Reference: K.A. Snyder, C. Ferraris, N.S. Martys and E.J. Garboczi, Journal of Research of the National Institute of Standards and Technology, Volume 105, Number 4, July-August, 2000.
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Using impedance spectroscopy to assess the viability of the rapid chloride test for determining concrete conductivity

K.A. Snyder, C. Ferraris, N.S. Martys, E.J. Garboczi
Building Materials Division
Building and Fire Research Laboratory
National Institute of Standards and Technology

Abstract:

The suitability of using the initial current from the rapid chloride test (ASTM C 1202) to determine specimen conductivity is tested using impedance spectroscopy with a frequency spectrum of 10 Hz to 1 MHz. The specimen conductivity has an analytical relationship to specimen diffusivity and so is a useful quantity in service life prediction. Measurements made on specimens of different lengths indicate that the total charge passed during the six hour conduction test carried out according to ASTM C 1202 is not a direct measure of specimen conductivity. Further, ohmic heating during the six hour test makes it nearly impossible to directly measure any specimen transport property from the results. The total charge passed during the six hour conduction test is, therefore, not a reliable quantity for service life prediction. Results indicate that the direct current (DC) measurement of resistance using a potential of 60 volts is sufficient to overwhelm polarization effects, thereby yielding an accurate estimate of the true specimen conductivity. Impedance spectroscopy measurements also indicate that corrosion may form on the brass electrodes, adding bias to a conductivity estimate based upon a DC measurement.