Comparative evaluation of piezoresistivity of CNTs/Cement composites measured by AC and DC techniques

By adding carbon nanotubes (CNTs) to the cement matrix, the electrical resistance of composite material decreases and, at the same time, the piezoresistivity increases. In this paper, data on AC and DC measurements of electrical properties of multi-walled carbon nanotube/cement composites unloaded or subjected to compressive stress by using a two-probe configuration were presented. Experimental results of the DC measurements were affected by the electrode polarization, which induced an increase of the electrical resistivity of the specimens. Therefore, DC method requires a pre-power time to allow electrical resistance reach a stable value. Alternate current (AC) impedance was adopted in order to limit the polarization effects, by evaluating the resistance and capacitance characteristics separately. The higher the frequency, the lower the capacitance and, consequently, the polarization effect. At 20 kHz, the capacitance was eliminated and the electrical resistance of the specimens was evaluated under repeated compressive load cycles.