Performance and evaluation of lignin modified loess under freeze-thaw cycles

Abstract

[Objective] Focusing on loess from the Xining region of Qinghai, the mechanical properties and micro-mechanisms of lignin-modified loess under freeze-thaw cycles are investigated. [Methods] Freeze-thaw cycle tests are conducted on ligninmodified soil under closed system conditions. Basic physical property tests, unconfined compressive strength tests, and thermal tests are performed to comprehensively evaluate the reinforcement effects of calcium lignosulfonate(CL), sodium lignosulfonate(SL), and unsulfonated lignin(SFL) on loess. Scanning electron microscopy and X-ray diffraction are used to analyze the soil structure and composition. [Results] With the increase in freeze-thaw cycles, the strength of the soils at the same dosage decreases in the following order: CL-modified soil > SFL-modified soil > SL-modified soil. The thermal conductivity decreases in the order of SFL-modified soil > CL-modified soil > SL-modified soil. SFL-modified soil exhibits the lowest pH value and the best conductivity. [Conclusion] The result indicate that the addition of lignin effectively enhances the strength and thermal insulation capacity of loess while reducing its pH value. SFL-modified soil demonstrates significant advantages, as the C = O double bonds present in SFL contribute to lower pH values and higher conductivity in the stabilized soil. The thermal insulation performance benefits from the high quartz content. Under freeze-thaw cycles, both CL and SFL-modified soils enhance frost resistance and structural stability by promoting the formation of calcium and magnesium cementation between soil particles, thereby mitigating the negative impacts of frost heave on the mechanical properties of the soil. Furthermore, considering the significant performance improvements and economic benefits of SFL, it is prioritized as the material for loess improvement in frozen soil regions. The research findings provide a theoretical basis and scientific reference for loess improvement efforts in Northwest China.

Keywords

freeze-thaw cycle / lignin / improving loess / mechanical properties / pH value / microscopic mechanism / infuencing factors