Geotechnical properties and microstructure of lignin-treated silty clay in seasonally frozen regions

Freeze–thaw weathering is critical to road engineering in seasonally frozen regions. To solve the adverse effects of inorganic stabilization materials on the environment, the lignin of the original polymer compound is used to improve the durability of silty clay. Lignin content, curing duration, and freeze-thawing were determined to have a significant influence on the geotechnical properties and microstructure of lignin-treated silty clay. An increase in lignin content resulted not only in an increase in the optimum moisture content, pH, and water absorption of the soils, but also a decrease in the maximum dry density, plasticity index, specific gravity, thermal conductivity, and swelling capacity. In contrast, an increase in lignin content led to an initial increase followed by a decrease in the liquid limit, plastic limit, and California bearing ratio of the soils. After freeze-thawing, the thermal conductivity and California bearing ratio of lignin-treated silty clay decreased, whereas the swelling capacity and water absorption increased. The optimum lignin content for silty clay in the Jilin Province of China is approximately 4%. The soil particles are bonded with the cementitious material. No new mineral composition, chemical elements, or functional groups are formed after the treatment. The bearing capacity and frost resistance of lignin-treated silty clay are affected by the cementitious materials, coated grains, and filled pores.