U.S. patent application number 14/163080 was filed with the patent office on 2014-07-24 for anode assembly for cathodic protection.
This patent application is currently assigned to The Euclid Chemical Company. The applicant listed for this patent is The Euclid Chemical Company. Invention is credited to John E. Bennett.
Application Number | 20140202879 14/163080 |
Document ID | / |
Family ID | 51206880 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140202879 |
Kind Code |
A1 |
Bennett; John E. |
July 24, 2014 |
ANODE ASSEMBLY FOR CATHODIC PROTECTION
Abstract
The cathodic protection of a reinforced concrete structure
utilizes sacrificial anodes such as aluminum or zinc as well as
alloys thereof. Each anode is embedded or substantially covered in
a material consisting of a hydrophilic non-cementious open-cell
foam. An activating agent such as one or more lithium salts is
contained within the cells of the foam to maintain the anodes in an
electrochemically active state. The activating agent may be
immobilized in the cells using an aqueous gel such as agar. One or
more metallic conductors electrically connect the anodes to the
metal reinforcing members.
Inventors: |
Bennett; John E.; (Prescott,
AR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Euclid Chemical Company |
Cleveland |
OH |
US |
|
|
Assignee: |
The Euclid Chemical Company
Cleveland
OH
|
Family ID: |
51206880 |
Appl. No.: |
14/163080 |
Filed: |
January 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61849291 |
Jan 24, 2013 |
|
|
|
Current U.S.
Class: |
205/734 ;
204/196.01 |
Current CPC
Class: |
C23F 13/02 20130101;
C23F 2213/22 20130101; C23F 13/06 20130101; C23F 2201/02
20130101 |
Class at
Publication: |
205/734 ;
204/196.01 |
International
Class: |
C23F 13/16 20060101
C23F013/16 |
Claims
1. An anode assembly for galvanic cathodic protection of a
reinforced concrete structure comprising: at least one sacrificial
anode member; a covering material consisting of a hydrophilic
non-cementitious open-cell foam substantially covering the
sacrificial anode member; an activating salt designed to keep the
sacrificial anode in an electrochemically active state within the
open-cell foam covering material; at least one elongated metallic
conductor metallurgically bonded to the sacrificial anode.
2. An anode assembly of claim 1 wherein the sacrificial anode
member is zinc or a zinc alloy.
3. An anode assembly of claim 1 wherein the sacrificial anode
member is a high surface area configuration having an actual
surface area from three to six times that of its superficial
surface area.
4. An anode assembly of claim 1 wherein the hydrophilic open-cell
foam is a phenolic resin.
5. An anode assembly of claim 1 wherein the hydrophilic open-cell
foam is compressible.
6. An anode assembly of claim 1 wherein the activating salt within
the hydrophilic open-cell foam is a deliquescent or hygroscopic
material.
7. An anode assembly of claim 1 wherein the activating salt within
the hydrophilic open-cell foam is lithium nitrate, lithium bromide,
or combinations thereof.
8. An anode assembly of claim 1 wherein the activating salt within
the hydrophilic open-cell foam is present in the amount of between
about 0.05 grams and about 1 gram per cubic centimeter.
9. An anode assembly of claim 1 wherein the hydrophilic open-cell
foam is impregnated with a gel.
10. An anode assembly of claim 9 wherein the gel has a viscosity
ranging from 1 to 500 pascal-seconds (Pas).
11. An anode assembly of claim 9 wherein the gel is based on the
agent agar-agar.
12. An method for galvanic cathodic protection of a reinforced
concrete structure, said method including: providing at least one
sacrificial anode member; substantially covering the sacrificial
anode member with a covering material consisting of a hydrophilic
non-cementitious open-cell foam; impregnating the open cell foam,
either before or after substantially covering the anode member,
with an activating salt designed to keep the sacrificial anode in
an electrochemically active state within the open-cell foam
covering material; metallurgically bonding at least one elongated
metallic conductor to the sacrificial anode, and; connecting the
elongated metallic conductor to a ferrous reinforcing member within
surrounding concrete, thus allowing protective current to flow.
13. The method according to claim 12 utilizing an open-cell foam
comprising a phenolic resin.
14. The method according to claim 12 wherein the open-cell foam is
compressible.
15. The method according to claim 12 utilizing an activating agent
selected from the group consisting of lithium nitrate, lithium
bromide and mixtures thereof in an amount of between about 0.05
gram and about 1 gram per cubic centimeter of foam.
16. The method according to claim 15 further impregnating the foam
with a gel.
