Lessons in Galvanic Cathodic Protection Technology from Soldier

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Lessons in Galvanic Cathodic Arne P. Johnson Protection Technology John S. Lawler from Soldier Field and the Michael S. Murphy

Franklin Avenue Bridge

Fig. 1. Franklin Avenue Bridge, Minneapolis, Minnesota, during construction in 1922. This bridge has been recently rehabilitated. Image courtesy of Hennepin County Library.

Deterioration of older reinforced concrete structures is commonly caused by one or more of four mechanisms: Design of galvanic chloride- or carbonation-induced corrosion of embed- cathodic protection ded steel, freeze-thaw deterioration of non-air-entrained systems requires concrete, and deterioration of the concrete matrix due to proper consideration deleterious internal chemical reactions. These deteriora- of five key design factors, which are tion mechanisms must be addressed in order to achieve particularly relevant successful rehabilitations (Fig. 1). for historic structures. Steel reinforcement in concrete is normally protected from corrosion by a thin oxide film (also known as a passive film) that develops around the bars as a result of the highly alkaline concrete pore solution that results from portland cement hydration reactions. As long as this passive film remains, corrosion is impeded. Chloride-induced corrosion can be initiated when chloride ions, in the presence of moisture and oxygen, accumulate to a sufficient concentration and then destroy the passive film around the reinforcing bars. Chloride ions can originate from external sources, such as deicing salts or seawater, or internal

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Fig. 2. Example of typical corrosion cell in reinforced concrete. All figures by Wiss, Janney, Elstner Associates, Inc., unless otherwise noted.

Fig. 3, opposite. Soldier Field, Chicago, Illinois, west grandstand and colonnade during construction in 1924. Image courtesy of the Chicago Park District.

sources, such as chloride-contaminated In concrete deterioration caused by Used in the 1800s to protect ships by aggregates or chloride-containing corrosion of embedded steel (either attaching billets of zinc to ferrous hulls, admixtures. Carbonation-induced chloride- or carbonation-induced), the CP was first used for reinforced concrete corrosion can be initiated when the corrosion process is an electrochemi- structures in the 1970s. In short, CP carbonation front in the concrete cal reaction that breaks down the steel involves making the reinforcing steel the reaches the level of the reinforcement. to more chemically stable iron-oxide cathode of a corrosion cell by supplying Carbonation is a natural process that compounds (also known as rust). For an alternative anode. There are two occurs when carbon dioxide in the air this reaction to occur, a corrosion cell basic types of CP: galvanic CP (also penetrates the concrete and reacts with must be formed; it consists of an anode known as sacrificial CP) and impressed the cement paste, lowering its pH from (location of oxidation reaction where current CP (ICCP). as high as 13 in its uncarbonated state electrons are lost) and a cathode (loca- Galvanic CP is a passive system in down to as low as 8.5, breaking down tion of reduction reaction where elec- which a galvanic anode, typically zinc the passive film. trons are gained) (Fig. 2). The anode in various shapes and sizes, is embed- and cathode are connected by an ionic Freeze-thaw deterioration occurs in ded in or attached to the concrete and current path (ions passing through an non-air-entrained concrete when the electrically connected to the steel. Be- electrolyte such as moist concrete) and concrete is critically saturated with cause the zinc is electrochemically more an electronic current path (electrons water and subjected to repeated freez- active than the steel, the zinc becomes passing through a metallic conductor). ing and thawing cycles. The damage the anode and corrodes preferentially The corrosion reaction results in rust first manifests in internal microcrack- to the reinforcement, which becomes at the anode that occupies a greater ing, progresses to paste deterioration the cathode and is polarized, reducing volume than the steel consumed, creat- or map-cracking visible on the surface, the rate of corrosion. A galvanic CP ing expansive pressures and eventually and culminates in disintegration of the system is usually relatively inexpensive concrete distress in the form of crack- concrete from the surface inward. to install and requires little to no main- ing, delaminating, and spalling of the Modern air entrainment avoids this tenance. The anode is consumed and concrete surface. eventually exhausted, at which time it damage mechanism by providing voids must be replaced to provide continued in the concrete into which internal Cathodic Protection Basics protection. Service life (i.e., the length water can expand when it freezes. Con- Cathodic protection (CP) is one of of time that protection is provided) crete deterioration can also be caused several technologies used to prolong depends on many factors, including the by deleterious chemical reactions such the life of historic concrete structures size of the anode and severity of the as alkali-silica reaction (ASR) and that are prone to damage from corrosion corrosion environment, but typically delayed ettringite formation (DEF). of embedded steel (i.e., CP does ranges, in a well-designed system, from Further information on all of these not address deterioration caused by 7 to 20 years. mechanisms can be found elsewhere.1 mechanisms other than corrosion).

