Impressed Current Cathodic Protection: A Corrosion Mitigation Technique For Transitional Steel-Frame Masonry-Clad Buildings

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IMPRESSED CURRENT CATHODIC PROTECTION:
A CORROSION MITIGATION TECHNIQUE
FOR TRANSITIONAL STEEL-FRAME
MASONRY-CLAD BUILDINGS
GINA L. CREVELLO AND
PAUL A. NOYCE
ECHEM CONSULTANTS LLC
72 Boodle Hole Road, Accord, NY 12404
Phone: 845-626-1205 • E-mail: gcrevello@e2chem.com
ABSTRACT
Impressed current cathodic protection (ICCP) has been used to mitigate corrosion damage in historic steel-frame
buildings since the early 1990s. This specific application of the technology originates from its use in concrete (1970s);
however, the discovery of cathodic protection dates to 1824.
The process of ICCP is the intentional application of current to a corroding piece of steel through an electrolyte. As
a redox reaction, oxidation and reduction occur simultaneously. The anodic reaction or oxidation is the loss of electrons,
which causes the steel to revert to rust. The volume of the rust can be as great as ten times the amount of steel
section loss. The accumulation of scale damages the exterior masonry cladding where the tensile forces of the corrosion
are greater than the masonry can withstand. Prior to large-scale losses and cracking, minor damages become apparent,
such as hairline cracking and open joints.
Simultaneous to this anodic reaction is the reduction reaction at the cathode site. The cathode reaction is harmless,
and the cathode gains electrons that have been lost at the anode site. The electrons pass from the anode as ionic
current through the masonry, moisture, or mortar electrolyte to the cathode site. The electrons return to the anode site
as electrical current, creating a full circuit. This reaction is the basis of cathodic protection, whereby the corrosion cell
is controlled, thus limiting damage to historic building fabric and providing a life extension to steel-frame structures.
The presentation will discuss corrosion reactions, investigative procedures, design challenges, and installation
requirements to help the audience understand the applicability of this technique as a means of corrosion control.
The paper will cover the steel-frame construction, corrosion onset, corrosion reactions, and installation and design
requirements needed for successful installations, as well as case studies.
SPEAKER
GINA L. CREVELLO — ECHEM CONSULTANTS LLC
GINA CREVELLO is the principal of Echem Consultants. She was professionally trained in architectural materials
conservation, having studied at Columbia University’s Graduate School of Architecture Planning and Preservation.
Upon completing her master’s of science, she completed the postgraduate certificate in Conservation of Historic
Buildings and Sites as the program’s first graduate. Crevello has 15 years experience in building diagnostics, with seven
years of experience in electrochemical treatments and corrosion engineering. Now she exclusively focuses on corrosion
failures of steel-frame and reinforced-concrete structures and material degradation. This work includes corrosion diagnostics,
nondestructive testing, life cycle assessments, durability engineering, and electrochemical remediation.
Crevello has been involved with the majority of installed impressed current cathodic protection systems on landmark
structures in the U.S. to date. Her work has included iconic structures, such as the Guggenheim Museum and
the United States Holocaust Memorial Museum.
NONPRESENTING COAUTHOR
PAUL A. NOYCE — ECHEM CONSULTANTS LLC
Paul Noyce is vice president and chief electrochemist for Electro Tech CP, LLC. Paul is professionally trained in electrical
and electronic engineering from the University of Bristol and received a diploma in electrochemistry 1991. He has
since been practicing corrosion engineering, and is regarded as a pioneer in the field of concrete and steel-frame corrosion
diagnostics and electrochemical corrosion remediation. Noyce was instrumental in the first use of ICCP for heritage
structures in both the United Kingdom and the United States and has extensive experience in galvanic cathodic
protection, electro-osmotic pulse, concrete realkalization, and electrochemical chloride extraction. He has been an advisor
on and designed electrochemical treatments for one-of-a-kind landmarks such as the Cutty Sark Clipper Ship, the
Thames Barrier, and Uxbridge Station. His traditional work includes transportation, civil, and industrial structures.
Noyce has designed and provided engineering oversight on the largest industrial and heritage ICCP protection systems
to be installed in the U.S to date. Noyce is chairman of NACE Committee NACE TG044 – (SP0290) Impressed Current
Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete, NACE TG460 – Testing and Evaluation
of Corrosion on Steel-Framed Buildings; vice chair of NACE TG048 – (SP0408) Reinforced Concrete Cathodic Protection
of Underground or Underwater Elements; and a member of NACE STG01 Reinforced Concrete, NACE TG047 – Sacrificial
Cathodic Protection of Reinforced Concrete Elements, NACE TG043X – Reinforced Concrete Cathodic Protection, ACI
201- Guide to Durable Concrete, ACI 365 – Service Life Prediction, and ACI 563 – Evaluation, Repair and Rehabilitation
of Concrete Buildings.
