Abstract:
An improved sacrificial galvanic anode assembly for cathodic protection of a steel reinforced concrete structure. A galvanic cathodic protection device uses an embedded sacrificial anode of metallic foam for increased reactive surface area covered with a flexible penetrating coating to provide a continuous electrolyte to keep it active. The formulated coating paste is inert to cement embedment material and is pre-applied on the anode body prior to encapsulation. An integrated conductive contact band extends from the coated anode to attachment to a reinforcement bar for establishing electrical conductively therewith within the concrete structure transferring galvanic corrosion to the anode.

Description:
This is a continuation in part patent application of Ser. No. 12/460,883, filed Jul. 27, 2009 now U.S. Pat. No. 7,998,321. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to galvanic cathodic protection of embedded steel in concrete and the like. Specifically, to sacrificial anodes electrically linked to the steel reinforcement. 
     2. Description of Prior Art 
     Prior art devices of this type have relied on sacrificial anodes to address the issue of steel reinforcement corrosion which can and will occur due to the inherent porous nature of the concrete in which it is embedded. Such corrosion occurs when the concrete becomes contaminated with, for example, chloride ions from structural exposure to nature and user applied salt or carbonation due to carbon dioxide penetration into the concrete and loosing therefore its protective alkalinity. Once this occurs, the reinforcement steel will corrode increasing its volume causing accelerated failures of the surrounding concrete structure. By the use of the electrically connected sacrificial anode connected to the reinforcement steel cathodic protection is achieved, reducing or eliminating the corrosion of the steel by making it the cathode of the electric chemical cell. 
     One of the issues encountered in such a galvanic cathodic protection assemblies using sacrificial anodes, such as zinc or aluminum, regardless of the application venue is the size proportion of the anode to the protected structure surface. 
     This dissimilar surface issue in inherent by the nature of the structure being protected and the viable limitation of fixed anode surface as a potential so matter. Since the anode and cathodic surface areas should be in equilibrium and if not the sacrificial anode is not able to provide enough polarization to the protected structure, although the current of the anode varies insignificantly and is referred to as “mixed potential theory” illustrated in  FIGS. 5 and 6  of the drawings showing a graphic display of “potential E” and anode and cathode related to increase cathode area. 
       FIG. 5  is a graphic depicting basis when dissimilar metals are connected electrically in a solution, they are forced to adapt the same potential and not their “at rest” potential. This example illustrates iron Fe and zinc Zn connected in an electrolyte with iron being the cathode and zinc the anode with the corrosion potential given at the illustration of the anode and cathode reactions. 
       FIG. 6 , however, illustrates the effect of changing the area of one electrode relation to the other with total current, not current density on the YX axis, as shown. This illustrates the increased cathode area in the corresponding intersection of the zinc to the iron as surface area increases. 
     It will be evident therefore that criticality of effectively increasing the surface of the anode is relevant to the efficiency and practicality in any galvanic cathodic protection system. 
     Galvanic cathodic protection using sacrificial anodes such as zinc and aluminum which have inherently negative electro chemical potentials establishes a passive protective current flow which is well known and understood in the art, see for example U.S. Pat. Nos. 4,435,263, 5,292,411, 6,022,469, 6,033,553, 6,165,346, 6,562,229, 6,572,760, 7,160,433 and 7,488,410. 
     In U.S. Pat. No. 4,435,263, a back fill composition for magnesium galvanic anodes is disclosed using calcium sulphite, bentonite and one compound from a group of sodium alkylates and sodium dialkyldithiocarbamates. 
     U.S. Pat. No. 5,292,411 is directed to a method of patching eroded concrete using a metal anode with an ionically conductive hydrogel attached to a portion of the anode being in elongated folded form. 
     U.S. Pat. No. 6,022,469 discloses a method by which a zinc or zinc alloyed anode is set in mortar that maintains a high PH to provide passivity of the zinc anode maintaining same in an electro chemical active state. 
     U.S. Pat. No. 6,033,533 discloses the most effective humectants, debquescent or hydroscopic chemicals, lithium, nitrate and lithium bromine respectively to maintain a galvanic sprayed anode in active state. 
     U.S. Pat. No. 6,165,346 also claims a use of deliquescent chemicals to enhance the performance of the galvanic anodes. 