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Calcium chloride had apparently been added as an accelerator to the face mix to aid in the two-layer placement method. In the concourses, sampling and testing showed that corrosion was due principally to carbonation of the concrete.5 Cathodic protection trials. In 2001, when adaptive reuse and rehabilitation of the stadium were being contem- plated, the authors’ firm was engaged to study means to prolong the life of the historic concrete elements (the firm was not involved in the adaptive-reuse design). Trials of five corrosion-mitigation systems were installed, including three galvanic CP systems: discrete zinc anodes, arc-sprayed zinc anodes, and zinc-hydrogel sheet anodes. The other methods were re-alkalization (an electrochemical treatment to address carbonization-induced corrosion) and surface-applied migrating corrosion ICCP is based on an active system in Soldier Field inhibitors (a spray-applied penetrating 6 which the anodes, powered by a DC Soldier Field was constructed between liquid intended to mitigate corrosion). power source, introduce an electrical 1922 and 1926 in Chicago, Illinois This paper focuses on the discrete current that promotes cathodic (Fig. 3). The stadium was listed on the galvanic CP system installed in the cof- reactions at the surface of embedded National Register of Historic Places fered ceilings of the colonnades con- steel. Use of a DC power supply in 1984 and designated a National sisting of equally spaced, cylindrically may allow for higher currents and Historic Landmark from 1987 to 2006. shaped anodes embedded in holes that greater control. An inert anode that Original elements of the structure that were cored from the attic into the top is not sacrificed over time is typically remain include the concourses at the of the colonnade beams and electrically utilized. ICCP systems are generally stadium perimeter and the east and connected to the reinforcement. Anodes more expensive to install and require west colonnades.4 were installed at two spacings: 22 inches more maintenance. Service life depends and 32 inches (Figs. 4 and 6). on many variables but can exceed 25 Overhead concrete in the concourses Performance evaluation. After years.2 Hybrid CP systems, which have includes large transfer girders and sec- installation, the corrosion-mitigation been introduced recently, function ondary framing for the promenades and systems were monitored for six months. as an impressed current system for a colonnades above. The coffered ceilings Monitoring consisted of measurements relatively short period of time (typically of the colonnades consist of an orthog- of corrosion potential (using copper- a few months) then revert to a galvanic onal grid of heavily reinforced concrete sulfate reference electrodes), corrosion system for the remainder of their beams that support a thin, lightly rate (using surface-contact linear service life. reinforced concrete slab (Fig. 4). The formwork for the ceilings of the colon- polarization instruments and em- This paper focuses on galvanic systems, nade was lined with a 2- to 3-inch-thick bedded corrosion-rate probes), and the type of system used in the case architectural face mix that resembles cathodic protection current (by studies presented, and, in the authors’ granite, with structural concrete backup direct measurement through a shunt experience, the more commonly used cast integrally behind. resistor). Initial test results indicated system for historic structures. The good performance of the galvanic intent is to provide an overview of Over the years, the concrete in the con- anodes in the colonnade ceilings, with galvanic CP design in order to make courses and the ceilings of the colon- sufficient protection current for the information accessible to people who nades has required annual inspections reinforcement (Fig. 5). Based on the are not corrosion engineers. More and frequent repairs to address distress initial measurements, it was predicted detailed treatment on the subject can from the corrosion of embedded rein- that the anodes would be consumed be found in corrosion engineering forcement. In the colonnade ceilings, in 9 to 15 years, depending on actual textbooks and National Association of sampling and testing showed that cor- environmental exposure conditions. Corrosion Engineers publications.3 rosion was due principally to chlorides present in the architectural face mix.

