CA2289887A1 - Improvement in cathodic protection system - Google Patents
Improvement in cathodic protection system Download PDFInfo
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- CA2289887A1 CA2289887A1 CA 2289887 CA2289887A CA2289887A1 CA 2289887 A1 CA2289887 A1 CA 2289887A1 CA 2289887 CA2289887 CA 2289887 CA 2289887 A CA2289887 A CA 2289887A CA 2289887 A1 CA2289887 A1 CA 2289887A1
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Abstract
The present invention relates to a method of cathodic protection of reinforced concrete, and more particularly, to a method of maintaining or improving current delivery from an anode used in a cathodic protection system.
The method of the present invention comprises applying a conductive paint onto an exposed surface of the concrete in an amount effective to form a conductive paint anode bonded to the surface. The anode and concrete have an interface.
The conductive paint anode is permeable. The conductive paint anode is electrically connected to the reinforcement through a source of impressed current.
A lithium salt solution selected from the group consisting of a lithium nitrate (LiNO3) solution, a lithium bromide (LIBr) solution, and combinations thereof, is applied to the external surface of the anode after the conductive paint anode has been applied to the concrete. The lithium salt solution quickly and effectively migrates through the pores of the permeable anode to the interface between the anode and the concrete. The lithium salt at the interface functions to provide improved current delivery.
The lithium salt solution preferably comprises a surface active agent which wets the exposed surface of the conductive paint anode and facilitates migration of the solution through the anode to the interface of the anode with the concrete.
The method of the present invention comprises applying a conductive paint onto an exposed surface of the concrete in an amount effective to form a conductive paint anode bonded to the surface. The anode and concrete have an interface.
The conductive paint anode is permeable. The conductive paint anode is electrically connected to the reinforcement through a source of impressed current.
A lithium salt solution selected from the group consisting of a lithium nitrate (LiNO3) solution, a lithium bromide (LIBr) solution, and combinations thereof, is applied to the external surface of the anode after the conductive paint anode has been applied to the concrete. The lithium salt solution quickly and effectively migrates through the pores of the permeable anode to the interface between the anode and the concrete. The lithium salt at the interface functions to provide improved current delivery.
The lithium salt solution preferably comprises a surface active agent which wets the exposed surface of the conductive paint anode and facilitates migration of the solution through the anode to the interface of the anode with the concrete.
Description
PATENT
IMPROVEMENT IN CATHODIC PROTECTION SYSTEM
Back round of the Invention Technical Pield This invention elates generally to the field of cathodic protection systems for steel-reinforced concrete structures, and is particularly concerned with the performance of cathodic protection systems utilizing conductive paint anodes.
Description of the Prior Art The problems associated with corrosion-induced deterioration of reinforced concrete structures are now well understood. Steel reinforcement has generally performed well over the years in concrete structures such as bridges, buildings, parking structures, piers, and wharves, since the alkaline environment of concrete causes the surface of the steel to "passivate" such that it does not corrode.
Unfortunately, since concrete is inherently somewhat porous, exposure to salt results in the concrete over a number of years becoming contaminated with chloride ions.
_2_ Salt is commonly introduced to the concrete in the form of seawater, set accelerators or deicing salt.
When the chloride contamination reaches the level of the reinforcing steel, it destroys the ability of the concrete to keep the steel in a passive, or non-corrosive state. It has been determined that a chloride concentration of 0.6 Kg per cubic meter of concrete is a critical value above which corrosion of steel can occur. The products of corrosion of the steel occupy 2.5 to 4 times the volume of the original steel, and this expansion exerts a tremendous tensile force on the surrounding concrete. When this tensile force exceeds the tensile strength of the concrete, cracking and delaminations develop. With continued corrosion, freezing and thawing, and traffic pounding, the utility or the integrity of the structure is finally compromised and repair or replacement becomes necessary. Reinforced concrete structures continue to deteriorate at an alarming rate today. In a recent report to Congress, the Federal Highway Administration reported that of the nation's 577,000 bridges, 226,000 (39% of the total) were classified as deficient, and that 134,000 (23% of the total) were classified as structurally deficient. Structurally deficient bridges are those that are closed, restricted to light vehicles only, or that require immediate rehabilitation to remain open. The damage on most of these bridges is caused by corrosion of reinforcing steel. The United States Department of Transportation has estimated that $90.9 billion will be needed to replace or repair the damage on these existing bridges.
Many solutions to this problem have been proposed, including higher quality concrete, improved construction practices, increased concrete cover over the reinforcing steel, specialty concretes, corrosion inhibiting admixtures, surface sealers, and electrochemical techniques such as cathodic protection and chloride removal. Of these techniques, only 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 types of anodes have evolved for specific circumstances and different types of structures.
One type of anode that has been used since the late 1970s on concrete surfaces not subject to traffic is conductive paints and mastics. These anodes typically consisted of carbon dispersed in solvent or water based paints, and typically covered the entire surface of the concrete to be protected. The anodes were applied by spray, brush, or roller coating the paint onto the concrete surface after surface preparation, which typically consisted of light sandblasting or medium to high pressure water blasting. The black-colored paint was then typically overcoated with a lighter colored topcoat to improve appearance. The paint was typically applied to a thickness of 0.20 to 0.25 mm (8 to 10 mils) dry film thickness.
Current was supplied to the paint by primary anode conductors, typically 0.8 mm (0.031 inch) diameter platinized wire or catalyzed ribbon. Since the conductive paint had limited electrical conductivity, primary anode conductors were placed relatively close together, typically 3 meters (10 feet), to avoid excessive voltage loss and uneven current distribution.
Cathodic protection systems utilizing conductive paint anodes were often successful, but problems were also commonly encountered. Excessive anode current density resulted in bond loss and deterioration of conductive paint anodes, sometimes in a year or less. Failures of conductive paint anodes were also recorded in wet, freeze-thaw and splash-zone environments. The durability of conductive paints in such environments has improved somewhat with the development of improved, longer lasting materials.
Conductive paint anodes have also experienced difficulty when they were placed on the underside of surfaces that were not chloride contaminated and not subject to direct wetting. This problem was especially common in very dry climates, such as the western United States and Canada. In these cases, it appeared that the thin layer of concrete immediately beneath the concrete dried out and became very resistive. In some cases, the resistance increased greatly and the desired protective current could not be delivered even at rectifier voltages of 50 volts.