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INTRODUCTION
The use of impressed current cathodic
protection has been employed on masonryclad
steel-frame heritage buildings since the
mid-1990s. The work originated out of
England, when the Department of the
Environment, English Heritage, and
Historic Scotland sought alternative treatments
to large-scale stripping of “listed”1
steel-frame heritage buildings for corrosion
mitigation. This endeavor employed the
knowledge base used by the corrosion engineering
community. Applicable investigative
methods and electrochemical treatments
traditionally used for corrosion of reinforcing
steel in concrete were studied over a
three-year period. The results were the first
use of impressed current cathodic protection
(ICCP) for steel frames embedded in
masonry structures.
Steel embedded in a highly alkaline
environment, such as new mortar or concrete,
is in a “passive” state and protected
by the formation of an oxide layer.
Additionally, steel is “immune” from corrosion
at specific voltages, e.g., -500 mV vs.
standard hydrogen electrode (SHE) for steel
in an aqueous solution. Pourbaix diagrams
can help better explain the relationship of
pH vs. Eh (voltage) and its significance to
corrosion, immunity, and passivity of steel
within a specific environment, as seen in
Figure 1.
The onset of corrosion of steel in a mortar/
concrete electrolyte occurs after the
passive oxide layer breaks down. The
breakdown of the oxide layer occurs
through a neutralizing reaction with carbon
dioxide, called carbonation, which lowers
the concrete pH.2 As moisture and oxygen
enter the concrete matrix at cracks in the
concrete or through diffusion, corrosion initiation
has begun. A corrosion reaction generates
a chemical change as well as an electrical
potential change (electrochemical).
The electrochemical reaction that occurs at
the steel surface utilizes the backup mortar,
masonry, or surface moisture as an electrolyte
through which corrosion current
flows. The corrosion reaction will be dependent
upon various elements: oxygen, moisture,
chlorides, and temperature, to name a
few. To halt the corrosion reaction, the environment
or the reaction must be changed.
The conceptual aspect of the ICCP as
applied to historic buildings is the same as
when ICCP is applied to reinforcing steel in
concrete. Construction details and cladding
materials differ, though the corrosion
process is the same. It is most often a general
carbonation-related (drop in pH),
atmospheric corrosion reaction that affects
steel-frame construction.
Chlorides are very important as corrosion
accelerants. While chlorides have the
ability to break down the oxide layer and
cause accelerated reactions, they are not a
primary cause of steel-frame corrosion. The
presence of chlorides in steel-frame construction
could be from 1) the use of deicing
salts at the sidewalk, thereby only affecting
the base; 2) marine mist, affecting coastal
buildings; and 3) the use of calcium chlorides
or other curing agents used in “winter”
construction. These would most likely be
found in concrete floors or roof slabs tied
into a steel frame.
To control corrosion, the anode, the
cathode, or the environment must be controlled.
If the steel cannot be protected by a
barrier (coating), corrosion will occur in the
presence of oxygen and moisture. To paint
the steel, significant amounts of masonry
are required to be removed. As this further
damages landmarked buildings and expensive
cladding, ICCP was tested for its use in
steel-frame construction.
Cathodic protection is the intentional
application of DC current to the steel. This
provides electrons from an external source.
This is called the anode. Thus, the anodic
IMPRESSED CURRENT CATHODIC PROTECTION:
A CORROSION MITIGATION TECHNIQUE
FOR TRANSITIONAL STEEL-FRAME
MASONRY-CLAD BUILDINGS
Figure 1 – Pourbaix diagram for steel in an aqueous environment.
reaction at the steel’s surface is halted, and
the entire steel frame becomes the cathode,
which is the harmless hydroxyl-generating
reaction. Like the corrosion cell, the electrochemical
treatment requires both the anodic
and cathodic reactions to occur simultaneously.
This reaction, key to the concept of
cathodic protection, is that steel is flooded
with electrons. The voltage or potential of
the steel is being pushed into immunity.
The steel will not corrode while it is in this
state.
Since its inception in 1824 by Sir
Humphry Davy, the use of cathodic protection3
has grown to include ships’ hulls; tank
bases; pipelines; reinforcing steel in concrete
in bridges, docks, cooling towers, and
balconies; and, more recently, as a corrosion
mitigation technique for historic steelframe
buildings.
Historic Construction
The use of masonry surrounding the
steel in historic building construction was
meant to provide fireproofing to the steel
frame. These changes in construction technology
were the
result of numerous
devastating fires that
struck cities around
the country. These include, but are not limited
to, the Great Chicago Fire of 1871 and
the Great Boston Fire of 1872. Both conflagrations
caused significant loss of life, as
well as the loss of wooden civil and residential
structures. As a consequence, the fires
were catalysts for change in construction
technology that emerged out of the late
1800s.4
Steel-frame systems utilize the frame to
bear the load of the structure. For fireproofing
purposes, the masonry was tightly built
around the steel, encasing the entire frame.
