NACE SP0107-2007
Standard Practice
Electrochemical Realkalization and Chloride Extraction
for Reinforced Concrete
This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies, which preclude the issuance of interpretations by individual volunteers.
Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard.
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ISBN 1-57590-210-9 ? 2007, NACE International
NACE SP0107-2007
Item No. 21113
SP0107-2007
________________________________________________________________________
Foreword
This NACE standard practice presents the requirements for electrochemical chloride extraction and
electrochemical realkalization of reinforcing steel in atmospherically exposed concrete structures.
The standard provides the design engineer and contractor with the requirements for control of
corrosion of conventional reinforcing steel in Portland cement concrete structures through the
application of chloride extraction or realkalization. This standard is aimed at owners, engineers,
architects, contractors, and all those concerned with rehabilitation of corrosion-damaged reinforced
concrete structures.
These electrochemical techniques are related to the use of impressed current cathodic protection
of steel in concrete as described in NACE SP0290.1 State-of-the-art reports on the techniques
were previously published by the task group and are available from NACE.2,3 For more information
on design, maintenance, and rehabilitation of reinforcing steel in concrete, refer to NACE Standard
RP01874 and NACE Standard RP0390.5
To provide for the necessary expertise on all aspects of the subject and to provide input from all
interested parties, Task Group (TG) 054 is composed of corrosion consultants, consulting
engineers, architect engineers, cathodic protection engineers, researchers, structure owners, and
representatives from both industry and government.
The provisions of this standard should be applied under the direction of a registered Professional
Engineer or a person certified by NACE International as a Corrosion Specialist or Cathodic
Protection Specialist. His or her professional experience should include suitable experience in
corrosion control of reinforced concrete structures.
This standard was prepared in 2007 by NACE TG 054, a component of Specific Technology Group
(STG) 01 on Reinforced Concrete, and is published under the auspices of STG 01.
In NACE standards, the terms shall, must, should, and may are used in accordance with the
definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall
and must are used to state mandatory requirements. The term should is used to state something
good and is recommended but is not mandatory. The term may is used to state something
considered optional.
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SP0107-2007
________________________________________________________________________
NACE International
Standard
Practice
Electrochemical Realkalization and Chloride Extraction for
Reinforced Concrete
Contents
1. General (1)
2. Electrochemical Chloride Extraction (2)
3. Electrochemical Realkalization (6)
References (10)
Bibliography (11)
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SP0107-2007 ________________________________________________________________________
Section 1: General
1.1 Background
1.1.1 Following this General section, this standard is
divided into two stand-alone sections, the first on electrochemical chloride extraction and the second on
electrochemical realkalization. This will help the user by ensuring that all the relevant provisions are in one place.
1.1.2 Reinforcing steel is compatible with concrete
because of similar coefficients of thermal expansion and because concrete normally provides the steel with
excellent corrosion protection. The corrosion protection
is the result of the formation of a highly alkaline passive
oxide film on the surface of the reinforcement by Portland cement contained in the concrete. This passive oxide film is compromised by (1) excessive amounts of chloride or other aggressive ions and gases
such as carbon dioxide, or (2) the concrete not fully encasing the steel.
1.1.3 Corrosion occurs as a result of the formation of
an electrochemical cell. An electrochemical cell consists of four components: an anode, where oxidation occurs; a cathode, where reduction occurs; a
metallic path, where the electrons flow; and an electrolyte (concrete), where the ions flow. The anodic
and cathodic areas occur as a result of coupling of dissimilar metals, exposure to differential environmental
conditions, or both. If any one of the four elements of
the electrochemical cell is eliminated, corrosion can be
prevented.
1.1.4 Corrosion of reinforcing steel in concrete is a
serious problem in certain environments throughout the
world. This corrosion is directly attributable to the presence of significant amounts of aggressive substances at the steel surface. Parking structures, bridges and roadways, buildings, sanitary and water facilities, marine structures, concrete pipe, storage facilities, and other reinforced concrete structures are being damaged by corrosion. Corrosion of the reinforcing steel can weaken or destroy a structure.
Corrosion of the reinforcing steel in concrete and the resulting cracking and spalling of concrete costs billions
of dollars/euros, etc., each year. These losses can be
reduced if proper corrosion control factors are considered during rehabilitation and maintenance repair of reinforced concrete structures.
1.1.5 Carbonation of concrete is a major cause of
reinforcement corrosion. Carbonation is a process by
which atmospheric carbon dioxide reacts with the alkalis in the pore water of the concrete. A carbonation
front proceeds through the cover concrete to the reinforcement, where it leads to the breakdown of the passive oxide layer, allowing corrosion to proceed.
Electrochemical realkalization can be used to reverse
this process and restore the alkaline environment to the
reinforcement, preventing further corrosion.
1.1.6 Chloride-induced corrosion is the other major
cause of reinforcement corrosion. It has been shown
that chloride ion content as low as approximately 0.2
percent by weight of cement (or approximately 0.6
kg/m3 [1 lb/yd3] of concrete, depending on the cement
content of the mix) at the steel depth can initiate the
corrosion process. Electrochemical realkalization can
be used to move chloride ions away from the steel
surface and reestablish the protective passive oxide
layer.