17. The method according to claim 16 wherein the gel is based on
the agent agar agar.
18. The method according to claim 16 wherein the gel has a
viscosity ranging from about 1 to about 500 pascal-seconds
(Pas).
19. The method according to claim 12 wherein the activating agent
is a hygroscopic or deliquescent material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of and priority to
provisional patent application Ser. No. 61/849,291, filed on Jan.
24, 2013, entitled "ANODE ASSEMBLY FOR CATHODIC PROTECTION which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] 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.
[0004] 2. Description of Prior Art
[0005] 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 (NaCl) over a number of years results in
the concrete becoming contaminated with chloride ions. Salt is
commonly introduced in the form of seawater, set accelerators, or
deicing salt.
[0006] When the chloride reaches the level of the reinforcing
steel, and exceeds a certain threshold level for contamination, it
destroys the ability of the concrete to keep the steel in a
passive, 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 the 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, coupled with traffic pounding, the utility or integrity of
the structure is finally compromised and repair or replacement
becomes necessary. Reinforced concrete structures continue to
deteriorate at an alarming rate. In a 2011 report to Congress, the
Federal Highway Administration reported that of the nation's
605,086 bridges, about 145,000 (24% of the total) were classified
as either functionally or 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.
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.
[0007] 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.
[0008] Cathodic protection reduces or eliminates corrosion of the
steel by making it the cathode of an electrochemical cell. This
cathodic polarization of the steel 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.
[0009] The most commonly used type of cathodic protection system is
impressed current cathodic protection (ICCP), which is
characterized by the use of 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.sup.+).
Acid attacks the integrity of the cement paste phase within
concrete. Finally, the complexity of ICCP systems requires
additional monitoring and maintenance, which results in additional
operating costs.
[0010] A second type of cathodic protection, known as galvanic
cathodic protection (GCP), offers certain important advantages over
ICCP. GCP uses sacrificial anodes, such as zinc and aluminum, and
alloys thereof, which have inherently negative electrochemical
potentials. When such anodes are used, protective current flows in
the circuit without need for an external power supply since the
reactions that occur are thermodynamically favored. GCP therefore
requires no rectifier, external wiring or conduit. This simplicity
increases reliability and reduces initial cost, as well as costs
associated with long term monitoring and maintenance. Also, the use
of GCP to protect high-strength prestressed steel from corrosion is
considered inherently safe from the standpoint of hydrogen
embrittlement. Recognizing these advantages, the Federal Highway
Administration issued a Broad Agency Announcement (BAA) in 1992 for
the study and development of sacrificial anode technology applied
to reinforced and prestressed bridge components. As a result of
this announcement and the technology that was developed because of
this BAA, interest in GCP has greatly increased over the past few
years.
[0011] In PCT Published Application WO94/29496 and in U.S. Pat. No.
6,022,469 by Page, a method of galvanic cathodic protection is
disclosed wherein a zinc or zinc alloy anode is surrounded by a
mortar containing an agent to maintain a high pH in the mortar
surrounding the anode. This agent, preferably lithium hydroxide
(LiOH), serves to prevent passivation of the zinc anode and
maintain the anode in an electrochemically active state. In this
method, the zinc anode is electrically attached to the reinforcing
steel causing protective current to flow and mitigating subsequent
corrosion of the steel.
[0012] In expired U.S. Pat. No. 5,292,411 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. In this
patent it is taught that the anode and the hydrogel are flexible
and are conformed within the eroded area, the anode being in
elongated foil form.
[0013] In U.S. patent application Ser. No. 08/839,292 filed on Apr.
17, 1997 by Bennett, abandoned in favor of CIP application now U.S.
Pat. No. 6,217,742 B1, the use of deliquescent or hygroscopic
chemicals, collectively called "humectants" is disclosed to
maintain a galvanic sprayed zinc anode in an active state and
delivering protective current. In U.S. Pat. No. 6,033,553, two of
the most effective such chemicals, namely lithium nitrate and
lithium bromide (LiNO.sub.3 and LiBr), are disclosed to enhance the
performance of sprayed zinc anodes. And in U.S. Pat. No. 6,217,742
B1, issued Apr. 17, 2001, Bennett discloses the use of LiNO.sub.3
and LiBr to enhance the performance of embedded discrete anodes.
The entire subject matter of these three patents and abandoned
application is incorporated herein by reference in full. And
finally, in U.S. Pat. No. 6,165,346, issued Dec. 26, 2000, Whitmore
discloses the use of deliquescent chemicals with the apparatus
disclosed by Page in U.S. Pat. No. 6,022,469.
