Development of a calorimetric method for measuring the content of unfrozen water in soil at a negative temperature

Abstract

The paper considers the task of determining the content of unfrozen water in frozen dispersed soils. It is known that the phase transformation of pore water into a solid phase at the freezing point is subject only to free water, which is not influenced by long-range electromolecular forces between the active centers of the surface of soil particles and water molecules. Distortion of the structure of pore water, called bound, leads to a decrease in its freezing temperature, and its amount is functionally dependent on the dispersion of the soil. The presence of liquid water in an array of frozen soil leads to a decrease in its strength properties, being a determining factor at near-zero temperatures. Therefore, along with other properties of frozen soil, the content of unfrozen water is an important criterion for calculating strength, thermophysical, and mass transfer processes. To quantify the content of unfrozen water, as well as determine the dependence of humidity on temperature, the calorimetric method is usually used, with its inherent disadvantages. In the work, to solve this problem, a method was developed based on the principles of calorimetry, but fundamentally different in the way of measuring the energy of phase transformations. The essence of the method is to continuously fix the energy released from the frozen sample to a predetermined temperature using a heat flux density sensor, and to continuously measure the soil’s own temperature. The standard calorimetric test procedure was adapted to process the results of a new experimental setup. The advantages of the new method for measuring the content of unfrozen water over the traditional calorimetric method are substantiated, first of all, this is a smaller number of experiments to obtain one experimental point. The applicability of the installation for studying equilibrium and nonequilibrium freezing processes of wet soil, including those with a high salt content in pore water, is shown. Comparisons of the results obtained by the calorimetric and proposed methods for the same soil showed sufficient convergence of the data, taking into account the difficulty of reproducing the experiments.