U.S. patent application number 14/395272 was filed with the patent office on 2015-03-05 for method for the galvanic protection of a reinforced concrete structure.
This patent application is currently assigned to SOLETANCHE FREYSSINET. The applicant listed for this patent is Christian Tourneur. Invention is credited to Christian Tourneur.
Application Number | 20150060298 14/395272 |
Document ID | / |
Family ID | 46147495 |
Filed Date | 2015-03-05 |
United States Patent
Application |
20150060298 |
Kind Code |
A1 |
Tourneur; Christian |
March 5, 2015 |
METHOD FOR THE GALVANIC PROTECTION OF A REINFORCED CONCRETE
STRUCTURE
Abstract
The invention relates to the galvanic protection of a concrete
structure (10) comprising metal reinforcements (12). Holes (15) are
previously made in the structure, for receiving sacrificial anodes.
Before arranging said sacrificial anodes, decontamination
electrodes (16) and an electrolyte are inserted into the holes in
order to carry out a decontamination phase wherein the negative
terminal of a power supply (18) is electrically connected to the
reinforcements of the structure and the positive terminal of the
power supply is electrically connected to the decontamination
electrodes. Once the power supply has been activated for a certain
amount of time in order to attract the chloride ions to the
decontamination electrodes and the electrolyte, the electrolyte and
the decontamination electrodes are removed from the holes (15) and
the sacrificial anodes are sealed therein and then electrically
connected to the reinforcements.
Inventors: |
Tourneur; Christian; (Le
Mesnil Saint Denis, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tourneur; Christian |
Le Mesnil Saint Denis |
|
FR |
|
|
Assignee: |
SOLETANCHE FREYSSINET
RUEIL MALMAISON
FR
|
Family ID: |
46147495 |
Appl. No.: |
14/395272 |
Filed: |
April 17, 2012 |
PCT Filed: |
April 17, 2012 |
PCT NO: |
PCT/FR2012/050834 |
371 Date: |
October 17, 2014 |
Current U.S.
Class: |
205/734 |
Current CPC
Class: |
C04B 41/009 20130101;
C04B 41/009 20130101; C23F 13/04 20130101; E04C 5/015 20130101;
C23F 13/02 20130101; C04B 41/72 20130101; C23F 13/06 20130101; C04B
28/02 20130101; C23F 2201/02 20130101; C04B 41/5376 20130101 |
Class at
Publication: |
205/734 |
International
Class: |
C23F 13/04 20060101
C23F013/04; C23F 13/06 20060101 C23F013/06 |
Claims
1. A method for galvanic protection of a concrete structure having
metallic armatures, the method comprising: boring holes in the
structure; inserting a decontamination electrode and an electrolyte
into at least one of the holes; electrically connecting a negative
terminal of a current source to the armatures and a positive
terminal of the current source to each decontamination electrode;
activating the current source; removing the electrolyte and each
decontamination electrode; arranging and sealing sacrificial anodes
in the holes bored in the structure; and electrically connecting
the sacrificial anodes to the armatures.
2. The method of claim 1, wherein the decontamination electrode is
made of a stainless material, in particular titanium, of stainless
steel or of carbon.
3. The method according to claim 1 wherein the decontamination
electrode is formed as a tube or spirally wound wire.
4. The method according to claim 1 wherein the decontamination
electrode is electrically connected to the positive terminal of the
current source by a wire made of stainless material, in particular
titanium, on at least part of its length on the side of the
decontamination electrode.
5. The method according to claim 1 wherein the electrolyte is
removed from each hole by applying a stream of water or air.
6. The method according to claim 1 wherein the electrolyte is in
the form of a gel.
7. The method according to claim 6, wherein the electrolyte is a
mixture comprising water, a gelifying agent or water retainer, such
as methylcellulose, and a base.
8. The method according to claim 7, wherein the base is sodium
hydroxide.
9. The method according to claim 7, wherein the base is potassium
carbonate to re alkalinize the concrete around the armatures.
10. The method according to claim 1 wherein the current source
comprises a battery or DC power supply connected to the mains,
activated to supply current in a range of 0.5 to 1 A per square
meter of armatures.
11. The method according to claim 1 wherein the sacrificial anodes
are zinc-based.
12. The method according to claim 1 wherein the decontamination
electrode is a tool used several times.
13. The method according to claim 1 wherein the holes have a depth
greater than a depth required for inserting the sacrificial anodes.
Description
[0001] The invention relates to reinforced concrete techniques, and
more particularly to a method of protecting armatures of concrete
against corrosion.
[0002] The steel armatures of reinforced concrete corrode because
of the pH decrease of the concrete in which they are embedded in
case of carbonation, and/or of penetration by diffusion of
polluting products such as chlorides for instance. These phenomena
which cause corrosion may happen even with a low humidity rate.
