| Résumé | A 1-month-old, saturated rod of hardened Portland cement paste with w/c=0.40 was formed with, and stored under, heavy water. This rod was studied undergoing two freeze-thaw cycles over the range 227-297 K, using neutron diffraction, at slow rates of heating and cooling. Neutron diffraction gives a direct and independent quantification of the amount of ice and liquid water in the pore system of hardened cement paste as a function of temperature. The amount of ice that formed was totally reproducible over two freeze-thaw cycles, implying negligible changes to the pore size distribution and geometry. An analysis of some of the factors that may contribute to the freeze-thaw hysteresis is given. There is significant broadening of the diffraction peaks of the ice, which corresponds to a small correlation length of crystalline order in the ice. Water was observed to be "irreversibly" expelled during the first freeze, above ca. 250 K. |
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