Sustainability in Ground Improvement: The Case of Xanthan Gum Biopolymer

Table of Contents

1. Frontmatter

2. Chapter 1. Unraveling the Challenges of Xanthan Gum Soil Stabilization

   Abdel-Mohsen O. Mohamed, Brendan C. O’Kelly, Amin Soltani

   Abstract

   Soil stabilization is a crucial aspect of civil engineering and construction projects, aimed at improving the engineering properties of soil materials. Xanthan gum (XG), a biopolymer derived from fermentation processes, has gained widespread attention as a potential soil-stabilizing agent due to its unique rheological properties. This chapter provides an overview of the traditional soil stabilization techniques, followed by outlining the potential benefits and main technical issues of employing XG as a soil-stabilizing agent. In addition, the chapter discusses the overall challenges and considerations associated with the utilization of XG for soil stabilization purposes, including its effectiveness, environmental impact, cost implications, and compatibility with different soil types. By examining these factors, engineers and researchers can make informed decisions regarding the application of XG in soil stabilization projects. The chapter concludes with an outline of the topics that are discussed in the later chapters of this book.

3. Chapter 2. Xanthan Gum Production and Structure

   Abdel-Mohsen O. Mohamed, Brendan C. O’Kelly, Amin Soltani

   Abstract

   In nature, microbial polysaccharides are essential components of biofilms, which are the main support form of life on earth (Flemming et al. in Nat Rev Microbiol 14:563–575, 2016), and microorganisms’ lifestyle (Penesyan et al. in NPJ Biofilms Microbiomes 5:34, 2019). These biofilms contain microbial cells that are fixed within a self-produced matrix of extracellular polymeric substances, which are composed of polysaccharides, proteins, lipids, and nucleic acids (Powell et al. in NPJ Biofilms Microbiomes 29:13, 2018). The relative composition and molecular structure of these polymeric substances vary depending on the producing microorganism and the environmental conditions (e.g., fluid chemistry, pressure, and temperature). Therefore, depending on the potential industrial application, different industrial fermentation processes can be adopted.

4. Chapter 3. Rheology of Xanthan Gum Aqueous Solution

   Abdel-Mohsen O. Mohamed, Brendan C. O’Kelly, Amin Soltani

   Abstract

   Xanthan Gum (XG) is a polysaccharide that is produced by the bacterium Xanthomonas campestris through fermentation, as discussed in Chap. 2. The practical use of XG in various industries, including food processing, pharmaceuticals, cosmetics, agriculture, and engineering, is mainly a result of its ability to induce high viscosity at low polymer concentrations in aqueous environments. It can modify the rheological behavior of fluids (i.e., the flow and deformation of XG suspension under applied stresses) by acting as a thickener and stabilizer. For the former, XG is a highly effective thickening agent. It forms a network of long-chain polymers that entrap water and increase the viscosity of the fluid. As elaborated later, the thickening properties of XG are dependent on various factors, such as XG concentration, the solution pH and temperature, shear rate, and the presence of salts and/or other chemical additives. Moreover, the rheological behavior of XG solutions is pseudoplastic, which means that the viscosity decreases with increasing shear rate. Additionally, XG is an effective stabilizer, particularly in emulsions. It can stabilize oil-in-water emulsions by forming a protective layer around the oil droplets, preventing them from coalescing. XG can also stabilize suspensions by preventing settling and maintaining a uniform distribution of particles.

5. Chapter 4. Xanthan Gum–Soil Interactions

   Abdel-Mohsen O. Mohamed, Brendan C. O’Kelly, Amin Soltani

   Abstract

   To the civil engineer, soil is any uncemented or weakly cemented accumulation of mineral grains formed by physical and/or chemical weathering of rocks, with the void spaces between the solids containing water (pore water) and/or air. Chemical weathering causes changes in mineral form of the parent rock leading to the formation of groups of colloidal crystalline particles (i.e., < 2-μm sized particles according to their civil engineering classification) known as clay minerals. Basic structural units of most clay minerals are a silicon–oxygen tetrahedron and an aluminum–hydroxyl octahedron, with the valency imbalances in both units resulting in net negative charges.

6. Chapter 5. Stability of Xanthan Gum–Soil Cohesive Networks

   Abdel-Mohsen O. Mohamed, Brendan C. O’Kelly, Amin Soltani

   Abstract

   As discussed in Chaps. 2 and 3, Xanthan Gum (XG) is a high-molecular-weight polysaccharide consisting of a repeating pentasaccharide unit, composed of glucose, mannose, and glucuronic acids, and which are linked by β(1,4)-glycosidic bonds. The anionic carboxyl and hydroxyl groups on the XG molecule make it highly hydrophilic, and it can interact with various compounds, including water and metal ions. XG has excellent water-holding capacity, thickening ability and stabilizing properties, making it widely used in various applications, including agriculture, food processing, pharmaceutical, environmental and geotechnical engineering, and petroleum industries. In recent years, XG has also been increasingly investigated as a soil stabilizer to improve the physical and mechanical properties of soils.

7. Chapter 6. Strength and Compressibility of Xanthan Gum-Treated Soils

   Abdel-Mohsen O. Mohamed, Brendan C. O’Kelly, Amin Soltani

   Abstract

   Xanthan gum (XG) is a high molecular weight anionic polysaccharide produced by the bacterium Xanthomonas campestris. Because of its unique rheological properties (as discussed in Chap. 3), XG is widely employed as a thickening, stabilizing, and gelling agent for a variety of industrial applications, including, food processing, cosmetics, pharmaceuticals, and oil and gas. Recently, XG has been explored as a chemical soil-stabilizing agent, owing to its ability to form a three-dimensional reinforcement-type network within soils for enhancing their geo-mechanical properties.

8. Chapter 7. Xanthan Gum (XG) Sorption and Hydraulic Conductivity of XG-Treated Soils

   Abdel-Mohsen O. Mohamed, Brendan C. O’Kelly, Amin Soltani

   Abstract

   As discussed in Chaps. 4, 5, and 6, properties of xanthan gum (XG), soil, and soil solution influence adsorption and aggregative success of XG–soil structure. Molecular weight, size, conformation and surface charge are all aspects of the XG that affect its sorption onto the soil particles. XG interacts more with the clay fraction of soils; as such, the particle surface area, type and amount of clay, soil structure, and pore-size distribution are soil attributes that influence the nature and level of XG sorption onto clay particle surfaces. The pH level, ionic strength, and electrolyte concentration of the soil solution also influence the sorption of XG onto clays.