Transient freezing–thawing phenomena in water-filled cohesive porous materials

An oscillator circuit-based capacitive method is used to study the ice/water phase transition in cohesive porous materials like water-filled fused glass beads. It straightforwardly gives the temperature domain of supercooling, freezing, or melting. It also provides an estimation of the ice content time-evolution during the transient stage of solidification and melting. This is done by calibration tests at 20 °C on a progressively dried sample and by an up-scaling dielectric model. The latter allows taking account of the temperature and frequency dependence of the water dielectric constant as well as the slight difference between the dielectric constants of water vapour (≃ 1) and ice (≃ 3.2). From the ice content-versus-time curve, the water-to-ice phase transition dynamics is found to follow the Avrami law with an exponent close to 0.5. This suggests that the ice/liquid interface is planar so that the liquid and ice pressures are equal, which is confirmed by the Thomson–Gibbs and Young–Laplace equations. The resulting pore pressure can then be predicted in the framework of linear poroelasticity. The analysis reveals a three-step time-history pressure: an increase at the onset of stable ice nuclei, then a relaxation induced by the unfrozen water Poiseuille-type flow and finally a further pressure increase until the end of crystallization. In all cases, the pressurization remains very low (0.1 MPa) at the 0 °C-isothermal transient stage of solidification.