Summary of the Invention The present invention relates to a method of cathodic protection of reinforced concrete, and more particularly, to a method of maintaining or improving current delivery from an anode used in a cathodic protection system.
The method of the present invention comprises applying a conductive paint onto an exposed surface of the concrete in an amount effective to form a conductive paint anode bonded to the surface. The anode and concrete have an interface. The conductive paint anode is permeable. The conductive paint anode is electrically connected to the reinforcement through a source of impressed current.
A lithium salt solution selected from the group consisting of a lithium nitrate (LiN03) solution, a lithium bromide (Liar) solution, and combinations thereof, is applied to the external surface of the anode after the conductive paint anode has been applied to the concrete.
The lithium salt solution quickly and effectively migrates through the pores of the permeable anode to the interface between the anode and the concrete. The lithium salt at the interface functions to provide improved current delivery.
The lithium salt solution preferably comprises a surface active agent which wets the exposed surface of the conductive paint anode and facilitates migration of the solution through the anode to the interface of the anode with the concrete.
Preferably, enough lithium salt solution is applied to the external surface of the conductive paint anode to position at the interface of the anode and the concrete structure at least 10 grams of lithium salt, dry basis, per square meter of anode.
Preferably, the conductive paint anode has a thickness which is less than about 20 mils (0.5 mm).
The present invention also resides in a liquid treating agent applied to an impressed current permeable _7_ conductive paint anode to provide improved current delivery, and in a reinforced concrete structure prepared by the method of the present invention.
Description of Preferred Embodiments The present invention relates broadly to all reinforced concrete structures with which cathodic protection systems are useful.
Generally, the reinforcing metal in a reinforced structure is steel. However, other ferrous based metals can also be used.
The cathodic protection system of the present invention comprises at least one conductive paint anode at a surface of the concrete structure. Multiple conductive paint anodes at spaced intervals are commonly used.
The cathodic protection system is of the impressed current type. In an impressed current system, a power supply is positioned in the connection between the anode and the concrete reinforcement. The power supply provides an impressed flow of electrical current between the anode and the reinforcement. The impressed current flow is opposite and essentially equal to that which naturally occurs in a reinforced structure which has no cathodic protection, thus "passivating" the reinforcement.
The net result is very little or no anodic action on the _$_ reinforcement, and little or no corrosion of the reinforcement occurs.
Conductive paints comprise an organic polymeric binder, which can be either water-based or solvent-based, and electrically conductive particles dispersed in the binder.
Binders commonly used are acrylic copolymers or homopolymers. A preferred electrically conductive particle to make the paint conductive is carbon or graphite. These materials have a relatively low density which aids in their dispersion in a polymeric binder. Conductive paints are typically 50-80% carbon or graphite by weight of dry film.
Examples of suitable conductive paint formulations useful for cathodic protection of reinforced concrete are disclosed in Patents Nos. 4,931,156 to Dowd et al., 5,364,511 to Moreland et al, and 5,431,795 to Moreland et al., incorporated by reference herein.
The conductive paint may be applied to the surface of the concrete by spray, brush, or roller coat. Other means of application of the paint will be apparent to those skilled in the art. Once applied to the concrete surface, the conductive paint anode forms an interface with the concrete. When properly applied and cured, a good bond results between the anode and the concrete at the anode-concrete interface. Preferably, the conductive paint is applied so that it has an average thickness when dried of less than about 20 mils and more than about eight (8) mils.
_g_ In addition, the conductive paint anode is permeable to permit the passage of both gasses, such as oxygen and chlorine from the electrolysis of water and sodium chloride, respectively, and moisture to and from the concrete structure. Without some permeability, the conductive paint would not adhere to the concrete. These criteria are disclosed, by way of example, in the aforementioned Patent No. 5,364,511. For the present invention, the conductive paint anode preferably is sufficiently permeable to allow the passage of at least 25m1 of solution per square meter of anode surface in a single application, or the placement of at least 10 grams, dry basis, of lithium salt (to be described) at the interface of the anode and concrete surface. Preferably, the anode will be sufficiently permeable to allow the passage of 100m1 of solution per square meter of anode surface in a singe application.
Customarily, the permeability of a conductive paint on a concrete surface is achieved by controlling the pigment-volume ratio in the paint, referred to as the PVC value.
This is the ratio of the volume of pigment in a unit volume of a dried paint film. At a loading of 50-80% carbon, the paint film is binder-starved, and the dried film is porous.
This technology is disclosed, by way of example, in Patent No. 4,716,188, incorporated by reference herein. A high ratio of carbon or graphite to polymer also enhances the conductivity of the dried film.
A lithium salt solution selected from the group consisting of lithium nitrate (LiN03) solution, lithium bromide (Liar) solution, and combinations thereof, is applied to the exposed surface of the dried or cured conductive paint anode. The application can be immediately after drying or curing of the conductive paint anode or much time after, for instance months or years.
For purposes of the present application, the term ~~solution" includes dispersions and suspensions. A
preferred liquid medium for the lithium salt is water. The pores within the dried or aired anode are typically small, but are of sufficient diameter to permit the passage of the solutions, dispersions or suspensions of a lithium salt to the anode-concrete interface, for instance by capillary attraction.
Alternatively, the lithium nitrate or lithium bromide may be dissolved in an organic solvent, such as alcohol, for application to the surface of the anode, followed by transport to or near the interface between the anode and the concrete by capillary action.
The lithium salt solutions can be applied by spraying, brushing, or roller coating. Other methods of application of the solutions will be apparent to those skilled in the art.
If the anode coating is thick (e.g., greater than about 20 mils dried), it may be advantageous to produce thin spots in the anode coating to facilitate penetration of the salt solution. This may be accomplished by drilling or abrading the anode coating in selected locations. It may also be accomplished by placing a template over the concrete substrate during the application of the anode. A
template in the form of a wire mesh with wires placed on four centimeter centerline spacing, for example, creates a pattern of thin areas in the anode through which the salt solution more easily penetrates. The thin areas of anode should be preferably less than about 20% of the total anode area.
The lithium salts of the present invention, once delivered to or near the interface, remain at or near the interface for a long period of time. The diffusion coefficients for such materials in concrete are small making further penetration of the lithium salts into the concrete more difficult.
If the lithium salts are, over a long period of time, eluded from the interface between the anode and the concrete, for instance by rainfall, then the salt solutions can be reapplied to the external surface of the anode to again deposit the lithium salts at or near the interface between the anode and the concrete. The lithium salt solutions can be reapplied as often as is necessary throughout the life of the cathodic protection system.
