AC-impedance response of multi-walled carbon nanotube/cement composites
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 percolation vs. discontinuous fiber effects in CNT-FRCs, with the potential for characterizing dispersion issues (e.g., clumping/aggregation) in nanocomposites.