1.2 Electrochemical Treatments
1.2.1 Electrochemical treatments for reinforced
concrete include cathodic protection (CP), electrochemical chloride extraction (ECE), and electrochemical realkalization (ER). ECE and ER are
short-term treatments with a temporary installation that
is removed after treatment. Treatment is intended to
remove the cause of corrosion. On the other hand, CP
is a permanent installation.
CP of atmospherically exposed steel in concrete is
described in NACE SP0290.1 Many of the practices
described in SP0290 are relevant to ECE and ER in
terms of preparation of the structure, testing, and
wiring.
1.3 Scope and Limitations
1.3.1 The provisions of this standard shall be applied
under the direction of a registered Professional
Engineer or a person certified by NACE International
as a Corrosion Specialist or certified as a Cathodic
Protection Specialist. The person’s professional
experience shall include suitable experience in CP,
ECE, and ER.
1.3.2 The requirements presented here are limited to
impressed current ECE and ER systems for new or
existing atmospherically exposed reinforced concrete
elements; they are not applicable to prestressed
concrete.
1.3.3 Normal reinforcement in post-tensioned
elements with the post-tensioning strands fully protected in ducts can be treated as long as adequate
precautions are taken to ensure that the prestressed
steel is not susceptible to hydrogen embrittlement and
that it is protected such that the potential of the steel
does not rise above the hydrogen evolution potential.
SP0107-2007
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Section 2: Electrochemical Chloride Extraction
2.1 Suitability for Treatment
A structure shall be suitable for ECE if:
2.1.1 There is sufficient chloride contamination to
warrant generalized or localized treatment to retard further chloride attack.
2.1.2 Water ingress can be controlled during treatment
so that the current density to the steel can be maintained and accurately monitored, especially in marine conditions. ECE is not suitable for application
to the elements of structures in splash and tidal zones.
2.1.3 There is no prestressed steel susceptible to
hydrogen embrittlement in the area to be treated. Any
prestressed steel shall be monitored to ensure that its
potential does not go more negative than -1,100 mV vs.
a copper/copper sulfate reference electrode.
2.1.4 Any susceptibility to alkali silica reaction (ASR) is
addressed by analysis of the risk of further ASR expansion and, if necessary, by the use of a suitable
electrolyte as discussed in Paragraph 2.3.2.
2.2 End Point Criteria
2.2.1 The criteria in this section have been found to
achieve corrosion control for reinforcing steel embedded in atmospherically exposed concrete after the application of ECE. Compliance with these criteria
is dependent on analysis of representative data in each
situation. The number and locations of measurements
made during data collection shall be commensurate with the complexity of the structure being protected.
Sampling plans shall be in accordance with ASTM(1)
E105.6 Sample size shall be determined in accordance
with ANSI(2)/ASQ(3)Z1.47 with the unit of product typically being 0.836 m2 (1.00 yd2) of protected metal
surface area. For structures in which ECE or ER systems are divided into discrete zones, testing inspection lots shall be defined. Acceptable quality and
confidence levels shall also be defined. Potentials of
reinforcing steel or other embedments measured against portable reference electrodes shall be obtained
in accordance with the techniques described in ASTM
C876.8 Sign conventions for potential and current density as well as conventions for graphical presentation of data shall be in accordance with ASTM
G3-89.9
2.2.2 NACE TG 054 developed these criteria through
evaluation of data obtained from successfully operated ECE systems. NOTE: Those using this standard shall review data made available after this standard’s publication to determine whether more effective criteria have been established. It is not intended that those responsible for corrosion control be limited to these criteria if it can be demonstrated by other means that adequate corrosion control can be achieved. A combination of criteria can be used on a single structure.
2.2.3 In all cases, the current density shall not exceed 4 A/m2 (0.4 A/ft2) of steel surface area, and the voltage shall be in the range of 30 to 50 V direct current (DC).
2.2.4 Electrochemical Chloride Extraction Criteria —At least one of criterion A, B, or C below (Paragraphs 2.2.4.1, 2.2.4.2, and 2.2.4.3) shall be used:
2.2.4.1 Criterion A—Chloride content within the
concrete: Treatment shall be continued until the
chloride content within the concrete in the vicinity
of the reinforcing steel is reduced to a predetermined level.
A suitable test method for chloride determination is
ASTM C1152/C1152M-04e1.10Treatment 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, samples are statistically analyzed to account for
natural variations in chloride content.
NOTE: Typical target values used for these measurements are acid-soluble chloride content of
less than 0.2 to 0.4% by weight of cement (when
corrected for background levels of chloride permanently bound in aggregates, if appropriate)
within 25 mm (1.0 in.) or one diameter of the
reinforcing steel.
2.2.4.2 Criterion B—Amp hours (A-h) per square
meter (per square foot): This criterion ensures a
minimum treatment of charge density per unit area
of steel. NOTE: 600 A-h/m2 (56 A-h/ft2) is a typical
minimum target. 1,500 A-h/m2 (140 A-h/ft2) is a
very conservative value and should not be exceeded for most applications. There are some
structures for which it might not be practical to
achieve a given accumulated charge.
___________________________
(1) ASTM International (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.
(2) American National Standards Institute (ANSI), 11 W. 42nd St., New York, NY 10036.
(3) American Society for Quality (ASQ), 611 East Wisconsin Ave., Milwaukee, WI 53201-3005.
