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Frequency-Dependent Electrical Mixing Law Behavior in Spherical Particle Composites.


pdf icon Frequency-Dependent Electrical Mixing Law Behavior in Spherical Particle Composites. (463 K)
Campo, M. A.; Woo, L. Y.; Mason, T. O.; Garboczi, E. J.

Journal of Electroceramics, Vol. 9, No. 1, 49-56, October 2002.

Keywords:

composite materials; mixing; cements; impedance; electrical conductivity; mixing laws

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-switching coating model," which accounts for the unusual frequency-dependent behavior of the steel particle composites.