Improvement of Problematic Soils with Biopolymer—An Environmentally Friendly Soil Stabilizer

Problematic soils with high compressibility and low shear strength are often treated with traditional chemical stabilizing additives such as cement and lime to improve their engineering properties. These additives are generally recognized as having less than ideal environmental impacts—in particular, the high quantity of greenhouse gases that are generally created during their production. With an increasing focus on the use of more environmentally friendly and sustainable materials in the built and natural environments, alternative eco-friendly additives to traditional chemical stabilizers have the potential to significantly change the field of soil improvement worldwide. The current study illustrates the viability of xanthan gum as an environmentally friendly stabilizer that can improve the engineering properties of both low- and high-swelling clays. Experimental mechanical tests were performed on both untreated and xanthan gum–stabilized montmorillonite and kaolinite clays at various curing times, including unconfined compression strength (UCS) tests, direct shear tests, and one-dimensional (1D) consolidation tests. Various microscopic techniques were also performed to characterize the microstructure of the stabilized soil matrix, including field emission scanning electron microscopy (FESEM) tests, Brunauer, Emmett, and Teller (N2-BET) surface area analysis tests, and particle size analysis (PSA) tests using a laser diffraction approach. From the results of the strength and compressibility testing, 1 and 1.5% xanthan gum contents were found to be optimum levels of additive use for the montmorillonite and kaolinite clays, respectively. The microstructural analysis tests performed indicated the formation of new cementitious products that result from chemical reactions between the xanthan gum and soil particles at the microlevel, which improved the soil structure by welding soil particles together and filling the pore space in the soil matrix. Significant engineering property improvement was observed during the first 28 days of curing; this improvement corresponded to significant changes in the soil’s microstructure that occurred over the same period of time.