(The) effects of electrode contact and compressive loading on hydration of O.P.C.

Abstract

The effect of bare electrode in the dielectric constant, $\varepsilon^\ast(\omega)$, of conductive dielectric materials including space charges was investigated by using three types of electrodes, bare, insulated and partially insulated electrode for the frequency range of $10^4-10^6$Hz at the environmental temperature of $T=30\,^\circ\!C$. the results obtained for de-ionized wate, natural water and cement paste during initial setting, showed that the dielectric constant measured with the bare electrode was explicitly different from that of measuring by the insulated electrode during initial setting of cement paste. These facts represents that the dielectric constant at the electrode masks the that of the specimen(bulk) containing space charges. The dielectric constant and conductivity of cement paste was obtained by the curve-fitting of $\varepsilon``$ and $\varepsilon"$ by using insulated electrode, which indicated well the change of viscosity and the amount of ions in the cement paste. the comparison of dielectric constant and heat evolution rate obtained by using the insulated electrode with the work of McCarter and Ashar by the bare electrode, indicated that the dielectric value measured by bare electrode was 10 times as large as that of the insulated electrode. The mechanical properties improved greatly after 7 days hydration under compressive loading. The improvement in density, ultrasonic velocity and modulus of cement paste hydrated under compressive loading was attributed due to the higher degree of compaction resulting from low pore density.