IMPRESSED CURRENT CATHODIC PROTECTION: A MITIGATION TECHNIQUE FOR TRANSITIONAL STEEL­FRAME MASONRY­CLAD BUILDINGS

GINA L. CREVELLO AND PAUL A. NOYCE

ECHEM CONSULTANTS LLC 72 Boodle Hole Road, Accord, NY 12404 Phone: 845­626­1205 • E­mail: [email protected]

S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 C R E V E L L O • 3 9 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 (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 elec- trons, which causes the steel to revert to . 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 appar- ent, such as hairline cracking and open joints. Simultaneous to this anodic reaction is the reduction reaction at the cathode site. The cathode reaction is harm- less, 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 diag- nostics, 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 land- mark 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 elec- trical 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 cor- rosion diagnostics and electrochemical corrosion remediation. Noyce was instrumental in the first use of ICCP for her- itage 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 advi- sor 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.

4 0 • C R E V E L L O S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 IMPRESSED CURRENT CATHODIC PROTECTION: A CORROSION MITIGATION TECHNIQUE FOR TRANSITIONAL STEEL­FRAME MASONRY­CLAD BUILDINGS

INTRODUCTION masonry, or surface moisture as an elec- struction could be from 1) the use of deicing The use of impressed current cathodic trolyte through which corrosion current salts at the sidewalk, thereby only affecting protection has been employed on masonry- flows. The corrosion reaction will be depen- the base; 2) marine mist, affecting coastal clad steel-frame heritage buildings since the dent upon various elements: oxygen, mois- buildings; and 3) the use of calcium chlo- mid-1990s. The work originated out of ture, chlorides, and temperature, to name a rides or other curing agents used in “winter” England, when the Department of the few. To halt the corrosion reaction, the envi- construction. These would most likely be Environment, English Heritage, and ronment or the reaction must be changed. found in concrete floors or roof slabs tied Historic Scotland sought alternative treat- The conceptual aspect of the ICCP as into a steel frame. ments to large-scale stripping of “listed”1 applied to historic buildings is the same as To control corrosion, the anode, the steel-frame heritage buildings for corrosion when ICCP is applied to reinforcing steel in cathode, or the environment must be con- mitigation. This endeavor employed the concrete. Construction details and cladding trolled. If the steel cannot be protected by a knowledge base used by the corrosion engi- materials differ, though the corrosion barrier (coating), corrosion will occur in the neering community. Applicable investigative process is the same. It is most often a gen- presence of oxygen and moisture. To paint methods and electrochemical treatments eral carbonation-related (drop in pH), the steel, significant amounts of masonry traditionally used for corrosion of reinforc- atmospheric corrosion reaction that affects are required to be removed. As this further ing steel in concrete were studied over a steel-frame construction. damages landmarked buildings and expen- three-year period. The results were the first Chlorides are very important as corro- sive cladding, ICCP was tested for its use in use of impressed current cathodic protec- sion accelerants. While chlorides have the steel-frame construction. tion (ICCP) for steel frames embedded in ability to break down the oxide layer and Cathodic protection is the intentional masonry structures. cause accelerated reactions, they are not a application of DC current to the steel. This Steel embedded in a highly alkaline primary cause of steel-frame corrosion. The provides electrons from an external source. environment, such as new mortar or con- presence of chlorides in steel-frame con- This is called the anode. Thus, the anodic crete, is in a “passive” state and protected by the formation of an oxide layer. Additionally, steel is “immune” from corro- sion 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 mor- tar/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 ini- tiation has begun. A corrosion reaction gen- erates a chemical change as well as an elec- trical potential change (electrochemical). The electrochemical reaction that occurs at the steel surface utilizes the backup mortar, Figur e1 – Pour baix diagr am for st eel in an aqu eo us env i r onment.

S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 C R E V E L L O • 4 1 Figur e 2 – 1884 Home Insur ance Bu ilding, Chicago, IL, s ince demolis hed. Ar chit ect William Le Barr on Jenney. Sour ce: Libr ary of Congr ess, Chicago Ar chit ectur al Phot ogr aphing Company.

