01101 Electrochemical Chloride Extraction from Ste

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Item No. 24214
NACE International Publication 01101
This Technical Committee Report has been prepared
by NACE International Task Group 054* on
Electrochemical Chloride Extraction and Realkalization
of Reinforced Concrete.
Electrochemical Chloride Extraction from Steel
Reinforced Concrete −− A State-of-the-Art Report
© May 2001, NACE International
This NACE International technical committee report represents a consensus of those individual members who
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Foreword
The purpose of this technical committee report is to
present state-of-the-art information on electrochemical
chloride extraction (ECE) from conventionally reinforced
concrete surfaces. Included are discussions of common
industry practices used by design engineers to control
corrosion of reinforcing steel in portland cement concrete
structures through the application of ECE.
This report is intended for use by engineers attempting to
protect corroding reinforced concrete structures by use of
electrochemical treatment techniques. The information
presented in this report is limited to ECE for atmospher-
ically exposed reinforced concrete and is not applicable to
prestressed or post-tensioned elements or concrete con-
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taining epoxy-coated reinforcing steel, galvanized, or
other coated or nonferrous reinforcement.
This report, focusing on electrochemical chloride extrac-
tion, is Part I of a two-part series. Part II is intended to
focus on the realkalization of carbonated concrete struc-
tures.
This technical committee report was prepared by Task
Group 054 on Electrochemical Chloride Extraction and
Realkalization of Reinforced Concrete. It is issued by
NACE International under the auspices of administrative
Specific Technology Group 01 on Concrete and Rebar. 
___________________________
*Chairman John Broomfield, Consulting Corrosion Engineer, London, UK.
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Introduction
Reinforced concrete is a versatile and widely used
construction material. Its excellent performance and dur-
ability rely on the compatibility of the steel with the
concrete surrounding it and the ability of the concrete to
protect the steel from corrosion in most circumstances.
Unfortunately, corrosion protection is not guaranteed, and
can fail if sufficient chlorides (usually in the form of sea
salt, deicing salt, or chloride contamination of the original
mix) or atmospheric carbon dioxide (CO2) penetrate the
concrete and break down the passive layer that protects
the steel. This breakdown of the passive oxide layer
leads to corrosion of the reinforcing steel if sufficient
oxygen and water are available.
Regardless of the cause of depassivation (chlorides or
carbonation), corrosion occurs by the movement of elec-
trical charge from an anode (a positively charged area of
steel where steel is dissolving) to the cathode (a nega-
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tively charged area of steel where a charge-balancing
reaction occurs, turning oxygen and water into hydroxyl
ions). This means that the process is both electrical and
chemical, i.e., electrochemical. In the case of chloride
attack, patch repairs are only a local solution to corro-
sion, and repairing an anode can accelerate corrosion in
adjoining areas.
One solution to this problem involves applying an electro-
chemical treatment that suppresses corrosion. Figure 1
shows the basic components of an electrochemical treat-
ment system. The components are a direct-current (DC)
power source and an anode (temporary or permanent)
usually distributed across the surface of the concrete.
Electrochemical methods work by applying an external
anode and passing current from it to the reinforcing steel
so that all of the steel becomes a cathode.
Figure 1: Schematic Diagram of Electrochemical Treatment System
Three electrochemical techniques are used to counter
corrosion of steel in concrete. The first of these tech-
niques is cathodic protection. A newer alternative for
chloride-contaminated structures is electrochemical chlor-
ide extraction (ECE), also known as electrochemical
chloride removal (ECR), or desalination, as the process is
called in Europe. A method for treating carbonated con-
crete has been developed and is gaining rapid accept-
ance as a rehabilitation method for carbonation in build-
ings and other structures. This is known as realkaliza-
tion.
Chloride removal was the subject of two major studies
conducted under Federal Highway Administration(1)
(FHWA) contracts in the 1970s.1,2 Both of these studies,
as well as follow-up reports, concluded that chloride
removed by electrochemical migration is a promising
technique for use on salt-contaminated concrete.
2
___________________________
(!) Federal Highway Administration (FHWA), 400 7th St. SW, Washington, DC 20590.
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Further research was undertaken in Norway by a private
company, and under the Strategic Highway Research
Program(2) (SHRP). As a result of that research a
number of patents were published. A list of some of the
principal U.S. patents directly relating to ECE is given in
the bibliography. The list is not comprehensive and does
not include patents from other countries. 
The chloride ion acts as though it is a catalyst to corro-
sion, and is not consumed in the corrosion reaction.
Chlorides enable corrosion to develop and expand once
they are present beyond a threshold level at the steel
surface. Because chlorides are negatively charged, the
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electrochemical process can be used torepel the chloride
ion from the steel surface and move it toward an external
anode. The ECE process uses an external anode that is
installed for the duration of the treatment process. A
higher electrical current density is applied than that used
for cathodic protection (see NACE Standard RP02903 on
cathodic protection and NACE Standard TM02944 for
testing embeddable anodes for cathodic protection of
atmospherically exposed steel-reinforced concrete). Nor-
mally, the ECE system runs for a limited time (typically
four to eight weeks), and is then dismantled and removed
from the structure. No permanent system is installed.
Theory
When direct current is passed through an electrolyte,
anions migrate toward the anode and cations migrate
toward the cathode. This is the mechanism by which
direct current is carried through concrete. All mobile ions
present migrate under the influence of the electric field
and therefore carry a portion of the current passed. In
chloride-contaminated concrete, these ions include chlo-
ride ions and other ions typically found in concrete, inclu-
ding hydroxyl, sodium, potassium, and calcium ions. The
amount of current carried by each ion depends on several
factors, including the total current passed, the mobility of
the ion, the concentration of the ions present, and
possibly temperature.
In the case of ECE, a principal objective is the extraction
and removal of chloride ions from the concrete. This has
been accomplished by placing an anode and electrolyte
temporarily on the concrete surface. The passage of
direct current between the reinforced steel and the exter-
nal anode has resulted in the transfer of chloride ions
toward the anode and into the electrolyte. At the con-
clusion of the treatment process the electrolyte, which
now contains a portion of chloride ions, can be removed.
