was cast with two blockouts for two test cells, each blockout forming a circular test cavity about 4 inches (10 cm) in diameter x 2.75 inches (7 cm) deep.
• a 'blockout' is a block or form that is placed in wet concrete when formed. When the blockout is removed from the concrete at a later time, it leaves a cavity or void.
• An anode was first constructed by soldering 40 grams of pure zinc to galvanized tie wires. The zinc was then cast into a mixture containing 65% sand, 15.2% Type III cement, and 19.8% lithium liquid mixture, prepared by combining 40% by volume saturated lithium bromide solution and 60% by volume saturated lithium nitrate solution. The mixture surrounding the anode was allowed to cure, and the anode was then placed into a cavity in the test block and mortared in place with Eucopatch, a one-part cementitious repair material produced by The Euclid Chemical Company. The anode was connected to the reinforcing bars in the test block with a 10 ohm resistor, which facilitated measurement of the flow of protective current.
• This anode was subjected to 5 mA of impressed current in constant current mode of operation. In this way, a total charge equivalent to several years of service life can be impressed on the anode in a period of about 60 days.
• the effectiveness of the anode can be determined by observation of the cell operating voltage. Lower operating voltage indicates that an anode will deliver a higher level of protective current when operated in galvanic mode.
• Control The operating voltage of the control anode is shown by the line labeled "Control" on Figure 3. Operating voltage began at about 1.0 volt, and increased to about 5.0 volts after 60 days.
• a second anode was prepared in a similar manner, except that the matrix surrounding the anode contained 8.6% vermiculite by weight. After curing of the mortar surrounding the anode, the anode was placed into a test cavity and mortared in place with Eucopatch. This anode was connected to the reinforcing bars in the same manner as the Control.
• the operating voltage of the anode surrounded with the vermiculite mixture is shown by the line labeled "8.6% Vermiculite" on Figure 3. In this case, operating voltage began at about 0.5 volts, and increased to only about 1.5 volts after 60 days. This improvement is again expected to result in a higher polarization of the steel surrounding the anode, a greater level of cathodic protection, and a longer effective service life of the anode.
• Figure 3 illustrates the results of the tests described hereinabove.
• This figure shows cell voltage of test blocks operated in accelerated mode using an impressed current of 5 milliamps as a function of time.
• the data labeled "Control” was obtained by a standard control test block as described in Example 1, and is again considered good performance.
• the data labeled "8.6% Vermiculite” was obtained from a test block in which 8.6% by weight of the matrix surrounding the anode consisted of vermiculite, a phyllosilicate mineral resembling mica.
• cracks had developed on the surface of the control block, with cracks measuring up to 0.047-inch wide after 51 days on line. Cracks were barely discernable on the surface of the block containing vermiculite, and measured no more than 0.002-inch wide after 57 days on line.
• the present invention is useful for providing an enhanced level of corrosion protection for steel reinforcement that is used in concrete structures such as bridges, buildings, parking structures, piers, and wharves.

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• 2007
  • 2007-03-24 US US12/295,875 patent/US20090183998A1/en not_active Abandoned
  • 2007-03-24 WO PCT/US2007/007317 patent/WO2007126715A2/en active Application Filing
• 2008
  • 2008-02-25 CA CA002681232A patent/CA2681232A1/en not_active Abandoned
  • 2008-02-25 EP EP08730606A patent/EP2132360A1/de not_active Withdrawn

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