[0003] To place the armatures in an immunizing medium which
protects them again, a typical method consists in scratching off
the covering concrete to replace it with healthy concrete. But this
method is expensive.
[0004] To protect the armatures in their original environment,
techniques related to chemistry can be used, such as the
application of inhibiting products, or related to electrochemistry,
such as methods for cathodic or galvanic protection.
[0005] The corrosion inhibiters are liquid products which, once
applied on the concrete surface, migrate by diffusion through the
latter and attach onto the armatures. They inhibit the cathodic or
anodic reactions or, for some of these products, they inhibit both
(mixt inhibiters). This method has a random aspect to it due to the
difficulty to predict the diffusion of molecules within the porous
network of the concrete. Some concretes do not allow the
penetration of inhibiters.
[0006] Cathodic protection consists in creating an anode by placing
a metal which is not easily corroded close to the armatures and by
leaving a certain thickness of concrete between this metal and the
armatures. A current generator is turned on with its positive
terminal connected to the anode and its negative terminal connected
to the armatures, so as to have a current greater than the
corrosion current of the armatures circulate in the concrete. The
armatures then act as a cathode in the electrolytic system.
[0007] The current applied to the system is adjustable through the
generator according to what is needed. Typically, the currents are
adjusted between 2 mA and 20 mA per square meter of armature.
[0008] The cathodic galvanic protection is based on a principle
similar to that of cathodic protection, but the supplied current is
obtained by the corrosion of the anode which is itself connected to
the armatures. Such an anode is referred to as a sacrificial anode.
The anodes are made of a metal which is easily oxidized such as
zinc, aluminum, magnesium or alloys thereof. The system functions
as a battery. The quantity of current delivered by such a system
depends on the surfaces of the anode and their composition. The
delivered current is limited by the corrosion speed of the
sacrificial anodes, their composition and their number.
[0009] The lack of a generator and of a system to regulate the
quantities of current is an advantage of the cathodic galvanic
protection. However the current generated by the corrosion of the
sacrificial anodes remains low and limits the applications of the
system. In general, they are below 2 mA per square meter of
armature after coupling with the steel has been set. This value is
often considered to be insufficient for the protection of armatures
exhibiting corroding pits.
[0010] Given that the quantity of galvanic current cannot be
increased, a solution consists in reducing the rates of chlorides
in the vicinity of the steel to suppress or reduce the effects of
corroding spots.
[0011] A known method consists in applying, onto the surface of the
concrete, a metallic anode which is embedded in a fibrous matrix
impregnated with an electrolyte to ensure electric continuity
between the anode and the concrete. The positive terminal of a
generator is connected to the anode and the negative terminal to
the armatures to apply a current having a high intensity
(approximately 1 A/m.sup.2 of armature) during about 200 hours. The
negative ions Cl.sup.- are then attracted to the positive polarity
of the anode and migrate to the exterior to concentrate around the
anode. At the end of the treatment, the anode and the matrix which
is impregnated with electrolyte are removed with the chloride ions
extracted. The steel armatures are then in a medium which has been
rid of aggressive ions, and can then be protected from then on by a
galvanic protection whose current is sufficient for a chlorine-free
medium.
[0012] Such chloride extraction methods are costly and lengthy.
Therefore, they are not used in this context.
[0013] The patent applications WO 2005/106076 A1 and WO 2006/097770
A2 disclose an intermediary solution which allows to drive the
Cl.sup.- ions away from the armatures in a galvanic protection
system. The method uses definitive sacrificial anodes located in
the concrete so as to, firstly, apply a forced current of a
quantity of 50 kilocoulombs (kC) via a generator. This current
drives the Cl.sup.- ions away from the armatures by concentrating
them around the anode. The generator can then be turned off and the
sacrificial anodes can be connected to the armatures. The objective
to use a low galvanic current to protect steel from corrosion in a
dechlorinated medium is obtained. The remaining chlorides and those
likely to enter at a later time will keep on concentrating around
the anode during the operating time of the galvanic system. But a
negative secondary effect is that the current applied in the first
phase accelerates the corrosion of the anode which quickly loses
weight and therefore reduces the energy reserve required to
maintain the galvanic protection system over time. This loss must
be compensated for by extra starting weight for the anode.
[0014] There is therefore a need to improve the galvanic protection
techniques in chlorinated environments. In particular, it is
desired to obtain a technique which allows to drive the chlorides
ions away from the steel armatures without consuming the matter of
the sacrificial anodes and/or to increase the pH value in the
vicinity of the steels so as to reduce the Cl.sup.-/OH.sup.- ratio
(re-alkalize).
