The theory to estimate amount of frozen water in cement paste was studied based on properties of electrolyte solution. A method to estimate amount of frozen water as a function of resistivity and temperature was proposed. Resistivity and temperature in cement paste with different moisture contents equilibrating to various relative humidity were measured in the temperature range from 20 to-45 C. Pore structure was measured by mercury penetration and adsorption. Conclusion is shown below. Moisture contents below approximately 3.5 monolayers is not freezable. The freezing point depends on supercooling and depression of melting point corresponding to pore radius. Few frozen water was observed below RH 90 % in the temperature range of freezing and thawing test (ASTM C 666). Water in the capillary pore larger than 100-150 λ is freezable in the temperature range of freezing and thawing test (ASTM C 666).
