Dielectric behaviour of hardened cementitious materials

The dielectric behaviour of mature Portland cement pastes prepared at water/cement ratios 0·3 to 0·7, and pastes containing various percentages of silica fume at water/cement ratio 0·3 was investigated over a frequency range of 1 MHz to 1·5 GHz. The value of dielectric constant is water content dependent. A linear correspondence between dielectric constant and evaporable water was obtained for water-saturated pastes. Experimental results relating dielectric constants to porosity for Portland cement pastes hydrated jor one year were in good agreement with Sen s approximation for rock, e.g. ϵ′_e = 1·5ϵ′_cp + P^1·5 (ϵ′_e = 1·5ϵ′_cp), where ϵ′_e = the real part of the effective dielectric constant, ϵ′_w = the real part of the dielectric constant of water, ϵ′_cp = the real part of the dielectric constant of cement paste and P is the porosity Addition of silica fume appears to have a small and indirect effect on the dielectric constant value of the paste. This is due to the pore size effects and evaporable water content.