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1) The dielectric amplification mechanism in cement paste comes from the microstructural relationship between the capillary porosity and the C-S-H gel phase. The large drop in the dielectric constant at the freezing point of the capillary pores indicates that the amplification occurs within the capillary pore network. The amplification may result from layers of C-S-H gel within the capillary pore network acting as small capacitors. Disconnected (not percolated) capillary pores are not required for the mechanism to be operative.
2) The magnitude of the large drop in both σ and k upon the first freezing of the larger capillary pores correlates well with the predicted percolation threshold of 18% for these pores [26], because when the cement paste samples reached a degree of hydration such that their capillary pore systems became disconnected, this large drop in properties vanished.
3) The influence of the C-S-H gel was found to dominate the electrical properties of the frozen cement paste matrix. The conductivity of frozen cement paste was successfully related to the volume fraction of C-S-H gel using the NIST/NU digital-based computer model.
4) Freezing the cement paste enabled the contributions of the capillary pores and the C-S-H phase to be approximately separated. Studying the frozen pastes, where the C-S-H gel is the main conductor, showed that the percolation threshold for C-S-H is at a volume fraction of about 18-20%, in good agreement with an earlier prediction [26].
5) The conductivity of the C-S-H phase, σCSH, at −40 ºC, for both 0.4 and 0.7 w/c portland cement pastes and for different degrees of hydration, was determined to be approximately 6 x 10−5 S/m, far lower than its value at room temperature.