SP0107-2007
2.2.4.3 Criterion C—Chloride/hydroxyl ratio: Using
this criterion, the chloride/hydroxyl ratio in the
vicinity of the reinforcing steel is reduced to less
than 0.6. A suitable method for measuring the
chloride content is ASTM C1152/C1152M-04e1. A
suitable method for measuring the pH of pore
water and chloride/hydroxyl ratio of pore water is
given in Cáseres, et. al.11
NOTE: Half-cell potentials and corrosion rate
monitoring before and after ECE 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. Potential or rate
measurements are typically taken approximately
six months after treatment to allow for
depolarization. A suitable method for measuring
half cell potentials is ASTM C876.8 One criterion
is to reduce the potential difference to less than
150 mV across the treated zone.
2.3 Design
2.3.1 Anode Systems
2.3.1.1 Anode systems shall be mild steel or
catalyzed titanium.
2.3.1.2 Mild steel anodes shall be welded wire
fabric. Mild steel anodes are suitable for
structures when some staining of the concrete
surface is not a concern, when the possible
evolution of small amounts of chlorine cannot be
tolerated, and when treatment time is short.
NOTE: A suitable steel mesh is 3.0 to 4.0 mm
(0.12 to 0.16 in.) diameter on a 50 x 50 or 100 x
100 mm (2 x 2 in. or 4 x 4 in.) mesh size.
Mild steel anodes shall be fixed apart from the
concrete surface so that the steel does not come
in direct contact with the concrete surface.
Electrical anode wires shall be attached to cleaned
surfaces of the steel anodes by a firm mechanical
bond, and the connections shall be sealed to
prevent corrosion during treatment. If staining of
the concrete surface occurs, discoloration shall be
removed, if desired, by a light abrasive blast
following treatment.
2.3.1.3 Catalyzed titanium anodes shall be used
when staining of the concrete is unacceptable and
when pH of the electrolyte can be carefully
monitored to prevent acidification and possible
chlorine evolution.
Catalyzed titanium anodes shall be in the form of a
flexible, highly expanded mesh that conforms easily to concrete surfaces.
Catalyzed titanium anodes shall, as a minimum,
meet the requirements of NACE Standard TM0294.12
Anode wires shall be attached to an ASTM B26513
Grade 1 titanium current distributor bar outside the
electrolyte. The current distributor bar shall distribute current to the catalyzed titanium anode
by resistance-welded connections extending the
length of the anode.
When catalyzed titanium anodes are used, the
electrolyte shall be buffered, or alkali shall be
periodically added to the electrolyte to prevent the
electrolyte from dropping below pH 7.
2.3.2 Electrolytes
2.3.2.1 Potable water is a suitable electrolyte and
ensures that the current carries the maximum amount of chloride with minimal competition from
other ions. However, water is liable to acidify and
may promote the evolution of chlorine gas on
mixed metal oxide coated titanium anodes.
2.3.2.1.1 Regular electrolyte replacement
may be required to maintain the pH above 6,
and control of evolved chlorine gas may be
required in confined areas. NOTE: Certain
fixtures and fittings to structures such as
window frames, light fittings, and railings may
be subject to attack from alkaline or acidified
electrolytes and may require additional
protection against electrolyte leakage.
2.3.2.2 Alkaline electrolytes minimize acidification
of the electrolyte and minimize chlorine gas evolution on inert anodes. The following alkaline
solutions are suitable:
2.3.2.2.1 Saturated calcium hydroxide with
an excess of solid material to maintain the
saturation.
2.3.2.2.2 Lithium borate is suitable where
there is concern about ASR in the concrete.
NOTE: A 0.2M lithium borate solution can be
prepared by mixing 14.4 g LiOH and 12 g
H3BO3 per liter of water (0.12 lb LiOH and 0.1
lb H3BO3 per gallon). The volume required to
neutralize the acid generated by an inert
anode for a charge Q is given by Equation (1):
SP0107-2007
V = 6 x 10-7QA (1) Where:
V = Volume (liters)
Q = Charge (A-h/m2)
A = Area of steel to be treated (m2)
2.3.2.2.3 Lithium borate electrolytes must be
mixed, handled, and disposed of according to
national and local health and safety
regulations.
2.3.3 Anode and Electrolyte Containment
2.3.3.1 For all systems, provision shall be made
for electrolyte replenishment, topping, and
circulation as required.
The electrolyte solution shall be protected against
climatic changes (sun, rain, wind, frost, etc.).
2.3.3.2 Sprayed cellulose fiber (shredded paper)
shall be sprayed onto an anode mesh fixed onto
wooden battens at suitable separations. The
electrolyte is sprayed onto the anode
simultaneously with the cellulose fiber.
2.3.3.3 Felt cloth or matting is suitable for decks
or vertical surfaces. The anode is sandwiched
between layers of suitable geotextiles and
continuously wetted with the electrolyte. A
waterproofing layer shall be applied to the external
surface to prevent electrolyte evaporation or
dilution by rainwater.
2.3.3.4 Tanks with built-in anode mesh are
suitable anodes. These shall be tailored to the
structure with suitable seals to prevent electrolyte
loss.
2.3.3.5 A ponding system is suitable for decks
that are flat and level over the required anode
area. Protection shall be applied to prevent
electrolyte evaporation or dilution by rainwater.
2.3.3.6 Other water-retaining systems may be
used.
2.3.3.7 Ion exchange resins may be used to
control the concentration of chloride ions in the
electrolyte.
