Reference:  Campo, M.A., Woo., L.Y., Mason, T.O. and Garboczi, E.J., Journal of Electroceramics, 9 (1), pp 49-56, (2002).

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Frequency-Dependent Electrical Mixing Law Behavior
in Spherical Particle Composites

M.A. CAMPO,¹ L.Y. WOO,¹ T.O. MASON¹, & E.J. GARBOCZI²

¹Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA
²National Institute of Standards and Technology, Building Materials Division, Gaithersburg, MD 20899, USA
Submitted April 30, 2002; Revised May 8, 2002; Accepted May 8, 2002

Abstract

The electrical properties of cement-based composites with mono-size conductive (steel) or insulating (glass) spherical inclusions were investigated by combined 2-point impedance spectroscopy and 4-point dc resistance
measurements. The matrix was ordinary Portland cement (w/c=0.4; cured for 7 days). Particle loading was varied over an extended range to as high as 42% volume fraction. The steel particle composites behaved like the glass particle composites at dc and low ac frequencies; conductivity decreased with increasing particle loading. Under ac excitation, however, the steel particles were rendered conductive; conductivity increased dramatically with particle loading. The results were analyzed in terms of various mixing laws and effective media theories and the proposed "frequency-switchable coating model," which accounts for the unusual frequency-dependent behavior of the steel particle composites.

Keywords: composites, cement, impedance, electrical conductivity, mixing laws

• Introduction
• Experimental Procedure
• Results and Discussion
• Conclusions
• Acknowledgments
• References