The efficiency of chloride extraction can be expressed in
terms of the chloride transference number, which can be
calculated using Equation (1).
current total
Cl by carried current of amount
= t
-
Cl − (1)
Operating conditions typically maximize this parameter.
Chloride transference numbers in chloride-contaminated
concrete range from 0.05 to 0.40.5, 6
The passage of direct current through concrete is also
characterized by electrochemical reactions that occur at
the anode and at the embedded steel (cathode). Catho-
dic reactions, which result in an increase in alkalinity at
the surface of the steel, are considered carefully. These
include the reduction of oxygen and water as shown in
Reactions (2) and (3).
)(OH4 4e + O2H O --22 →+ (2)
)(OH2 + H 2e + O2H -2
-
2 → (3)
The first of these reactions takes place very slowly
because the availability of oxygen in concrete is limited.
Most of the current entering the steel at current densities
typical of those used for chloride extraction results in the
production of hydrogen at the steel surface.
The electrochemical reactions that typically take place at
an inert anode include the oxidation of water and chloride
ions as shown in Reactions (4) and (5).
-+
22 4e + 4H + O O2H → (4)
-2e + Cl -Cl2 2→ (5)
If the electrolyte is allowed to become very acidic (pH <4),
a significant amount of chlorine gas can be evolved,
which could cause safety and environmental concerns.
For this reason, the electrolyte is typically kept basic (pH
>7) and the evolution of oxygen becomes the favored
anodic reaction. The small amount of chlorine that can
be evolved under this condition is rapidly hydrolyzed to
hypochlorous acid and hypochlorite ion shown by
Reactions (6) and (7).
+-
22 H+ Cl + HClO OH + Cl → (6)
+- H + ClO HClO→ (7)
3
___________________________
(2) Strategic Highway Research Program (SHRP), National Research Council, National Academy of Sciences, Box 289, Washington, DC 20055.
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All of the reactions that occur at an inert anode produce a
quantitative amount of acid (H+) according to Faraday’s
Law. If an anode (such as steel) that corrodes during the
process is used, a significant amount of the current can
be consumed by anodic dissolution of the metal, a lesser
amount of acid (if any) is produced, and chlorine gas is
not generated.
Both the extraction of ions and the electrochemical reac-
tions that occur cause concentration gradients to develop
because ionic diffusion, which tends to restore a uniform
concentration, is slow in concrete. These concentration
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gradients, which can persist for years, have a significant
effect on the long-term effectiveness of the treatment.
Chloride ions can still be present in the bulk of the
concrete, but these ions are typically greatly depleted
near the surface of the steel. This depletion of chloride
ions, together with the increase in alkalinity from cathodic
reactions, creates passive conditions that effectively miti-
gate corrosion. Such effects are generally considered
more important than the simple removal of chloride from
the concrete, because the real objective of this treatment
is to prevent or mitigate the corrosion of embedded steel.
Practice
A. Tests and Evaluations Prior to Treatment
Testing of Cores from Candidate Structures
The application of ECE is unique for each concrete struc-
ture. The total charge used (and therefore the duration of
the process) depends on the amount and distribution of
chloride present in the concrete. The current density
used depends on the resistivity of the concrete and depth-
of-cover over the rebars. The ECE process can aggra-
vate the reaction of alkali-sensitive aggregate if inapprop-
riate electrolytes are used. For these reasons, laboratory
treatment of cores removed from the candidate structure
is often completed before site work. These laboratory
tests are typically considered optional, but they help to
predict in advance the current density, total charge, treat-
ment time, and efficiency for chloride extraction. The lab-
oratory process has been conducted with and without
lithium ion if alkali-sensitive aggregate has been known to
be present.
Typical Criteria for Cores Submitted for ECE Testing
1. Duplicate cores are typically submitted for each
structure or for each 10,000 ft2 (900 m2) of treatment
area if variations within the structure are anticipated.
2. Cores typically include reinforcing steel.
3. Cores are typically at least 4 in. (100 mm) in
diameter.
4. Cores are typically representative of the struc-
ture in chloride content and depth-of-cover to the
reinforcing steel.
Laboratory Procedures
The sides of each core are typically sealed and an elec-
trolyte reservoir created on the top surface of the core. 
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Choice of anode and electrolyte is generally consistent
with that intended for use on the candidate structure.
Monitoring of current, voltage, and total charge allows
estimation of treatment time and efficiency of extraction.
Samples for chloride analyses are normally taken from
preselected levels of each core before and after the test.
If alkali-silica-reactive (ASR) aggregate is present, the
extent and nature of the alkali-silica reaction in the test
specimen are often analyzed before and after ECE using
standard petrographic procedures found in ASTM(3) C
856.7 A gel fluorescence procedure found in SHRP-C-
3158 is also often used. Based on these results the need
for ASR mitigation can then be assessed.
Results of ECE testing include:
• expected current density,
• recommended total charge,
• expected time of treatment,
• chloride removal efficiency,
• effect on alkali-sensitive aggregate, and
• effectiveness of lithium ion in mitigating ASR (if
lithium is used in the electrolyte).
B. System Selection and Installation
In order to achieve the full potential of an ECE project,
consideration and planning go into the design and selec-
tion of system components to meet the needs of each
specific project. Six main areas are typically considered
prior to installation.These are:
• site utilities and services,
• anode,
• electrolyte,
• electrolyte media,
• rebar connections, and
• system operation.
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___________________________
(3) ASTM, 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.
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1. Site Utilities and Services
ECE uses a number of site utilities and services.
The most notable of these are electricity, water (elec-
trolyte), and physical access to the site.
ECE uses a temporary electrical power supply for the
four- to eight-week treatment period. Most rectifiers
designed for ECE use alternating current (AC) input.
 Generally, this power is readily available near the
site. If a power supply is not available locally, or the
cost to access the local system is prohibitive, gener-
ators might be used.
An electrolyte solution is also typically used. Water
is generally available on site as the main constituent
of electrolyte solutions. A connection to the local
water supply is usually the most cost-effective source
of water. If this option is not available, water storage
tankage and pumping equipment are generally used.
Finally, site access such as scaffolding or portable
lifts are sometimes used to gain access to the struc-
ture to install and remove the system. 