2.3.4 Power Supply and Control System
2.3.4.1 The power supply shall be an alternating
current (AC) input transformer-rectifier with an
isolating transformer or other suitable regulated
power supply. 2.3.4.2 The power supply shall meet national electrical code or other relevant authority codes, shall be fully protected against short circuit, and shall be suitable for continuous operation in the environment in which it is intended to operate.
2.3.4.3 In the event that AC power from the electrical grid/domestic supply is not available, an electrical generator is a suitable power supply input.
2.3.4.4 DC output terminals shall be clearly marked anode (+) and reinforcement (-). All anode cables (+) shall be colored red, and all reinforcement cables (-) shall be colored black or as required by the national electrical code.
2.3.4.5 All cables shall be insulated and shall be properly sized based on current, length of cable, expected temperature range, and exposure condition.
2.3.4.6 The output of the power supply shall have constant current control with a maximum voltage limit of 40 V DC. There shall be an indicator light for AC power-on, and there shall be suitable methods for measuring DC voltage and current for each anode zone or group of subzones.
2.4 Installation
2.4.1 Much of the preparation for ECE installation is
similar to impressed current CP (see NACE SP02901).
2.4.2 Electrical continuity: The electrical continuity
between all the steel reinforcement and other metal embedments intended to be treated shall be tested at a representative number of locations. A minimum of two connections per ECE treatment zone is usually required for redundancy.
2.4.3 Each ECE treatment zone shall be provided with
multiple connection points to the reinforcement steel.
2.4.4 Performance Monitoring
2.4.4.1 Each anode zone to be treated shall be
provided with the means necessary to monitor the
total charge in A-h and duration of the treatment.
2.4.4.2 Installations in an enclosed area shall
include means of monitoring, controlling, and
extracting the evolved hydrogen, oxygen, and
chlorine gas.
2.4.5 Installation of Anode System
2.4.5.1 The concrete surfaces shall be free of
electrically insulating contaminants before the
anode system is installed.
SP0107-2007
2.4.5.2 Particular care shall be taken to avoid
short circuits between the anodes and any metallic
items at the surface of the concrete.
2.4.5.3 The anode in each zone to be treated
shall be provided with multiple anode connections.
2.4.5.4 Installation work shall be in accordance
with applicable national electrical codes and safety
standards.
2.4.6 Preliminary Testing and Documentation
2.4.6.1 Prior to commissioning the installation, the
following preliminary testing shall be carried out
and the results documented.
2.4.6.1.1 Polarity checks on all circuits.
2.4.6.1.2 Electrical continuity shall be
checked by measuring the resistances of all
anode connections and all cathode
connections within each treatment zone.
2.4.6.1.3 Electrical insulation checks shall be
carried out on all circuits to ensure the
electrical insulation of the DC positive side
from the DC negative side and from any
metallic items on or adjacent to the concrete
surface (e.g., scaffolding).
2.4.6.1.4 After applying the electrolyte
solution, anode/cathode resistance and
potential shall be measured for each zone to
further check for short circuits, which shall be
corrected prior to energizing the system.
2.4.6.1.5 Any gas monitoring and extraction
system shall be checked prior to energizing
the ECE system.
2.5 Energizing and System Adjustment
2.5.1 This portion presents recommended procedures
for the energizing and adjustment of the ECE processes.
2.5.2 Component Installation Inspection and Testing
Prior to Energizing
2.5.2.1 The AC service system shall be inspected
for compliance with the national electrical code
and such local codes and ordinances that are
applicable or in force. It shall be verified that the
AC service voltage, phase, and wiring sizes are
suitable for the calculated expected load from the
system. In the event that the system is run with a
temporary supply, the system still shall comply
with the national electrical code and local codes
and ordinances.
2.5.2.2 The rectifier/DC power supply shall be
inspected. The integrity of all AC input and DC
output connections shall be verified. All
mechanical fasteners shall be inspected and
tightened or replaced if appropriate.
2.5.2.3 The anodes, including feed circuitry, shall
be visually inspected for proper installation. It shall
be established that no short circuits exist between
any anode material (including electrolyte) and any
metal embedments.
2.5.2.4 The electrical continuity between all the
steel reinforcement and other metal embedments
intended to be treated shall be tested at
representative locations.
2.5.2.5 Electrical isolation of metal mounted on,
in, or adjacent to the protected concrete structure
and not designed to be treated and within the ECE
electric field shall also be tested.
2.5.2.6 All monitoring devices and attendant
hardware shall be inspected for proper installation
and operation in accordance with the manufacturer’s instructions and design specifications.
2.5.2.7 Additional equipment and associated
components shall be inspected for proper
installation and operation in accordance with the
manufacturer’s instructions and design specifications.
2.5.3 System Energizing and Adjustment
2.5.
3.1 The ECE system shall be energized after
completion and acceptance of the component
installation inspection.
2.5.
3.2 Each rectifier shall be turned on and
operated at a low current, typically not more than
1,100 mA/m2 (100 mA/ft2) of the steel surface
area.
2.5.
3.2.1 Proper circuit polarity shall be
verified.
2.5.
3.2.2 The rectifier shall be tested for
proper operation. The accuracy of all rectifier
meters shall be verified with a calibrated
portable meter.
2.5.
3.2.3 Current distribution to all individual
anode feed circuits shall be determined.
NOTE: If panel boards for such testing were
not included in the system design, clamp-on
DC ammeters or other techniques shall be
used.
