Relationship between temperature and water content of sodium saline soils without phase transformation

The relationship between water content without phase transformation of sodium sulfate saline soils and temperature is established above the freezing temperature of soils through theoretical analysis. In order to find the mechanism of the initial precipitation temperature of salt crystals in sodium sulfate saline soils and solution and change of water content under different temperature conditions, saline soil samples and solutions are tested in laboratory. By analyzing the cooling curves of soil samples and NMR single strength under different temperatures, the influence of temperature on water content without phase transformation is obtained. The research results show that, the precipitation of sodium sulfate decahydrate usually lags under specific cooling rate. Besides, the initial precipitation temperature is lower than the temperature of saturated solution. And also, the initial precipitation temperature decreases as the salt content of soil decreases. Meanwhile, the initial salt crystals are easier to form in solution than in soils. In addition, the decrease of water content in saline soils is greater than that in solution, and the water content without phase change decreases as the temperature decreases. The unfrozen water content of sodium sulfate saline soils with high salt content decreases exponentially, and the water content no longer changes when the temperature of soils is up to -10℃. For the sodium sulfate saline soils with low salt content, the unfrozen water content also decreases exponentially, and under the same temperature, the unfrozen water content of soils increases as the salt content increases.