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Publication Number: FHWA-HRT-10-069
Date: September 2011

 

Long-Term Effects of Electrochemical Chloride Extraction on Laboratory Specimens and Concrete Bridge Components

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FOREWORD

Electrochemical chloride extraction (ECE) is a process that extracts or removes chloride ions from chloride-contaminated reinforced concrete structures. An electrical current is applied between the embedded steel and an external anode as a rehabilitation option to mitigate ongoing corrosion of the embedded steel.

The structures portion of the Strategic Highway Research Program (SHRP) evaluated ECE technology in detail and determined its feasibility through a laboratory study. Additionally, it performed four field validation studies from 1987 to 1992. The laboratory portion of the study affirmed the feasibility of ECE application, and three of the four field validation studies were successful. Although the SHRP study established the feasibility of extracting sufficient amounts of chloride ions from concrete bridge elements, it was not designed to ascertain the long-term effectiveness of the technology in mitigating corrosion. The primary goal of this study was to monitor 10 SHRP concrete laboratory specimens and 3 SHRP field validation sites for 5 years to determine the long-term effectiveness of ECE.

Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the information contained in this document. This report does not constitute a standard, specification, or regulation.

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-10-069

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Long-Term Effects of Electrochemical Chloride Extraction on Laboratory Specimens and Concrete Bridge Components

5. Report Date

September 2011

6. Performing Organization Code
7. Author(s)

Ali Akbar Sohanghpurwala and William T. Scannell

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

CONCORR, Inc.
44633 Guilford Drive, Suite 101
Ashburn, VA 20147

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-94-C-00054

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

1987—2000

14. Sponsoring Agency Code

 

15. Supplementary Notes

The technical consultant was Donald Jackson, HIPA-20. The Contracting Officer's Technical Representative (COTR) was Aramis Lopez, HRDI-30.

16. Abstract

Electrochemical chloride extraction (ECE) is a process that extracts chloride ions from chloride-contaminated reinforced concrete structures by applying an electrical current between the embedded steel and an external anode. ECE is becoming increasingly popular as a rehabilitation option for chloride-contaminated reinforced concrete structures to mitigate ongoing corrosion of embedded steel.

In 1987, section 128 of the Surface Transportation and Uniform Relocation Assistance Act initiated the Strategic Highway Research Program (SHRP). The structures portion of SHRP evaluated ECE technology in detail and determined its feasibility through a laboratory study. Additionally, it performed four field validation studies from 1987 to 1992. The laboratory portion of the study affirmed the feasibility of ECE application, and three of the four field validation studies were successful. Although sufficient levels of chloride ions remained in the structure after the application of ECE, researchers found that the distribution of chloride ions in concrete and the production of hydroxyl ions at the concrete-steel interface could significantly delay the initiation of corrosion and provide an extension in service life. A long-term evaluation of ECE-treated laboratory concrete slabs was considered necessary to evaluate the remigration of chloride ions with time and to study the impact of the higher levels of hydroxyl ions at the concrete-steel interface in delaying the initiation of corrosion,. Although the SHRP study clearly established the feasibility of extracting sufficient amounts of chloride ions from concrete bridge elements, it was not designed to ascertain the long-term effectiveness of the technology in mitigating corrosion. The primary goal of this study was to monitor 10 SHRP concrete laboratory specimens and 3 SHRP field validation sites for 5 years to determine the long-term effectiveness of ECE.

17. Key Words

LTPP, SHRP, ECE, ECM, Pavements, Electrochemical
chloride extraction, bridges, Corrosion, Concrete

18. Distribution Statement

No restrictions. This document is available to the public
through the National Technical Information Service,
Springfield, VA 22161.

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

89

22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

Table of Contents

List of Figures

List of Tables

Executive Summary

Electrochemical chloride extraction (ECE) is a process that extracts chloride ions from chloride-contaminated reinforced concrete structures. An electrical current is applied between the embedded steel and an external anode. The process was originally referred to as electrochemical chloride removal (ECR); however, due to the popularity of the abbreviation ECR to denote epoxy coated rebar, ECE was adopted, particularly in North America. In Europe, the process is often referred to as desalination or sometimes as electrochemical chloride migration (ECM). ECE is becoming popular as a rehabilitation option for chloride-contaminated reinforced concrete structures to mitigate ongoing corrosion of embedded steel.

In 1987, section 128 of the Surface Transportation and Uniform Relocation Assistance Act initiated the Strategic Highway Research Program (SHRP). The structures portion of SHRP evaluated ECE technology in more detail and determined its feasibility through a laboratory study. Additionally, it performed four field validation studies from 1987 to 1992. The laboratory portion of the study affirmed the feasibility of ECE application, and three of the four field validation studies were successful.

