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Suggested Citation:"Chapter One - Introduction." National Academies of Sciences, Engineering, and Medicine. 2009. Cathodic Protection for Life Extension of Existing Reinforced Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14292.
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Suggested Citation:"Chapter One - Introduction." National Academies of Sciences, Engineering, and Medicine. 2009. Cathodic Protection for Life Extension of Existing Reinforced Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14292.
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Suggested Citation:"Chapter One - Introduction." National Academies of Sciences, Engineering, and Medicine. 2009. Cathodic Protection for Life Extension of Existing Reinforced Concrete Bridge Elements. Washington, DC: The National Academies Press. doi: 10.17226/14292.
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3As of 2002, the National Bridge Inventory (NBI) Database, maintained by the FHWA, contained a total of 587,964 bridges. The average age of the bridge structures in this database is 40 years, and 41% are at least 40 years old. Over the past three decades, significant attention has focused on the condition of the nation’s aging highway bridge infra- structure. Several independent evaluations of the condition of the nation’s infrastructure, based on condition ratings contained in the database, have been performed (1–3). These studies ascertained that 14% of the bridges were rated structurally deficient and the primary cause of the deficiency was corrosion of reinforcing steel. The cost to maintain the nation’s bridges during the 20-year period from 1999 to 2019 is estimated to be $5.8 billion per year, and the cost to improve and eliminate deficiencies over the same period is $10.6 billion (1). A cost-of-corrosion study determined that the annual cost of corrosion to all bridges (including steel bridges) is $8.29 billion and this does not include indi- rect cost incurred by the traveling public as a result of bridge closures (2). To address the corrosion problem on reinforced concrete structures, a research and development effort was initiated by both the public and the private sectors in the early 1970s. Numerous different technologies were introduced to repair damage caused by corrosion and to prevent or minimize fur- ther damage from occurring. In addition, strategies were also developed to delay the initiation of corrosion on new struc- tures, thereby increasing their service life. These were gener- ally categorized as “Prevention.” Strategies, technologies, and materials developed to repair the damage induced by cor- rosion are generally referred to as “Repairs” and the term “Rehabilitation” is used if the project either eliminates or controls the cause or interferes with the process of deteriora- tion to stop, control, or minimize it. On new structures there are many techniques available to delay the initiation of corrosion, which include the increase of clear concrete cover, installation of overlays, reduction in the permeability of the concrete (by the use of latex modi- fiers and replacement of cement by silica fume or fly ash), admixing of corrosion inhibitors, use of alternative reinforce- ments (such as epoxy-coated rebars, galvanized rebars, and corrosion-resistant rebars), and controlling the ingress of moisture and chloride ions (with the application of sealers, membranes, and waterproofing materials). In very corrosive environments, such as those encountered in the Middle East, cathodic protection systems are installed on new structures and are referred to as cathodic prevention. Patching of damaged concrete, replacement of deck con- crete, and encasement and jacketing of substructure elements generally fall in the Repair category. These methods do not do anything to prevent future corrosion-induced damage; they are primarily designed to restore the concrete element to an acceptable level of service, its original form or dimension, or its design structural capacity. Under certain circumstances, repair may accelerate the corrosion process and may result in its premature failure. In a Rehabilitation effort, in addition to repair of the dam- aged concrete, one or more of the following may be included to control corrosion: • Remove and replace all chloride-contaminated concrete; • Reduce the concentration of and change the distribu- tion of chloride ions by using electrochemical chloride extraction; • Stop or slow the ingress of future chloride ions by using a less permeable cementitious overlay comprised of latex, silica fume, or fly ash-modified concretes; • Stop or slow the ingress of future chloride ions by using sealers, membranes, and waterproofing materials; • Repair cracks to prevent chloride ion contamination; • Apply barrier coatings on the reinforcing steel in the repair areas; • Apply corrosion inhibitors in the repair or over the entire concrete element to either interfere with the corrosion process or modify the characteristics of the in-place con- crete; and • Apply a cathodic protection system. Among all strategies and techniques discussed previously, cathodic protection is the only technology that can directly stop corrosion, even in the most corrosive environment, if designed, installed, and applied correctly (4). As long as the cathodic protection system is operational at the required level, corrosion will not occur. Recognizing that this technology offered a mechanism to stop corrosion, the California Depart- ment of Transportation (DOT) (Caltrans) was the first to experiment with it as early as 1959 (5). It was not until 1972 that the first full-scale system was installed on the Sly Park Bridge in Placerville, California (6). Following the success of this experiment, Caltrans and the Ontario Ministry of CHAPTER ONE INTRODUCTION

