U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
| REPORT |
| This report is an archived publication and may contain dated technical, contact, and link information |
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| Publication Number: FHWA-HRT-17-074 Date: May 2018 |
Publication Number: FHWA-HRT-17-074 Date: May 2018 |
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The objective of this investigation was to provide bridge engineers with a practical methodology for projecting timing of corrosion-induced, post-tensioned (PT) tendon failures caused by a grout deficiency or deficiencies. Bridge tendons can be more susceptible to corrosion than conventional reinforcement with no indication that this is taking place, and failures from deficient grout–induced corrosion have been reported as soon as 2 yr post construction. Of particular concern are situations where the PT grout exhibits either chemical deficiencies (elevated chlorides beyond the allowable limit specified by the American Association of State Highway and Transportation Officials and other specifications or free sulfates, or both), physical deficiencies (soft, chalky, separated, segregated grout with air voids and free water), or a combination of these. Failure of relatively few tendons can compromise overall structural integrity.
The results of this study provide bridge owners with a practical protocol for projecting the timing of corrosion-induced tendon failures, given the extent of any grout deficiency or deficiencies, and thereby for responding to concerns arising therefrom.
Cheryl Allen Richter, Ph.D., P.E.
Director, Office of Infrastructure
Research and Development
Notice
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Technical Report Documentation Page
| 1. Report No.
FHWA-HRT-17-074 |
2. Government Accession No.
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3 Recipient's Catalog No.
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| 4. Title and Subtitle
Corrosion Forecasting and Failure Projection of Post-Tensioned Tendons in Deficient Cementitious Grout |
5. Report Date
May 2018 |
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| 6. Performing Organization Code
CAGE Code: 1YX01 |
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| 7. Author(s)
William H. Hartt and Seung-Kyoung Lee |
8. Performing Organization Report No.
Task Order #5009 |
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| 9. Performing Organization Name and Address
Engineering & Software Consultants, Inc. |
10. Work Unit No. (TRAIS)
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| 11. Contract or Grant No.
DTFH61-14-D-00011 |
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| 12. Sponsoring Agency Name and Address
Office of Infrastructure Research and Development |
13. Type of Report and Period Covered
Final Report; |
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| 14. Sponsoring Agency Code
HRDI-20 |
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| 15. Supplementary Notes
The Contracting Officer's Representative is Hoda Azari HRDI-20. |
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| 16. Abstract
Post-tensioning has evolved to become the construction method of choice for many large structures, including bridges. However, instances of corrosion-induced fracture of wires and strands and resultant tendon failures have occurred as a consequence of either chemically or physically deficient grout (or a combination of these), where the former involves elevated levels of chlorides or free sulfates (or both) and the latter soft, chalky, separated, segregated grout with free water. In the extreme, there is the possibility of structure collapse. The present project builds on results from a recently completed in-house Federal Highway Administration study, termed “phase 1,” which determined the extent of localized wire and strand corrosion as a function of grout chloride concentration, presence of free sulfates, and physical deficiencies.(1) The objective of the present study was twofold: first, to present results from a phase 2 experimental study that extended what was accomplished in phase 1 and, second, to develop a methodology whereby the onset and subsequent rate of wire and strand fractures and tendon failures can be forecast given information regarding the extent of grout deficiency or deficiencies.(1) The former involved stressed, single-wire specimens that were exposed to deficient grouts. The latter was accomplished by relating occurrence of fractures and failures to the extent of localized wire corrosion and to the resultant rate of wire cross-section loss with time, as affected by the severity of a grout deficiency or deficiencies. Primary inputs to the model are the mean and standard deviation of, first, localized wire corrosion rate and, second, residual wire fracture strength. Results indicate an initiation period for fractures and failures during which corrosion progresses and that, once these commence, they do so initially at a progressively increasing rate up to a point beyond which this rate moderates. Other variables that were investigated include level of prestress, wire strength, number of tendons, tendon length, and fracture and failure rates subsequent to initial occurrence. Equations are presented whereby bridge engineers can forecast the onset of fractures and failures based on either localized wire corrosion wastage statistics or grout chloride concentration, and examples are provided. |
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| 17. Key Words
Post-tension tendons, bridges, corrosion, fracture, failures, chlorides, grout, grout deficiency |
18. Distribution Statement
No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161. |
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| 19. Security Classification (of this report) Unclassified |
20. Security Classification (of this page) Unclassified |
21. No. of Pages
235 |
22. Price
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| Form DOT F 1700.7 (8-72) | Reproduction of completed page authorized |
