Geotechnical engineering behaviors of xanthan gum treated kaolin-group minerals

Abstract

The development of artificial materials, such as cement, has contributed to several advancements in various fields. However, it has also resulted in an increase in adverse environmental effects, such as CO2 emissions and toxicity. In the 2016 Paris Agreement on Climate Change, an agreement was reached to prevent global warming caused by global gas emissions. Consequently, soil treatment and ground reinforcement using biopolymers are being actively studied as a response to the environmental impact of ground reinforcement materials.Biopolymers, a polysaccharide produced by the metabolism of living organisms, have shown potential for soil strengthening, permeability reduction, dust control, and erosion resistance. However, most of the research on biopolymer-based soil treatment has focused on coarse-grained soils that do not have an electric charge on the surface. Moreover, few studies have been conducted on the interaction between electrically charged clay and biopolymers and the resulting macroscopic geotechnical analysis. Thus, this study aimed to analyze the geotechnical behavior of kaolin-group clays, a type of representative clay mineral, and xanthan gum biopolymer, one of the most widely used biopolymers in several industries, based on microscale interaction analysis.At the microscale, in situ liquid electron microscopy was used to assess the interaction between clay particles in an aqueous state. With an increase in salinity, the attraction force between the edge and face surfaces of the kaolin-group clays results in particle dispersion. Furthermore, the sedimentation velocity and sediment density increased due to particle aggregation induced by the xanthan gum treatment. Changes in the kaolinite fabrics induced by xanthan gum were analyzed using X-ray diffraction and environmental scanning electron microscopy. The negatively charged xanthan gum interacted with the positively charged edge surface of kaolin-group clays, resulting in a change in the alignment of the fabric to face-to-face. With respect to the content, the 0.5 % xanthan gum-to-clay ratio in mass was found to be most efficient for kaolinite-clay interactions. In addition, the viscosity of xanthan gum hydrogel and the interaction between kaolinite and xanthan gum increased the optimal moisture content and swelling characteristics, thereby reducing the maximum dry unit weight of kaolinite clays.The geotechnical properties, such as consolidation, undrained shear strength, and surface erosion resistance, of xanthan gum-treated kaolinites were assessed based on the investigation of microscale interactions among kaolinite, pore fluids, and xanthan gum. The experimental results showed that xanthan gum treatment slightly increased the compressibility of soils while drastically reducing the hydraulic conductivity and improving the undrained shear strength and erosion resistance of kaolinite. Furthermore, long-term erosion prediction was performed based on the results of EFA experiments, and an erosion depth within 1.0 m was predicted even after 10 years of xanthan gum treatment. It was confirmed that xanthan gum treatment could enhance construction efficiency by securing surface strength for the trafficability of construction equipment during dredging and reclamation. The results of this thesis can be used as a fundamental reference for analyzing the applicability of xanthan gum-treated kaolin-group minerals by analyzing microscale interactions to macroscale geotechnical behavior.