A comprehensive method of determining the soil unfrozen water curves: 2. Stages of the phase change process in frozen soil–water system

Results of determination of the unfrozen water function in frozen soil–water system involving analysis of the differential scanning calorimetry (DSC) signal in terms of convolution have been presented. Four homoionic forms of bentonite (Ca2+, Mg2+, Na+ and K+) and two homoionic forms of kaolin (Ca2+ and Na+) were used in the experimental program. Analysis of the obtained results indicates the existence of five separate stages of the phase change process during warming from −28 °C. Three of them, I, III and V, are characterised by quite a vanishing of the phase effects. The intensity of the phase effects during stage IV near the melting point T0 is almost two orders of magnitude greater than in the low-temperature stage II. A characteristic stage III without phase changes directly before the final melting was called “the plateau”. It seems that the presence of the plateau can be explained by the specific “gap” in the micropore size distribution (and strictly speaking, in possible water menisci sizes distribution).