[0015] A method for galvanic protection of a concrete structure
having metallic armatures is disclosed. The method comprises:
[0016] boring holes in the structure; [0017] inserting a
decontamination electrode and an electrolyte into at least one of
the holes; [0018] electrically connecting a negative terminal of a
current source to the armatures and a positive terminal of the
current source to each decontamination electrode; [0019] activating
the current source; [0020] removing the electrolyte and each
decontamination electrode; [0021] arranging and sealing sacrificial
anodes in the holes bored in the structure; and [0022] electrically
connecting the sacrificial anodes to the armatures.
[0023] A decontamination phase is carried out before placing the
sacrificial anodes. In this decontamination phase, the chloride
ions are drawn to the holes where the decontamination electrodes
and the electrolyte are located. After the activation of the
current source during a long enough time, the decontamination
electrodes are removed and so is the electrolyte, which evacuates
the majority of the chloride ions out of the structure. Then, the
sacrificial anodes are installed and sealed in the holes to ensure
a galvanic protection in an environment which holds little
chlorine.
[0024] The decontamination phase is carried with a very low
additional cost because it relies on holes already made to receive
the sacrificial anodes.
[0025] Moreover, by using anode-tools as decontamination
electrodes, the mass of the final anodes which will be sealed to
ensure the galvanic protection is not consumed. The anode-tools can
be used again at some other location of the work, or on another
site.
[0026] The decontamination electrode is advantageously made of
stainless material, for instance metallic (titanium, stainless
steel), or of carbon. It has a relatively important exterior
surface for the conduction of current, which can be obtained by
forming it as a tube or a spirally wound wire.
[0027] The electrolyte is a material chosen to be retained inside
the holes then removed in a simple manner by applying a water
stream or compressed air jet or sucked. It is typically in the form
of an electrolytic gel whose consistency makes it possible to have
the electrolyte maintained by itself in the holes whose diameter
does not exceed 25 mm, typically. For other forms of anodes, the
diameter of the hole can be increased or decreased.
[0028] The depth of the holes generally corresponds to the depth
required to house and correctly set up the final anodes relative to
the surface, but it is also possible, to extract chloride ions more
deeply during the step of forced current to make holes having a
greater depth which will be, after removal of the gel and
cleansing, filled with a hydraulic mortar at the time of the
sealing of the galvanic electrodes.
[0029] Other features and advantages of the invention will become
apparent from the following description of a non-limiting exemplary
embodiment, with reference to the accompanying drawings in
which:
[0030] FIG. 1 is a perspective view of a part of the reinforced
concrete structure to which the invention may be applied;
[0031] FIGS. 2 and 3 are other perspective views of the structure
part shown in FIG. 1, at two steps of a decontamination phase;
[0032] FIG. 4 is a perspective diagram illustrating the
introduction of a sacrificial electrode for galvanic protection
into a hole bored in the structure part of FIGS. 1-3; and
[0033] FIG. 5 is another perspective view showing diagrammatically
the galvanic protection system installed on the structure part.
[0034] Galvanic protection of the armatures of reinforced concrete
is generally obtained by sealing, into holes bored in the concrete,
small bodies of easily corrodible metals, such as zinc alloys for
example, connected together by an insulated wire and then connected
to the armatures of the concrete in one or several points. The
sacrificial anodes thus formed become corroded and generate
metallic particles in the form of ions. The electrons released by
the anodic reaction are distributed to the armatures by the wire
connecting them. The current returns through the concrete which
acts as an electrolyte.
[0035] The method proposed here uses the holes 15 bored in the
concrete 11 (FIG. 1), provided with a view of sealing the alloy
bodies forming galvanic anodes, to perform a prior processing by a
forced current so as to extract chloride ions and re-alkalinize the
concrete 11 around the armatures 12.
[0036] To implement the galvanic protection technique, holes 15 are
bored through the reinforced concrete structure 10, with
precautions to avoid hitting the metallic armatures 12. The holes
15 drilled in the structure are arranged so as to have an overlap
between the active ranges of the sacrificial electrodes that they
will accommodate, in order to cover the area of the armatures to be
protected. Typically, in the galvanic protection technique, each
sacrificial electrode has an active range of the order of 20 to 30
cm.
[0037] In the method according to the invention, before inserting
the sacrificial electrodes into the holes 15, a prior
decontamination phase is performed by means of electrodes 16
introduced into the holes 15 (FIG. 2).
[0038] The decontamination electrodes 16 are preferably made of a
stainless material or a weakly corrodible material. In particular,
they may be made of titanium, or else of stainless steel.
Nonmetallic materials, such as carbon, may also be used.
[0039] In the embodiment illustrated by FIG. 2, the decontamination
electrodes 16 are in the form of a spirally wound metallic wire.
Other geometries are possible. In particular, a tube shape is
appropriate for the decontamination electrodes 16.
[0040] Each decontamination electrode 16 has an extension
consisting of a wire 17 which is also made of stainless material.
