Impedance spectroscopy of fiber-reinforced cement composites

• Published in: Cement & concrete composites Vol. 24; no. 5; pp. 457 - 465
• Main Authors: Mason, T.O, Campo, M.A, Hixson, A.D, Woo, L.Y
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2002
• Subjects: Aspect ratio; Carbon fiber composites; Carbon fibers; Charge transfer; Electric impedance; Electrical impedance spectroscopy; Fiber reinforced materials; Microstructure; Percolation (solid state); Spectroscopic analysis; Steel fiber composites; Volume fraction; Electrical impedance spectroscopy; Steel fiber composites; Carbon fiber composites
• ISSN: 0958-9465; 1873-393X
• DOI: 10.1016/S0958-9465(01)00077-4

The addition of chopped conductive fibers to cement matrices results in a characteristic “dual-arc” electrical impedance spectrum below the percolation threshold. This behavior can be explained on the basis of a “frequency-switchable fiber coating” model, in which a “coating” (e.g., passive oxide film on steel or charge transfer resistance/double layer on other conductors) insulates the fibers at DC and low AC frequencies, but is shorted out at higher frequencies, where the fibers become short-circuit paths in the composite microstructure. The present work investigates various factors governing the impedance spectra of fiber-reinforced cement composites – fiber aspect ratio, fiber volume fraction, fiber orientation (relative to field direction), and fiber shape. The “gamma” factor (ratio of the low frequency arc diameter to DC resistance) is a useful parameter to characterize the microstructure–property relationships of fiber-reinforced composites.