Salt crystallization in cold sulfate saline soil

- The initial supersaturated ratio of saline solution is discussed below 0 °C.
- The effect of salt crystals on the freezing point of soil is studied.
- The critical nucleation radius of salt crystals is derived by physical-chemical method.
- The relation between salt expansion pressure and supersaturated ratio is investigated.

The effect of sodium sulfate crystallization on soil freezing temperature, and the changes in salt expansion and frost heave pressure with temperature were analyzed experimentally and using crystallization theory. The Pitzer ion model was used to find the supersaturation ratio of a sodium sulfate solution in soil. The relationship between the initial supersaturation ratio and temperature was obtained, which provided criteria for the presence of salt crystals over the entire temperature range. Experiments were carried out to determine the effect of cooling the sodium sulfate saline soil as well as the location of salt crystallization. Analysis of the location and shape change of salt crystals based on the experiments clarified the interaction between salt crystallization and ice-water phase change. A formula relating the surface free energy of a crystal to its critical nucleation radius was deduced based on the assumption of homogeneous nucleation. Finally, equations for the salt expansion force and frost heave pressure were obtained and their rationalizations were provided.