Utilization of biomass-based by-product lignin to suppress moisture loss-induced shrinkage of silty soil

The global stockpiles of by-product lignin are increasing rapidly with the growing demand on wood-based industry and biomass energy, creating a potential threat to environmental safety without proper disposal. The presented study aimed to evaluate the feasibility of utilizing biomass-based by-product lignin to suppress the shrinkage of silt expected as filling material in engineering construction. A series of laboratory experiments were conducted to investigate the variations in geometry size, mass loss Δm, moisture content w, and unconfined compressive strength qu of the treated samples exposed to the artificial dry condition. The effects of additive dosage and curing time on shrinkage behaviors of lignin treated silt were analyzed. The roles of matric suction on qu and soil microstructure were discussed to understand the mechanism leading to the soil shrinkage. The test results demonstrated that the addition of lignin effectively suppressed shrinkage of compacted silt subjected to dry curing. Both linear shrinkage rate es and volumetric shrinkage rate ev increased with an increase in lignin dosage, indicating excessive addition of lignin produced a negative impact on the shrinkage resistance. The values of es and ev of lignin treated samples were controlled within 1.0% and 3.0%, respectively. As compared to quicklime, lignin exhibited slightly inferior performance of suppressing shrinkage, while it promoted the water-holding capacity of the treated silt. The matric suction resulted from moisture loss was beneficial for strength improvement and also accelerated the process of soil shrinkage. The shrinkage characteristics of lignin treated silt mainly depended on the combined functions of lignin cementation and matric suction. Additional research is recommended to quantitatively evaluate the matric suction variation of lignin treated soils in dry environment. The outcomes of this study are invaluable in facilitating sustainable soil treatment in engineering construction and providing a viable answer to the cleaner production of biomass-based business.