Figur e 3 – 1889 Rand McNally Bu ilding, Chicago, IL, ear ly st eel- f r amed bu ilding demolis hed in 1911. Ar chit ects Bur nham and Root. Sour ce: Birds Eye View and Guide to Chicago, Rand McNally.

nology were the cladding, as well as damages (i.e., loss of result of numerous section, scale, oxide jacking) to the steel. devastating fires that Early examples of steel-frame buildings can struck cities around be seen in Figures 2 and 3; both have since reaction at the steel’s surface is halted, and the country. These include, but are not lim- been demolished. the entire steel frame becomes the cathode, ited to, the Great Chicago Fire of 1871 and which is the harmless hydroxyl-generating the Great Boston Fire of 1872. Both confla- Background reaction. Like the corrosion cell, the electro- grations caused significant loss of life, as Corrosion problems in early steel- chemical treatment requires both the anod- well as the loss of wooden civil and residen- framed buildings were inherent due to the ic and cathodic reactions to occur simulta- tial structures. As a consequence, the fires nature of early designs. Unlike modern neously. This reaction, key to the concept of were catalysts for change in construction buildings, which utilize cavity wall con- cathodic protection, is that steel is flooded technology that emerged out of the late struction to prevent moisture from collect- with electrons. The voltage or potential of 1800s.4 ing on the steel surface, early buildings had the steel is being pushed into immunity. Steel-frame systems utilize the frame to their external masonry tightly notched The steel will not corrode while it is in this bear the load of the structure. For fireproof- around the steelwork with cavities and state. ing purposes, the masonry was tightly built voids crudely infilled with mortar, bricks, or Since its inception in 1824 by Sir around the steel, encasing the entire frame. other porous rubble. This type of construc- Humphry Davy, the use of cathodic protec- This could either be terra cotta or brick or a tion enabled moisture to collect within the 3 tion has grown to include ships’ hulls; tank combination of both. The decorative façade masonry (or infill material), which is in con- bases; pipelines; reinforcing steel in con- cladding was built around this backup tact with the steel, making the initiation of crete in bridges, docks, cooling towers, and material. The exterior cladding and mason- corrosion inevitable. balconies; and, more recently, as a corro- ry were either keyed into the structure The steel frame was rarely protected sion mitigation technique for historic steel- through “header” courses of masonry or tied against corrosion. Engineers and architects frame buildings. back with an anchoring system, which was of the time considered that the stone often the case with terra cotta. In many cladding, which often exceeded a thickness Historic Construction instances, the backup or infill (electrolyte) is of 6 in., would prevent moisture ingress and The use of masonry surrounding the loose, deteriorated, or poorly constructed. prevent corrosion problems. steel in historic building construction was The condition and relation of the backup The earliest guidance5 covering steel meant to provide fireproofing to the steel materials to the steel frame can have a frames specified minimal methods of corro- frame. These changes in construction tech- bearing on future damages to the exterior sion protection such as coating the steel

