Experimental study and micro-mechanism analysis of freeze-thaw performance of expansive soils improved by phase-change materials

The complex freeze-thaw process experienced by expansive soils in seasonally frozen regions will cause the deterioration of freeze-thaw performance of soils. The phase-change materials can store and release a large amount of energy in the form of latent heat during the phase change process, and can be used to improve the freeze thaw performance of soils. For the case study of expansive soils in the canal base in high and cold regions of northern Xinjiang, the freeze-thaw cycle tests under the actual climatic conditions along the canal are conducted. The paraffin-based liquid phase-change material (pPCM) and the paraffin-based microcapsule phase-change material (mPCM) are selected. After undergoing freeze-thaw cycles, the modified expansive soils with different blending amounts of phase-change materials are subjected to the volume deformation tests, unconfined compressive strength tests, DSC thermal cycle tests and SEM tests. The results show that the pPCM can improve the toughness of soils under failure to some extent, and it is slightly better than mPCM in improving the internal temperature field of the foundation soils in the canal and improving the thermal stability of the soils. The mPCM can reduce the expansion and contraction deformation of the soils. It effectively inhibits the attenuation of the strength of the soils, and the mixing amount of 8% is the most significant. The mPCM reduces the impact of freeze and thaw on microscopic pore damage of the soils, and macroscopically weakens the attenuation effect of freeze and thaw cycles on soil strength. The tests show that the mPCM-modified expansive soils have obvious advantages in resisting repeated freeze-thaw cycles, which can provide a reference for the design of actual projects.