DC electric polarization of cured cement paste being unexpectedly hindered by free water

Abstract

AbstractElectric polarization is basic to the dielectric behavior, which is pertinent to the science and applications of cement‐based materials. This work reports the dynamics of the DC‐current‐induced electric polarization/depolarization of cured cement paste and their dependence on the water/cement ratio. This dependence has not been previously reported for any cement‐based material. The extent of the polarization is unexpectedly found in this work to decrease as the water/cement ratio increases, indicating that the free water hinders the polarization. This hindrance is due to (i) the dominance of ions behind the polarization (as supported by the previously reported increase in permittivity with increasing temperature), and (ii) the polar water molecules partly shielding the ions from the applied electric field. The fraction of ions in the pore solution that participates in the polarization increases with the polarization time and is 4.5 × 10‐14 for 570 s of polarization at a current of 1 μA for water/cement ratio 0.35. Upon increasing the water/cement ratio (0.3–0.4), the polarization rate decreases, the polarization extent at a given polarization time decreases, and the time to reach polarization saturation decreases. The polarization/depolarization rate decreases as the current application progresses because the polarization/depolarization hinders further polarization/depolarization. The degree of this hindrance increases with increasing water/cement ratio. Thus, a higher water/cement ratio is preferred if less polarization is desired as in resistance‐based self‐sensing, whereas a lower water/cement ratio is preferred if more polarization is desired as in capacitance‐based self‐sensing.