Dielectric amplification in cement pastes

Abstract

Dielectric amplification (dielectric constants >80) is observed in cement pastes at early ages. Standard nonlinear least squares fitting routines yield artificially large “capacitances” when constant phase elements are employed. Instead, capacitance vs. frequency analysis provides reliable evidence of dielectric amplification. A physical model system consisting of a polycarbonate box with electrodes at each end, divided into two compartments by a polycarbonate barrier with a single hole, and filled with electrolyte solution, simulates the impedance response in young cement pastes. The barrier represents hydration products whereas the hole represents the constriction between two adjacent capillary pores, i.e., the pore network remains percolated. Dielectric amplification is inversely proportional to barrier thickness, i.e., it decreases as the barrier (product phase) thickens. Impedance spectra from real pastes vs. water/cement (w/c) ratio and during freezing or solvent exchange (to preferentially reduce the conductivity of the capillary pores) exhibit significant dielectric amplification, even after freezing or exchange, suggesting that C-S-H gel also has a dielectrically amplified microstructure. Advanced Cement Based Materials 1997, 5, 41–48.