SP0107-2007
2.5.
3.3 After completion of the system energizing
inspection, the system shall be adjusted to the
required current or voltage. The system shall not
need further adjustment for the duration of the
treatment except under exceptional conditions.
2.5.
3.4 Tests shall be conducted to verify that
electrically isolated metal is not adversely affected
by stray current from the operation of the system.
NOTE: This may be done by measurement of the
potential shift, which should not exceed a
predetermined amount, e.g., 20 mV positive of the
rest potential.
2.6 Records
2.6.1 Records of the ECE process shall be maintained
at a minimum twice daily during the operation to ensure that accurate records of A-h are recorded. This provides reference to previously obtained data in the event that changes occur, troubleshooting is required, or modifications or additions are made to the system.
These records shall include all the physical, design, and test data accumulated on the installation.
2.6.2 The following information, collected during the
installation, shall be made an integral part of the record.
2.6.2.1 Results of chloride in concrete tests and
other chemical and physical tests and analyses.
2.6.2.2 Delamination survey data.
2.6.2.3 Depth-of-cover data.
2.6.2.4 Extent and location of concrete repair.
2.6.2.5 Steel surface area vs. concrete surface
area.
2.6.2.6 Electrical continuity and electrical isolating
data.
2.6.2.7 Current requirement data.
2.6.3 During installation of the system, certain tests shall be performed to ensure a quality installation. The following data shall be part of the records:
2.6.
3.1 Electrical continuity verification.
2.6.
3.2 Tests for electrical shorts.
2.6.
3.3 Tests for electrical isolation.
2.6.4 The following additional information, if available, shall be included in the permanent records of the system.
2.6.4.1 Tests conducted to determine that all
components are in working order prior to energizing.
2.6.4.2 Criterion compliance data.
2.6.4.3 Final rectifier data including voltage and
current outputs, mode of control including limits,
rectifier serial number, and AC and DC capacity.
2.6.4.4 Current density and distribution data.
2.6.5 Detailed as-built drawings and data shall be incorporated into the permanent records.
2.6.6 The operation and maintenance manual shall become a part of the permanent records for the system.
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Section 3: Electrochemical Realkalization
3.1 Suitability for Treatment
A structure shall be suitable for ER if:
3.1.1 There is carbonation down to and approaching
reinforcement depth in sufficient locations to warrant
generalized treatment to retard further carbonation attack.
3.1.2 Water ingress can be controlled during treatment
so that the current density to the steel can be maintained and accurately monitored, especially in marine conditions. Realkalization is not suitable for
application to structural elements in splash and tidal
zones.
3.1.3 The area to be treated has no prestressed steel
susceptible to hydrogen embrittlement. Any
prestressed steel shall be monitored to ensure that its
potential does not go more negative than -1,100 mV vs.
a copper/copper sulfate reference electrode.
3.2 End Point Criteria
3.2.1 The criteria in this portion have been found to
achieve corrosion control for reinforcing steel embedded in atmospherically exposed concrete after the application of ER. Compliance with these criteria is
dependent on analysis of representative data in each
situation. The number and locations of measurements
made during data collection shall be commensurate with the complexity of the structure being protected.
Sampling plans shall be in accordance with ASTM E105.6 Sample size shall be determined in accordance
with ANSI/ASQ Z1.47 with the unit of product typically
being 0.836 m2 (1.00 yd2) of protected metal surface
SP0107-2007 area. For structures in which ER systems are divided
into discrete zones, testing inspection lots shall be
defined.
Acceptable quality and confidence levels shall also be
defined. Potentials of reinforcing steel or other embedments measured against portable reference electrodes shall be obtained in accordance with the techniques described in ASTM C876.8 Sign conventions for potential and current density as well as
conventions for graphical presentation of data shall be
in accordance with ASTM G3-89.9
3.2.2 NACE TG 054 developed these criteria through
evaluation of data obtained from successfully operated
ER systems. NOTE: Those using this standard shall review data made available after this standard’s publication to determine whether more effective criteria
have been established. It is not intended that those responsible for corrosion control be limited to these criteria if it can be demonstrated by other means that adequate corrosion control can be achieved. A combination of criteria may be used on a single structure.
3.2.3 In all cases, the current density shall not exceed
4 A/m2 (0.37 A/ft2) of steel surface area.
3.2.4 The voltage in the range 30 to 50 V DC.
3.2.5 Electrochemical Realkalization Criteria – At
least one of criteria A or B below (Paragraphs 3.2.5.1
and 3.2.5.2) shall be used subject to Paragraphs 3.2.3
and 3.2.4 above.
3.2.5.1 Criterion A—Amp hours per square meter
(per square foot): This criterion ensures a
minimum treatment of charge density per unit area
of steel. NOTE: A treatment of 200 A?h/m2 (19 A-
h/ft2) delivered to the steel surface is a suitable
minimum target.
3.2.5.2 Criterion B—pH Level: The effectiveness
of the ER process is demonstrated by pH testing
using phenolphthalein solution in each anode zone
with the extent of ER indicated by pink coloration
surrounding the reinforcement to a minimum of 10
mm (0.4 in.) or the bar diameter, whichever is
greater. NOTE: BSEN 14630,14 is a suitable
method for preparing the phenolphthalein solution
and measuring carbonation depth.
