Experimental Study on Salt Expansion Characteristics of Coarse-Grained Sulfate Soils

In this paper, salt expansion tests were conducted on coarse-grained sulfate soils to investigate salt expansion characteristics. The experimental results indicate that the formation and growth of salt crystals are influenced by environmental temperature and humidity; during the cooling process, the specimen expands due to the growth of salt and ice crystals. The heave in the positive temperature range increases with increasing sulfate content, while the heave in the negative temperature range reaches a peak value when the salt content varies between 0.4% and 0.7%, indicating that the combined effect of precipitation and freezing contributes to significant volumetric expansion. The initial precipitation temperature increases with increasing pore solution concentration before it reaches 30°C. The freezing point is influenced by soil particles, pore solution concentration, and initial water content. The freezing point first decreases with increasing salt content and tends to be stable afterward when the water content is relatively high. However, the freezing point exhibits a continuous decreasing tendency if salt crystal precipitation occurs before freezing. An empirical model is proposed to predict the salt heave ratio in the positive temperature range based on salt crystal volume changes, and the relationship between the precipitation and freezing processes in the negative temperature range is examined.