This could either be terra cotta or brick or a
combination of both. The decorative façade
cladding was built around this backup
material. The exterior cladding and masonry
were either keyed into the structure
through “header” courses of masonry or tied
back with an anchoring system, which was
often the case with terra cotta. In many
instances, the backup or infill (electrolyte) is
loose, deteriorated, or poorly constructed.
The condition and relation of the backup
materials to the steel frame can have a
bearing on future damages to the exterior
cladding, as well as damages (i.e., loss of
section, scale, oxide jacking) to the steel.
Early examples of steel-frame buildings can
be seen in Figures 2 and 3; both have since
been demolished.
Background
Corrosion problems in early steelframed
buildings were inherent due to the
nature of early designs. Unlike modern
buildings, which utilize cavity wall construction
to prevent moisture from collecting
on the steel surface, early buildings had
their external masonry tightly notched
around the steelwork with cavities and
voids crudely infilled with mortar, bricks, or
other porous rubble. This type of construction
enabled moisture to collect within the
masonry (or infill material), which is in contact
with the steel, making the initiation of
corrosion inevitable.
The steel frame was rarely protected
against corrosion. Engineers and architects
of the time considered that the stone
cladding, which often exceeded a thickness
of 6 in., would prevent moisture ingress and
prevent corrosion problems.
The earliest guidance5 covering steel
frames specified minimal methods of corrosion
protection such as coating the steel
Figure 2 – 1884 Home Insurance Building, Chicago, IL,
since demolished. Architect William Le Barron Jenney.
Source: Library of Congress, Chicago Architectural
Photographing Company.
Figure 3 – 1889 Rand McNally Building, Chicago, IL,
early steel-framed building demolished in 1911.
Architects Burnham and Root. Source: Birds Eye
View and Guide to Chicago, Rand McNally.
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with boiled oil, tar, or
paint. The act also
states, “Where metal
work is embedded or
encased in brickwork,
terracotta, stone, tiles,
or other incombustible
matter, one coat of
Portland cement of
adequate consistency
can be applied in lieu
of coats of oil, tar, or
paint.” As this was the
cheapest option and
was equivalent to infilling
the voids between
the steel and stone
with mortar, this treatment
became the norm
for early buildings.
Unfortunately, the
assumption that the
external cladding
would prevent moisture
ingress and corrosion
problems was not
true. Sufficient levels
of moisture for corrosion
easily penetrated
the façade through the
various routes described below:
• Directly through porous cladding
materials
• Through open or degraded mortar
joints
• Through faulty, damaged, or degraded
services such as cracked rainwater
downspouts and gutters and
through damaged asphalt coverings
and flat roofing
Unlike reinforced concrete, the steel in
masonry-clad steel-frame buildings can
have a slower onset of corrosion-related
deterioration. General atmospheric corrosion
caused by the onset of carbonation and
exposure to oxygen and moisture primarily
affect steel-framed structures. In most early
skyscrapers and steel-framed buildings,
general age-related deterioration of the steel
frame is exhibited by cracking on the
cladding after 60 to 80 years.6 There are
recorded incidents of buildings exhibiting
corrosion-related failures early on in the
building’s life. This was the subject of much
debate at the turn of the century. Architect
George Post discussed corrosion-related
failures as early as 1895,7 when steel-frame
technology was in its infancy. However, the
remaining steel-frame building stock attests
to durability of well-maintained steel-frame
structures.
Steel-frame construction is prone to
deterioration based on the availability of
oxygen and moisture to the steel frame. As
the building cracks in its early life—perhaps
due to settlement, thermal dynamics, or
general movement—the damage is not
corrosion-related. Over time, oxygen and
moisture can penetrate through the cracks
of the masonry and electrolyte encasing the
steel. Where mortar is surrounding the
steel, it will carbonate, as with concrete,
and have a lower pH than when the structure
was initially built. This leaves the steel
in an environment where it is neither passive
(i.e., encased in an alkaline environment)
nor immune (at a voltage level where
it will be protected).
As the corrosion process begins to accelerate,
the tensile forces exerted by the
expansive corrosion scale, crack, and damage
the masonry cladding. See Figure 4.
Corrosion Onset
As steelwork was generally embedded in
low-quality, poorly compacted mortar and
concrete (or coated with OPC wash), a limited
degree of protection would have occurred
at the time of construction through the natural
passivation of the steel in an alkaline
environment. However, after a period of
time, the protective qualities of these environments
would be lost due to the natural
process of carbonation. Therefore, as a general
assumption, it can be stated that a
short period exists when the steelwork
remains protected against corrosion.
The time period for protection through
passivation is difficult to assess due to the
variability in construction and designs of
the time. However, it is reasonable to make
the following assumptions:
1. The average cover of a mortar infill is
10-40mm.
2. The mortar will have very similar
properties to a C10 concrete.
3. The environment in which the mortar
exists is ideal for carbonation.