The principle advantage of the use of the lithium salts as taught by the present invention is that the current flow from an impressed current anode will be maintained or improved.
The term ~~improved" as used herein may be taken to mean that either (1) the flow of protective current may be increased without undue increase in system voltage, or (2) the same protective current may be passed with a significant reduction in system voltage.
It is theorized that the high operating voltage sometimes observed when using conductive paint anodes in dry environments is due, at least in part, to a dry and highly resistive layer of concrete immediately beneath the anode-concrete interface. The lithium salts in the present invention are humectants and absorb water from the atmosphere. Moisture is thus retained at or drawn into the interface by the lithium salt positioned at the interface.
The moisture functions as an electrolyte, which helps counteract the increase in electrical resistance at the interface. However, the benefit is greater than would be expected from the presence of moisture alone.
It is also theorized that the dry and resistive layer immediately beneath the anode-concrete interface impedes the diffusion of ions to and from this region. This, in turn, results in the harmful build-up of acid adjacent to the anode. Acid is generated at the anode interface as a by-product of the dominant anodic electrochemical reaction, namely oxygen evolution. As follows:
2Hz0 -~ OZ + 4H+ + 4e-The use of the lithium salts of the present invention, by increasing the moisture content at the anode-concrete interface, increases the rate of diffusion of acid and diminishes the buildup of acid in this region. This, in turn, results in better long-term maintenance of the bond between the conductive paint anode and the concrete.
Although not to be held to any theory, it is also believed that operation of the conductive paint anode at a lower anodic potential, as results from the use of lithium salts of the present invention, prolongs the effective life of the carbon component of the conductive paint. Carbon is slowly oxidized to carbon monoxide and carbon dioxide at the operating potentials of the conductive paint anode on concrete. Such oxidation will be more rapid at higher operating potential, and lower at lower operating potential.
Lower operating potentials, as result from practice of the present invention, will also discourage the generation of chlorine, which can be deleterious to the binders in the conductive paint.
The amount of lithium salt required at or near the interface between the anode and the concrete varies depending upon the type of reinforced concrete structure, its location, its degree of salt contamination from such sources as seawater and deicers, and other factors.
Broadly, the amount of lithium salt is that amount effective to maintain or improve the current flow at the anode-concrete interface, and is relatively large compared for instance, to the amount of contaminating salt which may be present in the concrete from seawater and deicers.
Preferably, the lithium salt is applied in a range from about grams per square meter of anode to about 400 grams per square meter of anode, dry basis. The preferred range of lithium salt is from about 40 to 200 grams per square meter. If too little lithium salt is applied, the amount of 10 lithium salt retained at or near the interface will be insufficient to maintain or improve the current flow from the anode or reduce the resistivity at the interface between the anode and concrete. If too much lithium salt is applied, this will result in an additional expense for no benefit.
The concentration of lithium salt in an aqueous solution for application to the surface of a conductive paint anode may range from about 20 to about 900 grams per liter. If a solution is too dilute, then a large number of coats is required to deposit the required amount of lithium salt at or near the interface between the anode and the concrete. The upper end of the range of concentration of lithium salt in the aqueous solution is limited by the solubility of the salt in water. When using an aqueous solution containing about 300 grams per liter of lithium salt, for concrete with a typical degree of dryness, about three coats of solution are required to deposit the preferred amount of salt. The application is best done using brief drying periods between coats.
It may be advantageous to add certain agents to the lithium salt solutions prior to applying the solutions to the exposed surface of an applied anode.
For instance, it may be advantageous to include a surface active agent in the lithium salt solution. The surface active agent wets the surface of the thermally applied anode and increases the rate of diffusion of the solution through the anode to the interface of the anode with the concrete.
A large number of surface active agents are commercially available. The surface active agent should be one which has good wettability characteristics and preferably is one which is soluble in water or other polar solvent. A preferred surface active agent is a cationic amine or ammonium compound. Surface active agents generally have a hydrophobic portion, usually including a long hydrocarbon chain, and a hydrophilic portion which renders the compound soluble in water or other polar solvent. In a cationic surface active agent, the hydrophilic portion of the molecule carries a positive charge which is responsible for the surface active properties. Examples of cationic surface active agents are amine acetates, alkyl trimethyl ammonium chlorides, dialkyl dimethyl ammonium chlorides, alkyl pyridinium chlorides and lauryl dimethyl benzyl ammonium chloride.
A cationic surface active agent that has been found to be particularly useful in the present invention includes the following combination of ingredients:
n-alkyl (50% C14, 40% C12, 10% C16) dimethyl benzyl 80 ppm ammonium chloride Octyl decyl dimethyl ammonium chloride 12.5 ppm Dioctyl dimethyl ammonium chloride 6.25 ppm Didecyl dimethyl ammonium chloride 6.25 ppm This cationic surface active agent is marketed by Lysol~ as their deodorizing cleanser. It was found to be effective when used in the amount of about 0.2 to about 2% by volume, preferably about 1% by volume, of humectant solution. The Lysol cleanser is disclosed in Patents Nos. 5,454,984 and 5,522,942. Another surface active agent found to be effective is 'SPRAY AND WASH"
marketed by Dow Brands, Indianapolis, Indiana.
Preferably the surface active agent (active part) should be present in the humectant solution in a concentration of at least 50 parts per million (ppm). The preferred range of concentration of the surface active agent should be from about 100 ppm to about 1000 ppm.
In the practice of the present invention, the surface active agent locates at the surface of the anode and provides compatibility of the anode with the humectant solution or dispersion applied to the anode.
It may also be advantageous to decrease the diffusion of the lithium nitrate and lithium bromide away from the anode-concrete interface. This may be done by application of the lithium nitrate or lithium bromide together with a jelling agent capable of thickening the solution following placement at the anode-concrete interface. This may be accomplished by application of a hot solution, which congeals upon cooling, or by using a material which can be cross-linked following placement. Such materials are well known .
It has been found that the lithium salts applied as taught by the present invention have an additional benefit.
If a cathodic protection system utilizing an inert anode such as conductive paint is selectively wetted on only a portion of its surface, then current density is greatly enhanced in those wetted areas. This may cause large currents to flow in those select areas causing a high wear rate of the anode in those locations. This uneven wear rate may eventually cause the system to fail prematurely. By the use of the lithium salts as taught by the present invention, a more even distribution of current resulting in more uniform protection of the reinforcing steel and in extended service life of the cathodic protection system is achieved.
