A review of cement-based materials as electroceramics

The dielectric behavior of unpoled cured cement-based materials enables these materials to serve as electroceramics. The behavior entails the DC polarization (apparent DC electrical resistivity increase), permittivity (AC polarization, capacitance measurement) and DC electret (permanent electric dipole, voltage measurement). The dielectric behavior is not derived from functional admixtures such as the perovskite ceramics. The polarization involves charge-carrier polarization, with the carriers being primarily the ions in the pore solution. Dipolar polarization associated with the polar water molecules plays a minor role. Silica fume, if present, decreases the permittivity, partly due to the pore refinement. A polymer admixture, if present, increases the permittivity, with significant polarization resulting from the cement-polymer interface. Carbon fiber, if present, affects the electronic and ionic conduction, with the fiber's ozone treatment promoting the ionic conduction and enhancing the permittivity. As the water/cement ratio increases, the permittivity increases, but the DC polarization decreases. The DC polarization occurs faster and more significantly than the subsequent depolarization. This reflects the electret, which discharges upon short circuiting (as in capacitor discharge) and subsequently charges back upon open circuiting. The temperature increases the permittivity or the electret's electric field, whereas tension decreases the same, enabling capacitance-based/voltage-based self-sensing of temperature and stress/strain.