Anode, Electrolyte, and Electrolyte Media
The selection of the anode, electrolyte, and the elec-
trolyte media is a common consideration in assuring
a successful installation. There are numerous mater-
ials and combinations available, and each one has
its own advantages and disadvantages.
2. Repairs Prior to Installation
It is usual to carry out concrete repairs prior to apply-
ing ECE to:
• Restore the appearance of the structure
• Provide an electrolyte between the anode
and the reinforcing steel
The repair material is usually cementitious and is sel-
ected for its compatibility with the structure and with
the ECE process. It might be specified in terms of
shrinkage and resistivity when measured under con-
trolled laboratory conditions.
3. Anode
The two most common anodes currently being used
are catalyzed titanium and steel. Other anode mater-
ials might be suitable if sufficient field performance
data are provided.
(a) Catalyzed Titanium Anode
Catalyzed titanium has the advantage of being
an inert anode that, under suitable conditions,
does not corrode. The catalyzed coating on the
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anode is consumed over time, and after
repeated use this coating is generally signifi-
cantly deteriorated. Titanium anodes use a
buffered alkaline electrolyte or regular electrolyte
replacement to prevent the electrolyte from
becoming acidic and to prevent the possibility of
chlorine generation as the treatment progresses.
For electrical connections, current distributor
strips made of ASTM B 2659 Grade 1 titanium
are typically used.
(b) Steel Anode
Steel is not inert and is consumed during the
operation of the system. The use of steel mini-
mizes the acidification of the electrolyte and
chlorine gas evolution. By the completion of the
treatment a large percentage of the steel is oxi-
dized to rust. This rust can stain the surface of
the concrete during treatment. Depending on the
application, this is sometimes a concern. Gen-
erally, however, staining can be removed by a
light abrasive blast. Abrasive blasting is also
sometimes used as surface preparation for a
protective coating or sealer that is applied to
minimize recontamination by chlorides in the
future.
4. Electrolyte
Numerous types of electrolyte solutions have been
used. The most common of these are water, calcium
hydroxide solution (lime water), and to a limited
extent, lithium borate solution. As is the case with
the anodes, each of these electrolytes has unique
benefits and disadvantages. Circulation of the elec-
trolyte solution is generally beneficial. Some of the
major benefits and disadvantages are outlined below.
(a) Water
Potable water is inexpensive and readily avail-
able at many sites. No environmental protection
or containment is used with potable water. The
greatest disadvantage of using water as an elec-
trolyte is that it has no buffering capability. If
water is used as an electrolyte with an inert
anode in a closed system, electrolyte acidifi-
cation and chlorine evolution can occur if the
water is not regularly replaced.
(b) Calcium Hydroxide Solution
Calcium hydroxide solutions have been used to
provide a limited buffering capability. Calcium
hydroxide has a very low solubility in water, but
if a reservoir of solid calcium hydroxide is main-
tained, this material slowly dissolves over time
to replace the spent solution. Calcium hydroxide
solutions are somewhat more expensive than
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straight water and take some time to prepare
and maintain. Calcium hydroxide solution is
generally more suitable for use with an inert
anode.
(c) Lithium Borate
In cases in which there are concerns regarding
the risk susceptibility of the concrete, lithium
borate has been used to minimize ASR gel
formation in the concrete cover zone affected by
ECE treat-ment. A 0.2-mol lithium borate
(Li3BO3) solution has been used on some
projects. This can be prepared by mixing 0.12 lb
LiOH and 0.1 lb H3BO3 per gal (14.4 g LiOH and
12 g H3BO3 per L) of water. This electrolyte
provides a very highly buffered solution that is
suitable for closed-system applications in which
an inert anode is used.
At this concentration, the volume of the electro-
lyte used to neutralize the acid generated by an
inert anode during the treatment can be calcu-
lated using Equation (8):
V = 0.00026QA (8)
where:
V = volume in gallons
Q = total planned charge in A-hr/ft2
A = area of concrete to be treated (ft2).
Equation (9) can be used to calculate volume
using metric units.
V = 6 x 10-7QA (9)
V = volume in liters
Q = total planned charge in A-hr/m2
A = area of concrete to be treated in m2
Lithium-based electrolytes have been used when
concrete suffering from ASR is involved because
experiments have shown lithium to be effective
in mitigating ASR. Disadvantages of lithium
electrolyte solutions include their relatively high
cost and potential disposal concerns.
5. Electrolyte Media
Electrolyte media are simply materials used to sus-
pend, hold, or contain the electrolyte solution on the
surface of the concrete. Electrolyte media are also
used to provide separation between the anode and
the concrete surface. There are three main types of
electrolyte media currently in use. These are as
follows:
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• sprayed cellulose fiber that is primarily used
for vertical and overhead surfaces,
• felt mats that are primarily used in hori-
zontal applications, and
• surface-mounted tanks (SMTs) that are also
used to create a “ponded” environment on a
vertical surface.
Other materials might be suitable for use as electro-
lyte media, but no record of proven field experience
exists.
In addition to the ability to retain electrolyte for a long
period of time, another typical consideration is the
ability of electrolyte media to conform to irregular
concrete surfaces such that close and uniform con-
tact between the anode and the structure is main-
tained during the treatment. This is particularly true
on vertical surfaces and structures with complicated
geometrics.
(a) Sprayed Cellulose Fiber
The sprayed cellulose fiber system consists
essentially of a matrix of wet cellulose fiber
(recycled from old newspapers). The sprayed
cellulose fiber media provides electrical contact
between the anode and the concrete surface.
The spraying of the cellulose fiber can be done
in either a single application or two separate
applications, depending on the field conditions.
The cellulose fiber is generally applied approx-
imately 1.5 to 2.0 in. (40 to 50 mm) thick.
Sprayed cellulosefiber has the advantages of
being able to conform to any concrete shape,
being self-adherent, and being capable of retain-
ing a large volume of electrolyte solution. In
addition, the cost of the cellulose fiber is not
high. Disadvantages of using cellulose fiber
include the need to keep it wet during the treat-
ment process, and the clean-up and disposal of
the used material at the end of the project.