4 2 • C R E V E L L O S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 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 infill- ing the voids between the steel and stone with mortar, this treat- ment became the norm for early buildings. Unfortunately, the assumption that the external cladding would prevent mois- ture ingress and corro- sion problems was not true. Sufficient levels of moisture for corro- Figur e4 – Corr os ion -r elat ed cr ackingw he r e backu p mas on ry is in int imat e cont ac t w i t ht he st eel sion easily penetrated fr ame . the façade through the various routes described below: remaining steel-frame building stock attests ed degree of protection would have occurred • Directly through porous cladding to durability of well-maintained steel-frame at the time of construction through the nat- materials structures. ural passivation of the steel in an alkaline • Through open or degraded mortar Steel-frame construction is prone to environment. However, after a period of joints deterioration based on the availability of time, the protective qualities of these envi- • Through faulty, damaged, or degrad- oxygen and moisture to the steel frame. As ronments would be lost due to the natural ed services such as cracked rainwa- the building cracks in its early life—perhaps process of carbonation. Therefore, as a gen- ter downspouts and gutters and due to settlement, thermal dynamics, or eral assumption, it can be stated that a through damaged asphalt coverings general movement—the damage is not short period exists when the steelwork and flat roofing corrosion-related. Over time, oxygen and remains protected against corrosion. moisture can penetrate through the cracks The time period for protection through Unlike reinforced concrete, the steel in of the masonry and electrolyte encasing the passivation is difficult to assess due to the masonry-clad steel-frame buildings can steel. Where mortar is surrounding the variability in construction and designs of have a slower onset of corrosion-related steel, it will carbonate, as with concrete, the time. However, it is reasonable to make deterioration. General atmospheric corro- and have a lower pH than when the struc- the following assumptions: sion caused by the onset of carbonation and ture was initially built. This leaves the steel 1. The average cover of a mortar infill is exposure to oxygen and moisture primarily in an environment where it is neither pas- 10-40mm. affect steel-framed structures. In most early sive (i.e., encased in an alkaline environ- 2. The mortar will have very similar skyscrapers and steel-framed buildings, ment) nor immune (at a voltage level where properties to a C10 concrete. general age-related deterioration of the steel it will be protected). 3. The environment in which the mor- frame is exhibited by cracking on the As the corrosion process begins to accel- tar exists is ideal for carbonation. cladding after 60 to 80 years.6 There are erate, the tensile forces exerted by the recorded incidents of buildings exhibiting expansive corrosion scale, crack, and dam- Making the above assumptions, the corrosion-related failures early on in the age the masonry cladding. See Figure 4. time for carbonation can be estimated using building’s life. This was the subject of much the general equation: debate at the turn of the century. Architect Corrosion Onset Carbonation = (d/k)2 where: George Post discussed corrosion-related As steelwork was generally embedded in d = Cover failures as early as 1895,7 when steel-frame low-quality, poorly compacted mortar and k = Constant (mm/yr. ½) = 7 to 10 technology was in its infancy. However, the concrete (or coated with OPC wash), a limit- for a C10 concrete

S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 C R E V E L L O • 4 3 materials is an electrochemical process. Dissolution of steel (oxidation reaction) lib- erates 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 OH-

The 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 adja- cent cathodic areas and results in current flow between them. Subsequently, corro- sion of steel proceeds when the following conditions are maintained: 1. Acidity or lower pH within surface

Figur e5 – Car bonat ed mort ar backu p . profile pits 2. Lower potential within the surface profile pits Therefore, using the above, the time in trolled to a suitable level to prevent corro- 3. Electrical potential difference which carbonation will occur and loss of sion, only two practical methods of treat- between the anodic and cathodic corrosion protection is approximately ment are possible: areas between 16 and 32 years. See Figure 5. 1. Treat the steel and change the envi- Following the onset of corrosion, the ronment. Both oxidation and reduction reactions rate of corrosion is initially dominated by 2. Electrochemically halt the corrosion occur simultaneously, and the corrosion the resistivity of the stonework or mortar in process. rate is reduced and/or stopped when one of contact with the steelwork. However, the these reactions is controlled and/or ceased. situation changes as the corrosion process An Introduction to Cathodic Protection As the conditions are mostly ideal for both proceeds and a layer of corrosion product In a steel-framed building, it is both oxidation and reduction reactions, external (iron oxide) forms on the steel surface. Iron impractical and expensive to remove the control is required. oxide generally has a significantly lower thick outer cladding to enable the treatment To stop the corrosion process, the anod- resistivity than that of the surrounding of corrosion by methods such as painting or ic reaction must be suppressed. CP arrests masonry; the rate of corrosion can be concrete encasement. As such, corrosion the corrosion process by expected to accelerate as rust forms on the engineers have been steadily developing the 1. Lowering the steel potential in the steel surface. use of cathodic protection (CP) techniques negative direction to a level at which For corrosion to occur, it is essential for these structures. The use of CP technol- an oxidation reaction cannot recur that oxygen and water are present. ogy is highly applicable to steel-framed 2. Lowering the electrical potential dif- Unfortunately, oxygen is always present, structures that are analogous to carbonat- ference between the anodic and and the levels of moisture required to sup- ed concrete buildings for which CP is now a cathodic areas port corrosion are relatively low. It is gener- proven repair technique. CP offers many 3. Generating alkalinity at the steel ally found that moisture content of 2% by benefits over traditional repairs, requiring surface as a result of reduction reac- weight of the masonry or mortar in contact less masonry replacement and including tions with the steel will support significant corro- substantial cost savings, which is vital to 4. Removing aggressive ions, such as sion. A moisture level of less than 2% is dif- the preservation of listed buildings. chlorides, from the steel surface. ficult to achieve by waterproofing measures, CP techniques are directly applicable to and it is unlikely that the environment can steel-framed, masonry-clad buildings by Feasibility of Cathodic Protection for be significantly altered to halt corrosion. virtue of the mortar and masonry contact Steel­Framed Buildings Additionally, once a layer of iron oxide between the steelwork and cladding, which There are several important factors that exists on the steel surface, the environment acts as a suitable electrolyte to conduct the must be assessed before concluding that CP changes and it is possible for corrosion protective current to the corroding steel- is a viable option for a steel-framed building: rates to accelerate. work. • Continuity of the steel frame, fix- As the level of moisture cannot be con- The corrosion of steel in cement-based ings, and other metallic items

