Click for next page ( 26

The National Academies of Sciences, Engineering, and Medicine
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 25
25 TABLE 4 TABLE 5 MAGNITUDE OF THE SALT USAGE CORROSION PROBLEM Tons Per Lane- No. of Magnitude of Mile Per Year Respondents Corrosion No. of States None 1 Not a Problem 1 Minor 4 0 to 5 14 Moderate 23 6 to 10 7 Major 8 11 to 15 6 Total 36 16 to 20 2 Note: Table based on results of Question 4 of the survey. >20 2 Note: Table based on results of Question 7 of the survey. EXPOSURE CONDITIONS For bridge decks the primary chloride exposure is deicing salts. Twenty-one respondents indicated that more than 70% more corrosive exposure when they are located in a marine of decks are exposed to deicing salts and 13 of those stated environment. It may be noted that for the purpose of the sur- that all of their decks (100%) are exposed to deicing salts. A vey, marine exposure was defined to persist 2 miles around summary of exposure environments is presented in Table 6. a saline body of water. In addition to Mississippi, Washington The province of Prince Edward Island listed 100% of its State has more than 90% of its substructures listed as bridges in the "Both" category; that is, exposed to both the "Neither." deicing salts and the marine environment. Only Mississippi has more than 90% of its decks categorized as "Neither," PROCESS FOR SELECTION OF CORROSION which correlates well with their perception of the corrosion MITIGATION ALTERNATIVES problem. To ascertain the compatibility and the cost-effectiveness of a Understandably, the substructure exposure to deicing salts cathodic protection system on a reinforced concrete struc- is lower than that of the bridge decks; only 6 of the 13 re- ture, among other things, it is important that the severity of spondents (with 100% of bridge decks exposed to deicing exposure, the presence of chloride ions in sound concrete, the salts) reported that all of their bridge substructures are exposed presence of electrical continuity, the susceptibility of the to it. The deicing salt exposure to substructure elements concrete to alkalisilica reaction and freezethaw damage, comes in two forms: (1) leakage of chloride-contaminated and the presence of corrosion activity in sound areas be water through joints and (2) drains and splashing of the con- known. Analysis of test methods used by respondent agen- taminated solution onto the substructure elements by vehi- cies during Routine Bridge Inspection and corrosion condi- cles in the underpass. The substructure elements confront a tion evaluation was performed and is summarized in Table 7. TABLE 6 DISTRIBUTION OF BRIDGES BASED ON EXPOSURE CONDITION Bridge Deck Exposure Substructure Exposure Marine Deicing Salt Marine Deicing Salt % of Bridges Exposure Exposure Both Neither Exposure Exposure Both Neither 59 26 6 32 21 24 8 33 14 1019 2 1 1 2 4 1 1 1 2029 4 0 1 1 5 2 0 1 3039 0 3 0 2 0 5 0 0 4049 0 1 0 1 0 4 0 3 5059 2 2 0 2 2 4 0 2 6069 0 2 0 1 0 1 0 3 7079 0 2 0 1 0 0 0 3 8089 0 1 0 2 0 2 0 2 9099 0 2 0 1 0 2 0 4 100 1 16 1 1 1 7 1 2 Note: Table based on results of Questions 5 and 6 of the survey.

OCR for page 25
26 TABLE 7 based on the data collected during the evaluations. Sixteen TEST METHODS USED agencies include cathodic protection as an alternative in their No. of Respondents selection process (see Table 8). Of the agencies that cited Routine Corrosion the corrosion problem as a major one, four, Connecticut, New Bridge Condition York, Oregon, and Pennsylvania, include cathodic protection Test Method Inspection Evaluation as one of the options, but Oklahoma, Utah, and Virginia do not. Eight respondents stated that their agencies included cathodic Visual Survey 36 29 protection as an alternative because it provides service-life Crack Survey 19 16 extension desired for many of the high use structures and/or Delamination Survey 21 29 its agency staff has significant success in the use of the tech- Chloride Ion Content Analysis 4 28 nology. The province of New Brunswick includes it, as it does not have any alternatives for the severe exposure condi- Half-cell Potential Survey 4 23 tions its structures have to withstand. Carbonation Testing 0 3 Electrical Continuity Testing 2 6 The quantity of damage was reported by 16 agencies to Corrosion Rate Measurement 0 2 be the determining factor for the selection of a corrosion Concrete Resistivity Testing 1 3 control system and the cost of application and repair was None 0 1 identified by 6 agencies (see Table 9). Only four agencies reported that the presence of chloride ions would be the Other 0 2 determining factor and, for three respondents, the extension Note: Table based on results of Questions 8 and 9 of the survey. in service life was the determining factor. All other choices in the list were picked by two or fewer respondents. These All agencies perform a visual survey during the Routine responses suggest that the procedures, protocols, and Bridge Inspection and a majority of them perform delamina- methodologies used by these agencies may not be effec- tion and crack surveys. Only a few perform chloride ion con- tively using the data obtained during surveys to properly tent analysis, half-cell potential survey, electrical continuity select a corrosion mitigation system. The quantity of dam- testing, and concrete resistivity measurements. The testing age signifies the magnitude of the problem and not its protocol used by the majority of the agencies would provide cause. It is more appropriate for the selection of the repair; a good measure of the symptoms of corrosion, rust staining, however, it would have to be the presence and distribution cracking, delamination, and spalling, and would reasonably of chloride ions in the remaining sound concrete that would indicate the overall condition of the structure and provide a control which corrosion control system would be the most basis for more in-depth evaluation. During an in-depth sur- effective and viable in that application. vey or corrosion condition evaluation, the vast majority of the agencies perform a visual survey, delamination survey, Twenty-three agencies have or would consider cathodic chloride ion content analysis, and half-cell potential survey. protection for its ability to prevent future damage and to sub- Thus, information on the extent of chloride contamination stantially extend the service life (Table 10). Recommenda- and the presence of active corrosion is also being determined tions of their own agency research and development efforts during these evaluations. Only a few agencies conduct elec- have encouraged the use of cathodic protection for many trical continuity; three perform carbonation testing, one con- agencies. The cost of other alternatives, the level of chloride siders petrographic analysis on select projects, and one uses corrosion rate measurements. North Dakota does not perform TABLE 8 corrosion condition evaluation and only performs the visual USE OF PROCEDURES, PROTOCOLS, AND METHODOLOGIES survey during the Routine Bridge Inspection. Generally rein- Questions Yes No forcing steel on a bridge deck is electrically continuous, and 18 18 Are there agency-wide standard procedures, protocols, therefore, electing to test for continuity during the installa- or methodologies for conducting corrosion condition tion of the cathodic protection system is acceptable. How- evaluations of reinforced concrete structures? ever, ascertaining the susceptibility to alkalisilica reaction Does your agency have procedures, protocols, or 20 16 could be performed during the selection process, unless based methodologies to analyze the data collected during on materials used in standard concrete mixes the susceptibil- condition evaluation? ity is already known. Similarly, susceptibility to freezethaw Does your agency have procedures, protocols, or 20 16 could be ascertained during the selection of the alternative methodologies to select repair and corrosion control corrosion mitigation systems. alternatives based on data collected from condition evaluations? A majority of the agencies have standard procedures, pro- If your agency has procedures, protocols, and/or 16 17 tocols, or methodologies for conducting corrosion condition methodologies to select repair and corrosion control evaluations, analyzing the data collected during the evalua- alternatives, does it include cathodic protection? tions, and selecting repair and corrosion control alternatives Note: Table based on results of Questions 10 to 12 and 14 of the survey.

