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Publication Number: FHWA-RD-02-107
Date: September 2002

Electrochemical Chloride Extraction: Influence of Concrete Surface on Treatment

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Many now recognize that once chloride-induced corrosion of the reinforcing steel bars has initiated in a concrete bridge, the only truly effective means of stopping corrosion in the structure is by applying either cathodic protection or the relatively new electrochemical chloride extraction. In addition to providing some beneficial effects to a treated concrete bridge, electrochemical chloride extraction offers some advantages over the use of cathodic protection. Electrochemical chloride extraction extends the functional life of the treated structure, but does not require the long-term commitment generally required of cathodic protection systems. However, both cathodic protection and electrochemical chloride extraction are operated without requiring the excavation of structurally sound concrete that is contaminated with chlorides. This can provide an advantage that does not exist with other restoration techniques.

To facilitate wider application of electrochemical chloride extraction in the rehabilitation of concrete bridges, this investigation was initiated with the objectives of improving the effectiveness of the treatment and contributing to the determination of additional service life that results from treating a structure. This interim report describes the progress made in ascertaining the cause of the abrupt drop in the amount of current that can pass through salt-contaminated concrete. This reduction in current, typically observed during the first several days of treatment, in turn relates to a decrease in chloride removal.

T. Paul Teng, P.E.
Director, Office of Infrastructure
Research and Development

NOTICE

This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its content or use thereof. This report does not constitute a standard, specification, or regulation.

The United States Government does not endorse products or manufacturers. Trade and manufacturers' names appear in this report only because they are considered essential to the object of this document.

Technical Report Documentation Page

1. Report No. FHWA-RD-02-107		2. Government Accession No.	3. Recipient's Catalog No.
4. Title and Subtitle ELECTROCHEMICAL CHLORIDE EXTRACTION: INFLUENCE OF CONCRETE SURFACE ON TREATMENT			5. Report Date
			6. Performing Organization Code VTRC 02-R
7. Author(s) Stephen R. Sharp,* Gerry G. Clemeña,* Y. Paul Virmani, Glenn E. Stoner,* Robert G. Kelly ***			8. Performing Organization Report No.
9. Performing Organization Name and Address Virginia Transportation Research Council 530 Edgemont Road Charlottesville, Virginia 22903			10. Work Unit No. (TRAIS)
			11. Contract or Grant No.
12. Sponsoring Agency Name and Address Office of Infrastructure Research and Development Federal Highway Administration 6300 Georgetown Pike McLean, Virginia 22102-2296			13. Type of Report and Period Covered Interim Report
			14. Sponsoring Agency Code
15. Supplementary Notes * Virginia Transportation Research Council, 530 Edgemont Road, Charlottesville, Virginia 229031 Federal Highway Administration, Turner-Fairbank Highway Research Center, 6300 Georgetown Pike, McLean, VA 22101-2296 * University of Virginia, Material Science and Engineering, Charlottesville, VA 22903 Drs. O. M. Schneider and C. A. Dukes, and Messrs. C. M. Apusen, L. E. Dougald, and B. T. Ward, and Ms. E. F Aiken are each recognized for their contributions to this project
16. Abstract One bridge restoration technique available for reducing corrosion-induced concrete deterioration, which removes chloride ions while simultaneously realkalizing the concrete adjacent to the steel, is electrochemical chloride extraction (ECE). Studies have shown that ECE is capable of removing, in a single application, a significant portion of the chloride ions from a reinforced concrete structure. Prior research has also shown that the quantity of chloride ions removed is dependent on numerous factors including quantity and spacing of reinforcing steel, applied voltage, initial chloride concentration, etc. In addition, investigations into chloride binding and competition between other ions as current carriers have helped to clarify the probable mechanisms responsible for decreases in current efficiency with time during chloride removal. This portion of the investigation has focused on the influence of water-to cement (w/c) ratio. In addition, an investigation was conducted to identify the cause of decrease in efficiency during chloride removal. A clear relationship between the w/c ratio and the chloride extraction rate was not evident. However, the investigation revealed that the resistance of the concrete surface layer increases considerably during ECE, which effectively restricts the current flow, while the resistance of the underlying layer of concrete either decreases or remains constant. It appears that the increased resistance of the surface layer concrete is accompanied by the formation of a tightly adhering residue on the concrete surface. Preliminary analysis of the surface formation indicates it contains calcium carbonate and calcium chloride.
17. Key Words Cathodic protection, chloride ions, electrochemical chloride extraction, rehabilitation of concrete bridges, reinforced concrete, removal of chloride, steel corrosion in concrete.			18. Distribution Statement No restrictions. This document is available to the public through NTIS, Springfield, VA 22161.
19. Security Classif. (of this report) Unclassified	20. Security Classif. (of this page) Unclassified	21. No. of Pages 49	22. Price