EXAMPLE I
Four newly constructed 12 x 9 x 2 inch (30.3 x 22.9 x 5.1 centimeter) concrete blocks were cast containing a mild steel expanded mesh 0.1875 inch (0.475 centimeter) thick having diamond dimensions of 1.0 inch LWD x 0.5 inch SWD
(2.54 centimeter LWD x 1.27 centimeter SWD). The surface area of the steel mesh was about 1 square foot per square foot of top concrete surface. The mix proportions for the concrete specimens were as follows:
Type 1A Portland Cement - 715 Ib/yd3 (425 kg/m3) Lake Sand Fine Aggregate - 1010 Ib/yd3 (600 kg/m3) No. 8 Marblehead Limestone - 1830 Ib/yd3 (1090 kg/m3) Water - 285 Ib/yd3 (170 kg/m3) Air - about 6%
Sodium chloride was added to the mixture for two of the blocks to a concentration of 7.5 Ib/yd3 (0.195% by weight) of chloride ion. Sodium chloride was added to the mixture for the other two blocks to a concentration of 10 Ib/yd3 (0.260% by weight) of chloride ion.
Following a 24-hour mold-curing period, the blocks were wrapped in plastic to retain moisture for 28 days.
After the 28-day curing period, the blocks were lightly sandblasted to produce a rough, clean surface. The top surface of all four blocks was then brush coated with about 30 mils (750 microns) of Duodac 85 WB Conductive Coating marketed by Duochem Inc. The coating comprises a water-based acrylic copolymer and is about 40% by volume solids.
Duochem Inc is the assignee of Patent No. 4,931,156.
After curing, the conductive coating was about 12 mils (300 microns) dry film thickness. The active surface area of the Duodac 85 Conductive Coating was 0.677 ft2 (0.0629 mz) for each block. The paint was allowed to cure one week before energizing.
One of the blocks with 7.5 Ib/yd3 (0.195% by weight) of chloride, and one of the blocks with 10 Ib/yd3 (0.260%
by weight) of chloride were maintained as controls. The other block with 7.5 Ib/yd3 (0.195% by weight) of chloride was brush coated with 3 coats of 360 gram/liter lithium nitrate solution. The solution also contained 1% by volume Lysol~ deodorizing cleanser. A total of 22.8 milliliters were used resulting in a treatment of 8.21 grams, or 12.1 grams/ft2 (130 grams/m2) lithium nitrate. The other block with 10 Ib/yd3 (0.260 by weight) of chloride was brush coated with 3 coats of 360 gram/liter lithium nitrate solution. This solution also contained 1% by volume Lysol~ deodorizing cleanser. A total of 24.1 milliliters were used resulting in a treatment of 8.68 grams, or 12.8 grams/ft2 (137.7 grams/m2) dry basis lithium nitrate.
After drying for 3 days, each conductive paint anode was connected to the anode of a power supply and the steel was connected to the cathode of the power supply.
The blocks were then energized at a current density of 1.46 mA/ft2 (15.7 mA/mZ). The blocks with 7.5 Ib/yd3 (0.195%
by weight) of chloride were maintained at room temperature and 55% relative humidity (RH), while the blocks with 10 Ib/yd3 (0.260 by weight) of chloride were maintained at room temperature and 80% RH. Voltage for each of the blocks was recorded as follows:
Anode-Cathode Voltage 55% RH 80% RH
Time-on-line Control Treated Control Treated 1 hour ~ 2.73V 1.81V 1.89V 1.709V
1 days 3.79V 2.24V 2,16V 1.85V
2 days 4.46V 2.29V 2.17V 1.88V
IMPROVEMENT IN CATHODIC PROTECTION SYSTEM
Back round of the Invention Technical Pield This invention elates generally to the field of cathodic protection systems for steel-reinforced concrete structures, and is particularly concerned with the performance of cathodic protection systems utilizing conductive paint anodes.
Description of the Prior Art The problems associated with corrosion-induced deterioration of reinforced concrete structures are now well understood. Steel reinforcement has generally performed well over the years in concrete structures such as bridges, buildings, parking structures, piers, and wharves, since the alkaline environment of concrete causes the surface of the steel to "passivate" such that it does not corrode.
Unfortunately, since concrete is inherently somewhat porous, exposure to salt results in the concrete over a number of years becoming contaminated with chloride ions.
_2_ Salt is commonly introduced to the concrete in the form of seawater, set accelerators or deicing salt.
When the chloride contamination reaches the level of the reinforcing steel, it destroys the ability of the concrete to keep the steel in a passive, or non-corrosive state. It has been determined that a chloride concentration of 0.6 Kg per cubic meter of concrete is a critical value above which corrosion of steel can occur. The products of corrosion of the steel occupy 2.5 to 4 times the volume of the original steel, and this expansion exerts a tremendous tensile force on the surrounding concrete. When this tensile force exceeds the tensile strength of the concrete, cracking and delaminations develop. With continued corrosion, freezing and thawing, and traffic pounding, the utility or the integrity of the structure is finally compromised and repair or replacement becomes necessary. Reinforced concrete structures continue to deteriorate at an alarming rate today. In a recent report to Congress, the Federal Highway Administration reported that of the nation's 577,000 bridges, 226,000 (39% of the total) were classified as deficient, and that 134,000 (23% of the total) were classified as structurally deficient. Structurally deficient bridges are those that are closed, restricted to light vehicles only, or that require immediate rehabilitation to remain open. The damage on most of these bridges is caused by corrosion of reinforcing steel. The United States Department of Transportation has estimated that $90.9 billion will be needed to replace or repair the damage on these existing bridges.
Many solutions to this problem have been proposed, including higher quality concrete, improved construction practices, increased concrete cover over the reinforcing steel, specialty concretes, corrosion inhibiting admixtures, surface sealers, and electrochemical techniques such as cathodic protection and chloride removal. Of these techniques, only 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 types of anodes have evolved for specific circumstances and different types of structures.
One type of anode that has been used since the late 1970s on concrete surfaces not subject to traffic is conductive paints and mastics. These anodes typically consisted of carbon dispersed in solvent or water based paints, and typically covered the entire surface of the concrete to be protected. The anodes were applied by spray, brush, or roller coating the paint onto the concrete surface after surface preparation, which typically consisted of light sandblasting or medium to high pressure water blasting. The black-colored paint was then typically overcoated with a lighter colored topcoat to improve appearance. The paint was typically applied to a thickness of 0.20 to 0.25 mm (8 to 10 mils) dry film thickness.