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Fig. 4. Soldier Field, cut-away isometric ohm-cm) just exceeded the upper view of coffered ceiling of colonnade, limit on resistivity permitted by anode showing reinforcement and galvanic manufacturers. Resistivity of the origi- anodes (highlighted in orange). nal concrete surrounding the embedding mortar was also high when dry (1,520,000 ohm-cm), though within the recommended limit when saturated in the laboratory (12,700 ohm-cm). Considering these results, the poor long-term performance of this galvanic depolarization potential shift was ob- CP installation was attributed to the served, which was consistent with the following: observed lack of current flow. • Wet or dry, the embedding mortar To assess the situation, three of the an- used in this installation was far too odes and the surrounding embedding Due to budgetary constraints, the resistive to allow adequate current to mortar were extracted by coring from owner elected not to install the anode flow along the ionic current path. the attic side. The embedding mortar system throughout the colonnade ceil- was removed using an acid dissolution • When the surrounding concrete in the ings, but the trial installations were process, and the anodes were inspected ionic current path was dry, as in the left in place. Each year, since that time, and weighed. The extracted anodes subject installation where moisture the historic concrete surfaces at Soldier showed only surficial zinc oxide and reaches only the bottom surface of the Field have been inspected close-up. essentially no consumption of zinc com- ceiling from ambient humidity and Corrosion-induced delaminations and pared to unused identical anodes. occasional condensation, the concrete spalls have continued to develop at a was likely to be too resistive to allow slow rate, and potentially loose mate- Laboratory resistivity testing was per- adequate current flow. rial has been removed annually. formed on both the embedding mortar • The high chloride concentration in and the original concrete surround- In 2014 the authors’ firm performed this assembly is in the architectural ing the embedding mortar in the core follow-up testing to examine how face mix and not in the backup con- samples. Resistivity measures the degree the corrosion-mitigation trials were crete. As such, chloride ions, which to which a material conducts electrical performing after 13 years of service. can reduce resistivity and enhance current, which is needed along the ionic Evaluation of the galvanic anode sys- current flow, were not present along current path in a corrosion-cell or CP tem in the colonnade ceilings involved the ionic current path behind the rein- system (Figs. 2 and 6). Low resistivity measurements of corrosion (half-cell) forcing bars. indicates that the material readily al- potential, measurements of cathodic lows current flow, while high resistivity The good performance of the anodes protection current, and extraction of indicates impeded current flow. High for the first six months of monitoring is select anodes to observe the amount of resistivity values may result where the believed to be attributable to the mois- zinc consumption and to measure the concrete is dry and if the concrete is ture introduced into the system by the resistivity of the materials along the dense and impermeable (such as from mixing water in the embedding mortar current distribution path. very low water-to-cement ratios or in and the water used in the coring to in- As shown in Figure 5, the cathodic pro- silica fume mixes). The significance stall the anodes. The added water likely tection current in 2014 was found to of embedding-mortar resistivity on permeated the concrete temporarily and be effectively zero, meaning no current galvanic anode effectiveness was not then took some time to dissipate, so was flowing from the anodes to protect widely known in 2001 and thus was that the initial resistivity of the moist- the reinforcement. The current was not adequately considered in the de- ened materials along the ionic current expected to be only modestly less than sign. Manufacturers of galvanic anodes path was low enough to allow protec- that measured at the end of the moni- now recommend that materials have tion current to flow. However, once toring in 2001, unless the zinc in the resistivity of less than 15,000 to 50,000 the added moisture dissipated and the anodes had been fully consumed. De- ohm-cm, depending on the supplier, to materials along the ionic current path polarization testing, an electrical tech- support the function of the anodes. dried out, the dry materials no longer nique used to assess CP systems by dis- allowed current to flow. Resistivity of the embedding mortar connecting the anodes and measuring used at Soldier Field measured across Franklin Avenue Bridge the shift in the electric potential, was the sample with an AC resistance meter performed to assess the function and The Franklin Avenue Bridge over the was found to be very high (3,810,000 throwing distance (zone of influence) Mississippi River in Minneapolis, Min- ohm-cm) under dry in situ conditions. of the anodes based on a reference cell nesota, is a five-span open-spandrel When the mortar was saturated in placed on the surface. No discernable concrete arch bridge built between the laboratory, the resistivity (51,000 1919 and 1923 (Fig. 1). At the time of