Making the above assumptions, the
time for carbonation can be estimated using
the general equation:
Carbonation = (d/k)2 where:
d = Cover
k = Constant (mm/yr. ½) = 7 to 10
for a C10 concrete
Figure 4 – Corrosion-related cracking where backup masonry is in intimate contact with the steel
frame.
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Therefore, using the above, the time in
which carbonation will occur and loss of
corrosion protection is approximately
between 16 and 32 years. See Figure 5.
Following the onset of corrosion, the
rate of corrosion is initially dominated by
the resistivity of the stonework or mortar in
contact with the steelwork. However, the
situation changes as the corrosion process
proceeds and a layer of corrosion product
(iron oxide) forms on the steel surface. Iron
oxide generally has a significantly lower
resistivity than that of the surrounding
masonry; the rate of corrosion can be
expected to accelerate as rust forms on the
steel surface.
For corrosion to occur, it is essential
that oxygen and water are present.
Unfortunately, oxygen is always present,
and the levels of moisture required to support
corrosion are relatively low. It is generally
found that moisture content of 2% by
weight of the masonry or mortar in contact
with the steel will support significant corrosion.
A moisture level of less than 2% is difficult
to achieve by waterproofing measures,
and it is unlikely that the environment can
be significantly altered to halt corrosion.
Additionally, once a layer of iron oxide
exists on the steel surface, the environment
changes and it is possible for corrosion
rates to accelerate.
As the level of moisture cannot be controlled
to a suitable level to prevent corrosion,
only two practical methods of treatment
are possible:
1. Treat the steel and change the environment.
2. Electrochemically halt the corrosion
process.
An Introduction to Cathodic Protection
In a steel-framed building, it is both
impractical and expensive to remove the
thick outer cladding to enable the treatment
of corrosion by methods such as painting or
concrete encasement. As such, corrosion
engineers have been steadily developing the
use of cathodic protection (CP) techniques
for these structures. The use of CP technology
is highly applicable to steel-framed
structures that are analogous to carbonated
concrete buildings for which CP is now a
proven repair technique. CP offers many
benefits over traditional repairs, requiring
less masonry replacement and including
substantial cost savings, which is vital to
the preservation of listed buildings.
CP techniques are directly applicable to
steel-framed, masonry-clad buildings by
virtue of the mortar and masonry contact
between the steelwork and cladding, which
acts as a suitable electrolyte to conduct the
protective current to the corroding steelwork.
The corrosion of steel in cement-based
materials is an electrochemical process.
Dissolution of steel (oxidation reaction) liberates
electrons and forms anodic sites.
Fe Fe2 + 2e-
In order to maintain charge neutrality, a
reduction reaction occurs at an adjacent
area called the cathode:
½ O2 + H2O + 2e- 2 OHThe
oxidation reaction is the first step in
the process of forming rust. It is initiated
where acidic conditions on the steel surface
(resulting from carbonation) are sustained
within the incipient anodic sites and result
in lowering the steel potential locally. This
causes an electrical potential difference
between the incipient anodes and the adjacent
cathodic areas and results in current
flow between them. Subsequently, corrosion
of steel proceeds when the following
conditions are maintained:
1. Acidity or lower pH within surface
profile pits
2. Lower potential within the surface
profile pits
3. Electrical potential difference
between the anodic and cathodic
areas
Both oxidation and reduction reactions
occur simultaneously, and the corrosion
rate is reduced and/or stopped when one of
these reactions is controlled and/or ceased.
As the conditions are mostly ideal for both
oxidation and reduction reactions, external
control is required.
To stop the corrosion process, the anodic
reaction must be suppressed. CP arrests
the corrosion process by
1. Lowering the steel potential in the
negative direction to a level at which
an oxidation reaction cannot recur
2. Lowering the electrical potential difference
between the anodic and
cathodic areas
3. Generating alkalinity at the steel
surface as a result of reduction reactions
4. Removing aggressive ions, such as
chlorides, from the steel surface.
Feasibility of Cathodic Protection for
Steel-Framed Buildings
There are several important factors that
must be assessed before concluding that CP
is a viable option for a steel-framed building:
• Continuity of the steel frame, fixings,
and other metallic items
Figure 5 – Carbonated mortar backup.
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• Contact between steel and mortar
• Current distribution (controlled by
mortar and stone resistivity)
• Location of anodes (joint details and
steel work detailing)
• Aesthetic constraints (installation
details)
Each of these items, as explained in the
following paragraphs, is assessed during a
site evaluation. While cathodic protection is
a viable solution to arrest steel-frame corrosion,
it is not suitable for every structure. A
thorough analysis involving corrosion condition
testing and feasibility trials, and a
thorough understanding of details and previous
repairs are required prior to moving
forward to a design.
