The chemical potential of unfrozen water and frozen water content were measured by the modified electric method in some range of lowest temperature. We used a thermal mechanical analyzer (TMA) and measured the dilation under freezing and thawing cycle. The rate of frozen water content under both super cooling and depression of melting point was described statisically. The relation between the radius of capillary pore and depression of melting point was shown statistically. Subsequently we proposed the method to estimate the amount of frozen water by the temperature and pore structure taking account of the thick of unfrozen water layer. The dilation that is calculated from freezing of supercooled water shows the similar tendency to the one that measured by TMA. Consequently we proposed the modified mechanism of frost damage. The rapid growth of ice crystal under supercooling makes rapid flow and large hydraulic pressure of unfrozen water. The large hydraulic pressure cause frost damage of Concrete.