Current was supplied to the paint by primary anode conductors, typically 0.8 mm (0.031 inch) diameter platinized wire or catalyzed ribbon. Since the conductive paint had limited electrical conductivity, primary anode conductors were placed relatively close together, typically 3 meters (10 feet), to avoid excessive voltage loss and uneven current distribution.
Cathodic protection systems utilizing conductive paint anodes were often successful, but problems were also commonly encountered. Excessive anode current density resulted in bond loss and deterioration of conductive paint anodes, sometimes in a year or less. Failures of conductive paint anodes were also recorded in wet, freeze-thaw and splash-zone environments. The durability of conductive paints in such environments has improved somewhat with the development of improved, longer lasting materials.
Conductive paint anodes have also experienced difficulty when they were placed on the underside of surfaces that were not chloride contaminated and not subject to direct wetting. This problem was especially common in very dry climates, such as the western United States and Canada. In these cases, it appeared that the thin layer of concrete immediately beneath the concrete dried out and became very resistive. In some cases, the resistance increased greatly and the desired protective current could not be delivered even at rectifier voltages of 50 volts.
Summary of the Invention The present invention relates to a method of cathodic protection of reinforced concrete, and more particularly, to a method of maintaining or improving current delivery from an anode used in a cathodic protection system.
The method of the present invention comprises applying a conductive paint onto an exposed surface of the concrete in an amount effective to form a conductive paint anode bonded to the surface. The anode and concrete have an interface. The conductive paint anode is permeable. The conductive paint anode is electrically connected to the reinforcement through a source of impressed current.
A lithium salt solution selected from the group consisting of a lithium nitrate (LiN03) solution, a lithium bromide (Liar) solution, and combinations thereof, is applied to the external surface of the anode after the conductive paint anode has been applied to the concrete.
The lithium salt solution quickly and effectively migrates through the pores of the permeable anode to the interface between the anode and the concrete. The lithium salt at the interface functions to provide improved current delivery.
The lithium salt solution preferably comprises a surface active agent which wets the exposed surface of the conductive paint anode and facilitates migration of the solution through the anode to the interface of the anode with the concrete.
Preferably, enough lithium salt solution is applied to the external surface of the conductive paint anode to position at the interface of the anode and the concrete structure at least 10 grams of lithium salt, dry basis, per square meter of anode.
Preferably, the conductive paint anode has a thickness which is less than about 20 mils (0.5 mm).
The present invention also resides in a liquid treating agent applied to an impressed current permeable _7_ conductive paint anode to provide improved current delivery, and in a reinforced concrete structure prepared by the method of the present invention.
Description of Preferred Embodiments The present invention relates broadly to all reinforced concrete structures with which cathodic protection systems are useful.
Generally, the reinforcing metal in a reinforced structure is steel. However, other ferrous based metals can also be used.
The cathodic protection system of the present invention comprises at least one conductive paint anode at a surface of the concrete structure. Multiple conductive paint anodes at spaced intervals are commonly used.
The cathodic protection system is of the impressed current type. In an impressed current system, a power supply is positioned in the connection between the anode and the concrete reinforcement. The power supply provides an impressed flow of electrical current between the anode and the reinforcement. The impressed current flow is opposite and essentially equal to that which naturally occurs in a reinforced structure which has no cathodic protection, thus "passivating" the reinforcement.
The net result is very little or no anodic action on the _$_ reinforcement, and little or no corrosion of the reinforcement occurs.
Conductive paints comprise an organic polymeric binder, which can be either water-based or solvent-based, and electrically conductive particles dispersed in the binder.
Binders commonly used are acrylic copolymers or homopolymers. A preferred electrically conductive particle to make the paint conductive is carbon or graphite. These materials have a relatively low density which aids in their dispersion in a polymeric binder. Conductive paints are typically 50-80% carbon or graphite by weight of dry film.
Examples of suitable conductive paint formulations useful for cathodic protection of reinforced concrete are disclosed in Patents Nos. 4,931,156 to Dowd et al., 5,364,511 to Moreland et al, and 5,431,795 to Moreland et al., incorporated by reference herein.
The conductive paint may be applied to the surface of the concrete by spray, brush, or roller coat. Other means of application of the paint will be apparent to those skilled in the art. Once applied to the concrete surface, the conductive paint anode forms an interface with the concrete. When properly applied and cured, a good bond results between the anode and the concrete at the anode-concrete interface. Preferably, the conductive paint is applied so that it has an average thickness when dried of less than about 20 mils and more than about eight (8) mils.
_g_ In addition, the conductive paint anode is permeable to permit the passage of both gasses, such as oxygen and chlorine from the electrolysis of water and sodium chloride, respectively, and moisture to and from the concrete structure. Without some permeability, the conductive paint would not adhere to the concrete. These criteria are disclosed, by way of example, in the aforementioned Patent No. 5,364,511. For the present invention, the conductive paint anode preferably is sufficiently permeable to allow the passage of at least 25m1 of solution per square meter of anode surface in a single application, or the placement of at least 10 grams, dry basis, of lithium salt (to be described) at the interface of the anode and concrete surface. Preferably, the anode will be sufficiently permeable to allow the passage of 100m1 of solution per square meter of anode surface in a singe application.
Customarily, the permeability of a conductive paint on a concrete surface is achieved by controlling the pigment-volume ratio in the paint, referred to as the PVC value.
This is the ratio of the volume of pigment in a unit volume of a dried paint film. At a loading of 50-80% carbon, the paint film is binder-starved, and the dried film is porous.
This technology is disclosed, by way of example, in Patent No. 4,716,188, incorporated by reference herein. A high ratio of carbon or graphite to polymer also enhances the conductivity of the dried film.
A lithium salt solution selected from the group consisting of lithium nitrate (LiN03) solution, lithium bromide (Liar) solution, and combinations thereof, is applied to the exposed surface of the dried or cured conductive paint anode. The application can be immediately after drying or curing of the conductive paint anode or much time after, for instance months or years.
For purposes of the present application, the term ~~solution" includes dispersions and suspensions. A
preferred liquid medium for the lithium salt is water. The pores within the dried or aired anode are typically small, but are of sufficient diameter to permit the passage of the solutions, dispersions or suspensions of a lithium salt to the anode-concrete interface, for instance by capillary attraction.