4 4 • C R E V E L L O S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 • Contact between steel and mortar cathodic protection systems for steel- Resistivity • Current distribution (controlled by framed buildings. Designers and engineers The resistivity of most masonry materi- mortar and stone resistivity) involved with the development of steel- als is in a suitable range for the application • Location of anodes (joint details and framed buildings should therefore be fully of cathodic protection when containing steel work detailing) acquainted with more than 2% moisture by weight. However, • Aesthetic constraints (installation • All common design details as with any porous material, it is important details) • Historical methods of building con- to understand the behavior of moisture con- struction tent on resistivity. Most masonry materials Each of these items, as explained in the • Testing and inspection methods for have resistivity that exceeds 1M .cm when following paragraphs, is assessed during a checking continuity and the identifi- moisture contents fall below 2%;Ω therefore, site evaluation. While cathodic protection is cation of discontinuous metallic the placement of anodes and rating of power a viable solution to arrest steel-frame corro- items supply output voltage must be correctly sion, it is not suitable for every structure. A chosen to ensure adequate protection of the thorough analysis involving corrosion con- Electrolyte steelwork. dition testing and feasibility trials, and a Corrosion prevention in historic steel- Particular care is required when design- thorough understanding of details and pre- framed buildings is possible by cathodic ing CP systems for use in materials such as vious repairs are required prior to moving protection techniques since the protective terra cotta, faience, and glazed bricks. In forward to a design. current can be passed through the these materials, the glazing or fire skin layer stonework or masonry via a mortar or con- will effectively act as an insulator, making it Continuity crete connection with the steel frame. impossible to throw protective currents to Early 20th-Century steel-frame build- Although details often exist of the steel and the steel surface. Protection is possible, ings contain a large variety of metallic ele- masonry layout, knowledge of the mortar or however, if the anode materials are made to ments in their construction. Typical details concrete connection between the two ele- contact the underlying porous material often include at least two of the following ments is not always known. It is often found beyond the surface layer. To ensure effec- items and often more: that the quality and consistency of the mor- tive contact, anode materials must be laid • Steel beams and columns tar infill between the steel-frame and directly within the main body of the mason- • Fixings that are bronze, iron, steel, masonry façade is highly variable. The mor- ry block work. In the case of listed or land- or galvanized steel tar infill contains large voids and, in certain marked buildings, it is essential that dam- • Iron, steel, galvanized steel, or circumstances, is completely absent. This is age to the façade is not incurred during the bronze cramps between stone ele- particularly true for regions of the façade installation of anode materials and that the ments that would have been difficult to fill during outward appearance remains unaltered. • Steel reinforcement bars hooked construction, such as behind the stonework over the top flanges of spandrel of window heads, etc. As the mortar infill is CATHODIC PROTECTION MATERIALS beams in concrete floor construction essential for ensuring the passage of the Anodes • Small steel reinforcement wires con- protective current to the steel beam, it is A number of anodes are applicable in nected to the top and bottom flanges vitally important to ensure adequate con- the protection of steel-framed buildings. of beams to form a cage for the con- sideration for voids in any CP design. However, the most suitable types are dis- crete encasement of the inner faces Knowledge of historic building construc- crete rod anodes. These can either be of steel beams tion methods is essential when establishing ceramic- or titanium-coated, with a mixed- • Chicken wire meshes to aid in the the possibility of voids. Expert knowledge of metal oxide coating. Expanded mesh probe internal works such as concreting steel-frame construction enables a rapid anodes are particularly useful for insertion and plastering risk assessment of voids and enables areas into the backup masonry at the fine jointing • Cast-iron rainwater downspouts requiring further inspection to be pinpoint- of stonework and the mortar joints of brick- and copper water pipes ed. Following risk assessments and inspec- work. Theses anodes are generally installed tion, it is often reasonable to make one of using a specialized cathodic-protection Failure to ensure the electrical continu- the following choices: grout, which is then pointed over using tra- ity of all metallic elements in a steel-framed 1. A large, consistent void exists ditional masonry pointing techniques. All of building can result in stray current interac- (greater than 25mm) in which corro- the anodes are installed and interconnected tions among the various elements of the sion rates are minimal and protec- with a feeder wire. The anodes are then ter- structure, resulting in accelerated corrosion tion is not required. minated at the positive terminal of the DC of discontinuous items. The importance of 2. A large void exists in which corro- power supply unit. electrical continuity is well-established in sion is occurring at a significant rate As all exterior components are installed concrete CP, and early investigations and and treatment is required. The void- within the backup and never through the site trials have shown the importance of elec- ed cavity must therefore be grouted façade stone, the particular advantages of trical continuity in steel-framed buildings. to ensure protection. this system are Ensuring electrical continuity of the 3. Small voids exist (less than 10mm) • The anodes are not visible. steel-frame, stonework, and masonry fix- in which corrosion has occurred. • Anodes can be installed using stan- ings and reinforcement bars is, therefore, dard grouting and masonry pointing an essential element to the application of techniques at the time of external