Depending on the type used, the mixture of cel-
lulose fiber and electrolyte solution can provide
some buffering and generally provides a greater
spacing between the anode and the concrete
surface.
(b) Felt Mats
Felt mats or other similar media can be used for
horizontal “ponded” applications such as bridge
or parking decks. Depending on the application,
the felt mats can be rolled up and reused on
future projects. The felt mats are typically main-
tained wet during the treatment process. Instal-
lation of this system generally involves building a
dam to confine the electrolyte within the area to
be treated.10
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Felt mats have been used on vertical surfaces in
three SHRP-related field trials in the U.S. The
system utilized a nonreusable absorbent inner
pad to help hold moisture while it was secured in
a vertical orientation. A prefabricated anode
blanket system, placed over the inner pad, con-
sisted of a titanium mesh anode sandwiched
between two different geotextile blankets, sel-
ected primarily for their strength, in order to
support straps and buckles used to secure the
assembly on the concrete members. The whole
assembly was wrapped tightly around the con-
crete member and then secured with the straps
and buckles attached to the blanket system.
This assembly can be wrapped with a plastic
film to minimize evaporative losses or dilution of
electrolyte caused by entry of rainwater. Per-
formance of the system depends on its ability to
retain electrolyte and provide intimate contact
between the anode, electrolyte media, and con-
crete surface.
(c) Surface-Mounted Tanks (SMTs)
SMTs have been built to fit a given structure or
built in panels to cover a larger area. Individual
SMTs have been produced in various sizes and
curvatures as needed. Each tank has been
sealed to prevent leakage of electrolyte. Before
installation one catalyzed titanium anode has
been placed inside each tank to serve as the
anode.
Installation of the SMTs has involved the use of
anchors and brackets. The initial cost has been
high, but if they can be reused many times, the
cost per usage can be reduced. Tanks do not
always need frequent “topping up” if evaporation
and leakage are minimized. Prevention of leak-
age can sometimes be difficult if concrete sur-
faces are not smooth or uniform.
6. Rebar Connections and Cabling
Electrical connections to the rebar, anode, and recti-
fier have been used to complete the installation.
Wiring has been installed to meet all local electrical
code requirements. Wiring has been color-coded
such that anode and cathode cables can be easily
identified. Generally, anode cables are color-coded
red (positive) and cathode cables are coded black.
For the cathode, a minimum of one connection per
500 ft2 (50 m2) with a minimum of two connections
per rectifier output circuit have typically been used.
Operation of an ECE system requires electrical cont-
inuity of the reinforcing steel. Electrical continuity
has been confirmed and additional cathode connec-
tions or rebar bonding have been sought if continuity
is not sufficient. Cables have been of sufficient wire
gauge size for the current and distance involved.
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Connections have been sealed to prevent corrosion,
and all cables to zones and subzones have been
marked and accessible to allow measurement during
treatment.
7. System Operation
ECE treatment duration has typically been between
four and eight weeks. During this time frame, the
system has been maintained and operated. Varying
degrees of maintenance and periodic inspection have
been used with different system configurations.
The installation has been kept wet during the
treatment process. For cellulose and felt installations
this has involved either daily wetting by a person on
site or the installation of an automatic wetting
system. Tank systems or other “ponded” systems
use electrolyte circulation. Electrolyte is sometimes
added to make up for evaporation or leakage. Also,
electrolyte might be replaced to reduce the chloride
content and prevent the acidification of the elec-
trolyte. Generally, a buffered electrolyte is used for
these systems. Operating limits and modes, opera-
ting duration, and provision for maintenance and
testing are normally designed into an effective sys-
tem.
C. Treatment Regimes
Appendix A provides guidance on performing the ECE
process.
D. End Point Determination and Typical Acceptance
Criteria
A number of different methods have been used to deter-
mine when sufficient treatment has been provided to the
structure. Each of the typical acceptance criteria listed in
Appendix B has its own benefits and disadvantages.
Each individual criterion has not always been suitable for
every structure.
In most situations, the treatment of a given structure is
concluded when one of the criteria listed in Appendix B is
achieved. In many cases all of these criteria are
achieved more or less simultaneously. In some situa-
tions it is not possible to achieve one or more of the
criteria because of the pre-existing conditions or the
nature of the structure. Additional acceptance criteria,
e.g., total treatment duration, have been used to meet
specific project objectives.
It is impossible to remove all the chlorides from the con-
crete by electrical means. The area immediately around
the rebar is typically left almost chloride-free, but farther
away there is less effect. This is particularly true behind
the steel. Chloride extraction depletes the amount of
chloride immediately in contact with the steel and replen-
ishes the passive layer. Between 40% and 95% of the
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chlorides are generally removed. Field data so far show
that this is effective in stopping corrosion for at least eight
years. The U.S. FHWA predicts that ECE technology can
extend the life of bridges by 5 to 10 years or more. The
main factor that determines longevity of the treatment is
the degree to which the structure can be protected from
further chloride contamination.
If large amounts of chloride have penetrated beyond the
steel or were cast uniformly into the concrete, chloride
extraction can remove much of the chloride in the cover
concrete. Current flowing from successive layers helps to
remove chlorides from below the first layer of reinforce-
ment. However, depending on rebar spacing and other
factors, less current goes behind the bars, so much of the
chloride beyond the steel might remain. If large reserves
of chlorides are left in the bulk of the concrete, these chlo-
rides can, over time, diffuse toward the steel, and the
benefits of the removal process can be limited. 
However, research shows that some important aspects of
the chloride extraction process are the generation of
hydroxyl ions, the rebuilding of the protective passive
film, and the removal of the chlorides immediately around
the rebar. SHRP research showed that even with a
modest total charge passed and only 50% to 80% chlor-
ide removal, and with chloride levels still above the
corrosion threshold, ECE gives a very low corrosion rate
and very passive half-cell potentials that last more than
10 years without reactivation. On this basis, the process
could perhaps be called “electrochemical chloride miti-
gation,” and removing high percentages of the chloride is
not always necessary.
E. Post-Treatment of Treated Structures
The post-treatment of treated structuresis a consid-
eration that is typically incorporated into the planning and
implementation of any ECE project. Considerations
include type of post-treatment, timing of post-treatment
application, and need for reapplication in the future.