OCR for page 25
27 TABLE 9 TABLE 11 FACTORS MOST LIKELY TO DETERMINE WHICH CATHODIC PROTECTION USED FOR THE FOLLOWING CORROSION CONTROL SYSTEM WILL BE SELECTED REASONS No. of No. of Factors Respondents Reason Respondents Quantity of Damage 16 Marine environment where exposure is very 8 corrosive and no other corrosion control Presence of Chloride Ions 4 system provides service life extension of more Extension of Service Life 3 than 5 years Life-Cycle Costs 2 Deicing salt exposure that has resulted in high 9 Cost of Repair and Rehabilitation 6 and uniform chloride ion contamination and no other corrosion control system is expected Disruption in Bridge Operation 0 to provide service life extension of more than Structure Type 0 5 years Funds Available 1 Life-cycle cost of cathodic protection system 3 Consultant Familiarity with Corrosion Control 0 was lower than any other corrosion control System system Cathodic protection system was expected to 13 Past Experience with Corrosion Control System 2 provide service life extension in excess of Agency Practice 2 20 years Agency Research Findings 0 Location of the structure required use of an 10 Note: Table based on results of Question 13 of the survey. aggressive corrosion protection system Type of structure 7 ion contamination, and the location of the structure were Other 6 also considered by several agencies as reasons for its use. Note: Table based on results of Question 29 of the survey. The summary in Table 11 indicates cathodic protection has been used when service life in excess of 20 years was desired Funding from other sources has encouraged the use of the if the structure was located in a very aggressive environment, technology for some agencies and their experience with the if no other alternatives are available, or if it is located in a technology only encouraged its use in seven agencies. This marine environment. last response raises a question; what has been the experience of user agencies with cathodic protection systems? The sum- TABLE 10 mary of responses in Table 12 provides some answers to this REASONS FOR WHICH CATHODIC PROTECTION question; nine agencies do not include cathodic protection WAS CONSIDERED as an alternative corrosion mitigation system in their proce- dures, protocols, and methodologies for selecting repair and No. of corrosion control alternatives owing to disappointing past Reason Respondents experience and eight agencies do not use it because it is more Quantity of Concrete Damage 9 TABLE 12 Level of Chloride Ion Contamination 12 REASONS FOR NOT INCLUDING CATHODIC PROTECTION Cost of Other Alternatives 13 AS AN ALTERNATIVE CORROSION CONTROL SYSTEM Prevention of Future Damage 22 No. of Agency Research and Development Recommendation 13 Reason Respondents Funding Available from Other Sources such as 10 Exposure environment is not sufficiently 4 FHWA or Congressional Mandate to Use corrosive to warrant the use of cathodic Cathodic Protection protection Location of Structure 11 Cathodic protection technology is relatively 8 Structure Type 8 more expensive than other options available Severity of Exposure 11 Engineers and contractors that serve the 5 Extension of Service Life Provided by Cathodic 23 agency do not have any experience with Protection Life-Cycle Cost Analysis 6 the technology Cathodic protection is too complicated and 3 Consultant Recommendation 1 the agency does not have sufficient FHWA Recommendation 3 understanding to use it Experience with Cathodic Protection 7 Past experience with cathodic protection has 9 Other 4 been disappointing Note: Table based on results of Question 18 of the Survey Note: Table based on results of Question 15 of the survey.