S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 C R E V E L L O • 4 5 sure that over- This was the first historic building in the protection and United States to have ICCP installed. The hydrogen em- area protected was the 1914 Wabash build- brittlement do ing’s pilaster colonnade at the Randolph not occur. Power and Wabash Street elevations at the 11th to supplies with 13th floors. The work on ’s multiple chan- Marshall Field’s flagship store in Chicago nels can provide came about from the engineers’ previous protection to a corrosion investigations and ICCP system number of design carried out on Selfridges’ Depart- “zones,” as each ment Store in , also designed by zone requires Burnham. Both buildings had the same independent detailed pilaster colonnades along the power. All units façade; both buildings were suffering from must have ad- corrosion of the embedded steel columns. justable control, The engineers working on the repair accommodate scope of the Marshall Field’s flagship store9 monitoring cells, were looking for a method to mitigate corro- Figur e6 – ICCPs chemat ic . record and store sion, minimize masonry removal, and pro- data, and they vide the owner with a long-term corrosion repairs. must provide power interruptions for test- solution. This was the third repair cycle for • Anodes are usually situated parallel ing requirements. Units can be independent the pilaster columns. Any further damages to beam and columns. of one another or be linked to a main con- sustained to the terra cotta could have • There is minimal internal disturbance. trol that manages and stores the collective caused irreparable damage requiring full data from the independent units. replacement and posed a life safety risk for Cathodes A schematic is provided below in Figure pedestrians. The estimated cost savings to While anodes are installed to provide 6, showing the layout of a system in a the client was $500,000.00 where the ICCP electrons to the steel, the areas of the steel masonry-clad, steel-frame building. The rod was installed. frame targeted for treatment become the anodes are attached to the [+] of the power In keeping with standard design proto- cathode. Wire connections to the steel frame supply (red), and the steel frame (cathode) is col, the system was designed to have four provide a return path to the power supply connected back to the [-] of the power supply. “zones” or independently powered areas. unit, as the negative portion of the circuit. Zones are defined by the amount of steel TRACK RECORD AND CASE surface area to be protected, the proximity Monitoring Cells STUDIES of the steel elements to one other, and the Reference electrodes or half-cell poten- The first cathodic protection system for even distribution of current within the zone. tial electrodes are permanently embedded the prevention of steel beam corrosion in a Each zone has two monitoring cells to pro- as part of the system. All systems require masonry structure was designed by vide data for polarization and potential performance evaluations according to the Taywood Engineering Ltd. and completed in decay. All wiring was routed internally and National Association of Corrosion Engineers 1991. The CP system provided protection distributed to the power supply units, (NACE) and British Standards European for the entrance colonnade of the Royal which were then linked by a communica- Norm (BSEN) standards, and all perfor- College of Science, Dublin. The entrance tions cable to a main control unit (MCU). mance is based upon the native potentials colonnade is a limestone structure contain- The MCU has an independent phone line, and changes in Ecorr once the system is ing two parallel structural I-beam members. providing dial-up access for remote moni- commissioned. Since its completion in 1991, regular toring. remote monitoring via embedded reference The project posed a unique installation Power Supplies electrodes has shown no corrosion prob- challenge, as the materials and installations All external wiring is brought into the lems. This has also been confirmed via procedures require a DC electrical system building and routed to the power supply annual visual inspections. Since the devel- to be embedded in masonry. This crosses units (PSU) or where most suitable for the opment of this first CP system for masonry, “union-owned” work, and it required full- structure, roof, etc. PSUs are generally over 150 systems have been designed and time installation support. Though the placed on the interior of a building in a installed for masonry buildings in the UK. anodes and wiring should be installed by an maintenance closet, drop-ceiling space, electrician, the components are embedded basement, etc. Commercial Department Store, within mortar and grout, which is “owned” PSUs or transformer rectifiers (T/Rs) Chicago, IL by the masonry union. The design engineers utilized in steel-frame cathodic protection In 2003, UK corrosion engineers8 were were on site full-time to assist in the train- require finite control of current output and engaged to carry out corrosion investiga- ing and installation process in order to voltage limitation. The systems require so tions and testing, design services, and appease the trades, the owner, and to little current to polarize the steel that there installation support for an ICCP system on ensure that all work was carried out seam- must be adequate control measures to en- the Marshall Field’s Building in Chicago, IL. lessly. The design team worked on the

