Effect of Microencapsulated Phase Change Materials on the Physical, Mechanical, and Microscopic Properties of Loess under Freeze-Thaw Cycles

Abstract The freeze-thaw (F-T) cycles have adverse effects on the strength and durability of loess in seasonal frozen ground regions. By absorbing or releasing a significant amount of energy, microencapsulated phase change materials (mPCM) can be utilized to modify the soil’s internal temperature and weaken the negative impacts of F-T cycles. This study utilized different contents of mPCM (i.e., 0%, 3%, 6%, 9%, and 12%) to improve the loess. The mechanical, physical, and microstructural characteristics of mPCM stabilized loess under F-T cycles were investigated using freezing point, temperature variation, unconfined compressive strength (UCS), splitting tensile strength (STS), direct shear test, volume change, surface hardness, ultrasonic pulse velocity (UPV), and mercury intrusion porosimetry (MIP). The results show that adding mPCM improved the freeze-thaw resistance of the loess, which effectively reduced the temperature variation and volume change during the F-T cycles. As the mPCM content rose, the surface hardness of the samples enhanced, and the variation in UPV decreased. The mPCM enhanced the mechanical strength and alleviated the strength attenuation during the F-T cycles, especially for the UCS. The UCS of the pure loess dropped by 30.55% after ten F-T cycles, whereas the UCS of the sample with 12% mPCM decreased by 9.89%. As the mPCM content increased, the content of large pores dropped, whereas the content of middle pores grew significantly. Furthermore, the addition of mPCM inhibited the pore development and enhanced the surface fractal dimension during the F-T cycles.