30 LESSONS IN GALVANIC CATHODIC PROTECTION TECHNOLOGY

its construction, it had the longest concrete arch span in the world at 400 feet. The arch ribs were constructed using the Melan system patented in 1892 by Joseph Melan, an Austrian bridge engineer. Steel trusses fabricated from riveted steel angles were erected between massive concrete piers; the arch-rib concrete was then cast in place around the trusses. In 1970 the bridge deck, cap beams, and spandrel columns were removed and replaced as part of a major rehabilitation effort to address advanced deterioration. Localized concrete repairs were also performed on the arch ribs, piers, and abutments. The bridge was listed in the National Register of Historic Places in 1978. The authors’ firm was retained in 2007 to perform a condition assessment and a study of rehabilitation alternatives for the bridge. Follow-up inspections and rehabilitation design began in 2013, and rehabilitation construction took place from 2015 to 2017. Complete information about the condition assessment, rehabilitation design, and construction are available elsewhere.7 This paper focuses on the rehabilitation of the arch ribs using targeted galvanic cathodic protection. The assessments and materials testing identified widespread deterioration in the original concrete caused primarily by chloride-induced corrosion of the reinforcing steel, as well as freeze-thaw chorage into the substrate concrete, Fig. 5. Instantaneous protection deterioration (cracking and eventual and crack-control reinforcement within currents generated by embedded disintegration of concrete due to freeze- the repair. anodes as measured in 2001 and thaw cycling of saturated, non-air- 2014, showing high initial currents entrained concrete). In the arches, the Installation of galvanic cathodic but near-zero current when tested most prevalent damage was corrosion- protection. Between the arch-rib cor- 13 years after installation. induced cracking and spalling along the ner repairs, where chloride contamina- Fig. 6. Schematic illustration of arch corners where deicing salts used tion was likely but cracking had not problems with the anode perfor- on the deck had penetrated (Fig. 7). yet begun, galvanic cathodic protection mance. High-resistivity embedding Freeze-thaw damage was also present was installed to prolong the service life mortar (dark gray) and dry zone below leaking deck expansion joints until the next repairs would be needed of original concrete (orange, dot- and in the spring-line zones where in approximately 15 to 25 years. The ted shading) interrupt current flow. long-term moisture exposure was most cathodic protection consisted of con- Chlorides (yellow shading) and tinuous rod-shaped zinc anodes placed moisture source (blue arrows) are severe. remote from ionic current path. in saw-cut grooves and electrically con- Customized concrete-repair details were nected to the Melan truss angles with developed for the arch-rib corners, as wires at intermittent locations (Fig. 8). illustrated in Figure 8, including remov- Slots for the anodes were located to be al beyond deteriorated regions, cleaning least visible from the ground, minimizing and coating of the embedded steel, an- 31 APT BULLETIN: THE JOURNAL OF PRESERVATION TECHNOLOGY / 50:2–3 2019