4 6 • C R E V E L L O S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 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 elec- trical 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 Adminis­ tration Building, Washington, DC The Ross Admin- istration Building at Figur e7 – Image of cor nicet o be pr o t ec t ed . the United States Holo- caust Memorial Museum (USHMM) is a masonry, the masons were instructed to Collegiate Gothic Dormitory, 1905 load-bearing brick building with a remove the corrosion product from the New Haven, CT terra cotta cornice. As typical of cornice underneath side of the outriggers. The To date, the largest ICCP system detailing, the terra cotta armature com- removal of corrosion product (oxide) is not installed in the U.S. is on a Collegiate prised steel channels, outriggers, J hooks, required for successful CP installations, but Gothic dormitory at Yale University. In etc. to anchor the cornice and parapet in it was felt that the pressure exerted on the 2008, the owners required a 50-year design place. In 2005, the building was undergoing masonry was a health and safety risk life for the complete restoration and renova- an exterior restoration campaign. The eval- should a modillion crack and fall. tion of the 1931 masonry-clad steel-frame uating team noticed corrosion of the steel A cost benefit analysis was easily made, building. Prior to restoration, a thorough outriggers, which were causing downward and the prices of individual terra cotta units exterior building envelope investigation was displacement on the terra cotta modillions ranged from $3,000 to $5,000, with three to carried out. Water infiltration of the exterior and cracking of the soffit stones. Being one five verticals units that would be affected walls had put the steel frame at risk, and of the United States’ preeminent museums, per outrigger location. areas near water tables, gables, and water- the facility maintenance team at the The system was installed in 2005 and shedding elements were showing corrosion- USHMM took a proactive approach to the commissioned in 2006. Quarterly monitor- related deterioration. building’s upkeep and required a 25-year ing has been carried out by the authors The building was constructed between life extension. since commissioning, and the system has 1931 and 1932 and is part of the central Cornices are challenging elements, with achieved NACE and BSEN criteria for pro- core of the campus. Situated at the corner many electrically discontinuous metallic tection for the last seven years. The benefit of College and Elm Streets in New Haven, items, so a detailed inspection was of the system is that it provides remote CT, it is an exquisite example of the required. The trial allowed the team to access so that the engineers can access Neogothic architecture found at Yale. The determine the best technique to bond the data without having to make multiple site residential building houses students, class- discontinuous elements and to provide a visits. In 2011, the five-year visual inspec- rooms, entertainment facilities, and the mock-up of anode arrangements. After an tion was carried out. Each modillion and headmaster’s house. The details seen in investigation and trials, the decision was terra cotta unit in the area of cathodic pro- some of the masonry represent the ideals of made to install an ICCP system at the pre- tection was inspected and documented. All the college at the time of construction. Built sent time rather than risk further corro- changes to the structure were noted and in a remarkably short time frame, the build- sion-related damage to the masonry. compared to the previous year’s ground- ing was constructed with a steel frame to The cornice system of the Ross building side inspections. There was evidence of carry the floor loads, as well as to increase differed from the majority of the previous movement in the area of previous cracking productivity during construction. The build- steel-frame building projects as it was pos- and repairs; however, this was due to the ing was erected in just five months after sible to access the majority of the corroding removal of the building’s diaphragm when breaking ground. steel outriggers from a large masonry joint. the building was converted from a printing The building is a quadrangle with eight The internal steel elements of the cornice facility to the Administration Building of the unique elevations—all different heights— armature were in very good condition. To USHMM. See Figure 7. clad in a variety of materials. The Gothic remove the downward stresses to the towers, gables, balconies, and turrets are all