Continuity
Early 20th-Century steel-frame buildings
contain a large variety of metallic elements
in their construction. Typical details
often include at least two of the following
items and often more:
• Steel beams and columns
• Fixings that are bronze, iron, steel,
or galvanized steel
• Iron, steel, galvanized steel, or
bronze cramps between stone elements
• Steel reinforcement bars hooked
over the top flanges of spandrel
beams in concrete floor construction
• Small steel reinforcement wires connected
to the top and bottom flanges
of beams to form a cage for the concrete
encasement of the inner faces
of steel beams
• Chicken wire meshes to aid in the
internal works such as concreting
and plastering
• Cast-iron rainwater downspouts
and copper water pipes
Failure to ensure the electrical continuity
of all metallic elements in a steel-framed
building can result in stray current interactions
among the various elements of the
structure, resulting in accelerated corrosion
of discontinuous items. The importance of
electrical continuity is well-established in
concrete CP, and early investigations and
site trials have shown the importance of electrical
continuity in steel-framed buildings.
Ensuring electrical continuity of the
steel-frame, stonework, and masonry fixings
and reinforcement bars is, therefore,
an essential element to the application of
cathodic protection systems for steelframed
buildings. Designers and engineers
involved with the development of steelframed
buildings should therefore be fully
acquainted with
• All common design details
• Historical methods of building construction
• Testing and inspection methods for
checking continuity and the identification
of discontinuous metallic
items
Electrolyte
Corrosion prevention in historic steelframed
buildings is possible by cathodic
protection techniques since the protective
current can be passed through the
stonework or masonry via a mortar or concrete
connection with the steel frame.
Although details often exist of the steel and
masonry layout, knowledge of the mortar or
concrete connection between the two elements
is not always known. It is often found
that the quality and consistency of the mortar
infill between the steel-frame and
masonry façade is highly variable. The mortar
infill contains large voids and, in certain
circumstances, is completely absent. This is
particularly true for regions of the façade
that would have been difficult to fill during
construction, such as behind the stonework
of window heads, etc. As the mortar infill is
essential for ensuring the passage of the
protective current to the steel beam, it is
vitally important to ensure adequate consideration
for voids in any CP design.
Knowledge of historic building construction
methods is essential when establishing
the possibility of voids. Expert knowledge of
steel-frame construction enables a rapid
risk assessment of voids and enables areas
requiring further inspection to be pinpointed.
Following risk assessments and inspection,
it is often reasonable to make one of
the following choices:
1. A large, consistent void exists
(greater than 25mm) in which corrosion
rates are minimal and protection
is not required.
2. A large void exists in which corrosion
is occurring at a significant rate
and treatment is required. The voided
cavity must therefore be grouted
to ensure protection.
3. Small voids exist (less than 10mm)
in which corrosion has occurred.
Resistivity
The resistivity of most masonry materials
is in a suitable range for the application
of cathodic protection when containing
more than 2% moisture by weight. However,
as with any porous material, it is important
to understand the behavior of moisture content
on resistivity. Most masonry materials
have resistivity that exceeds 1MΩ.cm when
moisture contents fall below 2%; therefore,
the placement of anodes and rating of power
supply output voltage must be correctly
chosen to ensure adequate protection of the
steelwork.
Particular care is required when designing
CP systems for use in materials such as
terra cotta, faience, and glazed bricks. In
these materials, the glazing or fire skin layer
will effectively act as an insulator, making it
impossible to throw protective currents to
the steel surface. Protection is possible,
however, if the anode materials are made to
contact the underlying porous material
beyond the surface layer. To ensure effective
contact, anode materials must be laid
directly within the main body of the masonry
block work. In the case of listed or landmarked
buildings, it is essential that damage
to the façade is not incurred during the
installation of anode materials and that the
outward appearance remains unaltered.
CATHODIC PROTECTION MATERIALS
Anodes
A number of anodes are applicable in
the protection of steel-framed buildings.
However, the most suitable types are discrete
rod anodes. These can either be
ceramic- or titanium-coated, with a mixedmetal
oxide coating. Expanded mesh probe
anodes are particularly useful for insertion
into the backup masonry at the fine jointing
of stonework and the mortar joints of brickwork.
Theses anodes are generally installed
using a specialized cathodic-protection
grout, which is then pointed over using traditional
masonry pointing techniques. All of
the anodes are installed and interconnected
with a feeder wire. The anodes are then terminated
at the positive terminal of the DC
power supply unit.
As all exterior components are installed
within the backup and never through the
façade stone, the particular advantages of
this system are
• The anodes are not visible.
• Anodes can be installed using standard
grouting and masonry pointing
techniques at the time of external
repairs.
• Anodes are usually situated parallel
to beam and columns.
• There is minimal internal disturbance.
Cathodes
While anodes are installed to provide
electrons to the steel, the areas of the steel
frame targeted for treatment become the
cathode. Wire connections to the steel frame
provide a return path to the power supply
unit, as the negative portion of the circuit.