Fig. 7. Franklin Avenue Bridge, aesthetic impact. The anodes were sized example of chloride-induced to provide sufficient current density and corrosion spalling along the arch- were embedded in a pre-packaged low- rib corner, 2012. resistivity mortar containing lithium Fig. 8. Schematic drawing of hydroxide with a manufacturer-reported typical arch-rib corner repairs, resistivity of 5,000 ohm-cm that filled showing adhesive-grouted dowels the slots. for anchorage (A); saw cuts at perimeter (B); clean and coat In this design, current flow along the existing steel (C); crack-control ionic current path was promoted by reinforcement (D); properly the availability of moisture, presence prepared concrete substrate (E); of chloride ions, low-resistivity embed- and continuous zinc anodes in slots between concrete repairs, with wire ding mortar, and low-resistivity original connections to Melan angles (F). concrete (when moist). Two permanent built-in monitoring stations were in- Fig. 9. Franklin Avenue Bridge, cluded in the cathodic protection instal- example of built-in monitoring station (before surface of concrete lation, one at each end of the bridge was cleaned and coated), 2017. (Fig. 9). Performance evaluation. System commissioning using the monitoring stations was performed soon after installation, and system monitoring has been ongoing since that time. Each monitoring station included an embedded reference cell and current shunt to support depolarization testing and CP current. The reference cells were within 6 inches of the reinforcing steel, near the midpoint of the instrumented section. The monitoring consisted of routine measurements of the protection current and system depolarization, typically performed monthly at each monitoring station. The protection-current density provides a general sense of the cathodic protection system effectiveness, while the anode consumption rate is dependent on the total protection current. Figure 10 shows the performance data that has been measured over the past two years. The measured protection currents fluctuate with temperature changes, as expected, since corrosion rates decrease with decreasing temperatures and can become almost dormant in very low temperatures. Based on an average measured current of approximately 40 mA and the surface area of the protected truss angles, the current density was 3.8 mA/m2. Depolarization is measured by temporarily interrupting the protective current (i.e., disconnecting the anode and the reinforcing steel) and monitoring the reinforcement’s decay in polarization over time. Numerically, depolarization is the 32 LESSONS IN GALVANIC CATHODIC PROTECTION TECHNOLOGY

voltage difference between the final depo- to mitigate concrete deterioration in an ask regarding impact on the historic larized potential (typically after at least individual situation, and, if so, how it resource include: four hours) and the potential measured can be implemented effectively. • Do the repairs retain (rather than immediately when the system is turned 1. Technical and economic merits replace) the original historic fabric? off. According to the National Asso- of cathodic protection. The technical ciation of Corrosion Engineers (NACE • Is the appearance of the original and economic merits of cathodic protec- SP0216-2016), depolarization values structure altered unacceptably by the tion should be assessed in the context repairs? of 100 mV or greater indicate that of the individual structure, beginning cathodic protection is being achieved. with a thorough condition assessment • Are the repairs reversible? The monitoring stations have registered and materials-testing program to iden- • Is the repair a proven technology? polarization values greater than the 100 tify the cause or causes, extent, and mV throughout the monitoring period, 3. Sufficient source of protection severity of any deterioration present. current in a galvanic CP system. To indicating good system performance Targeted sampling and testing of the over more than two years. design a galvanic CP system suitable concrete are essential to understand the for the project context and goals, the Lessons Learned: nature and cause of the deterioration anode material (normally zinc) and in each individual structure. Without geometry must first be selected in order Key Design Factors for an understanding of the deterioration Galvanic CP Systems to provide a sufficient source of protec- mechanisms, repairs may become un- tion current to the steel that is to be The Soldier Field example emphasizes necessarily extensive and expensive if protected. Anode selection should con- the need to provide a sufficient and they attempt to address deterioration sider material, shape, surface area, and complete path of protection current in mechanisms that are not relevant, or mass of the anode. In general, a greater a galvanic CP system. The protection the repairs may be ineffective if they mass, electrical activity, and surface path can be different depending on the fail to address the root causes of the area of zinc are needed to achieve both geometry of each installation; for each deterioration. Cathodic protection a longer service life and a higher degree case, the protection path should be addresses only corrosion-induced dete- of protection to the steel. The types of identified and all of the materials along rioration; hence, if the primary cause zinc anodes commercially available for the path evaluated to ensure they will of deterioration is not corrosion (such use in concrete vary widely. Various an- effectively conduct the protection cur- as freeze-thaw deterioration), then ode types include puck-shaped anodes, rent. Materials should be low resistivity cathodic protection is not a technically cylindrical anodes (like the ones used at and should be exposed to a sufficient appropriate solution. Soldier Field), rod-type anodes (like the and lasting moisture source. In the From an economic standpoint, the costs ones used at Franklin Avenue Bridge), Franklin Avenue Bridge example, these and benefits associated with repairs and surface-applied anodes (like those 9 factors were addressed, and testing is that include a cathodic protection sys- used elsewhere at Soldier Field). showing good performance. tem should be weighed against those In order for the anodes to generate Based on these two examples and the associated with conventional concrete current, the conditions at the anode fundamental corrosion principles dis- repairs without cathodic protection. must also be suitable to promote anode cussed above, five key design factors Various types and extents of galvanic corrosion. Various strategies, including need to be considered to achieve long- and impressed current cathodic protec- potting the anode in a high pH mortar term corrosion protection of historic tion should be considered. Alternatives or chloride-rich mortar, have been im- concrete structures using galvanic CP. should be compared using realistic plemented by anode manufacturers to These factors are as follows: service-life predictions and life-cycle encourage the corrosion reaction. This cost analyses. Since factors such as con- corrosion process also requires mois- • technical and economical merits of dition, access, local contractor exper- ture at the anode site. cathodic protection tise, and targeted service life may vary 4. Complete path of protection cur- • impacts on the historic resource widely between structures, each struc- Next, ture should be evaluated separately. rent in a galvanic CP system. • sufficient source of protection current and the most important lesson learned in a galvanic CP system 2. Impacts on the historic resource. through the case studies described • complete path of protection current in If cathodic protection is determined to herein, a complete and long-lasting a galvanic CP system be a viable option, a paramount con- current path must be provided for the • performance specifications and field sideration is whether it can be achieved CP system to be effective. As discussed verification. with minimal impact to the historic above, completing the corrosion cell character of the structure. For such (and thus supporting the function of the The authors suggest that these five gen- consideration, the Secretary of the galvanic anode) requires ionic current eral factors be used as a step-by-step Interior’s Standards and the National to pass through the concrete between guide to navigate the process of whether Park Service’s Preservation Brief 15 are anode and steel. The resistance to ionic galvanic CP is an appropriate solution critical resources.8 Key questions to current flow is increased with greater 33 APT BULLETIN: THE JOURNAL OF PRESERVATION TECHNOLOGY / 50:2–3 2019