S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 C R E V E L L O • 4 7 Figur e8 – Dor mit ory w it hv ar ious mas onry configur at ions.

Figur e9 – Int er nal courty ar d elev at ions.

ornately detailed masonry units. The steel frame of the building was not meant to exclusively carry the mason- ry 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 inti- mate contact with masonry. As such, the corrosion prod- uct was causing cracking of the masonry. The author was engaged by the architects of record to simultaneously controlling corrosion. Due All work was carried out by specialist engage in a corrosion condition analysis. to the success of the feasibility investiga- contractors, masons, and electricians, with The corrosion rate testing indicated that tions, commercial viability, and conserva- oversight from the design team. The anode areas that had not begun to show signs of tion benefits, a full-scale CP design was car- electrodes were wired back to the positive corrosion would crack within six to ten ried out. In the end, the upper two floors of terminals of an intelligent power supply and years. After the survey, the facilities man- the entire building, which were prioritized monitoring system. The steel was wired sep- agement department engaged the team to as high-risk, were protected, equaling over arately to the negative terminals. Protective carry out a CP feasibility trial. As there are 6000 LF of steel. The design comprised currents were then applied to the steel via multiple masonry types on the building, drawings, specifications, and material the masonry using a computer system to three trials had to be carried out: one each schedules, detailing the safe extra-low-vol- control the intelligent power supplies. Each on sandstone, granite, and brick elevations. age electrical circuits, 110V AC electrical “zone” has four monitoring cells that pro- As a result of the trial, it was concluded circuits, and masonry installation works. In vide the client with data to ensure the sys- that a CP system could be developed as a total, there were 35 independently powered tem is working according to specifications. masonry conservation technique while “anode zones.” See Figures 8, 9, and 10.

4 8 • C R E V E L L O S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 Figur e10 – Inst allat ion det ails at gable.

