A neutron diffraction study of ice and water within a hardened cement paste during freeze–thaw

Abstract 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.