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Publication Number:  FHWA-HRT-17-074    Date:  May 2018
Publication Number: FHWA-HRT-17-074
Date: May 2018

 

Corrosion Forecasting and Failure Projection of Post-Tensioned Tendons in Deficient Cementitious Grout

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FOREWORD

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

This document is disseminated under the sponsorship of the U.S. Department of Transportation (USDOT) in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

Technical Report Documentation Page

1. Report No.

FHWA-HRT-17-074

2. Government Accession No.

 

3 Recipient's Catalog No.

 

4. Title and Subtitle

Corrosion Forecasting and Failure Projection of Post-Tensioned Tendons in Deficient Cementitious Grout

5. Report Date

May 2018

6. Performing Organization Code

CAGE Code: 1YX01

7. Author(s)

William H. Hartt and Seung-Kyoung Lee

8. Performing Organization Report No.

Task Order #5009

9. Performing Organization Name and Address

Engineering & Software Consultants, Inc.
14123 Robert Paris Court
Chantilly, VA 20151

10. Work Unit No. (TRAIS)

 

11. Contract or Grant No.

DTFH61-14-D-00011

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report;
September 2014–January 2017

14. Sponsoring Agency Code

HRDI-20

15. Supplementary Notes

The Contracting Officer's Representative is Hoda Azari HRDI-20.

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.

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.
http://www.ntis.gov

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

235

22. Price

 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

 

 

 

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