where it may be desirable to place anodes in unusual locations and orientations to hide them from public view and to protect historic fabric. 5. Performance specifications and field verification. If cathodic protection is pursued, it is critical that the performance requirements be thorough- ly defined in the project specifications and that the installation details be described carefully on the plans. It is also critical that the installation include pro- visions for initial system commissioning and ongoing monitoring to verify the intended performance. The authors recommend built-in monitoring stations that can be used to measure protection current and depolarization for a period of at least three years. For the installation at Soldier Field, the six-month period of monitoring was not sufficiently long to detect that the performance was not as intended. Conclusion Fig. 10. Franklin Avenue • Highly resistive embedding mortar To design an effective galvanic ca- Bridge, protection current and and original concrete were present thodic protection system, one must depolarization monitoring data, along the ionic current path. showing depolarization values understand corrosion fundamentals greater than 100 mV over the • There was a lack of sufficient and and the condition of each individual testing period and variation in lasting moisture along the current structure. Claims of product manufac- current with temperature. path. turers should be verified by independent • Chlorides were present in the system, review and testing by qualified design- but not along the current path. ers. The design of galvanic CP systems should carefully consider all five key distance and greater resistivity of the In contrast, the CP system installed in design factors described above. In the concrete. Therefore, to support ionic the arch ribs of the Franklin Avenue authors’ experience, the two design current flow, the anodes must be in Bridge has been shown to be effective factors that are most often neglected in relatively close proximity to the rein- for the following reasons: practice are the provision of a complete forcement that needs protection; the • The embedding mortar and original current-distribution path and sufficient ionic current path must not include concrete along the ionic current path field-performance verification testing. high-resistivity materials that will im- have low resistivity. These often-neglected factors can be pede the current (see recommendations • There is an ample and lasting source particularly relevant in applications for above for resistivity limits); and an of moisture throughout the current historic structures where anodes are adequate and lasting source of moisture path. often placed in unusual orientations must be present. Galvanic CP systems • Chlorides may be present along the and where built-in test stations are not may be less successful in environments current path. installed in order to minimize visual where moisture exposure is limited, impact and retain historic fabric. such as concrete in climate-controlled, In addition to the ionic current path, interior environments. One should also an electronic current path must connect Acknowledgement consider where chloride ions may be all steel to be protected to the anode, The authors acknowledge the contri- present in the system since their pres- and the connections between the anode bution of Vector Corrosion Technologies ence will reduce resistivity locally and and the protected steel must be durable. Ltd. of Winnipeg, Manitoba, for its enhance ionic current flow. A qualified corrosion professional should evaluate both the ionic and electronic assistance in performing the automated For example, the galvanic CP system current path for each potential application data collection of cathodic protection installed in the colonnades at Soldier of galvanic CP. Proper consideration of system performance at the Franklin Field was not effective in the long term the current distribution path is particu- Avenue Bridge. for the following reasons: larly important for historic structures

