Reclaimed Lignin-Stabilized Silty Soil: Undrained Shear Strength, Atterberg Limits, and Microstructure Characteristics

Lignin is an organic industrial by-product, stockpiles of which are rapidly accumulating worldwide. A feasibility investigation was carried out with respect to the stabilization of silty soils using lignin. The fall cone test method was employed to determine the undrained shear strength (su) and Atterberg limits of the lignin-stabilized silty soil with 7days of curing. In addition, scanning electron microscopy (SEM) was conducted to qualitatively evaluate the changes in the microstructure of silty soil after treatment and better understand the mechanisms controlling the improvement in su of the stabilized silty soil. The study revealed that the su of silty soil increased with an increase in lignin content. This was mainly attributed to the bonding effect of lignin-based cementing materials, which creates the aggregation of soil particles and fills the pores between detached particles. The liquid limit (wL) increased remarkably with increasing lignin content and the maxium increment of 27% occurred at 12% lignin-stabilized soil. The chemical composition of added lignin had a considerable influence on the Atterberg limits of the stabilized silty soil. The su was found to exhibit good exponential decreasing correlation with the moisture content (w) as well as the liquidity index (IL). By comparing the su values with the empirical models in the literature, the new relationships among su, w, and liquidity index (IL) were finally proposed for estimating the su value of the lignin-stabilized soils. It is concluded that the application of reclaimed lignin as a silty soil stabilizer can be one of many viable answers to the development of environmentally friendly soil stabilizer and the profitability of industrial by-products.