The freezing of water in portland cement paste was investigated using ac impedance spectroscopy (ACIS) techniques. Length change and impedance measurements on cooling and warming were obtained simultaneously using a specially designed coupling technique. A new descriptor of frost resistance is described in terms of the high-frequency arc (HFA) depression angle in the impedance plane. Curves of the depression angle parameter φ versus temperature are shown to be indicative of the pore structure and its effect on mass transfer of water and nucleation and growth of ice crystals. The φ–temperature and resistance–temperature curves are used in combination to assess structural damage. Results are compared with those obtained for model pore systems, i.e., Vycor glass and clay brick.