1. Purpose of Post-Treatment
When ECE is effective in removing chlorides and
reestablishing the passive environment around the
embedded reinforcing steel, it is sometimes bene-
ficial to protect the treated structure in some manner
to extend the service life of the treatment and the
structure. Although it is possible to allow the struc-
ture to be recontaminated and retreat it on a periodic
basis, this option might not be economically viable.
2. Types of Post-Treatment
Types of post-treatment include, but are not limited
to, “no post-treatment”; applications of various
“breathable” sealers and impermeable barrier coat-
ings; and concrete overlays.
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• “No post-treatment” is typically considered
to be an option in some applications in
which the source of the chlorides has been
or can be eliminated.
• Breathable or impermeable sealers and
coatings can be used to prevent treated
structures from becoming contaminated
because of the continued exposure of the
structure to chlorides. Typical considera-
tions in selecting an appropriate material for
a given application include, among others,
chloride-screening effectiveness of the pro-
duct, mechanical/abrasion resistance of the
product, and moisture-permeability proper-
ties.
• Concrete overlays can provide protection by
increasing the concrete-cover thickness
(distance from the surface to the reinforcing
steel). A good quality overlay can provide
protection because new chlorides applied to
the surface diffuse through the additional
overlay material before reaching the steel.
3. Timing of Post-Treatment Application
In most cases, the application of post-treatment (if
applicable) is driven by the overall project sched-
uling. Some factors that can influence the ideal
timing of such an application include environmental
factors such as temperature, but also include con-
straints such as the moisture content of the concrete
immediately after treatment.
F. Typical Monitoring Methods Used in Treated
Structures
During the process of ECE, deleterious chloride ions at or
near the interface of the reinforcing steel are forced to
migrate away under the influence of a negative potential
applied to the steel (i.e., by making the steel a cathode).
It is well known that the minimum threshold chloride con-
centration (total chloride ion content) to initiate corrosion
of steel in normal concrete is approximately 260 ppm (wt
concrete), approximately 0.2% (wt cement). The
threshold chloride concentration in electrochemically
treated concrete can be somewhat higher because of the
concentration of hydroxyl ions that are generated during
treatment. The objective of ECE is to reestablish the
passive oxide film on the reinforcing steel. Generally this
is achieved by reducing the chloride content to below the
threshold value at the concrete/steel interface. Once the
chloride content is lowered, other parameters, such as
the corrosion potential and the rate of corrosion of the
steel, are also impacted.
When treated structures are not sufficiently protected and
become recontaminated with sufficient chlorides, cor-
8
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rosion is reinitiated. Although there is no record of any
field structure that has been treated more than once,
there is no reason why it could not be done. From an
economic point of view, it would generally be much more
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NACE International
cost effective to protect a treated structure than to retreat
it sometime in the future. Therefore, steps for monitoring
ECE-treated structures, provided in Appendix C, are gen-
erally used.
Limitations and Benefits of ECE Treatment
A. Limitations of ECE Treatment
Passing large amounts of electricity through concrete can
have effects on its chemistry and therefore its physical
condition. Brown staining around the rebar has been
observed on test specimens when high current densities
(over 0.5 A/ft2 [5 A/m2]) are used. This is an effect on the
concrete, not the steel. Current levels are therefore nor-
mally maintained at less than 0.2 A/ft2 (2 A/m2) (usually
in the range of 0.05 to 0.1 A/ft2 [0.5 to 1 A/m2]).
There are three known potential side effects of ECE. The
first is hydrogen evolution and its effects on prestressing
steels. Another is reduction in bond at the steel/concrete
interface. The third side effect is the acceleration of ASR.
1. Prestressing Steels
Prestressing steels are generally sensitive to hydro-
gen embrittlement. Hydrogen is generated at the
concrete/steel interface during treatment. As a result,
the ECE process has not been used on concrete ele-
ments containing prestressing steel. In some cases,
electrochemical techniques are directed toward con-
ventional reinforcement in structures that also con-
tain prestressing steels. Previous research has
shown that stray current interference can occur on
electrically isolated prestressing wires. Typically the
stray current corrosion has occurred where the wire
crossed in close proximity to conventional reinforce-
ments (stirrups) that were involved in cathodic pro-
tection applications. If this type of structure is
treated, these wires are usually isolated or otherwise
protected. Electrochemical treatment of convention-
ally reinforced bridge decks and piers has been
completed on structures that contained prestressed
concrete girders with no apparent detrimental effects.
In general, the process is not applied to the pre-
stressed elements themselves.
Structures containing prestressing steels can be
treated in certain specific applications. Portions of
post-tensioned structures have been treated when
the tendons were protected by metal or other protec-
tive sheaths within the area being treated.
2. Bond Strength
Some earlier laboratory tests showed that electro-
chemical treatment at high current densities could
reduce bond strength between the concrete and
smooth bars by as much as 50%. A very high cur-
rent density and about five times as much charge as
is used normally in an ECE treatment was applied.
No significant changes were noted when normal
current densities and total charge were used.
The effect of current on the bond strength of steel in
concrete has been a subject of discussion in the
technical literature for many years. This is usually
with reference to cathodic protection, but no effects
have been observed in the field on the many hun-
dreds of CP systems in service for up to 20 years. In
most practical applications, the major part of the
bond is supplied by the ribbing on the bars. The
details of the performance of the steel/concrete inter-
face are, therefore, irrelevant.
Experiments reported by Buenfeld and Broomfield11
show that bond strength increases as the test speci-
men corrodes. ECE appeared to eliminate this effect,
although the pull-out strength did not fall below the
level of uncorroded control specimens. Other work
reported by Ihekwaba, Hope, and Hansson12 shows a
significant bond strength reduction following ECE
treatment for plain, unribbed steel bars.
3. Loss of Ductility of Reinforcement
The failure of conventional reinforcement under load
while ECE is being applied was addressed by
Bennett et al.6 The results were evaluated by a
structural engineer. It was concluded that “testing of
notched specimens revealed no effect on the fracture
load strength of conventional reinforcing steel under
any conditions of electrochemical chloride removal.
