Microstructure and Reinforcement Mechanism of Lignin-Modified Loess

Abstract

To develop a new modification method with environmentally friendly and seismically resistant characteristics for saturated loess foundations, lignin extracted from paper industrial wastes was selected for mixing into the loess. Mixtures with different lignin contents were prepared under static pressure. A series of dynamic triaxial tests were performed by applying sine loads after the lignin-modified loess specimens were saturated and consolidated on the dynamic triaxial apparatus. The microstructural images and the mineral components of the modified loess with different lignin contents were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Based on the test results, the variation regularity of the dynamic residual deformation and the dynamic pore water pressure of the lignin-modified loess was analyzed. The microstructural characteristic parameters of the lignin-modified loess were extracted, and the relationship between these parameters and the lignin contents was obtained. Based on the dynamic triaxial test, the SEM, and the XRD results, the mechanical mechanism of the liquefaction resistance of the lignin-modified loess is discussed. The results show that lignin can significantly improve the resistance of cyclic shear deformation of the saturated loess and can effectively control the increase of the pore water pressure. When the lignin content was 4%, the liquefaction resistance of the lignin-modified loess was the most significant. Compared with the unsaturated compacted loess, the number of small and micropores in the lignin-modified loess increased significantly, and the apparent pore ratio decreased. Additionally, the arrangement sequence of pores deteriorated, the pore structure became more complex, and the pores were more compactly arranged. However, when the lignin content was higher than 4%, the microstructural characteristic parameters reflected a reduction in compactness of the lignin-modified loess. No other new minerals were formed in the lignin-modified loess except for a small amount of albite (NaAlSi3O8), which was generated by the ion exchange between the lignin and loess. Furthermore, the liquefaction resistance mechanism of the lignin-modified saturated loess mainly included the filling and cementation of the lignin, thinning of the electric double layer in the modified loess, reinforcement of the lignin fiber, adsorption of fine particles and water by the fiber, and ion exchange between the lignin and loess.