Transportation (MTO) started to install cathodic protection systems on bridge decks. By 1975, the FHWA became involved and initiated a Demonstration Project. This project provided funds to the state DOTs to experiment with and test the various materials and systems that were being developed at the time. In addition, it also controlled the application of the technology and ensured that the systems were installed in accordance with the best practice of the time. By 1978, cathodic protection had become one of the three standard rehabilitation techniques used by the Ontario MTO. By 1989, a total of 275 bridge structures in the U.S. and Canada had been cathodically protected (7). It is reported that by 1989, slotted cathodic protection systems had been installed on more than 100 bridge decks, and the state of Missouri had the highest number of such systems installed (8). By 1990, the technology had matured and many different types of anode materials and system configurations were available. By 1994, there were 350 operational cathodic protection systems in the United States and Canada (9). The results of the survey conducted in this effort indicated that the responding public agencies have a total of 586 bridge structures with cathodic protection systems installed. The actual number is probably higher than this as not all public agencies responded to the survey. Several states, including California, Florida, Missouri, and Oregon, and provinces including Alberta, New Brunswick, and Ontario, have made cathodic protection a standard bridge preservation tool. Of the 586 bridges in North America, 464 are located in these 7 jurisdictions. Several existing cathodic protection systems have been operational for more than 20 years. Although no formal studies have been performed, in interviews several states using cathodic protection systems indicated that it has stopped corrosion and reduced bridge maintenance costs, especially in very corrosive environments. The TRB Corro- sion Committee has estimated that 30,000 more bridges are at risk and could be candidates for installation of galvanic cathodic protection systems. In 1985, a National Association of Corrosion Engineers (NACE) publication reported that 300,000 of the 500,000 bridge decks in the United States are candidates for cathodic protection (10). Corrosion is an electrochemical process in which electri- cal energy is associated with chemical reactions. There are two types of reactions that occur in an electrochemical process, anodic and cathodic. Metal loss (i.e., corrosion) results from the anodic reaction. A cathodic protection system impresses an electrical field on to the surface of the corroding rein- forcement such that it favors the cathodic and deters the anodic reaction. If the applied electric field is strong enough, it will shut down the anodic reaction on the surface of the metal being protected and, thereby, stop corrosion. The protec- tive electric field in a cathodic protection system is impressed by an anode. The anode is the primary component, and gen- erally a cathodic protection system is defined by the anode material it uses. Many different types of anode materials have been developed for this purpose. 4 There are two different types of cathodic protection sys- tems; the galvanic (or Passive System) and the impressed current (or Active System). In a galvanic system, an anode, a material that naturally is more electro-negative than the steel to be protected in the environment of use, is connected to the reinforcing steel to be protected. The difference in electrical potential between the anode and the reinforcing steel drives an electrical current that flows through concrete to the surface of the steel to be protected. In an impressed current cathodic protection system, the electrical potential is provided by an external source such as a rectifier (a device that provides unidirectional or direct current electrical current) and the anode delivers the current through the concrete to the surface of the steel to be protected. All anodes, galvanic or impressed current, are consumed during the transfer of current to the concrete, some at a slower rate than others. Cathodic protection systems are capable of providing a significantly larger extension in service life compared with other corrosion mitigation systems. This is possible because they completely stop the corrosion process. As cathodic pro- tection directly interferes with the process of corrosion, it does not matter if corrosion was initiated by the presence of chloride ions, carbonation of the concrete, dissimilar metals, or presence of stray currents. Generally, the extension in service life is dependent on the service life of the anode material and the maintenance of the system. Although the installation costs can be capital intensive, the life-cycle costs, when compared with other corrosion mitigation systems, are generally lower. The primary impediment to the use of this technology is the higher levels of monitoring and mainte- nance that are required, which can be burdensome for public agencies that do not have the resources. This technology is not well understood by the transportation community and has not been standardized for large-scale application. The goals of this synthesis are to examine the extent of use of cathodic protection technology for controlling corrosion on reinforced concrete structures, ascertain why public agencies do or do not use this technology, and explore how to encour- age the appropriate use of this technology. In their 1978 report, Battelle Columbus Laboratories estimated that 30% of the $82 billion cost of corrosion to the U.S. economy in 1975 could have been avoided by effective application of known science and technology (11). Once again a similar question is being raised; is a technology as effective as cathodic protection being optimally used to minimize bridge preservation costs? To accomplish the goals of this project, two question- naires were developed to try and gain insight into the use of this technology on reinforced concrete bridge structures. The first was targeted toward public agencies that own, operate, and maintain bridge structures in North America, and the second was targeted toward the industry dealing with the cathodic protection technology. The first questionnaire was sent to all members of AASHTO and the industry question- naire was sent to the major players in the field as determined by the author of the synthesis. A total of 37 responses were

5received from public agencies, 32 of which were from U.S. state DOTs and 5 from Canadian provincial DOTs. The state of Ohio only provided a verbal response with regard to its experience with cathodic protection. A detailed response to the survey questions was not available. Only five responses were received from private industry. A literature survey was also performed to obtain information on practices and expe- rience with the use of this technology. The results of this exercise are documented in this report. The following chapter (chapter two) provides a primer on the cathodic protection technology, and the history of use of the technology is documented in chapter three. The results of the survey and the literature review with regard to policies and practices are summarized in chapter four. The problems encountered with the use of the technology are presented in chapter five and the long-term performance of the technology is presented in chapter six. Conclusions and best practices are noted in chapter seven.

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 398: Cathodic Protection for Life Extension of Existing Reinforced Concrete Bridge Elements examines the use of cathodic protection by state transportation agencies for controlling corrosion on existing reinforced concrete bridge elements. The report also explores the different types of cathodic protection systems, highlights case studies of states using these systems, and reviews reasons why public agencies may or may not employ cathodic protection.

Appendix A: Summaries of Questionnaires and Interview Results is available online.

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