Following these results, further testing of smooth
specimens did reveal a short-term loss in ductility
within the range of current density appropriate for
chloride removal. After reviewing the available data
it was concluded that this modest lossof ductility
does not create any significant problems or adversely
affect the useful life of concrete structures.”
4. Alkali-Aggregate Reactions
When a direct electrical current flows through con-
crete, negatively charged anions, such as chlorides,
migrate toward the anode. Concurrent with anion
extraction, positively charged cations migrate toward
the cathodically charged reinforcement. The most
mobile cations typically found in concrete are sodium
and potassium. The application of direct current
causes the molar concentrations of sodium and
potassium to increase near the reinforcement. The
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NACE International
degree of molar increase detected is proportional to
the charge passed at the observed location.
Certain aggregate types can react with the alkaline
pore solution of the cement paste. These alkali-
aggregate reactions can take several forms, inclu-
ding alkali-silica, alkali-silicate/silica, and alkali-car-
bonate reactions. These reactions can be expansive.
In a mechanical sense the expansive processes from
alkali-aggregate reactions are akin to reinforcement
corrosion. If expansive, the reaction generates pro-
ducts with greater volume than the parent. The vol-
ume increase generates tensile stress that can crack
the concrete.
A number of reports on ASR have been published.
SHRP has published a handbook for field identifica-
tion of ASR. The handbook discusses the causes of
ASR, the effects, and manifestations of ASR-related
volume changes in highway pavements, and test
methods to identify ASR.8
ACI(4) Publications ACI 201.1R13 and ACI 201.3R14
are also helpful in conducting field examinations to
evaluate distress resulting from alkali-aggregate
reactions.
Lithium salts can inhibit expansion due to ASR.
Lithium borate has been successfully employed in
the electrochemical extraction of chlorides from
structures that manifest ASR distress. It appears
that the lithium-bearing silicate reaction product that
forms does not have the capacity to expand when
present in the sodium-potassium silicates. If either
ASR or alkali-silicate/silica reactivity (ASSR) is a
problem, the use of lithium-based electrolyte is one
option typically considered.
5. Epoxy-Coated and Discontinuous Reinforce-
ment
ECE is not applicable for concrete elements con-
taining epoxy-coated reinforcement unless all indiv-
idual bars can be connected. Discontinuous steel
stray current corrosion can result in structures that
do not have sufficient continuity. There is also a risk
that ECE might lead to severe cathodic disbondment
of the coating.
6. Dissimilar Metals
Concrete elements containing electrically connected
dissimilar metals (aluminum conduit, for example)
might be damaged or given special consideration.
Brad Harrison - Invoice 27434 downloaded on 3/5/201
B. Benefits of ECE Treatment
ECE is an effective and nondestructive electrochemical
measure to remove chloride ions and stop reinforcing
steel corrosion from chloride-contaminated concrete. The
benefits associated with this treatment include:
• reduction of steel corrosion rate through the
extraction of chloride (the cause of the corrosion)
from the steel/concrete interface and the sur-
rounding concrete matrix;
• restoration of the passive oxide film on the
embedded rebar;
• increase of the alkalinity at the steel/concrete
interface;
• reduction of the chloride concentration within the
concrete
• reduction of macrocell corrosion caused by the
reduction of electrochemical incompatibility (dif-
ferences) between various sections of the same
structure
• reduction of future maintenance required on the
structure
• increased service life of treated structures.
The application of ECE as part of an overall repair can be
particularly useful because it reduces the electrochemical
potential difference between the reinforcing steel in vari-
ous sections of the structure. A durable repair can there-
fore be anticipated.
Example Benefits of Treatment
Comparisons of corrosion rates before and after treat-
ment have consistently showed significant reductions.
On the Tees Viaduct in the UK,15 field measurements of
corrosion rates were in the range of 2.1 to 10.7 µA/in.2
(0.33 to 1.66 µA/cm2) with a mean of 2.43 µA/in.2 (0.377
µA/cm2). On a block that was treated with ECE, readings
a year later ranged from 0.003 to 0.61 µA/in.2 (0.0005 to
0.094 µA/cm2) with a mean of 0.018 µA/in.2 (0.0028
µA/cm2). Although no direct “before and after” measure-
ments were conducted, this shows a difference of two
orders of magnitude in corrosion rate between (initially
similar) treated and untreated steel in concrete.
Resistivity measurements showed large increases after
treatment to more than 200 kΩ-cm in the field, and from
5 kΩ-cm on untreated lab specimens to 30 kΩ-cm after
treatment on specimens vacuum saturated with distilled
water. The treatment seemed to block pores, reducing
transport of water, oxygen, and chloride ions. This is
possibly because of redistribution of calcium hydroxide.
There was also an improvement in freeze/thaw resist-
ance.
10
___________________________
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8 1:13:00 PM Single-user licence only, copying/networking prohibited
On the Burlington Skyway in Canada, corrosion potentials
and corrosion currents have been monitored on an
annual basis since treatment in 1989. Both the corrosion
potentials and corrosion currents were significantly
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NACE International
reduced after treatment to a level within the passive
range. Readings have remained passive since the ECE
treatment was completed.
References
1. J.E. Slater, D.R. Lankard, and P.J. Moreland,
“Electrochemical Removal of Chlorides from Concrete
Bridge Decks,” Transportation Research Record 604
(1976).
2. G.L. Morrison et al., “Chloride Removal and
Monomer Impregnation of Bridge Deck Concrete by
Electro-Osmosis,” Kansas Department of Transporta-
tion,(5) Report No. FHWA-KS-RD 74-1, 1976.
3. NACE Standard RP0290 (latest revision), “Cathodic
Protection of Reinforcing Steel in Atmospherically
Exposed Concrete Structures” (Houston, TX: NACE).
4. NACE Standard TM0294 (latest revision), “Testing of
Embeddable Anodes for Use in Cathodic Protection of
Atmospherically Exposed Steel-Reinforced Concrete”
(Houston, TX: NACE).
J.E. Bennett, T.J. Schue, “Electrochemical Chloride
Removal from Concrete: A SHRP Contract Status
Report,” CORROSION/90, paper no. 316 (Houston, TX: 
NACE, 1990).