     U.S. Pat. No. 6,562,229 is drawn to a louvered metal anode with an electrocatalytically active coating on a substrate. 
     U.S. Pat. No. 6,572,760 illustrated the use of deliquescent material bound into a porous anode body to maintain the anodes electro chemical active properties. 
     U.S. Pat. No. 7,160,433 claims a cathodic protection system in which zinc anode embedded in mortar in which a humectant is employed to impart high ionic conductivity. 
     Finally, U.S. Pat. No. 7,488,410 shows an anode assembly for cathodic protection using an anode covered with an ionically conductive material having an electro chemical activating agent configured to conform closely to the steel reinforcing bar in which it adjacently protects. 
     SUMMARY OF THE INVENTION 
     A galvanic cathodic protection system using a zinc anode electrically connected to an embedded reinforcing steel within a concrete structure. The anode is precoated with a unique flexible lightly acidic paste formulation to maintain continuous reaction keeping the anode active. The paste coating is an auto moistening electrolyte configuration maintaining the zinc as zinc-ions (Zn 2 ) in the acidic environment. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graphic side elevational view partially in cross-section of the present invention in use. 
         FIG. 2  is an enlarged partial sectional view of the assembled anode. 
         FIG. 3  is an exploded isometric view of the anode assembly of the invention. 
         FIG. 4  is an enlarged perspective partial view of an electrically conductive tie for securing the anode conductors to the reinforcing bar. 
         FIG. 5  is a “Potential E” graph showing the baseline of intersection of cathode to anode connected electrically in a solution. 
         FIG. 6  is a graphic illustration showing “Potential E” of cathode to anode in increasing cathode area points of intersection. 
         FIG. 7  is an exploded isometric view of an alternate anode assembly with increased surface anode material achieved by metallic foam construction. 
         FIG. 8  is a graphic side elevational view partially in cross section of the alternate form of the invention in use. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  of the drawings, an anode assembly  10  of the invention can be seen, in use, embedded within a concrete structure  11  having a steel reinforcing bar  12  therewithin. The anode assembly  10  is in this example positioned adjacent the reinforcing bar  12  with an electrical interconnection band  13  extending in oppositely disposed relation outwardly therefrom. The electrical connection band  13  extending portions  13 A and  13 B are secured to the surface S of the reinforcement bar  12  in longitudinally spaced relation defining an electrical link with the steel reinforcement bar  12  and an electrically charged transfer flow current circuit. An anode  14  is of a multiple layer configuration, best seen in  FIGS. 2 and 3  of the drawings having zinc sheets  15  and  16  each having an upper and lower contact surface  15 A,  15 B,  16 A and  16 B respectively. The zinc sheets  15  and  16  are secured together by spot welding W by their respective contact surfaces  15 A and lower contact surface  16 B with the electrically conductive band  13  secured first to the contact surface  15 A by spot welding between the sheets  15  and  16  which are then secured together surrounding the conductive band  13  by the hereinbefore described spot welding W defining a pre-assembled anode configuration at  14 . 
     Referring now to  FIG. 7  of the drawings, an example of an alternate anode construction assembly  23  can be seen to address an inherent problem directed towards anode and cathode surface area equilibrium. It has been an established solution that by simply increasing the anode surface area by use of a larger anode is simply not a practical solution given the venue embodiments required. 
     The alternate anode assembly  23  addresses the shortcoming by effectively increasing the anode&#39;s reactive surface by the use of a metallic foam material  24 . Such metallic foam materials  24  are referred to as a class of materials that are characterized by a structural nature that is not completely monolithic and having a somewhat random structure of increased surface area within the same dimensional parameters. Such metallic foam materials  24  can be taken from a group defining, but not limited to the following, “cellular metal” divided into distinct cells with interconnecting voids, “porous metal” containing multiple pores and curved gas voids with smooth surfaces, “metallic foam” in which a solid foam is derived from a liquid foam and also a synthetic plastic foam with corresponding open pore structures, all well known. 
     Additionally, the group may include “metal sponge” wherein space is filled by pieces of metal that form a continuous network which co-exist with a network of empty space which is also inter-reactive and such mesh configuration that would so enable same. 