In the example shown, the electrode 16 is made of a titanium wire
wound in the part dipped into the hole 15 and extended to form a
rod 17 outside the hole 15.
[0041] The electrodes 16 are introduced into the holes 15 with an
electrolytic agent, preferably in the form of a gel. In practice,
the holes 15 may be first filled with electrolytic gel which, due
to its gelified consistency, is self-maintained inside the holes.
The decontamination electrodes 16 are then introduced therein, so
as to occupy the whole inner space of the holes 15 with the
electrolytic gel.
[0042] The electrolytic gel may be essentially made of a water
retention agent and a base, such as soda lye or the like. For
example, for a gel containing 400 g of water, 50 g of sodium
hydroxide (NaOH) at 30% and 40 g of S35-type methylcellulose may be
added. With the same proportions, NaOH may be replaced by potassium
carbonate (K.sub.2CO.sub.3) to increase the pH in the immediate
vicinity of the armatures.
[0043] After introducing the electrolytic gel and the electrodes 16
into the holes 15, the electrodes 16 are electrically connected to
each other and to the positive terminal of a current source 18
(FIG. 3). Regarding the negative terminal of the current source 18,
it is electrically connected to the array of metallic armatures 12
of the reinforced concrete structure 10.
[0044] After installing and connecting the decontamination
electrodes 16, the decontamination phase comprises activating the
current source 18 to apply a current which, at the end of the
decontamination phase, may represent, e.g., an integrated charge of
50 kC per m.sup.2 of armatures, that value being non-limiting. The
current supplied by the source 18 may be in a range of 0.5 to 1 A
per m.sup.2 of armatures contacting the concrete, which gives rise,
depending on the surface of the armatures to be protected, to an
activation time of the source 18 of the order of a few tens of
hours.
[0045] The wire 17 is used to electrically connect the
decontamination electrodes 16 to the positive terminal of the
current source. Its constitution as an stainless material, on at
least part of its length on the side of the decontamination
electrode, prevents the electrodes 16 from degrading when being
used.
[0046] The current source 18 is a battery or a DC power supply
connected to the mains. It is activated to supply a DC current with
intensity in a range of 0.5 to 1 A per square meter of
armatures.
[0047] In the example shown in FIG. 3, the electrodes 16 are
installed together in the structure 10 to perform the
decontamination phase. It will be understood that, depending on the
hardware and time available, another option is to introduce and
activate successively one electrode 16 or a group of electrodes 16
to decontaminate in turn several regions of the structure.
[0048] At the end of the decontamination phase, the electrodes 16
are removed from the holes 15, as well as the electrolytic gel
which then contains a certain amount of chloride ions which have
migrated from the concrete body 11.
[0049] To remove the gel from the holes 15, a stream of water or a
compressed air jet is applied, or the gel is sucked.
[0050] The holes 15 are then released and the sacrificial anodes 20
can be introduced therein. By way of illustration, the sacrificial
anodes 20 may have a shape as shown in FIG. 4. In that example, the
sacrificial anodes 20 are in the form of a profile having a
star-shaped cross-section, so as to provide a relatively important
contact area with the mortar 21 which will be used to seal them in
the holes 15.
[0051] The sacrificial anodes 20 may be made of any material known
for its use in the galvanic protection techniques, i.e. an easily
corrodible metal. Zinc or a zinc alloy is a preferred material for
the sacrificial anodes 20.
[0052] After introducing the sacrificial anodes 20 into the holes
15 bored in the concrete structure 10, those holes 15 are filled
with a sealing mortar 21 (FIG. 5). Each sacrificial anode has a
conducting connection rod 22 which protrudes out of the sealing
mortar 21. Those connection rods 22 are electrically connected to
each other as well as to the array of metallic armatures of the
concrete, as shown in FIG. 5.
[0053] The installation of the galvanic protection system is then
finished. During the future life of the structure, the
corrosion-generating electrolytic phenomena cause consumption of
the sacrificial anodes 20 rather than corrosion of the metallic
armatures 12 of the reinforced concrete structure 10.
[0054] The proposed method enables low-cost extraction of chloride
ions since it uses the holes that are already bored. The chloride
ions are drained out of the structure by drawing them through the
holes rather than to the surface. The migration time of the ions
can thus be reduced.
[0055] Employing reusable anode tools makes it possible not to
damage the definitive anode bodies that will be sealed after the
extraction and re-alkanization processing.
[0056] The method makes it possible, if desired, to carry on with
the processing until the chloride ions are completely extracted. By
using anode tools which are not consumed, it is not limited to
application of a specific charge.
[0057] The embodiments described or mentioned above are
illustrations of the present invention. Various changes can be made
to them without departing from the scope of the invention as set
forth in the appended claims.
* * * * *