6. J.E. Bennett, T.J. Schue, K.C. Clear, D.L. Lankard,
W.H. Hartt, W.J. Swiat, “Electrochemical Chloride
Removal and Protection of Concrete Bridge Components:
Laboratory Studies,” National Research Council, Report
No. SHRP-S-657, 1993.
7. ASTM C 856 (latest revision), “Standard Practice for
Petrographic Examination of Hardened Concrete” (West
Conshohocken, PA: ASTM).
8
8. Handbook for the Identification of Alkali-Silica Reac-
tivity in Highway Structures, SHRP-C-315 (Washington,
DC: National Research Council(6)/SHRP, 1991).
9. ASTM B 265 (latest revision), “Standard Specification
for Titanium and Titanium Alloy Strip, Sheet, and Plate”
(West Conshohocken, PA: ASTM).
10. J.E. Bennett, K.F. Fong, T.J. Schue, “Electro-
chemical Chloride Removal and Protection of Concrete
Bridge Components: Field Trials,” National Research
Council, Report No. SHRP-S-669, 1993.
11. N.R. Buenfeld, J.P. Broomfield, “Effect of Chloride
Removal on Rebar Bond Strength and Concrete Prop-
erties,” in Corrosion and Corrosion Protection of Steel in
Concrete, ed. R.N. Swamy (Sheffield, UK: Sheffield
Academic Press,(7) 1994), pp. 1438-1450.
12. N.M. Ihekwaba, B.B. Hope, C.M. Hanson, “Pull-Out
and Bond Degregation of Steel Bars in ECE Concrete,”
Cement & Concrete Research 26, 2 (1996): pp. 267-82.
13. ACI 201.1R (latest revision), “Guide for Making a
Condition Survey of Concrete in Service” (Farmington
Hills,MI: ACI International).
14. ACI 201.3R (latest revision), “Guide for Making a
Condition Survey of Concrete Pavements” (Farmington
Hills, MI: ACI International).
15. J.P. Broomfield, Corrosion of Steel in Concrete:
Understanding, Investigation and Repair (London, UK: 
E.& F.N. Spon,(8) 1997), p. 156.
Bibliography
Armstrong. K., M.G. Grantham, and B. McFarland. “The
Trial Repair of Victoria Pier, St. Helier, Jersey, Using
Electrochemical Desalination.” Fourth International
Symposium on Corrosion of Reinforcement in Con-
crete Construction. C.L. Page, P.B. Bamforth, J.W.
Figg, eds. London, UK: Royal Society of Chemistry,
1996.
Asaro, M.F., A.T. Gaynor, and S. Hettiarachchi. “Electro-
chemical Chloride Removal and Protection of Con-
crete Bridge Components (Injection of Synergistic
Corrosion Inhibitors).” National Research Council
Report No. SHRP-S/FR-90-002. 1990.
Bennett, J.E., and T.J. Schue. “Chloride Removal Imple-
mentation Guide.” National Research Council Report
No. SHRP-S-347. 1993.
11
___________________________
(5) Kansas Department of Transportation, 915 Harrison, Room 754 - Docking State Office Building, Topeka, KS 66612-1568.
(6) National Research Council, National Academy of Sciences, Box 289, Washington, DC 20055.
(7) Sheffield Academic Press, Mansion House, 19 Kingfield Road, Sheffield S11 9AS, UK.
(8) E. & F.N. Spon, 11 New Fetter Lane, London, UK.
 1:13:00 PM Single-user licence only, copying/networking prohibited
NACE International
Bennett, J.E., and T.J. Schue. “Evaluation of NORCURE
Process of Electrochemical Chloride Removal from
Steel-Reinforced Concrete Bridge Components.”
National Research Council Report No. SHRP-C-620.
1993.
Broomfield, J.P. “Field Measurements of the Corrosion
Rate of Steel in Concrete Using a Microprocessor
Controlled Guard Ring for Signal Confinement.” In
ASTM STP 1276, Techniques to Assess the Corro-
sion Activity of Steel Reinforced Concrete Structures.
 Eds. N.S. Berke, E. Escalante, C.K. Nmai, and D.
Whiting. West Conshohocken, PA: ASTM, 1995.
Clemena, G.G., and D.R. Jackson. “Pilot Applications of
Electrochemical Chloride Extraction on Concrete
Bridge Decks in Virginia.” Virginia Transportation
Research Council(9) Report No. VTRC 96-IR3. 1996.
Clemena, G.G., and D.R. Jackson. “Pilot Applications of
Electrochemical Chloride Extraction on Concrete
Piers in Virginia.” Virginia Transportation Research
Council Report No. VTRC 96-IR4. 1996.
Manning, D.G., and A.K.C. Ip. “Rehabilitating Corrosion
Damaged Bridges Through the Electrochemical
Extraction of Chloride Ions” In ACI Special Publica-
tion 151-12, Concrete Bridges in Aggressive Environ-
ments − Philip D. Cady Symposium. Ed. R.E.
Weyers. Farmington Hills, MI: ACI International,
1994.
Miller, J. “The perception of the ASR problem with
particular reference to electrochemical treatments of
reinforced concrete.” In European Federation of Cor-
rosion Publication No. 25, Corrosion of Reinforce-
ment in Concrete – Monitoring, prevention and
rehabilitation, papers from Eurocorr ’97. London,
UK: IOM Communications, 1997.
Brad Harrison - Invoice 27434 downloaded on 3/5/201
“Norcure Desalination – Specification Guideline.”
Fosroc/NCT,(10) October 1991.
Page, C.L. “Interfacial Effects of Electrochemical Protec-
tion Methods Applied to Steel in Chloride Containing
Concrete.” In Rehabilitation of Concrete Structures. 
Ed. D.W.S. Ho and F. Collins. Cachan, Cedex,
France: RILEM,(11) 1992.
Sergi, G., and C.L. Page. “The Effects of Cathodic Pro-
tection on Alkali-Silica Reaction in Reinforced Con-
crete.” Transport Research Laboratory Contractor’s
Report, No. 310. 1992.
“SHRP Road Savers 1996.” Federal Highway Admini-
stration Publication, No. FHWA-SA-96-045 CS122.
1996.