Monitoring Cells
Reference electrodes or half-cell potential
electrodes are permanently embedded
as part of the system. All systems require
performance evaluations according to the
National Association of Corrosion Engineers
(NACE) and British Standards European
Norm (BSEN) standards, and all performance
is based upon the native potentials
and changes in Ecorr once the system is
commissioned.
Power Supplies
All external wiring is brought into the
building and routed to the power supply
units (PSU) or where most suitable for the
structure, roof, etc. PSUs are generally
placed on the interior of a building in a
maintenance closet, drop-ceiling space,
basement, etc.
PSUs or transformer rectifiers (T/Rs)
utilized in steel-frame cathodic protection
require finite control of current output and
voltage limitation. The systems require so
little current to polarize the steel that there
must be adequate control measures to ensure
that overprotection
and
hydrogen embrittlement
do
not occur. Power
supplies with
multiple channels
can provide
protection to a
number of
“zones,” as each
zone requires
i n d e p e n d e n t
power. All units
must have adjustable
control,
a c c ommo d a t e
monitoring cells,
record and store
data, and they
must provide power interruptions for testing
requirements. Units can be independent
of one another or be linked to a main control
that manages and stores the collective
data from the independent units.
A schematic is provided below in Figure
6, showing the layout of a system in a
masonry-clad, steel-frame building. The rod
anodes are attached to the [+] of the power
supply (red), and the steel frame (cathode) is
connected back to the [-] of the power supply.
TRACK RECORD AND CASE
STUDIES
The first cathodic protection system for
the prevention of steel beam corrosion in a
masonry structure was designed by
Taywood Engineering Ltd. and completed in
1991. The CP system provided protection
for the entrance colonnade of the Royal
College of Science, Dublin. The entrance
colonnade is a limestone structure containing
two parallel structural I-beam members.
Since its completion in 1991, regular
remote monitoring via embedded reference
electrodes has shown no corrosion problems.
This has also been confirmed via
annual visual inspections. Since the development
of this first CP system for masonry,
over 150 systems have been designed and
installed for masonry buildings in the UK.
Commercial Department Store,
Chicago, IL
In 2003, UK corrosion engineers8 were
engaged to carry out corrosion investigations
and testing, design services, and
installation support for an ICCP system on
the Marshall Field’s Building in Chicago, IL.
This was the first historic building in the
United States to have ICCP installed. The
area protected was the 1914 Wabash building’s
pilaster colonnade at the Randolph
and Wabash Street elevations at the 11th to
13th floors. The work on Daniel Burnham’s
Marshall Field’s flagship store in Chicago
came about from the engineers’ previous
corrosion investigations and ICCP system
design carried out on Selfridges’ Department
Store in London, also designed by
Burnham. Both buildings had the same
detailed pilaster colonnades along the
façade; both buildings were suffering from
corrosion of the embedded steel columns.
The engineers working on the repair
scope of the Marshall Field’s flagship store9
were looking for a method to mitigate corrosion,
minimize masonry removal, and provide
the owner with a long-term corrosion
solution. This was the third repair cycle for
the pilaster columns. Any further damages
sustained to the terra cotta could have
caused irreparable damage requiring full
replacement and posed a life safety risk for
pedestrians. The estimated cost savings to
the client was $500,000.00 where the ICCP
was installed.
In keeping with standard design protocol,
the system was designed to have four
“zones” or independently powered areas.
Zones are defined by the amount of steel
surface area to be protected, the proximity
of the steel elements to one other, and the
even distribution of current within the zone.
Each zone has two monitoring cells to provide
data for polarization and potential
decay. All wiring was routed internally and
distributed to the power supply units,
which were then linked by a communications
cable to a main control unit (MCU).
The MCU has an independent phone line,
providing dial-up access for remote monitoring.
The project posed a unique installation
challenge, as the materials and installations
procedures require a DC electrical system
to be embedded in masonry. This crosses
“union-owned” work, and it required fulltime
installation support. Though the
anodes and wiring should be installed by an
electrician, the components are embedded
within mortar and grout, which is “owned”
by the masonry union. The design engineers
were on site full-time to assist in the training
and installation process in order to
appease the trades, the owner, and to
ensure that all work was carried out seamlessly.
The design team worked on the
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Figure 6 – ICCP schematic.
swing stages, providing
guidance for bonding of
the terra cotta anchors,
installing the anodes,
and running the wires
within the joints back
to the through-wall
holes. The design team
then assisted the electrical
team with the
internal splicing and
wiring layout to both
the PSU and the MCU.
To date, the system
is still running.
U.S. Government
Museum Administration
Building,
Washington, DC
The Ross Administration
Building at
the United States Holocaust
Memorial Museum (USHMM) is a
1905 load-bearing brick building with a
terra cotta cornice. As typical of cornice
detailing, the terra cotta armature comprised
steel channels, outriggers, J hooks,
etc. to anchor the cornice and parapet in
place. In 2005, the building was undergoing
an exterior restoration campaign. The evaluating
team noticed corrosion of the steel
outriggers, which were causing downward
displacement on the terra cotta modillions
and cracking of the soffit stones. Being one
of the United States’ preeminent museums,
the facility maintenance team at the
USHMM took a proactive approach to the
building’s upkeep and required a 25-year
life extension.