34 LESSONS IN GALVANIC CATHODIC PROTECTION TECHNOLOGY

Arne P. Johnson, principal at Wiss, American Concrete Institute, 2016), 10–37. Bridge Part 2: Analysis, Design, and Acceler- Janney, Elstner Associates, Inc., is a A. M. Neville, Properties of Concrete (Essex, ated Bridge Construction,” Concrete Interna- England: Pearson Education Limited, 2011), tional 39, no. 8 (2017): 29–36. structural engineer with 30 years of 144–147, 539–563. 8. Paul Gaudette and Deborah Slaton, experience at WJE and expertise in 2. Matthew B. Gries, Kevin A. Michols, John Preservation Brief 15: Preservation of Historic evaluation, testing, and rehabilitation, S. Lawler, David W. Whitmore, and Matt Milt- Concrete (Washington, D.C.: Technical particularly for historic structures. He enberger, “Evaluation and Repair of Natural Preservation Services, National Park Service, can be reached at [email protected]. Draft Cooling Towers,” in NACE Interna- U.S. Dept. of the Interior, 2007), https://www. tional Corrosion 2018 Conference & Expo nps.gov/tps/how-to-preserve/briefs/15-concrete. John S. Lawler, associate principal at Series (Phoenix, Ariz.: NACE International, htm. Wiss, Janney, Elstner Associates, Inc., 2018), 15. 9. Johnson and Lee, 72–73. The Concrete Soci- is a materials engineer with 18 years 3. Denny Jones, Principles and Prevention of ety, TR73 Cathodic Protection of Steel in Con- Corrosion, 2nd ed. (Upper Saddle River, N.J.: crete, including Model Specification (Camber- of experience at WJE and expertise in Prentice-Hall, Inc, 1996), 439–476. NACE In- ley, England: Concrete Society, 2011), 45–54. materials evaluations, field and labo- ternational, SP0216-2016, Sacrificial Cathodic ratory testing, service-life analysis, and Protection of Reinforcing Steel in Atmospheri- cally Exposed Concrete Structures (Houston, repair design. He can be reached at Tex.: NACE International, 2016), 1–16. [email protected]. 4. Construction of which is detailed in Arne P. Michael S. Murphy, associate III at Johnson and Seung Kyoung Lee, “Soldier Field Stadium: Corrosion Mitigation for Historic The APT Bulletin is published by the Wiss, Janney, Elstner Associates, Inc., Concrete,” APT Bulletin: Journal of Preserva- Association for Preservation Technology. is a structural engineer with nine years tion Technology 35, nos. 2–3 (2004): 67–75. APT’s mission is to advance appropriate of experience and expertise in evalua- 5. Johnson and Lee, 67–75. traditional and new technologies to care tions, condition assessments, materials 6. Johnson and Lee, 67–75. for, protect, and promote the longevity of testing, and repair design. He can be 7. Arne P. Johnson, John S. Lawler, Dan Enser, the built environment and to cultivate the reached at [email protected]. Travis Konda, and Paul Backer, “The Franklin exchange of knowledge throughout the Avenue Bridge Part 1: History, Investigation, international community. A subscription Notes and Rehabilitation,” Concrete International 39, no. 6 (2017): 33–42. Dan Enser, Mario to the Bulletin and free online access to 1. ACI Committee 201, ACI 201.2R-16 Guide Grenville Ratnaraj, Arne P. Johnson, John S. past articles are member benefits. For more to Durable Concrete (Farmington Hills, Mich.: Lawler, and Paul Backer, “The Franklin Avenue information, please visit www.apti.org.