CONCLUSIONS • Impressed current cathodic protec- • ICCP adheres to preservation and Since the 1990s, ICCP has been used on tion systems have been shown as an conservation guidelines. hundreds of heritage buildings in the U.K. appropriate method of repair for the and numerous historic buildings in the U.S. prevention of corrosion in early- The design life of the systems range These systems have shown the possibility of 20th-Century steel-framed build- from 25 to 50 years, and this is dictated by protecting full-building façades and the ver- ings. the power supply technology and internal satility of CP systems for listed and land- • Cathodic protection systems for wiring systems. While the design life of the marked buildings. Where ICCP has been masonry-clad steel-framed buildings anode and titanium wiring can exceed 40 installed, it has been found to have a cost- require specialist knowledge of his- years, based on the amount of current saving in excess of 50% in comparison with torical construction techniques. passed (i.e., lower current density, longer traditional approaches of repair involving • A corrosion survey with in­situ trials anode life), the design life of the control sys- the removal of masonry and steel painting. is necessary prior to moving forward tems will change as rapidly as technology Additionally, the cost of ICCP at targeted with a design. allows. locations, determined by thorough corro- • The overall investment in a long- The ICCP systems will require mainte- sion investigations to be at risk, is usually term corrosion mitigation system nance in the form of monitoring and system in the range of 10% of the overall exterior provides economic incentive to a review. It is advisable to report quarterly on envelope repair scope. proactive approach. the data, and this is a requirement in NACE The following conclusions can be made • The loss of historic masonry and and BSEN standards. from the brief discussions presented: façade damage can be minimized • Steel-framed buildings constructed with a proactive, long-term repair REFERENCES prior to 1940 are prone to corrosion- strategy. D. Friedman, “Early Predictions of Steel- related problems such as the crack- • ICCP is specifically tailored to each Frame Deterioration: Permanency in ing and displacement of masonry. building. High-Rise Construction,” Proceed­

S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2 C R E V E L L O • 4 9 ings of the Third International ly important and of special interest. is required. ICCP systems are gener- Congress on Construction History, 2. Chlorides can also affect the oxide ally considered permanent installa- May 2009, Bath, England. layer, though they do not always tions, whereas galvanic systems are P.A.J. Gibbs, “Corrosion in Masonry- affect pH. considered shorter term. Clad Early-20th-Century Steel- 3. Cathodic protection as it was first 4. Donald Friedman discusses changes framed Buildings,” Historic Scotland, discovered was galvanic. A less in building technologies and applic- 2000, Edinburgh, Scotland. noble metal was used to provide able codes in relation to disasters in electrons, thus sacrificing itself in Historic Building Construction: De­ ACKNOWLEDGEMENTS order to protect a more noble metal. sign, Materials, and Technology. The author would like to acknowledge This is based on the Galvanic Series 5. In the UK, the LCC (General Powers) prior work carried out by colleagues Peter of Metals. Still used today, sacrificial Act 1909 covers steel frame con- A.J. Gibbs and Paul Andrew Noyce. Their zinc and zinc alloys are applied in struction. U.S. documentation is early studies and trials made this work pos- bulk, thermal spray, and mesh slightly earlier. sible, and the case studies in this paper all underlay for protection of steel in 6. P.A.J. Gibbs. Corrosion in Masonry­ came to fruition from efforts based on the concrete and atmospherically Clad Early­20th­Century Steel­ track record established by Gibbs and exposed steels. Due to the low resis- Framed Buildings. Historic Scotland, Noyce in the United Kingdom. tivity of the concrete electrolyte in 2000, Edinburgh, Scotland. the presence of moisture and salts 7. D. Friedman, “Early Predictions of FOOTNOTES (i.e., marine environment in particu- Steel Frame Deterioration: Perman- 1. English Heritage and Historic lar), galvanic CP can be less expen- ency in High Rise Construction,” Scotland, like the National Register sive than ICCP. It does not have the Proceedings of the Third Inter­ of Historic Places, has the following same design life and must be reap- national Congress on Construction categories of building significance: plied when the sacrificial alloy is History, May 2009, Bath, England. Grade I buildings are of exceptional consumed. 8. Paul Noyce and Peter Gibbs of interest, sometimes considered to be For historic steel-frame buildings, Electro Tech CP, Ltd. internationally important; Grade II* the high resistivity of the stone 9. Construction dates are 1893, 1907, buildings are particularly important cladding requires a higher driving and the 1920s. There were various buildings of more than special inter- voltage than provided by a galvanic construction stages and expansions est; Grade II buildings are national- cell. Thus, an external power source of the department store.

5 0 • C R E V E L L O S Y M P O S I U M O N B U I L D I N G E N V E L O P E T E C H N O L O G Y • O C T O B E R 2 0 1 2