Alternatively, the lithium nitrate or lithium bromide may be dissolved in an organic solvent, such as alcohol, for application to the surface of the anode, followed by transport to or near the interface between the anode and the concrete by capillary action.
The lithium salt solutions can be applied by spraying, brushing, or roller coating. Other methods of application of the solutions will be apparent to those skilled in the art.
If the anode coating is thick (e.g., greater than about 20 mils dried), it may be advantageous to produce thin spots in the anode coating to facilitate penetration of the salt solution. This may be accomplished by drilling or abrading the anode coating in selected locations. It may also be accomplished by placing a template over the concrete substrate during the application of the anode. A
template in the form of a wire mesh with wires placed on four centimeter centerline spacing, for example, creates a pattern of thin areas in the anode through which the salt solution more easily penetrates. The thin areas of anode should be preferably less than about 20% of the total anode area.
The lithium salts of the present invention, once delivered to or near the interface, remain at or near the interface for a long period of time. The diffusion coefficients for such materials in concrete are small making further penetration of the lithium salts into the concrete more difficult.
If the lithium salts are, over a long period of time, eluded from the interface between the anode and the concrete, for instance by rainfall, then the salt solutions can be reapplied to the external surface of the anode to again deposit the lithium salts at or near the interface between the anode and the concrete. The lithium salt solutions can be reapplied as often as is necessary throughout the life of the cathodic protection system.
The principle advantage of the use of the lithium salts as taught by the present invention is that the current flow from an impressed current anode will be maintained or improved.
The term ~~improved" as used herein may be taken to mean that either (1) the flow of protective current may be increased without undue increase in system voltage, or (2) the same protective current may be passed with a significant reduction in system voltage.
It is theorized that the high operating voltage sometimes observed when using conductive paint anodes in dry environments is due, at least in part, to a dry and highly resistive layer of concrete immediately beneath the anode-concrete interface. The lithium salts in the present invention are humectants and absorb water from the atmosphere. Moisture is thus retained at or drawn into the interface by the lithium salt positioned at the interface.
The moisture functions as an electrolyte, which helps counteract the increase in electrical resistance at the interface. However, the benefit is greater than would be expected from the presence of moisture alone.
It is also theorized that the dry and resistive layer immediately beneath the anode-concrete interface impedes the diffusion of ions to and from this region. This, in turn, results in the harmful build-up of acid adjacent to the anode. Acid is generated at the anode interface as a by-product of the dominant anodic electrochemical reaction, namely oxygen evolution. As follows:
2Hz0 -~ OZ + 4H+ + 4e-The use of the lithium salts of the present invention, by increasing the moisture content at the anode-concrete interface, increases the rate of diffusion of acid and diminishes the buildup of acid in this region. This, in turn, results in better long-term maintenance of the bond between the conductive paint anode and the concrete.
Although not to be held to any theory, it is also believed that operation of the conductive paint anode at a lower anodic potential, as results from the use of lithium salts of the present invention, prolongs the effective life of the carbon component of the conductive paint. Carbon is slowly oxidized to carbon monoxide and carbon dioxide at the operating potentials of the conductive paint anode on concrete. Such oxidation will be more rapid at higher operating potential, and lower at lower operating potential.
Lower operating potentials, as result from practice of the present invention, will also discourage the generation of chlorine, which can be deleterious to the binders in the conductive paint.
The amount of lithium salt required at or near the interface between the anode and the concrete varies depending upon the type of reinforced concrete structure, its location, its degree of salt contamination from such sources as seawater and deicers, and other factors.
Broadly, the amount of lithium salt is that amount effective to maintain or improve the current flow at the anode-concrete interface, and is relatively large compared for instance, to the amount of contaminating salt which may be present in the concrete from seawater and deicers.
Preferably, the lithium salt is applied in a range from about grams per square meter of anode to about 400 grams per square meter of anode, dry basis. The preferred range of lithium salt is from about 40 to 200 grams per square meter. If too little lithium salt is applied, the amount of 10 lithium salt retained at or near the interface will be insufficient to maintain or improve the current flow from the anode or reduce the resistivity at the interface between the anode and concrete. If too much lithium salt is applied, this will result in an additional expense for no benefit.
The concentration of lithium salt in an aqueous solution for application to the surface of a conductive paint anode may range from about 20 to about 900 grams per liter. If a solution is too dilute, then a large number of coats is required to deposit the required amount of lithium salt at or near the interface between the anode and the concrete. The upper end of the range of concentration of lithium salt in the aqueous solution is limited by the solubility of the salt in water. When using an aqueous solution containing about 300 grams per liter of lithium salt, for concrete with a typical degree of dryness, about three coats of solution are required to deposit the preferred amount of salt. The application is best done using brief drying periods between coats.
It may be advantageous to add certain agents to the lithium salt solutions prior to applying the solutions to the exposed surface of an applied anode.
For instance, it may be advantageous to include a surface active agent in the lithium salt solution. The surface active agent wets the surface of the thermally applied anode and increases the rate of diffusion of the solution through the anode to the interface of the anode with the concrete.
A large number of surface active agents are commercially available. The surface active agent should be one which has good wettability characteristics and preferably is one which is soluble in water or other polar solvent. A preferred surface active agent is a cationic amine or ammonium compound. Surface active agents generally have a hydrophobic portion, usually including a long hydrocarbon chain, and a hydrophilic portion which renders the compound soluble in water or other polar solvent. In a cationic surface active agent, the hydrophilic portion of the molecule carries a positive charge which is responsible for the surface active properties. Examples of cationic surface active agents are amine acetates, alkyl trimethyl ammonium chlorides, dialkyl dimethyl ammonium chlorides, alkyl pyridinium chlorides and lauryl dimethyl benzyl ammonium chloride.
A cationic surface active agent that has been found to be particularly useful in the present invention includes the following combination of ingredients:
n-alkyl (50% C14, 40% C12, 10% C16) dimethyl benzyl 80 ppm ammonium chloride Octyl decyl dimethyl ammonium chloride 12.5 ppm Dioctyl dimethyl ammonium chloride 6.25 ppm Didecyl dimethyl ammonium chloride 6.25 ppm This cationic surface active agent is marketed by Lysol~ as their deodorizing cleanser. It was found to be effective when used in the amount of about 0.2 to about 2% by volume, preferably about 1% by volume, of humectant solution. The Lysol cleanser is disclosed in Patents Nos. 5,454,984 and 5,522,942. Another surface active agent found to be effective is 'SPRAY AND WASH"
marketed by Dow Brands, Indianapolis, Indiana.