3.3 Design
3.3.1 Anode Systems
3.3.1.1 Anode systems shall be mild steel or
catalyzed titanium.
3.3.1.2 Mild steel anodes are suitable for
structures when staining of the concrete surface is
not a concern.
Mild steel anodes shall be welded wire fabric.
NOTE: A suitable steel mesh is 8 to 10 diameter (3
to 4 mm [0.12 to 0.16 in.]) wire on a 50 x 50 or 100
x 100 mm (2 x 2 in. or 4 x 4 in.) mesh size.
3.3.1.3 Mild steel anodes shall be fixed away from
the concrete surface so that the steel does not
come in direct contact with the concrete surface.
Electrical anode wires shall be attached to cleaned
surfaces of the steel anodes by a firm mechanical
bond, and the connections shall be sealed to
prevent corrosion during treatment. NOTE: If
staining of the concrete surface occurs, a suitable
method for removing discoloration is by a light
abrasive blast following treatment.
3.3.1.4 Catalyzed titanium anodes shall be used
when staining of the concrete is a concern, and
when pH of the electrolyte can be carefully
monitored to prevent acidification and possible
chlorine evolution.
3.3.1.
4.1 The anodes shall be in the form
of a flexible, highly expanded mesh that
conforms easily to concrete surfaces.
3.3.1.
4.2 The anodes shall, as a
minimum, comply with the requirements of
NACE TM0294.12
3.3.1.
4.3 Anode wires shall be attached
to an ASTM B26513 Grade 1 titanium
current distributor bar outside the
electrolyte. The current distributor bar
shall in turn distribute current to the
catalyzed titanium anode by resistance-
welded connections extending the length
of the anode.
3.3.1.
4.4 When catalyzed titanium
anodes are used, the electrolyte shall be
buffered, or alkali shall be periodically
added to the electrolyte to prevent the
electrolyte from dropping below pH 7.
3.3.2 Electrolytes
3.3.2.1 Alkaline electrolytes are generally
beneficial to the performance of the system, to
minimize the risk of etching of the concrete surface
and to minimize chlorine gas evolution on inert
anodes. The following alkaline solutions are
suitable. NOTE: certain fixtures and fittings to
structures such as window frames, light fittings,
and railings may be subject to attack from alkaline
or acidified electrolytes and may require additional
protection against electrolyte leakage.
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3.3.2.1.1 Potassium carbonate is a
suitable electrolyte for ER. A 1M solution
is suitable and is made from 107 g of
Na2CO3 per liter (0.89 lb/gal) of water.
3.3.2.1.2 The volume required to
neutralize the acid generated by an inert
anode for a charge Q is given by Equation
(2):
V = 1.2 x 10-7QA (2) Where:
V = volume (liters)
Q = Charge (A-h/m2)
A = Area of steel to be treated (m2)
3.3.3 Anode and Electrolyte Containment
3.3.3.1 For all systems, provision shall be made
for electrolyte replenishment, topping, and circulation as required.
3.3.3.2 The electrolyte solution shall be protected
against climatic changes (sun, rain, wind, frost,
etc.).
3.3.3.3 Sprayed cellulose fiber (shredded paper)
shall be sprayed onto an anode mesh fixed onto
wooden battens as suitable separations. The
electrolyte is sprayed onto the anode simultaneously with the cellulose fiber.
3.3.3.4 Felt cloth or matting is suitable for decks
or vertical surfaces. The anode shall be
sandwiched between layers of suitable geotextiles
and continuously wetted with the electrolyte. A
waterproofing layer shall be applied to the surface
to prevent electrolyte evaporation or dilution by
rainwater.
3.3.3.5 Tanks with built-in anode mesh are
suitable systems. These shall be tailored to the
structure with suitable seals to prevent electrolyte
loss.
3.3.3.6 A ponding system is suitable for decks
that are flat and level over the required anode
area. Protection shall be applied to prevent
electrolyte evaporation or dilution by rainwater.
3.3.4 Power Supply and Control System
3.3.
4.1 The power supply shall be an AC input
transformer-rectifier with an isolating transformer
or other suitable regulated DC power supply.
3.3.
4.2 The power supply shall meet national
electrical code and other relevant authority codes,
shall be fully protected against short circuits, and
shall be suitable for continuous operation in the
environment in which it is intended to operate.
3.3.
4.3 In the event that AC power from the
electrical grid/domestic supply is not available, a
suitable power supply input is an electrical
generator. DC output terminals shall be clearly
marked anode (+) and reinforcement (-).
3.3.
4.4 All anode cables (+) shall be colored red,
and all reinforcement cables (-) shall be colored
black. All cables shall be insulated and shall be
properly sized based on current, length of cable,
and expected temperature range.
3.3.
4.5 The output of the power supply shall have
constant current control with a maximum voltage
limit of 40 V DC. There shall be an indicator light
for AC power-on, and there shall be meters for DC
voltage and current for each anode zone or group
of subzones.
3.4 Installation
3.4.1 Much of the preparation for ER is the same as
for impressed current CP (see NACE SP02901).
3.4.2 Electrical continuity: The electrical continuity of
reinforcement shall be tested at a minimum of two locations per zone before applying realkalization treatment.
3.4.3 Each zone to be treated with ER shall be
provided with multiple connection points to the reinforcement steel.
