Click for next page ( 4


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 3
3 CHAPTER ONE INTRODUCTION As of 2002, the National Bridge Inventory (NBI) Database, cathodic protection systems are installed on new structures maintained by the FHWA, contained a total of 587,964 and are referred to as cathodic prevention. bridges. The average age of the bridge structures in this database is 40 years, and 41% are at least 40 years old. Over Patching of damaged concrete, replacement of deck con- the past three decades, significant attention has focused on crete, and encasement and jacketing of substructure elements the condition of the nation's aging highway bridge infra- generally fall in the Repair category. These methods do not do structure. Several independent evaluations of the condition anything to prevent future corrosion-induced damage; they of the nation's infrastructure, based on condition ratings are primarily designed to restore the concrete element to an contained in the database, have been performed (13). acceptable level of service, its original form or dimension, or These studies ascertained that 14% of the bridges were rated its design structural capacity. Under certain circumstances, structurally deficient and the primary cause of the deficiency repair may accelerate the corrosion process and may result in was corrosion of reinforcing steel. The cost to maintain its premature failure. 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 In a Rehabilitation effort, in addition to repair of the dam- to improve and eliminate deficiencies over the same period aged concrete, one or more of the following may be included is $10.6 billion (1). A cost-of-corrosion study determined to control corrosion: that the annual cost of corrosion to all bridges (including steel bridges) is $8.29 billion and this does not include indi- Remove and replace all chloride-contaminated concrete; rect cost incurred by the traveling public as a result of bridge Reduce the concentration of and change the distribu- closures (2). tion of chloride ions by using electrochemical chloride extraction; To address the corrosion problem on reinforced concrete Stop or slow the ingress of future chloride ions by using a structures, a research and development effort was initiated by less permeable cementitious overlay comprised of latex, both the public and the private sectors in the early 1970s. silica fume, or fly ash-modified concretes; Numerous different technologies were introduced to repair Stop or slow the ingress of future chloride ions by using damage caused by corrosion and to prevent or minimize fur- sealers, membranes, and waterproofing materials; ther damage from occurring. In addition, strategies were also Repair cracks to prevent chloride ion contamination; developed to delay the initiation of corrosion on new struc- Apply barrier coatings on the reinforcing steel in the tures, thereby increasing their service life. These were gener- repair areas; ally categorized as "Prevention." Strategies, technologies, Apply corrosion inhibitors in the repair or over the entire and materials developed to repair the damage induced by cor- concrete element to either interfere with the corrosion rosion are generally referred to as "Repairs" and the term process or modify the characteristics of the in-place con- "Rehabilitation" is used if the project either eliminates or crete; and controls the cause or interferes with the process of deteriora- Apply a cathodic protection system. tion to stop, control, or minimize it. Among all strategies and techniques discussed previously, On new structures there are many techniques available to cathodic protection is the only technology that can directly delay the initiation of corrosion, which include the increase stop corrosion, even in the most corrosive environment, if of clear concrete cover, installation of overlays, reduction in designed, installed, and applied correctly (4). As long as the the permeability of the concrete (by the use of latex modi- cathodic protection system is operational at the required level, fiers and replacement of cement by silica fume or fly ash), corrosion will not occur. Recognizing that this technology admixing of corrosion inhibitors, use of alternative reinforce- offered a mechanism to stop corrosion, the California Depart- ments (such as epoxy-coated rebars, galvanized rebars, and ment of Transportation (DOT) (Caltrans) was the first to corrosion-resistant rebars), and controlling the ingress of experiment with it as early as 1959 (5). It was not until 1972 moisture and chloride ions (with the application of sealers, that the first full-scale system was installed on the Sly Park membranes, and waterproofing materials). In very corrosive Bridge in Placerville, California (6). Following the success environments, such as those encountered in the Middle East, of this experiment, Caltrans and the Ontario Ministry of

