Physicochemical Interaction of Natural Organic Biopolymers with Expansive Clay: A Sustainable Material Approach

Expansive clayey soils, predominantly composed of montmorillonite minerals, pose significant geotechnical challenges owing to their high swelling potential and poor load-bearing characteristics.The utilization of chemical stabilizers such as lime and cement, while effective, raises environmental and sustainability concerns.This study investigates the physicochemical interaction mechanisms between two naturally derived polysaccharide biopolymersxanthan gum and guar gum-and expansive clay at dosage levels of 0.5%, 1%, 1.5%, and 2% by dry weight of soil.The untreated soil exhibited a Liquid Limit (LL) of 68%, Plasticity Index (PI) of 36%, Free Swell Index (FSI) of 92%, Unconfined Compressive Strength (UCS) of 165 kPa, and soaked California Bearing Ratio (CBR) of 2.8%.Treatment with 1.5% xanthan gum yielded the most favorable outcomes, reducing LL to 58%, PI to 22%, and FSI to 40%, while elevating UCS to 480 kPa and CBR to 8.5%.Guar gum demonstrated comparatively moderate enhancement, achieving peak UCS of 420 kPa and CBR of 7.2%.Physicochemical characterization via Fourier Transform Infrared Spectroscopy (FTIR) confirmed hydrogen bonding between the hydroxyl (-OH) groups of the polysaccharide chains and the clay mineral surface, evidenced by a shift in the O-H stretching vibration from 3420 cm⁻¹ to 3385 cm⁻¹.Scanning Electron Microscopy (SEM) revealed a transition from dispersed flaky clay particles to a cohesive, aggregated matrix following biopolymer treatment.The interdisciplinary findings demonstrate that xanthan gum, at an optimal dosage of 1.5%, represents a viable, biodegradable, and low-carbon substitute for conventional chemical stabilizers in expansive soil treatment.