Water and salt phase change in sodium sulfate soil based on differential scanning calorimetry

Abstract

Strong salt expansion and frost heave are induced to make the infrastructure in the salted region damaged with water or salt phase change at low temperature. Laboratory test based on differential scanning calorimetry is used to investigate salt and water phase transformation and their crystallization mechanism in sodium sulfate soils and solutions. During the experimental process, crystallization heat release, crystallization period and supercooling are measured. According to the conservation principle of mass and heat, salt and ice crystallization are separated, and unfrozen water content is calculated at different temperatures. Moreover, variations of unfrozen water content, as well as the supercooling degree of sodium sulfate soils with different size are compared and analyzed based on heterogeneous nucleation theory. The results demonstarte occurance of the ice crystallization before salt crystallization in minor soil samples; however, salt crystallization appears first in pure solution at high concentration. The interval at which the ice and salt crystallization begin decreases as the salt content increases, and the supercooling decreases as the salt content or sample size increases. Additionally, water freezing in small soil samples is more difficult than that in larger soil samples, and the unfrozen water content increases as the salt content or sample size decreases.