[0014] In U.S. Pat. No. 7,160,433 B2, issued Jan. 9, 2007, a method
of cathodic protection of reinforcing steel is disclosed comprising
a sacrificial anode embedded in an ionically conductive
compressible matrix designed to absorb the expansive products of
corrosion of the sacrificial anode metal. And in U.S. Pat. No.
8,157,983 B2, issued Apr. 17, 2012, a covering material
incorporating a compressible water-retaining mineral in exfoliated
form surrounding the anode is disclosed. The subject matter of both
of these patents is incorporated herein by reference in full.
[0015] In U.S. Pat. No. No. 6,572,760 B2, issued Jun. 3, 2003,
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, with attendant drawbacks. In U.S. Pat. No.
6,193,857, issued Feb. 27, 2001, Davison, et al describes an anode
assembly comprising a block of anode material cast around an
elongated electrical connector (wire). It further discloses making
contact between the elongated connector and the reinforcing steel
by winding the connector around the reinforcing steel and twisting
the ends of the connector together using a twisting tool.
[0016] Finally, in U.S. Pat. No. 7,488,410 B2, issued Feb. 10,
2009, an anode assembly for cathodic protection is disclosed in
which a non-conductive barrier is disclosed that covers one side of
the anode assembly. The purpose of the non-conductive barrier is to
reduce the passage of current to the adjacent portion of the
reinforcing member to which the anode assembly is attached. The
subject matter of this patent is incorporated herein by reference
in full.
[0017] 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 disclosed by Bennett, such as
lithium nitrate and lithium bromide, result in a higher current. In
cases of high chloride contamination and the presence of strong
corrosion of the reinforcing steel, higher protective current is
desirable, and sometimes necessary to prevent corrosion of steel
embedded in concrete.
[0018] Also, some of the chemicals used to maintain the zinc anode
in an electrochemically active state render the corrosion products
of zinc largely insoluble. In this case the expansive corrosion
products apply stress to the surrounding concrete, and when this
stress exceeds the tensile strength of the concrete, cracking of
the concrete can occur. Although several potential solutions have
been proposed, including the ionically compressible conductive
matrix described in U.S. Pat. No. 7,160,433, cracking remains a
problem in some cases.
[0019] Cracking of the concrete overlay has been largely overcome
by the addition of a compressible, ionically conductive
phyllosilicate mineral such as vermiculite, as described in Bennett
U.S. Pat. No. 8,157,983 B2. In this patent, the subject matter of
which is incorporated herein by reference in full, 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.
[0020] It is noteworthy that, although one or two patent
applications in this field have been broadly worded, there have
been no commercial applications or reported positive results
utilizing anything other than a cementitious covering material for
the sacrificial anode.
SUMMARY OF THE INVENTION
[0021] The present invention relates to an anode assembly for
cathodic protection of reinforced concrete, and more particularly,
to a method 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 anode assembly for cathodic protection
wherein the performance of the sacrificial anode is enhanced by the
use of a non-cementitious hydrophilic open-cell foam as a covering
material for the sacrificial anode.
[0022] In this invention the open-cell foam covering material is
impregnated by an activating salt intended to render the zinc anode
in an electrochemically active state. The activating salt may be
any one of several salts capable of breaking down the passive film
that forms on the surface of the sacrificial anode material, thus
preventing corrosion of the sacrificial anode material. Suitable
activating salts for this purpose have been shown to be nitrates,
and bromides, specifically lithium nitrate (LiNO.sub.3) and lithium
bromide (LiBr) and mixtures thereof.
[0023] It is further contemplated to immobilize the activating salt
within the open-cell foam with an immobilizing agent designed to
render the activating salt substantially stationary within the open
cell foam. One immobilizing agent found to be especially
advantageous is a gel, or semi-solid jelly-like material within the
open-cell foam and substantially surrounding the sacrificial anode.
The gel for use in the present invention has a degree of
flexibility and flowability due to its significant water content.
The gel of the present invention contains a significant amount of
the activating salt. A preferred gelling agent for these salts is
that known as Agar Agar, or simply Agar for short.
[0024] The anode assembly 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
[0025] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Further features of the present invention will become
apparent to those skilled in the art to which the invention
relates, with particular reference to the accompanying drawings, in
which:
[0027] FIG. 1 is an elevational view in cross-section showing the
cathodic protection system to which the present invention
appertains; and
[0028] FIG. 2 is a graph showing protection current delivery versus
duration in days.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The present invention relates broadly to all reinforced
concrete structures with which cathodic protection systems are
useful. Generally, the reinforcing metal in a reinforced concrete
structure is carbon steel. However, other ferrous-based metals can
also be used.