3.4.4 Performance Monitoring
3.4.4.1 Each anode zone to be treated shall be
provided with the means necessary to monitor the
total charge in A-h and duration of the treatment.
3.4.4.2 Installation in an enclosed area shall
include means of monitoring, controlling, and
extracting any evolved hydrogen, oxygen, or other
evolved gas.
3.4.5 Installation of Anode System
3.4.5.1 The concrete surfaces shall be free of
electrically insulating contaminants before the
anode system is installed.
3.4.5.2 Particular care shall be taken to avoid
short circuits between the anodes and any metallic
items at the surface of the concrete.
3.4.5.3 The anode in each zone to be treated
shall be provided with multiple anode connections.
SP0107-2007
3.4.5.4 Installation work shall be undertaken in
accordance with applicable national electrical
codes and safety standards.
3.4.6 Preliminary testing and documentation
3.4.6.1 Prior to commissioning the installation,
the following preliminary testing shall be carried
out and the results documented.
3.4.6.2 Electrical continuity shall be checked by
measuring resistances of all anode connections
and all cathode connections within each
treatment zone.
3.4.6.3 Electrical insulation checks shall be
carried out on all circuits to ensure the electrical
insulation of the DC positive side from the DC
negative side and from any metallic items on or
adjacent to the concrete surface (e.g.,
scaffolding).
3.4.6.4 After applying the electrolyte solution,
anode/cathode resistance and potential shall be
measured for each zone to further check for short
circuits, which shall be corrected prior to
energizing the system.
3.4.6.5 Any gas monitoring and extraction
system shall be checked prior to monitoring the
ER system.
3.5 Energizing and System Adjustment
3.5.1 This portion presents recommended procedures
for the energizing and adjustment of the ER processes.
3.5.2 Component Installation Inspection and Testing
Prior to Energizing
3.5.2.1 The AC service to the system shall be
inspected for compliance with the national
electrical code and such local codes and
ordinances that are applicable or in force. It shall
be verified that the AC service voltage, phase,
and wiring sizes are suitable for the calculated
expected load from the system. In the event that
the system is run with a temporary supply, the
system still shall comply with the national
electrical code and all codes and ordinances.
3.5.2.2 The rectifier/power supply shall be
inspected. The integrity of all AC input and DC
output connections shall be verified. All
mechanical fasteners shall be inspected and
tightened or replaced, if appropriate.
3.5.2.3 The anodes, including feed circuitry, shall
be visually inspected for proper installation. It
shall be established that no short circuits exist
between any anode material (including
electrolyte) and any metal embedments.
3.5.2.4 The electrical continuity between steel
reinforcement and other metal embedments
intended to be treated shall be tested at
representative locations.
3.5.2.5 Electrical isolation of metal mounted on,
in, or adjacent to the protected concrete structure
and not designed to be treated and within the
electrical field shall also be tested.
3.5.2.6 All monitoring devices and attendant
hardware shall be inspected for proper
installation and operation in accordance with the
manufacturer’s instructions and design specifications.
3.5.2.7 Additional equipment and associated
components shall be inspected for proper
installation and operation in accordance with the
manufacturer’s instructions and design specifications.
3.5.3 System Energizing and Adjustment
3.5.3.1 The ER system shall be energized after
completion of the component installation
inspection. Each rectifier shall be turned on and
operated at a low current, typically not more than
1,100 mA/m2 (100 mA/ft2) of the steel surface
area. During this initial energizing period, all
circuits shall be tested.
3.5.3.1.1 Proper circuit polarity shall be
verified.
3.5.3.1.2 The rectifier shall be tested for
proper operation. The accuracy of all
rectifier meters shall be verified with a
calibrated portable meter.
3.5.3.1.3 Current distribution to all individual
anode feed circuits shall be determined. If
panel boards for such testing were not
included in the system design, clamp-on DC
ammeters or other techniques shall be used.
3.5.3.2 Tests shall be conducted to verify that
electrically isolated metal is not adversely
affected by stray current from the operation of the
system. NOTE: This may be done by
measurement of the potential shift, which should
not exceed a predetermined amount, e.g., 20 mV
positive of the rest potential.
3.5.3.3 After completion of the system energizing
inspection, the system shall be adjusted to the
required current or voltage. The system shall not
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need further adjustment for the duration of the
treatment except under unusual conditions.
3.6 Records
3.6.1 Records of the ER process shall be maintained
at a minimum twice daily during the operation to ensure
that accurate records of A-h are recorded. This
provides reference to previously obtained data in the
event that changes occur, troubleshooting is required,
or modifications or additions are made to the system.
These records shall include all the physical, design,
and test data accumulated on the installation.
3.6.2 The following information, collected during the
installation, shall be made an integral part of the record.
3.6.2.1 Results of chloride in concrete tests and
other chemical and physical analyses.
3.6.2.2 Delamination survey data.
3.6.2.3 Depth-of-cover data.
3.6.2.4 Extent and location of concrete repair.
3.6.2.5 Steel surface area vs. concrete surface
area.
3.6.2.6 Electrical continuity and electrical
isolating data.
3.6.2.7 Current requirement data. 3.6.3 During installation of the system, certain tests shall be performed to ensure a quality installation. The following data shall be part of the records:
3.6.3.1 Electrical continuity verification.
3.6.3.2 Tests for electrical shorts.
3.6.3.3 Tests for electrical isolation.
3.6.4 The following additional information, if available, shall be included in the permanent records of the system:
3.6.