Preferably the surface active agent (active part) should be present in the humectant solution in a concentration of at least 50 parts per million (ppm). The preferred range of concentration of the surface active agent should be from about 100 ppm to about 1000 ppm.
In the practice of the present invention, the surface active agent locates at the surface of the anode and provides compatibility of the anode with the humectant solution or dispersion applied to the anode.
It may also be advantageous to decrease the diffusion of the lithium nitrate and lithium bromide away from the anode-concrete interface. This may be done by application of the lithium nitrate or lithium bromide together with a jelling agent capable of thickening the solution following placement at the anode-concrete interface. This may be accomplished by application of a hot solution, which congeals upon cooling, or by using a material which can be cross-linked following placement. Such materials are well known .
It has been found that the lithium salts applied as taught by the present invention have an additional benefit.
If a cathodic protection system utilizing an inert anode such as conductive paint is selectively wetted on only a portion of its surface, then current density is greatly enhanced in those wetted areas. This may cause large currents to flow in those select areas causing a high wear rate of the anode in those locations. This uneven wear rate may eventually cause the system to fail prematurely. By the use of the lithium salts as taught by the present invention, a more even distribution of current resulting in more uniform protection of the reinforcing steel and in extended service life of the cathodic protection system is achieved.
EXAMPLE I
Four newly constructed 12 x 9 x 2 inch (30.3 x 22.9 x 5.1 centimeter) concrete blocks were cast containing a mild steel expanded mesh 0.1875 inch (0.475 centimeter) thick having diamond dimensions of 1.0 inch LWD x 0.5 inch SWD
(2.54 centimeter LWD x 1.27 centimeter SWD). The surface area of the steel mesh was about 1 square foot per square foot of top concrete surface. The mix proportions for the concrete specimens were as follows:
Type 1A Portland Cement - 715 Ib/yd3 (425 kg/m3) Lake Sand Fine Aggregate - 1010 Ib/yd3 (600 kg/m3) No. 8 Marblehead Limestone - 1830 Ib/yd3 (1090 kg/m3) Water - 285 Ib/yd3 (170 kg/m3) Air - about 6%
Sodium chloride was added to the mixture for two of the blocks to a concentration of 7.5 Ib/yd3 (0.195% by weight) of chloride ion. Sodium chloride was added to the mixture for the other two blocks to a concentration of 10 Ib/yd3 (0.260% by weight) of chloride ion.
Following a 24-hour mold-curing period, the blocks were wrapped in plastic to retain moisture for 28 days.
After the 28-day curing period, the blocks were lightly sandblasted to produce a rough, clean surface. The top surface of all four blocks was then brush coated with about 30 mils (750 microns) of Duodac 85 WB Conductive Coating marketed by Duochem Inc. The coating comprises a water-based acrylic copolymer and is about 40% by volume solids.
Duochem Inc is the assignee of Patent No. 4,931,156.
After curing, the conductive coating was about 12 mils (300 microns) dry film thickness. The active surface area of the Duodac 85 Conductive Coating was 0.677 ft2 (0.0629 mz) for each block. The paint was allowed to cure one week before energizing.
One of the blocks with 7.5 Ib/yd3 (0.195% by weight) of chloride, and one of the blocks with 10 Ib/yd3 (0.260%
by weight) of chloride were maintained as controls. The other block with 7.5 Ib/yd3 (0.195% by weight) of chloride was brush coated with 3 coats of 360 gram/liter lithium nitrate solution. The solution also contained 1% by volume Lysol~ deodorizing cleanser. A total of 22.8 milliliters were used resulting in a treatment of 8.21 grams, or 12.1 grams/ft2 (130 grams/m2) lithium nitrate. The other block with 10 Ib/yd3 (0.260 by weight) of chloride was brush coated with 3 coats of 360 gram/liter lithium nitrate solution. This solution also contained 1% by volume Lysol~ deodorizing cleanser. A total of 24.1 milliliters were used resulting in a treatment of 8.68 grams, or 12.8 grams/ft2 (137.7 grams/m2) dry basis lithium nitrate.
After drying for 3 days, each conductive paint anode was connected to the anode of a power supply and the steel was connected to the cathode of the power supply.
The blocks were then energized at a current density of 1.46 mA/ft2 (15.7 mA/mZ). The blocks with 7.5 Ib/yd3 (0.195%
by weight) of chloride were maintained at room temperature and 55% relative humidity (RH), while the blocks with 10 Ib/yd3 (0.260 by weight) of chloride were maintained at room temperature and 80% RH. Voltage for each of the blocks was recorded as follows:
Anode-Cathode Voltage 55% RH 80% RH
Time-on-line Control Treated Control Treated 1 hour ~ 2.73V 1.81V 1.89V 1.709V
1 days 3.79V 2.24V 2,16V 1.85V
2 days 4.46V 2.29V 2.17V 1.88V
3 days 4.46V 2.27V 2.24V 1.94V
days 5.49V 2.46V 2.11V 1.89V
17 days 6.86V 2.71V 2.04V 1.89V
24 days 9.01V 3.12V 2.01V 1.88V
In both environments, the voltage for the blocks 5 treated with lithium nitrate is seen to be much lower than the voltage for the untreated blocks. This lower voltage is expected to result in less stress to both the anode and the cement paste at the anode-concrete interface and a longer service life for the cathodic protection system.
10 From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.
days 5.49V 2.46V 2.11V 1.89V
17 days 6.86V 2.71V 2.04V 1.89V
24 days 9.01V 3.12V 2.01V 1.88V
In both environments, the voltage for the blocks 5 treated with lithium nitrate is seen to be much lower than the voltage for the untreated blocks. This lower voltage is expected to result in less stress to both the anode and the cement paste at the anode-concrete interface and a longer service life for the cathodic protection system.
10 From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.
Claims (20)
1. A method of cathodic protection of reinforced concrete having reinforcement comprising the steps of:
(a) applying a conductive paint onto an exposed surface of the reinforced concrete in an amount effective to form an impressed current conductive paint anode bonded to such surface, wherein said conductive paint anode is permeable and has an interface with said concrete surface;
(b) electrically connecting said anode to said reinforcement;
(c) applying onto the exposed surface of said conductive paint anode a lithium salt in liquid form, said lithium salt being selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
and (d) allowing said liquid lithium salt to migrate through the pores of said conductive paint anode to said anode and concrete interface, said salt at said interface providing improved current delivery from said anode at said interface.