[0030] 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 high surface area configuration, such as an expanded
metal mesh or a cast form with fins, protrusions, or the like,
intended to increase the surface area of the anode. The actual
surface area of the anode member preferably is from three to six
times that of its superficial surface area. All elements of the
anode should be metallurgically bonded to one another to comprise a
single anode element within the anode assembly.
[0031] An important feature of the present invention is the use of
non-cementitious open-cell hydrophilic foam substantially covering
the sacrificial anode material. In this context, "non-cementitious"
will be understood to mean that the foam is not impregnated with or
encapsulated by a cementitious mortar in the manner described in
the above-noted U.S. Pat. No. 7,160,433 to Bennett. Also, a
non-cementitious open-cell hydrophilic foam will be understood to
mean a non-cementitious open-cell foam which has the ability to
provide a pathway for ionic conductivity from the sacrificial anode
to the surrounding material. Preferably, this non-cementitious
open-cell hydrophilic foam is compressible. This open-cell foam is
in direct contact with the surface of the sacrificial anode,
providing a pathway for ionic conductivity from the sacrificial
anode to the surrounding material.
[0032] "Hydrophilic" means the ability to readily absorb and retain
moisture. Also, within the scope of the present invention, it is
important for the foam to provide a low resistance pathway for
ionic conductivity. Impregnating the foam with a solution of a salt
such as lithium nitrate or lithium bromide or a mixture of the two
serves this purpose.
[0033] The non-cementitious hydrophilic open-cell foam may be
naturally hydrophilic such as phenolic foam and other foams known
as "floral foams," which are used in the floral industry to
maintain cut flowers moist and fresh. One source for such floral
foams is Smithers Oasis. Such foams are desirable not only because
they are naturally hydrophilic but also because they are capable of
wicking water.
[0034] The non-cementitious hydrophilic open-cell foam can also be
made from an open-cell foam which is not naturally hydrophilic but
which is impregnated with a material which renders the
non-cementitious open-cell foam hydrophilic. For example, the
non-cementitious hydrophilic open-cell foam can also be made from a
polystyrene foam which has be impregnated with an aqueous gel
(i.e., a hydrogel) such as the agar agar and other hydrogels
described below.
[0035] There are four commercial products marketed as discrete
anodes used for the purpose of mitigation of corrosion of steel in
reinforced concrete. All four of those products use a rigid
cementitious-based material covering the anode. Although these
products all provide a degree of protection against corrosion, the
protective current they deliver is limited by the properties of the
covering material. Rigid cementitious-based covering materials are
characterized by inflexibility and very low diffusion coefficients.
This has the result of limiting the mobility of ions in the
covering material, causing excessive polarization, and therefore
limiting protective current delivered. These materials also have
the tendency to trap anode corrosion products against the anode
surface, again resulting in polarization and limiting protective
current. In cases of severe corrosion, the protective current
delivered by these products may not be sufficient to control
corrosion, resulting in a limited service life, resumption of
corrosion, and eventual cracking and spalling of the concrete cover
over the reinforcing steel. In some cases, cracking and spalling
may resume after only very few years. It has been desired to
increase the protective current delivery, and thereby to improve
the protection against corrosion and extend the working service
life of these products. This goal is, to large degree, achieved by
the present invention, because the material surrounding the
sacrificial anode is made from an open-cell foam which is
non-cementitious, hydrophilic and desirably compressible as
well.
[0036] In this invention the open-cell foam covering material is
impregnated by an activating salt intended to render the zinc anode
in an electrochemically active state. The activating salt may be
any one of several salts capable of breaking down the passive film
that forms on the surface of the sacrificial anode material, thus
preventing corrosion of the sacrificial anode material. Salts known
to be effective for this purpose include chlorides, acetates,
iodides, fluorides, hydroxides, bromides, nitrates, phosphates,
phosphites, and chlorates, as well as other less common salts. The
best activating salts for this purpose have been shown to be
nitrates, and bromides, especially lithium nitrate (LiNO.sub.3) and
lithium bromide (LiBr) and combinations thereof. The activating
salts must be in amount sufficient to maintain the sacrificial
anode material active, and in amount such that diffusion of
activating salt away from the anode will not cause its
concentration to drop below an effective amount. Generally, the
activating salt should be present in an amount of at least 0.05 up
to about 1 gram per cubic centimeter of the open-cell foam. The
activating salt is typically added to the open-cell foam as an
aqueous solution. This is particularly advantageous since the
preferred lithium salts are both readily available and economically
viable when supplied as aqueous solutions.