Cornices are challenging elements, with
many electrically discontinuous metallic
items, so a detailed inspection was
required. The trial allowed the team to
determine the best technique to bond the
discontinuous elements and to provide a
mock-up of anode arrangements. After an
investigation and trials, the decision was
made to install an ICCP system at the present
time rather than risk further corrosion-
related damage to the masonry.
The cornice system of the Ross building
differed from the majority of the previous
steel-frame building projects as it was possible
to access the majority of the corroding
steel outriggers from a large masonry joint.
The internal steel elements of the cornice
armature were in very good condition. To
remove the downward stresses to the
masonry, the masons were instructed to
remove the corrosion product from the
underneath side of the outriggers. The
removal of corrosion product (oxide) is not
required for successful CP installations, but
it was felt that the pressure exerted on the
masonry was a health and safety risk
should a modillion crack and fall.
A cost benefit analysis was easily made,
and the prices of individual terra cotta units
ranged from $3,000 to $5,000, with three to
five verticals units that would be affected
per outrigger location.
The system was installed in 2005 and
commissioned in 2006. Quarterly monitoring
has been carried out by the authors
since commissioning, and the system has
achieved NACE and BSEN criteria for protection
for the last seven years. The benefit
of the system is that it provides remote
access so that the engineers can access
data without having to make multiple site
visits. In 2011, the five-year visual inspection
was carried out. Each modillion and
terra cotta unit in the area of cathodic protection
was inspected and documented. All
changes to the structure were noted and
compared to the previous year’s groundside
inspections. There was evidence of
movement in the area of previous cracking
and repairs; however, this was due to the
removal of the building’s diaphragm when
the building was converted from a printing
facility to the Administration Building of the
USHMM. See Figure 7.
Collegiate Gothic Dormitory,
New Haven, CT
To date, the largest ICCP system
installed in the U.S. is on a Collegiate
Gothic dormitory at Yale University. In
2008, the owners required a 50-year design
life for the complete restoration and renovation
of the 1931 masonry-clad steel-frame
building. Prior to restoration, a thorough
exterior building envelope investigation was
carried out. Water infiltration of the exterior
walls had put the steel frame at risk, and
areas near water tables, gables, and watershedding
elements were showing corrosionrelated
deterioration.
The building was constructed between
1931 and 1932 and is part of the central
core of the campus. Situated at the corner
of College and Elm Streets in New Haven,
CT, it is an exquisite example of the
Neogothic architecture found at Yale. The
residential building houses students, classrooms,
entertainment facilities, and the
headmaster’s house. The details seen in
some of the masonry represent the ideals of
the college at the time of construction. Built
in a remarkably short time frame, the building
was constructed with a steel frame to
carry the floor loads, as well as to increase
productivity during construction. The building
was erected in just five months after
breaking ground.
The building is a quadrangle with eight
unique elevations—all different heights—
clad in a variety of materials. The Gothic
towers, gables, balconies, and turrets are all
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Figure 7 – Image of cornice to be protected.
ornately detailed masonry
units. The steel frame of the
building was not meant to
exclusively carry the masonry
load; thus, it is acting as
an armature. The infill
materials between the steel
frame and cladding are
tightly compacted around
the steel. The steel is in intimate
contact with masonry.
As such, the corrosion product
was causing cracking of
the masonry.
The author was engaged
by the architects of record to
engage in a corrosion condition analysis.
The corrosion rate testing indicated that
areas that had not begun to show signs of
corrosion would crack within six to ten
years. After the survey, the facilities management
department engaged the team to
carry out a CP feasibility trial. As there are
multiple masonry types on the building,
three trials had to be carried out: one each
on sandstone, granite, and brick elevations.
As a result of the trial, it was concluded
that a CP system could be developed as a
masonry conservation technique while
simultaneously controlling corrosion. Due
to the success of the feasibility investigations,
commercial viability, and conservation
benefits, a full-scale CP design was carried
out. In the end, the upper two floors of
the entire building, which were prioritized
as high-risk, were protected, equaling over
6000 LF of steel. The design comprised
drawings, specifications, and material
schedules, detailing the safe extra-low-volage
electrical circuits, 110V AC electrical
circuits, and masonry installation works. In
total, there were 35 independently powered
“anode zones.”
All work was carried out by specialist
contractors, masons, and electricians, with
oversight from the design team. The anode
electrodes were wired back to the positive
terminals of an intelligent power supply and
monitoring system. The steel was wired separately
to the negative terminals. Protective
currents were then applied to the steel via
the masonry using a computer system to
control the intelligent power supplies. Each
“zone” has four monitoring cells that provide
the client with data to ensure the system
is working according to specifications.
See Figures 8, 9, and 10.
