Phase Transitions of Adsorbates: IV, Mechanism of Frost Action in Hardened Cement Paste*

The dimensional changes and the thermograms of cement specimens were determined during temperature cycles (+5° to ‐ 60°C, 0.33°C/min). In each case, freezing processes at ‐8° and ‐40°C and melting processes at ‐11° and 0°C were observed. The results could be explained by a theory previously developed for the porous‐glass‐water system. At the higher temperature, freezing occurs on the outer surface of the specimen; at the lower temperature, it occurs in the pores after redistribution of the water. Because water does not freeze in pores filled on adsorption, it migrates out of these pores when the relative humidity (expressed in terms of the vapor pressure of undercooled water), unavoidably decreases on cooling. Expansion is deleterious when the water content of the paste is significantly greater than the equilibrium value at the prevailing relative humidity. The effects of the water/ cement ratio, degree of saturation, air entrainment, sample dimensions, and cooling rate were consistent with the theory.