Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.
Issue link: http://mp.epubxp.com/i/889936
40 NOVEMBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 11 the rebar exhibited passive potentials. Linear polarization results also support this conclusion. The combination of cathodic polarization of the rebar and chloride removal prob- ably led to this effect. Cathodic polarization effec tively stopped corrosion during treatment, and the level of chloride after treatment was insufficient to reinitiate the corrosion. The long term effect of the extraction procedure on rebar corrosion is not yet known. After treatment of a full size bridge deck, a waterproofing treatment of the concrete surface would be undertaken, to ensure that further application of deicing salt did not lead to chloride penetration (this was not practi- cable in the field experiment described here). However, since not all the chloride is removed, there may be a tendency for chloride redistribution by diffusion under concentration gradi- ents. The effect of this process on long term initiation of rebar corrosion is unclear at this time. The hardware used in the field experiment described herein is probably not wholly suited for scale up to treatment of a full size deck, particularly if that deck shows sharp trans- verse or longitudinal gradients. Further development of sur- face electrolyte containment procedures are necessary to opti- mize the technique. Summary 1. The extraction of chloride from salt contaminated con- crete by electromigration techniques has been shown to be possible. 2. Optimum applied voltages, treatment times, surface elec trolyte, and anode material were determined from labora- tory investigations. 3. A 24 hour treatment of a 3 x 6 m (10 x 20 ft) section of an actual bridge deck removed up to 90% of the chloride present in the concrete above the top reinforcing steel. 4. Pretreatment and post-treatment potential scans showed that all active corrosion of the reinforcing steel in the treat- ment area had been halted by the chloride extraction. Acknowledgments The research described in this paper was performed under Contract No. DOT-FH-11-8133 for the Federal Highway Adminis - tration. The contents of the paper reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official view or policies of the Federal Highway Administration. This paper does not constitute a standard, specification, or regulation. FIGURE 10 — Potential scan of bridge deck treatment area 3 months after treatment. The guidance and council provided by R. E. Hay, H. A. Arni, and K. C. Clear of FHWA's Fairbank Highway Research Station is greatly appreciated. The authors also gratefully acknowl- edge the contributions of A. J. Walker, P. R. Patton, R. N. Smith, L. A. Salmons, C. J. Martin, 0. E. Niesz, C. A. Watson, W. E. Cop- pins, W. E. Hedden, and W. K. Boyd, of Battelle's Columbus Laboratories, and W. Cheatham and E. L. Nichols of the Ohio Department of Transportation. References 1. Berman, H. A. Journal of Materials, Vol. 7, p. 330 (1972). 2. Spellman, D. L., Stratfull, R. F. Highway Research Record, Vol. 328, p. 38 (1970). From the Author—Today's Practice Our work at Battelle Memorial Institute on the electrochemical removal of chloride ions from concrete began in the laboratory in 1973 under FHWA Contract DOT-FH-11-8133. Encouraging results from the lab work led to the selection of an eight-year-old reinforced concrete bridge deck northwest of Columbus, Ohio for what turned out to be a success- ful field trial. Since that time, electrochemical chloride extraction (ECE), as it's now called, has been the subject of research and trials in a number of countries, including those in the U.S. sponsored by FHWA and the Strategic Highway Research Program (SHRP). The process has also been commercialized in the U.S., Canada, and Europe. In our 1970s work, the technique for the chloride removal process used a DC power source connected to reinforcing steel in the deck, with an external anode immersed in a ponded electrolyte solution. The same basic components have been (and are being) used since that time. The ensuing research and trial studies have involved efforts to optimize material and process variables, including studies of (1) anode materials, (2) electrolyte type and containment, (3) electrical variables, (4) the duration of treatment, and (5) post-treatment monitoring strate- gies. Depending on the source of the claims, the use of ECE is ex- pected to potentially provide 10 to 15 years of extended life for chloride- contaminated reinforced concrete structures facing unacceptably high steel reinforcement corrosion rates. It has been rewarding to learn that the process has evolved from the laboratory to successful use in the field; not only on bridge decks, but on beams, columns, pier caps, and other chloride-contaminated concrete elements. My thanks to the editors of NACE for highlighting our original work at Battelle. —David R. Lankard C L A S S I C