Characterizing cement pastes incorporating two high silica fine materials using electrical impedance

Synopsis: This paper investigates the influence of two silica rich fine materials - a fine glass powder used as an inert filler, and nano-silica used as a supplementary cementing material - on the behavior of cement pastes at early ages using electrical impedance. The effective electrical conductivities of the pastes as a function of time, and their derivatives are used to identify the different stages in the microstructure development of the pastes. The incorporation of fine glass powder in the cement pastes in the proportions used in this study does not significantly influence the setting and hardening behavior of the pastes. The increased normalized conductivity of glass powder modified pastes at very early ages even when the local pore volume is reduced by the addition of glass powder filler, and the near equivalence with plain pastes at relatively later times is explained using the pore connectivity factor. The nano-silica modified pastes show significantly different conductivity-time response. It is seen that the setting and hardening phases of cement hydration are accelerated by the presence of nano-silica in the mixture. The nano-silica modified pastes exhibit a significant degree of matrix densification at early ages as could be observed from their conductivity responses as well as compressive strength results.