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Figure 8 – Dormitory with various masonry
configurations.
Figure 9 – Internal courtyard elevations.
CONCLUSIONS
Since the 1990s, ICCP has been used on
hundreds of heritage buildings in the U.K.
and numerous historic buildings in the U.S.
These systems have shown the possibility of
protecting full-building façades and the versatility
of CP systems for listed and landmarked
buildings. Where ICCP has been
installed, it has been found to have a costsaving
in excess of 50% in comparison with
traditional approaches of repair involving
the removal of masonry and steel painting.
Additionally, the cost of ICCP at targeted
locations, determined by thorough corrosion
investigations to be at risk, is usually
in the range of 10% of the overall exterior
envelope repair scope.
The following conclusions can be made
from the brief discussions presented:
• Steel-framed buildings constructed
prior to 1940 are prone to corrosionrelated
problems such as the cracking
and displacement of masonry.
• Impressed current cathodic protection
systems have been shown as an
appropriate method of repair for the
prevention of corrosion in early-
20th-Century steel-framed buildings.
• Cathodic protection systems for
masonry-clad steel-framed buildings
require specialist knowledge of historical
construction techniques.
• A corrosion survey with in-situ trials
is necessary prior to moving forward
with a design.
• The overall investment in a longterm
corrosion mitigation system
provides economic incentive to a
proactive approach.
• The loss of historic masonry and
façade damage can be minimized
with a proactive, long-term repair
strategy.
• ICCP is specifically tailored to each
building.
• ICCP adheres to preservation and
conservation guidelines.
The design life of the systems range
from 25 to 50 years, and this is dictated by
the power supply technology and internal
wiring systems. While the design life of the
anode and titanium wiring can exceed 40
years, based on the amount of current
passed (i.e., lower current density, longer
anode life), the design life of the control systems
will change as rapidly as technology
allows.
The ICCP systems will require maintenance
in the form of monitoring and system
review. It is advisable to report quarterly on
the data, and this is a requirement in NACE
and BSEN standards.
REFERENCES
D. Friedman, “Early Predictions of Steel-
Frame Deterioration: Permanency in
High-Rise Construction,” Proceed-
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Figure 10 – Installation details at gable.
ings of the Third International
Congress on Construction History,
May 2009, Bath, England.
P.A.J. Gibbs, “Corrosion in Masonry-
Clad Early-20th-Century Steelframed
Buildings,” Historic Scotland,
2000, Edinburgh, Scotland.
ACKNOWLEDGEMENTS
The author would like to acknowledge
prior work carried out by colleagues Peter
A.J. Gibbs and Paul Andrew Noyce. Their
early studies and trials made this work possible,
and the case studies in this paper all
came to fruition from efforts based on the
track record established by Gibbs and
Noyce in the United Kingdom.
FOOTNOTES
1. English Heritage and Historic
Scotland, like the National Register
of Historic Places, has the following
categories of building significance:
Grade I buildings are of exceptional
interest, sometimes considered to be
internationally important; Grade II*
buildings are particularly important
buildings of more than special interest;
Grade II buildings are nationally
important and of special interest.
2. Chlorides can also affect the oxide
layer, though they do not always
affect pH.
3. Cathodic protection as it was first
discovered was galvanic. A less
noble metal was used to provide
electrons, thus sacrificing itself in
order to protect a more noble metal.
This is based on the Galvanic Series
of Metals. Still used today, sacrificial
zinc and zinc alloys are applied in
bulk, thermal spray, and mesh
underlay for protection of steel in
concrete and atmospherically
exposed steels. Due to the low resistivity
of the concrete electrolyte in
the presence of moisture and salts
(i.e., marine environment in particular),
galvanic CP can be less expensive
than ICCP. It does not have the
same design life and must be reapplied
when the sacrificial alloy is
consumed.
For historic steel-frame buildings,
the high resistivity of the stone
cladding requires a higher driving
voltage than provided by a galvanic
cell. Thus, an external power source
is required. ICCP systems are generally
considered permanent installations,
whereas galvanic systems are
considered shorter term.
4. Donald Friedman discusses changes
in building technologies and applicable
codes in relation to disasters in
Historic Building Construction: Design,
Materials, and Technology.
5. In the UK, the LCC (General Powers)
Act 1909 covers steel frame construction.
U.S. documentation is
slightly earlier.
6. P.A.J. Gibbs. Corrosion in Masonry-
Clad Early-20th-Century Steel-
Framed Buildings. Historic Scotland,
2000, Edinburgh, Scotland.
7. D. Friedman, “Early Predictions of
Steel Frame Deterioration: Permanency
in High Rise Construction,”
Proceedings of the Third International
Congress on Construction
History, May 2009, Bath, England.
8. Paul Noyce and Peter Gibbs of
Electro Tech CP, Ltd.
9. Construction dates are 1893, 1907,
and the 1920s. There were various
construction stages and expansions
of the department store.
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