INFLUENCE OF SILICA FUME ON THE EARLY HYDRATION OF PORTLAND CEMENTS USING IMPEDANCE SPECTROSCOPY

Electrical properties of hydrating portland cements (PC) and portland cements containing silica fume were studied from 5 min to 90 days. Cement pastes with water to solids ratios (w/s) of 0.30, 0.35, and 0.40, as well as silica fume to portland cement ratios (s/c) of 0.05, 0.10, and 0.20, were made and impedance was measured within the frequencies of 13 MHz to 5 Hz. The impedance spectra exhibit electrode arcs at low frequencies and bulk material arcs at high frequencies. The bulk resistance of the paste increases with increasing silica fume content and/or decreasing water content. The conductivity of pore fluid from PC pastes increases rapidly with time during the early stages and then remains constant, while that of the silica fume pastes increases then decreases sharply.