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

SI* (Modern Metric) Conversion Factors

	LIST OF FIGURES
	LIST OF TABLES
1.	INTRODUCTION, LITERATURE REVIEW, AND PURPOSE
	Introduction
	Literature Review
	Corrosion Threshold
	Electrochemical Chloride Extraction
	Conductivity and Electrochemical Chloride Extraction
	Purpose
2.	EXPERIMENTAL METHOD
	Specimen Design
	Electrochemical Chloride Extraction
	Current and Voltage Measurements
	IR Drop Measurements
	4-Pin Resistivity Measurements
	Half-Cell Measurements
	Collection of Concrete Samples
	Potentiometric Titration
	X-Ray Diffraction
	X-Ray Photoelectron Spectroscopy
3.	RESULTS AND DISCUSSION
	Changes in the Current and Voltage during ECE
	Influence of Concrete Surface on Voltage and Current
	Changes in the Concrete Resistance During ECE
	Resistivity
	Chloride Concentration in Concrete with ECE
	Visual Observations
	Surface Deposit Analysis
4.	CONCLUSIONS AND FUTURE WORK
	Conclusions
	Future Work
5.	REFERENCES

Figures

1.	Potential influences on the corrosion threshold for steels exposed to chlorides.
2.	Cathodic protection system for reinforced concrete.
3.	Illustration of ECE setup on the 34th Street Bridge in Arlington, Virginia, USA.
4.	Illustration of a Type I Specimen.
5.	Illustration of a Type II Specimen.
6.	Illustration of voltage components for a driven system.
7.	Change in voltage after interruption of applied current.
8.	Four pin resistivity test method.
9.	Type II specimen drill pattern for sample collection.
10.	Measured voltage changes during ECE in a set of Type I specimens.
11.	Comparison of the voltages measured in two Type II specimens.
12.	Timeline of concrete surface study.
13.	Influence of concrete exterior surface on the voltage and current in a 0.45-w/c Type I specimen.
14.	Example showing the change in resistances for a single set of Type I specimens during ECE.
15.	Change in Resistivity for Type I specimens of various w/c ratios.
16.	Resistivity change in the upper layer of concrete.
17.	Resistivity change in the lower layer of concrete.
18.	Average change in chloride concentrations due to ECE in Type I specimens with 4.4 cm of concrete cover over rebar.
19.	Average change in chloride concentrations due to ECE in Type I specimens with 5.7 cm of concrete cover over rebar.
20.	Change in chloride concentrations due to ECE in a single set of Type II specimens with 3.8 cm of concrete cover over rebar.
21.	Average change in chloride concentrations due to ECE in Type II specimens with 6.4 cm of concrete cover over rebar.
22.	Tightly adhering layer of white material formed on the concrete surface during ECE.
23.	Various views of surface layer that formed on the concrete during ECE.
24.	Layer of white material formed on the concrete surface directly above the reinforcing steel following ECE on an actual bridge deck.
25.	Surface appearance of a Type I specimen.
26.	Surface deposit XRD pattern from a Type II specimen.
27.	Proposed Type III specimen.

Tables

1.	Factors influencing corrosion threshold value.
2.	Ionic conductivity values.
3.	Calculated transference values for a solution containing 0.5 mol/l NaCl and 0.5 mol/l NaOH.
4.	Influences of various factors on ECE.
5.	ECE treatment on selected North American structures.
6.	Half-cell potentials on treated and untreated North American structures.
7.	Description of Type I concrete test blocks.
8.	Description of Type II concrete test blocks.
9.	Mix design for Type I concrete specimens.
10.	Mix design for Type II concrete specimens.
11.	Description of contact points used to make measurements in Type I concrete test blocks.
12.	Description of contact points used to make measurements in Type II concrete test blocks.
13.	ECE comparison between the different specimens.
14.	ECE parameters.
15.	Surface deposit peak data using x-ray diffraction.
16.	Surface deposit peak data using x-ray photoelectron spectroscopy.

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Page Owner: Office of Research, Development, and Technology, Office of Infrastructure, RDT

Topics: research, infrastructure, structures
Keywords: research, structures, Cathodic protection, chloride ions, electrochemical chloride extraction, rehabilitation of concrete bridges, reinforced concrete, removal of chloride, steel corrosion in concrete
TRT Terms: research, infrastructure, Facilities, Structures, Bridges, Concrete--Foundations and piers, Reinforced concrete--Electrochemical chloride extraction, Reinforced concrete--Corrosion, Cathodic protection, Chlorides, Electrochemical processes, Reinforced concrete bridges
Scheduled Update: Archive - No Update needed

This page last modified on 04/23/2012