Effect of Phase Change Materials on Mechanical Properties of Stabilized Loess Subgrade Subjected to Freeze–Thaw Cycle

Abstract

Freeze–thaw (F-T) cycle is a critical factor that deteriorates the mechanical properties of loess subgrade, leading to pavement structure distress. Phase change materials (PCMs) can be employed to stabilize loess subgrades. This study investigated the effect of PCMs on the mechanical properties of loess and explored the corresponding mechanism of stabilizing loess subjected to F-T cycles. First, macroscopic mechanical tests were conducted to examine the influence of PCMs on the mechanical properties of stabilized loess. Through a series of microscopic tests, the mechanism of PCM effects on loess before and after it was subjected to F-T cycles was analyzed from the chemical, thermal, and physical perspectives. The findings demonstrated that PCMs could considerably alleviate the adverse effects of F-T cycles on loess strength by 37%–182%. The strength of PCM-stabilized loess reached a maximum when liquid PCM (pPCM) and microencapsulated PCM (mPCM) doping were 8% and 5%, respectively. No new functional groups were generated after mixing the PCMs with loess. The strength of PCM-stabilized loess was mainly enhanced by physical gluing and filling. Additionally, the PCMs could counteract the external temperature by the latent heat of the phase change, thus increasing the thermal stability of the loess. Finally, through a scanning electron microscopy test, it was verified that the incorporation of PCMs improved the loess density and mechanical strength as well as enhanced sustainability against a few penetration cracks and large pores when the loess was subjected to F-T cycles. This study provides insights into the use of PCM-stabilized loess subgrade in seasonally frozen regions.