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AC-impedance response of multi-walled carbon nanotube-cement composites.pdf

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AC-impedance response of multi-walled carbon nanotube-cement composites

/locate/cemconcomp Cement Concrete Composites 28 (2006) 509–519AC-impedance response of multi-walled carbon nanotube/cement composites S. Wansom, N.J. Kidner, L.Y. Woo, T.O. Mason * Materials Research Center, Department of Materials Science and Engineering, Northwestern University, 2220 North Campus Drive, Evanston, IL 60208-0001, USA Accepted 18 January 2006 Available online 22 March 2006Abstract AC-impedance spectroscopy (AC-IS) was combined with time-domain reflectometry (TDR) to investigate the impedance response of fiber-reinforced cement (FRC) composites with multi-walled carbon nanotubes (MWCNTs). In Nyquist plots (imaginary impedance vs. +real impedance) three impedance arcs/features were observed, similar to Nyquist plots for macrofiber and microfiber FRCs. The intersection of the electrode arc and the intermediate frequency feature (RDC(FRC)) corresponds to the DC resistance of the composite. The intersection of the two bulk features (Rcusp) corresponds to the AC resistance of the composite. Reductions in (RDC(FRC)) from the matrix resistance are indicative of a nanotube percolating network. Reductions in Rcusp from the matrix resistance are indicative of a discontinuous fiber–fiber path. Both shifts increased with fiber loading. AC-IS measurements are therefore able to discriminate perco- lation vs. discontinuous fiber effects in CNT-FRCs, with the potential for characterizing dispersion issues (e.g., clumping/aggregation) in nanocomposites. 2006 Elsevier Ltd. All rights reserved. Keywords: Cement-based composites; Nanocomposites; Carbon nanotubes; Impedance spectroscopy; Time-domain reflectometry1. Introduction Since their discovery by Iijima in 1991 [1], there has been growing interest in carbon nanotubes (CNTs) for various composite applications owing to their outstanding physical properties. Mechanically, they exhibit elastic moduli in the TPa range [2]. Their exceptionally high theoretical strength is 100 times that of steel, at only 1/6th the sp