(a) applying a conductive paint onto an exposed surface of the reinforced concrete in an amount effective to form an impressed current conductive paint anode bonded to such surface, wherein said conductive paint anode is permeable and has an interface with said concrete surface;
(b) electrically connecting said anode to said reinforcement;
(c) applying onto the exposed surface of said conductive paint anode a lithium salt in liquid form, said lithium salt being selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
and (d) allowing said liquid lithium salt to migrate through the pores of said conductive paint anode to said anode and concrete interface, said salt at said interface providing improved current delivery from said anode at said interface.
2. The method of claim 1 wherein said lithium salt in liquid form is an aqueous solution of said lithium salt.
3. The method of claim 2 wherein said solution comprises a surface active agent in an amount effective to wet the exposed surface of said conductive paint anode.
4. The method of claim 3 wherein said surface active agent is a cationic amine or ammonium compound.
5. The method of claim 4 wherein said conductive paint has a permeability effective to allow the passage of at least 25 milliliters of solution per square meter of anode
6. The method of claim 5 wherein said conductive paint anode has a permeability effective to allow the passage of at least 100 milliliters of solution per square meter of anode.
7. The method of claim 6 wherein said conductive paint anode has an average thickness less than 20 mils dried.
8. The method of claim 7 wherein the permeability of the paint anode is effective to position at or near the interface of the anode and concrete surface lithium salt in the amount of at least 10 grams, dry basis, per square meter of anode.
9. A liquid treating agent for application to an exposed surface of an impressed current permeable conductive paint anode which has been applied and is bonded to a reinforced concrete structure having reinforcement for cathodic protection of said structure wherein said anode is electrically connected to said reinforcement and has permeability, which liquid agent migrates through the pores of said anode to the interface between the anode and said structure, comprising:
a lithium salt selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
a liquid medium for said salt; and a surface active agent present in said liquid medium in an amount effective to wet the exposed surface of said porous conductive metal anode.
a lithium salt selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
a liquid medium for said salt; and a surface active agent present in said liquid medium in an amount effective to wet the exposed surface of said porous conductive metal anode.
10. The liquid treating agent of claim 9 wherein said liquid medium is water and said surface active agent is a cationic amine or ammonium compound.
11. The liquid treating agent of claim 10 having a lithium salt concentration of 20 to 900 grams per liter.
12. A reinforced concrete structure having reinforcement comprising:
(a) a surface;
(b) an improved current conductive paint anode at said surface, said anode comprising an exposed anode surface and being permeable, said anode being bonded to said concrete structure surface and having an interface with said concrete structure surface;
(c) an electrical connection through a source of impressed current between said anode and the reinforcement of said structure; and (d) a lithium salt selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof at or near said interface in an amount effective to improve the current delivery from said anode.
(a) a surface;
(b) an improved current conductive paint anode at said surface, said anode comprising an exposed anode surface and being permeable, said anode being bonded to said concrete structure surface and having an interface with said concrete structure surface;
(c) an electrical connection through a source of impressed current between said anode and the reinforcement of said structure; and (d) a lithium salt selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof at or near said interface in an amount effective to improve the current delivery from said anode.
13. The structure of claim 12 wherein said lithium salt is present at said interface in the amount of at least 10 grams, dry basis, per square meter of anode.
14. The structure of claim 13 prepared by the method comprising the steps of:
(a) applying a conductive paint onto an exposed surface of the reinforced concrete in an amount effective to form an impressed current conductive paint anode on such surface, wherein said conductive paint anode after application and drying is permeable, said conductive paint anode being bonded to the concrete surface and having an interface with the concrete surface;
(b) applying onto the exposed surface of said conductive paint anode a lithium salt in liquid form, said lithium salt being selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
and (c) allowing said liquid lithium salt to migrate through the pores of said conductive paint anode to said anode and concrete interface, said salt at said interface improving the current delivery from said anode at said interface.
(a) applying a conductive paint onto an exposed surface of the reinforced concrete in an amount effective to form an impressed current conductive paint anode on such surface, wherein said conductive paint anode after application and drying is permeable, said conductive paint anode being bonded to the concrete surface and having an interface with the concrete surface;
(b) applying onto the exposed surface of said conductive paint anode a lithium salt in liquid form, said lithium salt being selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
and (c) allowing said liquid lithium salt to migrate through the pores of said conductive paint anode to said anode and concrete interface, said salt at said interface improving the current delivery from said anode at said interface.
15. A method of cathodic protection of reinforced concrete having reinforcement and a conductive paint impressed current anode on an exposed surface of the reinforced concrete, wherein said conductive paint anode is electrically connected through a source of impressed current to said reinforcement, is permeable, is bonded to the concrete surface, and has an interface with the concrete surface, comprising the steps of:
(a) applying onto an exposed surface of said conductive paint anode a lithium salt in liquid form, said lithium salt being selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
(b) allowing said liquid lithium salt to migrate through the pores of said conductive paint anode to said anode and concrete interface, said salt at said interface improving the current delivery from said anode at said interface.
(a) applying onto an exposed surface of said conductive paint anode a lithium salt in liquid form, said lithium salt being selected from the group consisting of lithium bromide, lithium nitrate, and combinations thereof;
(b) allowing said liquid lithium salt to migrate through the pores of said conductive paint anode to said anode and concrete interface, said salt at said interface improving the current delivery from said anode at said interface.
16. The method of claim 15 wherein said aqueous solution comprises a surface active agent.
17. The method of claim 16 wherein said surface active agent is a cationic amine or ammonium compound.
18. The method of claim 17 wherein said lithium salt in liquid form is an aqueous solution of said lithium salt and said anode has a permeability effective for the passage of at least 25 milliliters of solution per square meter of anode.
19. The method of claim 18 wherein said anode has an average thickness less than about 20 mils.
20. The method of claim 19 wherein the permeability of the anode is effective to position at or near the interface of the anode and concrete surface lithium salt in the amount of at least 10 grams, dry basis, per square meter of anode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US42890099A | 1999-10-28 | 1999-10-28 | |
| US09/428,900 | 1999-10-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2289887A1 true CA2289887A1 (en) | 2001-04-28 |
Family
ID=23700879
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2289887 Abandoned CA2289887A1 (en) | 1999-10-28 | 1999-11-18 | Improvement in cathodic protection system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2289887A1 (en) |
-
1999
- 1999-11-18 CA CA 2289887 patent/CA2289887A1/en not_active Abandoned
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