4.1 Tests conducted to determine that all
components are in working order prior to
energizing.
3.6.
4.2 Criterion compliance data.
3.6.
4.3 Final rectifier data including voltage and
current outputs, mode of control including limits,
rectifier serial number, and AC and DC capacity.
3.6.
4.4 Current density and distribution data.
3.6.5 Detailed as-built drawings and data shall be incorporated into the permanent records.
3.6.6 The operation and maintenance manual shall become a part of the permanent records for the system.
________________________________________________________________________
References
1. NACE SP0290 (latest revision), “Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures” (Houston, TX: NACE).
2. NACE Publication 01101 (latest revision), “Electrochemical Chloride Extraction form Steel Reinforced ConcreteA State-of-the-Art Report” (Houston, TX: NACE).
3. NACE Publication 01104 (latest revision), “Electrochemical Realkalization of Steel Reinforced Concrete—A State-of-the-Art Report” (Houston, TX: NACE).
4. NACE Standard RP0187 (latest revision), “Design Considerations for Corrosion Control of Reinforcing Steel in Concrete” (Houston, TX: NACE).
5. NACE Standard RP0390 (latest revision), “Maintenance and Rehabilitation Considerations for Corrosion Control of Atmospherically Exposed Existing Steel Reinforced Concrete Structures” (Houston, TX: NACE).
6. ASTM E105 (latest revision), “Standard Practice for Probability Sampling of Materials” (West Conshohocken, PA: ASTM).
7. ANSI/ASQ Z1.4 (latest revision), “Sampling Procedures and Tables for Inspection by Attributes” (New York, NY: ANSI).
8. ASTM C876 (latest revision), “Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete” (West Conshohocken, PA: ASTM).
9. ASTM G3-89 (latest revision), “Standard Practice for Conventions Applicable to Electrochemical Measurements
in Corrosion Testing” (West Conshohocken, PA: ASTM).
10. ASTM C1152/C1152M-04e1 (latest revision), “Standard Test Method for Acid-Soluble Chloride in Mortar and Concrete” (West Conshohocken, PA: ASTM).
11. L. Cáseres, A.A. Sagüés; S.C. Kranc: and R.E. Weyers. “In Situ Leaching Method for Determination of
SP0107-2007
Chloride in Pore Water.” Cement and Concrete Research 36 (2006): pp. 492 to 503.
12. NACE Standard Test Method TM0294 (latest revision), “Testing of Embeddable Impressed Current Anodes for Use in Cathodic Protection of Atmospherically Exposed Steel-Reinforced Concrete” (Houston, TX: NACE). 13. ASTM B265 (latest revision), “Standard Specification for Titanium and Titanium Alloy Strip, Sheet, and Plate” (West Conshohocken, PA: ASTM).
14. BSEN 14630 (latest version), “Determination of Carbonation Depth in Hardened Concrete” (London, UK: British Standards Institute).
_______________________________________________________________________________
Bibliography
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Sheffield Academic Press, Vol. 2, 1994, pp. 1489-1498. Bennett, J.E., and T.J. Schue. Chloride Removal Implementation Guide. Strategic Highway Research
Program Report SHRP-S-347, 1993, National Research Council, Washington, DC.
Broomfield, J.P., and N.R. Buenfeld. Effect of Electrochemical Chloride Extraction on Concrete Properties: Investigation of Field Concrete.
Transportation Research Record, No 1597, 1997, pp.
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Broomfield, J.P., and N.R. Buenfeld. Electrochemical Chloride Extraction For Reinforced Concrete Structures
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Steel in Concrete, Vol. 2, Ed. R.N. Swamy, London,
UK, Sheffield Academic Press, 1994, pp. 1438-1450. Buenfeld, N.R., and J.P. Broomfield. Influence of Electrochemical Chloride Extraction on the Bond
between Steel and Concrete. Magazine of Concrete
Research 52, 2 (2000): pp. 79-91. Glass, G.K., A.C. Roberts, and N. Davison. “Achieving High Chloride Threshold Levels on Steel in Concrete.”
CORROSION/2004, paper no 332. Houston, TX: NACE, 2003.
Glass, G.K., and N.R. Buenfeld. The Inhibitive Effects of Electrochemical Treatment Applied to Steel in Concrete. Corrosion Science 42, 6 (2000): pp. 923-
927.
Glass, G.K., J. Taylor, A. Roberts, and N. Davison. “The Protective Effects of Electrochemical Treatment in Reinforced Concrete.” CORROSION/2003, paper no.
291. Houston, TX: NACE, 2003.
Hassanein, A.M., G.K. Glass G.K., and N.R. Buenfeld. “A Mathematical Model for Electrochemical Removal of
Chloride from Concrete Structures.” Corrosion 54, 4
(1998).
Mietz, J. Electrochemical Rehabilitation Methods for Reinforced Concrete Structures - A state-of-the-art-
report. Frankfurt, Germany. European Federation of
Corrosion/Institute of Materials, publication no. 24, 1998.
Miller, J.B. The Perception of the ASR Problem with Particular Reference to Electrochemical Treatments of
Reinforced Concrete. Corrosion of Reinforcement in
Concrete - Monitoring, Prevention and Rehabilitation.;
Frankfurt, Germany. European Federation of Corrosion, publication no. 25: 1997, pp. 141 to 149.
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