[0037] An additional feature of the present invention is the use of
an immobilizing agent designed to render the activating salt
substantially stationary within the open cell foam, thus preventing
the activating agent from diffusion away from the sacrificial
anode. One immobilizing agent found to be especially advantageous
is a gel, or semi-solid jelly-like material within the open-cell
foam and substantially surrounding the sacrificial anode. Gels are
mostly liquid by weight, yet they behave like solids due to a
three-dimensional cross-linked network within the liquid. Gels may
have properties ranging from very soft and weak to hard and tough,
but for the purposes of the present invention the gel used as an
immobilizing agent within the open-cell foam is a jelly-like
substance having a degree of flexibility and flowability. Preferred
are water-based gels.
[0038] It has been found that, in order to achieve maximum
long-term performance, the gel material should have a certain range
of viscosity. If the covering material is too rigid, anode
corrosion materials will be trapped against the anode surface and
polarization will limit the protective current delivered to the
steel, as is the case with cementitious covering materials. If the
gel material covering the anode is too fluid, as a liquid, then it
will be difficult to contain and the activating salt may migrate
away from the anode surface. It has been found that, for optimum
performance, the gel material covering the anode must therefore
have a certain range of viscosity.
[0039] A fluid's internal resistance to flow, which is a measure of
fluid friction, is its viscosity. Viscosity, which can be measured
using various types of viscometers, may be thought of as the
"thickness" or "internal friction" of a fluid. The SI physical unit
of dynamic viscosity is the pascal-second (Pas). If a fluid with a
viscosity of 1.0 Pas is placed between two plates, and one plate is
pushed sideways with a shear stress of one pascal, it will move a
distance equal to the thickness of the layer between the plates in
one second.
[0040] It has been found in the present invention that for enhanced
performance, the gel material covering the anode should have a
viscosity between about 1 and 500 Pas. This is a viscosity ranging
from about that of honey to about that of peanut butter. For a gel
of this viscosity, ionic mobility will be relatively high, allowing
the anode to operate with minimum polarization.
[0041] Common ingredients that can be used to promote gelling
include polyvinyl alcohol, acrylate polymers and copolymers with an
abundance of hydrophilic groups. The anode covering material also
incorporates a strong activating agent (discussed above), and these
may be particularly difficult to gel. In such cases it may be
particularly advantageous to use a gelling agent known as
agar-agar, or simply agar. Agar is a gelatinous substance derived
from a polysaccharide obtained from the cell walls of some species
of red algae. It is unofficially known as the "queen of gelling
agents". Chemically, it is a mixture of two components: the linear
polysaccharide agarose, and a heterogeneous mixture of smaller
molecules called agaropectin. Agar is the preferred gelling agent
for this application. The gel, if used, may be incorporated into
the sponge along with the activating agent.
[0042] The anode assembly for cathodic protection also incorporates
an elongated metallic conductor such as insulated #16 AWG copper
wire 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.
[0043] A system that utilizes the anode assembly described above is
shown in FIG. 1. In this case , one end of the elongated metallic
conductors 20 is electrically joined to a sacrificial metal anode
10, and the other end is wrapped securely around or otherwise
coupled to a reinforcing bar 18 that has been cleaned to bright
metal. The anode assembly is covered with or embedded in an open
cell foam 12 as previously described. Together with the reinforcing
bars and surrounding excavation, the anode assembly is then
embedded in mortar or concrete 22. As soon as the assembly is
positioned, the circuit is completed and protective current will
begin to flow to the reinforcing bar in the vicinity of the anode
assembly, thus imparting a degree of cathodic protection and
mitigating corrosion of the steel. It is particularly desirable to
cathodically protect the steel in the original concrete outside the
patch area, thereby preventing the so called "halo effect," or
"anode ring effect." In this manner, the service life of the
concrete patch can be greatly extended.
[0044] FIG. 2 is a line graph showing the protective current
delivered by Sentinel-GL, a commercial product provided by The
Euclid Chemical Company (labeled in FIG. 2 as "Performance without
Foam") to the protective current delivered by an anode assembly of
the present invention (labeled in FIG. 2 as "Performance with
Foam") The advantage of the present invention is shown by an
increased level of protective current.
[0045] 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 presented
below.
[0046] Having described the invention, the following is
claimed:
* * * * *