OCR for page 3
4 Transportation (MTO) started to install cathodic protection There are two different types of cathodic protection sys- systems on bridge decks. By 1975, the FHWA became tems; the galvanic (or Passive System) and the impressed involved and initiated a Demonstration Project. This project current (or Active System). In a galvanic system, an anode, a provided funds to the state DOTs to experiment with and test material that naturally is more electro-negative than the steel the various materials and systems that were being developed to be protected in the environment of use, is connected to the at the time. In addition, it also controlled the application of reinforcing steel to be protected. The difference in electrical the technology and ensured that the systems were installed potential between the anode and the reinforcing steel drives in accordance with the best practice of the time. By 1978, an electrical current that flows through concrete to the surface cathodic protection had become one of the three standard of the steel to be protected. In an impressed current cathodic rehabilitation techniques used by the Ontario MTO. By 1989, protection system, the electrical potential is provided by an a total of 275 bridge structures in the U.S. and Canada had external source such as a rectifier (a device that provides been cathodically protected (7). It is reported that by 1989, unidirectional or direct current electrical current) and the slotted cathodic protection systems had been installed on anode delivers the current through the concrete to the surface more than 100 bridge decks, and the state of Missouri had the of the steel to be protected. All anodes, galvanic or impressed highest number of such systems installed (8). By 1990, the current, are consumed during the transfer of current to the technology had matured and many different types of anode concrete, some at a slower rate than others. materials and system configurations were available. By 1994, there were 350 operational cathodic protection systems in the Cathodic protection systems are capable of providing a United States and Canada (9). significantly larger extension in service life compared with other corrosion mitigation systems. This is possible because The results of the survey conducted in this effort indicated they completely stop the corrosion process. As cathodic pro- tection directly interferes with the process of corrosion, it that the responding public agencies have a total of 586 bridge does not matter if corrosion was initiated by the presence of structures with cathodic protection systems installed. The chloride ions, carbonation of the concrete, dissimilar metals, actual number is probably higher than this as not all public or presence of stray currents. Generally, the extension in agencies responded to the survey. Several states, including service life is dependent on the service life of the anode California, Florida, Missouri, and Oregon, and provinces material and the maintenance of the system. Although the including Alberta, New Brunswick, and Ontario, have made installation costs can be capital intensive, the life-cycle costs, cathodic protection a standard bridge preservation tool. Of when compared with other corrosion mitigation systems, are the 586 bridges in North America, 464 are located in these generally lower. The primary impediment to the use of this 7 jurisdictions. Several existing cathodic protection systems technology is the higher levels of monitoring and mainte- have been operational for more than 20 years. Although no nance that are required, which can be burdensome for public formal studies have been performed, in interviews several agencies that do not have the resources. This technology is states using cathodic protection systems indicated that it has not well understood by the transportation community and has stopped corrosion and reduced bridge maintenance costs, not been standardized for large-scale application. especially in very corrosive environments. The TRB Corro- sion Committee has estimated that 30,000 more bridges are The goals of this synthesis are to examine the extent of use at risk and could be candidates for installation of galvanic of cathodic protection technology for controlling corrosion on cathodic protection systems. In 1985, a National Association reinforced concrete structures, ascertain why public agencies of Corrosion Engineers (NACE) publication reported that do or do not use this technology, and explore how to encour- 300,000 of the 500,000 bridge decks in the United States are age the appropriate use of this technology. In their 1978 report, candidates for cathodic protection (10). Battelle Columbus Laboratories estimated that 30% of the $82 billion cost of corrosion to the U.S. economy in 1975 Corrosion is an electrochemical process in which electri- could have been avoided by effective application of known cal energy is associated with chemical reactions. There are science and technology (11). Once again a similar question is two types of reactions that occur in an electrochemical process, being raised; is a technology as effective as cathodic protection anodic and cathodic. Metal loss (i.e., corrosion) results from being optimally used to minimize bridge preservation costs? the anodic reaction. A cathodic protection system impresses an electrical field on to the surface of the corroding rein- To accomplish the goals of this project, two question- forcement such that it favors the cathodic and deters the naires were developed to try and gain insight into the use of anodic reaction. If the applied electric field is strong enough, this technology on reinforced concrete bridge structures. The it will shut down the anodic reaction on the surface of the first was targeted toward public agencies that own, operate, metal being protected and, thereby, stop corrosion. The protec- and maintain bridge structures in North America, and the tive electric field in a cathodic protection system is impressed second was targeted toward the industry dealing with the by an anode. The anode is the primary component, and gen- cathodic protection technology. The first questionnaire was erally a cathodic protection system is defined by the anode sent to all members of AASHTO and the industry question- material it uses. Many different types of anode materials naire was sent to the major players in the field as determined have been developed for this purpose. by the author of the synthesis. A total of 37 responses were

OCR for page 3
5 received from public agencies, 32 of which were from U.S. The following chapter (chapter two) provides a primer on state DOTs and 5 from Canadian provincial DOTs. The state the cathodic protection technology, and the history of use of Ohio only provided a verbal response with regard to its of the technology is documented in chapter three. The results experience with cathodic protection. A detailed response to of the survey and the literature review with regard to policies the survey questions was not available. Only five responses and practices are summarized in chapter four. The problems were received from private industry. A literature survey was encountered with the use of the technology are presented in also performed to obtain information on practices and expe- chapter five and the long-term performance of the technology rience with the use of this technology. The results of this is presented in chapter six. Conclusions and best practices are exercise are documented in this report. noted in chapter seven.