Using impedance spectroscopy to assess the viability of the rapid chloridetest for determining concrete conductivity

The suitability of using the initial current from the rapid chloride test ( ASTM C 1202) to determine specimen conductivity is tested using impedance s pectroscopy with a frequency spectrum of 10 Hz to 1 MHz. The specimen condu ctivity 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 h our conduction test carried out according to ASTM C 1202 is not a direct me asure of specimen conductivity. Further, ohmic heating during the 6 hour te st makes it nearly impossible to directly measure any specimen transport pr operty from the results. The total charge passed during the 6 hour conducti on test is, therefore, not a reliable quantity for service life prediction. Results indicate that the direct current (dc) measurement of resistance us ing a voltage of 60 V is sufficient to overwhelm polarization effects, ther eby yielding an accurate estimate of the true specimen conductivity. Impeda nce spectroscopy measurements also indicate that corrosion may form on the brass electrodes, adding bias to a conductivity estimate based upon a dc me asurement.