Immittance spectra for Portland cement fly ash-based binders during early hydration

A range of immittance formalisms is exploited to understand the nature of conduction and polarization within Portland cement-based binders over the frequency range 1 Hz to 1 MHz. Data are presented for binders with and without aggregate additions; of particular interest was the electrical response of a binary combination of ordinary Portland cement and fly ash. Regarding the latter, when presented on a Nyquist diagram, a characteristic plateau region emerged between the electrode spur and the bulk are. When presented in the form of dielectric constant and conductivity as a function of frequency, a region of dispersion was evident for all systems. Furthermore, it was shown that by undertaking a dielectric frequency-domain analysis of the data, the experimental results could be synthesized across the frequency range 1 Wt to 1 MHz. Rather than ascribing separate processes to each impedance zone, the observed response could be attributed to a single bulk polarization process. When transformed into the complex impedance plane, there was also good agreement between synthesized and measured response. It is postulated that polarization is as a result of double-layer effects on the grain with a relaxation frequency in the low kilohertz region. (C) 1999 Elsevier Science Ltd. All rights reserved.