Mechanical and Thermal Properties of Lignin Fiber–Reinforced Loess Subjected to Freeze–Thaw Cycles

As a derivative of woods, lignin fibers are considered a sustainable material for stabilizing soils. However, their applications in loess in seasonally frozen regions and the underlying mechanisms of loess reinforcement are not well understood. This study conducted a series of laboratory tests to investigate the effects of lignin fiber content and freeze–thaw cycles on the mechanical and thermal properties of lignin fiber–reinforced loess, followed by an experimental investigation into the microstructure and mineralogy of the reinforced loess. The results showed that the addition of lignin fibers increased both strength and ductility and drastically reduced the thermal conductivity of loess. In the repeated freeze–thaw condition, the unreinforced loess exhibited a slight increase in brittleness whereas the lignin fiber–reinforced loess showed an overall increase in ductility. The reinforcement of lignin fibers was found to be primarily attributed to bridging loess particles while reducing pore size and connectivity.