ELECTRODE CONFIGURATIONS AND IMPEDANCE SPECTRA OF CEMENT PASTES

Electrode effects on impedance spectra of cement pastes were investiga ted by two-, three-, and four-point measurements without a potentiosta t over the frequency range 0.01 Hz-10 MHz. Electrode immittance effect s arising from highly resistive/capacitive contacts cannot be fully co rrected by nulling procedures. Two-point measurements are much more su sceptible to such effects than three- or four-point measurements. The three- and four-point results on pastes suggest that there is negligib le high-frequency ''offset'' resistance, and that bulk paste arcs are not significantly depressed below the real axis in Nyquist plots. The important impedance-derived equivalent circuit parameters are bulk res istance and capacitance; offset resistance and arc depression angle ma y not be physically meaningful parameters. Whereas all electrode confi gurations give reliable values of bulk paste resistance, only the thre e-point configuration provides the total paste/electrode dual are spec trum involving a single electrode. Multielectrode (three- or four-poin t) measurements may be necessary to establish the true bulk paste diel ectric constant.