Durability of Silty Soil Stabilized with Recycled Lignin for Sustainable Engineering Materials

Abstract Lignin is an industrial waste derived from the paper plant, which poses a potential threat to the surrounding environment without proper disposal. The present study aims to evaluate the durability performance of recycled lignin stabilized silty soil subjected to different adverse environments. A series of laboratory experiments were conducted to determine unconfined compressive strength (qu), moisture stability coefficient (Kr), mass loss (Sm) and pH value of the stabilized silt exposed to water soaking and wetting-drying cycles. The results showed that the strength and durability of natural silt were obviously improved with the inclusion of lignin. Lignin cementation and matrix suction played important roles in the strength behavior of the unsaturated stabilized silt. The compressive strength suffered a dramatic drop after 1 day of soaking due to the dissolution of cementing materials and the loss of suction. Lignin stabilized silt possessed a higher Kr than that of quicklime stabilized one, indicating its superiority in durability. After 28 days of standard curing, 12% lignin stabilized silt had an ability to resist 4 cycles of wetting-drying, resulting in the cumulative mass loss (Cm) of approximately 20%. Soil pH value presented a decreasing trend with wetting-drying cycles, and an exponential correlation of pH with Cm was found by data fitting. Scanning electron microscope analysis revealed that the lignin-based cementing materials are gradually lost during the process of wetting-drying cycles. Additional research is encouraged to explore an effective method to prevent the deterioration of mechanical properties of lignin stabilized soils in practical projects.