Although sufficient levels of chloride ions remained in the structure after the application of ECE, it was concluded that the distribution of chloride ions in concrete (lower concentrations around the reinforcing steel and higher concentrations away from the reinforcement) and the production of hydroxyl ions at the concrete-steel interface could significantly delay the initiation of corrosion and provide an extension in service life. A long-term evaluation of ECE-treated laboratory concrete slabs was necessary to evaluate the remigration of chloride ions with time and to study the impact of the higher levels of hydroxyl ions at the concrete-steel interface in delaying the initiation of corrosion.

Four field validation trials were conducted between fall 1991 and fall 1992. Chloride removal was conducted using a variety of anode-electrolyte configurations on structures in four locations: a bridge deck in Ohio, marine bridge pilings in Florida, columns in New York, and an abutment in Ontario. Each field site was selected based on criteria established by the laboratory studies and the SHRP Expert Task Group (ETG). Active corrosion was occurring on a substantial portion of each selected component of each structure, and chloride contamination was well above the threshold level. To establish the effectiveness of lithium ion in controlling alkali-silica reaction (ASR), the abutment of the Ontario structure containing alkali reactive aggregate was selected.

Although the SHRP study established the feasibility of extracting sufficient amounts of chloride ions from concrete bridge elements, it was not designed to ascertain the long-term effectiveness of the technology in mitigating corrosion. The primary goal of this study was to monitor 10 SHRP concrete laboratory specimens and 3 SHRP field validation sites for 5 years to determine the long-term effectiveness of ECE.

The concrete laboratory specimens were exposed to Northern Virginia climate and were monitored once every quarter from 1995 to 1998. Previously, under the SHRP study, the specimens were monitored for 40 months; however, quarterly monitoring was terminated in 1998 due to noncommitment of funds to the contract. Data collected every quarter included visual, delamination, half-cell potential surveys, macrocell current and driving volt data, alternating current (AC) resistance between the two mats, slab temperature, and corrosion rate measurements. At the conclusion of the study in 1999, one core was collected from each slab, and powdered concrete samples were collected from various depths to determine the distribution of chloride ions as a function of depth.

Of the four field validation sites, the marine piles in Florida were not included in this study due to concerns about the applicability of ECE in a marine environment. The Ontario site could not be monitored because it had been replaced with a new structure. The Federal Highway Administration (FHWA) had funded several piloted ECE treatments on bridge structures, two of which were selected for long-term evaluation in this study. One pilot application was performed on a bridge deck, and the other was performed on columns and cap beams. These structures are located in Arlington, VA, and Charlottesville, VA.

With the exception of the structure in Arlington, VA, three evaluations of treated elements and elements designated as controls on each bridge were performed during the 5-year monitoring period from 1994 to 1998. The Arlington, VA, structure was evaluated twice due to noncommitment of funds to the contract.

After 10.25 years of exposure, the control slab (not treated) had suffered significant damage due to corrosion. Two slabs treated at a lower total charge of 59.9 A-h/ft2 (645 A-h/m2) started to exhibit early signs of corrosion initiation. The other seven ECE-treated slabs had a total charge greater than 186 A-h/ft2 (2,000 A-h/m2) and did not exhibit any signs of corrosion initiation. The trends in data collected over 10.25 years suggest that the presently insignificant levels of corrosion activity in the slabs can be maintained for a minimum of an additional 10 years if the slabs are protected from future ingress of chloride ions from the environment.

Long-term evaluation of the field validation studies indicated that no corrosion activity had initiated in two of the four sites evaluated (Arlington, VA, and Charlottesville, VA). Sufficient time had not elapsed after the application of ECE to determine its effectiveness.

The presence or lack of corrosion could not be determined at the Lucas County, OH, site due to a thin epoxy overlay. Chloride data suggest that ECE was successful in extracting the chloride ions from the deck. Due to similarities in treatment and lower chloride content in the treated sections of the deck, it is expected that ECE treatment could effectively mitigate corrosion for a minimum of 10 years.

ECE treatment was ineffective on the structure located in Albany, NY. Corrosion was ongoing, and damage due to corrosion was observed. The failure of the treatment was attributed to the lack of quality of the repairs performed (i.e., cracking of patch material), nonrepair of cracks, no barrier to future ingress of chloride ions installed, and problems encountered during the application of ECE including containment of the electrolyte, nonuniform distribution of current, and lower pH values.

 


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