     It will be evident to one skilled in the art that such characterized “metallic foam” materials  24  including “mesh” configurations have increased surface dimensionality over a solid prescribed anode, such as zinc sheet  15  which is limited to its surface dimension illustrated hereinbefore. 
     By the use of such metallic foam materials  24  in an alternate anode construction assembly  23  in which metallic foam sheets  25  with an electrically conductive band  26  secured to by known attachment methods AM. The metallic foam sheets  25  are coated with a modified electrolyte paste  27  which is capable of a surface coating penetration so that all such foam induced voids are filled. This defines a stronger polarization with a total anode surface polarization efficiently increasing therefore the relative surface area of the anode assembly  23  to achieve and improve “equilibrium” of such dissimilar metals in a cathodic surface area induced reaction thereby affording greater and longer lasting protection of the protected material such as steel enforcing bars  23  illustrated in an alternate construction hereinbefore described and as seen in  FIG. 8  of the drawings. 
     The final assembly step of the preferred pre-assembled anode  17  hereinbefore described which is a key and critical aspect of the invention is an auto-moistening electrolyte paste coating  18  of the invention which is applied to the opposing exposed zinc surfaces  15 B and  16 A after the anode  14  is pre-assembled as hereinbefore described. The electrolyte paste coating  18  is of a flexible compound requiring no additional humectants or deliquescent to be added to keep the zinc active as is required in traditional galvanic protection process. The electrolyte paste coating  18  provides a number of important properties to assure adherence and flexibility between the anode  14  and surrounding concrete C in which it is embedded. The electrolyte paste  18  is comprised of by weight an ion conductive water based acrylic binder in the range of 10-400 parts, preferably 100 parts for a total of 25% by weight. 
     A hydrochloric acid in 10% solution in a range of 5-60 parts preferably 60 parts or 15% by weight. 
     An inert filler material, in this example, mica in the range of 50-400 parts or 50% by weight. 
     An alcohol based water binder, in this example, polyol in the range of 0-100 parts preferably 40 parts or 10% by weight. 
     It will be evident that components of the electrolyte paste  18  such as the acrylic binder and inert filler mica can be one selected from a corresponding family of like materials having similar properties and can be easily substituted within the perview of one skilled within the art and such composition as defined by this example are therefore not limited thereto. 
     Given this composition, the electrolyte paste coating  18  is thus lightly acidic with a PH in the range of 4.5 to 6 therefore not neutralized by the alkaline cement and provides higher current densities and is more durable than the prior art alkaline coatings having a typical PH of 12 or above which was previously thought to be required and helped to maintain the zinc in an active state. 
     Such acidic environment maintained by the paste  18 , the coated zinc anode remains active and remains as a zinc-ion Zn 2 . Thus when even small amounts of chlorides are present, a preferential reaction will occur between the zinc and the chloride into ZnCL 2 . Zinc chlorides are found to be highly soluble and hygroscopic and therefore will not form any insoluble passive layer on the zinc thus effectively auto moistening, assuring that no additional humectants or deliquescent as needed to keep the zinc active. The electrolyte paste  18  formulation used with the anode assembly  17  of the invention will be of superior performance binding sufficient water for proper conductivity with no chemical interaction between the paste  18  and concrete alkaline pore water solution. 
     Referring now to  FIGS. 1 and 4  of the drawings, an anode attachment tie  20  can be seen for securing the anode electrical interconnection bands  13  to the reinforcing bar  12  before embedding into the concrete C of the so defined structure  11  as hereinbefore described. The anode attachment tie  20  preferably formed from a flexible steel band body  21  having an adjustable lock to length pass through one-way ratchet fastener fitting  22  on one end thereof. The band body  21  defines a ladder tie configuration with engageable surface openings at  20 A therein which allows for adjustable registration within the fastener fitting  22 , locking the effective tie band engagement length about the reinforcement bar  12  mechanically and electrically joining the interconnecting bands  13 A and  13 B thereto illustrated by adjustment arrows A in broken lines in  FIG. 4  of the drawings and fasteners F in solid lines in  FIG. 1  of the drawings. 
     It will thus be seen that a new and novel galvanic cathodic protection system utilizing a zinc anode assembly coated with a unique auto moistening electrolyte paste having an effective low PH range has been illustrated and described and it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.