Whitmore, D.W. “Electrochemical Chloride Extraction
from Concrete Bridge Elements.” CORROSION/96,
paper no. 299. Houston, TX: NACE, 1996.
Patents
“Apparatus for the Removal of Chloride from Reinforced
Concrete Structures.” U.S. Patent No. 5,296,120.
April 17, 1994.
“Method and Apparatus for Removal of Chlorides from
Steel Reinforced Concrete Structures.” U.S. Patent
No. 5,141,607. August 25, 1992.
“Process for Rehabilitating Internally Reinforced Concrete
by Removal of Chlorides.” U.S. Patent No.
5,228,959. July 20, 1993.
12
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(10) Fosroc International Ltd., Coleshill Road Tamworth B78 3TL, UK.
(11) RILEM, The International Union of Testing and Research Laboratories for Materials and Structures, Secretariat General, E N S - Bâtiment
Cournot, 61 avenue du Président Wilson, F-94235 Cachan Cedex, France.
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Appendix A: The ECE Process
The ECE process is typically performed as follows:
After the temporary anode system has been installed and
all electrical connections have been made, the rectifier is
switched on and the current density is typically set to 0.1
A/ft2 (1 A/m2) concrete surface area. If a voltage-regul-
ated unit is used, the voltage is adjusted until a current
density of 0.1 A/ft2 (1 A/m2) is reached. Maximum sys-
tem voltage is kept below 50 volts for safety reasons.
The initial current level (0.1 A/ft2 [1 A/m2]) is typically
maintained for one to four weeks before the system
voltage eventually reaches the preset maximum. As the
chloride content decreases, the electrical resistance of the
concrete increases. Because the power supply tries to
maintain a constant current, the system voltage is
increased over time until the preset maximum voltage has
been achieved. Beyond this point, the voltage is held
constant and the current decreases as further chloride
extraction takes place and the electrical resistance of the
concrete continues to increase.
If voltage-regulated power supplies are used, the current
typically increases, as the concrete becomes wet. Cur-
rent density is generally maintained below 0.2 A/ft2 (2
A/m2) of concrete surface area. SHRP testing concluded
that 0.5 A/ft2 (5 A/m2) of steel surface area was an accep-
table current density level. To avoid damage to the con-
crete and bond loss to the steel, the current density limit
is typically not exceeded.
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While the process is running, the total current to each
zone is measured regularly to control the current density
and, indirectly, to verify that sections of the system are
receiving similar treatment. For voltage-regulated power
supplies, the voltage is often adjusted.
For the first one or two days of treatment, voltage and
current for each zone are typically measured once or
twice a day. When the voltage and current have stabil-
ized, measurements are usually reduced to once a day or
once every second day. Alternately, voltage and currents
can be measured and recorded automatically using data
loggers.
After the system is energized, the current distribution is
checked regularly by measuring the current in each zone
or subzone. The readings are generally of similar magni-
tude when adjusted for differences in area or steel
density. 
The chloride extraction rate is highest at the beginning of
the process. A charge of 14 to 37 A-h/ft2 (150 to 400 A-
h/m2) represents approximately 25% of the total charge
used to complete the treatment in most cases. If testing
at this time indicates low efficiency, the cause is typically
investigated and a plan of corrective action is developed.
When sufficient chloride has been migrated away from
the reinforcing steel, or other predetermined condition is
reached, the current is switched off and the temporary
anode system is removed.
Appendix B: End Point Determination and Typical Acceptance Criteria
A number of different methods have been used to deter-
mine when sufficient treatment has been provided to the
structure. Each of the following typical acceptance cri-
teria has its own benefits and disadvantages.The indiv-
idual criterion has not always been suitable for every
structure.
1. Chloride content within the concrete: Using this
criterion, the treatment is continued until the chloride
content within the concrete in the vicinity of the reinfor-
cing steel is reduced to a predetermined level. Typically
the target values used for these measurements are water-
soluble chloride content of less than 0.2 to 0.4% by
weight of cement (when corrected for background chlo-
ride levels if appropriate) within 1.0 in. (2.5 cm) or one
diameter of the reinforcing steel.
To measure the chloride content, concrete samples are
taken and chloride level is measured. Treatment is halted
when the target chloride value is reached. Samples are
collected carefully to prevent contamination and are
located relative to the location of the rebar. Because of
the inhomogeneous nature of embedded concrete, sam-
ples are statistically analyzed to account for natural
variations in chloride content.
2. Amp hours per square meter: The most common
criterion for treatment involves assuring a minimum treat-
ment of 600 to 1,500 A-hr/m2 (56 to 140 A-hr/ft2). 1,500
A-hr/m2 (140 A-hr/ft2) is a very conservative value for
most applications. There are some structures for which it
might not be practical to achieve a given accumulated
charge.
3. Chloride/hydroxyl ratio: Using this criterion, the
chloride/hydroxyl ratio in the vicinity of the reinforcing
steel is generally reduced to less than 0.6.
4. Half-cell potentials and corrosion-rate monitoring
before and after treatment have been used in some
cases, but these measurements have limitations because
of the polarization of the reinforcing steel and the time
required for depolarization. Corrosion-potential measure-
ments are typically taken approximately six months after
treatment to allow for depolarization.
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Appendix C: Monitoring ECE-Treated Structures
The following steps are generally taken in monitoring
ECE-treated structures.
1. Visual survey: A careful survey to document the
condition of the structure is conducted.
2. Delamination survey: A delamination survey of the
structure is conducted.
3. Determination of chloride ion content: Concrete
core or powder samples are collected from the structure.
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Chloride ion content is determined at intervals up to the
steel depth to establish the chloride concentration profile.
4. Corrosion potential (half-cell) survey: A corrosion
potential survey is conducted on a grid pattern when
desired.
5. Corrosion rate measurements: Corrosion rate
measurements are conducted at predetermined points on
the structure when desired.
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	NACE International Publication 01101
	Foreword
	Introduction
	Theory
	Practice
	Limitations and Benefits of ECE Treatment
	References
	Bibliography
	Appendix A: The ECE Process
	Appendix B: End Point Determination and Typical Acceptance Criteria
	Appendix C: Monitoring ECE-Treated Structures