STP713

    Laboratory Testing and Monitoring of Stray Current Corrosion of Prestressed Concrete in Seawater

    Published: Jan 1980


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    Abstract

    Stray current corrosion of prestressed concrete beams was investigated in the laboratory by exposing 40 specimens 6.4 by 6.4 by 122 cm (2.5 by 2.5 by 48 in.), prestressed by a central high-strength steel wire to 1.86 × 109 N/m2 (270 ksi), in seawater. The steel wire was made anodic to a copper cathode, with steel current densities maintained at fixed values between 27 and 915 mA/m2 (2.5 and 85 mA/ft2).

    Monitoring was done by measuring steel potential relative to a silver/silver chloride reference electrode with current on, weekly, and with current off, biweekly. Beams were examined visually biweekly; the presence of rust spots and longitudinal cracks was noted, and lengths of cracks were measured, for exposures which ranged between 8 and 83 weeks. After exposure, the prestressing wire was tensioned to failure.

    Reductions in breaking strength of 70 percent were observed in 25 weeks' exposure at 915 mA/m2 (85 mA/ft2), with lesser reductions in strength for shorter exposures and lower current densities.

    Ampere-hours did not correlate satisfactorily with the reduction in breaking strength of the wire. Potentials measured with current on or off indicated that corrosion was occurring, but gave no quantitative indication of the reduction in breaking strength. Resistance measurements of the electrochemical circuit did not relate to the extent of corrosion damage. Time to change in potential of the prestressing steel did correlate with time for initiation of steel corrosion. Existence and length of longitudinal cracks in the concrete beam did not correlate quantitatively with the reduction in breaking strength of the prestressing steel.

    After the tension test, beams were notched lengthwise with a saw and opened. The prestressing wire was then examined to determine the distribution and extent of corrosion. Quantitative estimates of the corroded length were made. Qualitatively, where there was considerable localized corrosion attack, there was great reduction in breaking strength for a given number of ampere-hours' exposure. Where the corrosion attack was well distributed, an equal number of ampere-hours gave less reduction in fracture strength.

    Stray electrical currents can cause serious deterioration in the strength of prestressed concrete structures, as measured by testing to destruction. However, none of the methods of monitoring used in this investigation can predict the extent of the damage quantitatively.

    Keywords:

    laboratory testing, monitoring, stray current corrosion, prestressed concrete in seawater


    Author Information:

    Cornet, I
    Professor emeritus, Department of Mechanical Engineering, and professors, University of California, Berkeley, Calif.

    Pirtz, D
    Professor emeritus, Department of Mechanical Engineering, and professors, University of California, Berkeley, Calif.

    Polivka, M
    Professor emeritus, Department of Mechanical Engineering, and professors, University of California, Berkeley, Calif.

    Gau, Y
    Engineer, Union Carbide Corp., Bound Brook, N.J.

    Shimizu, A
    Assistant manager, Coen Co., Burlingame, Calif.


    Paper ID: STP27466S

    Committee/Subcommittee: G01.05

    DOI: 10.1520/STP27466S


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