Abstract
This study investigates the microstructural transition and densification behavior of xanthan gum–modified soil using quantitative scanning electron microscopy (SEM) analysis. Soil specimens were prepared with 0%, 3%, 6%, and 9% xanthan gum content. SEM images were processed using image analysis techniques to determine the solid area fraction and characteristic particle size parameters. A densification index was introduced to quantify the ratio between solid and pore phases within the observed microstructure. The results reveal a non-monotonic structural evolution with increasing polymer content. The solid area fraction reached its maximum at 3%, indicating the compact particle arrangement. At 6%, a pronounced decrease in densification was observed, suggesting disruption of particle packing due to non-uniform polymer distribution. At 9%, partial recovery of structural continuity occurred, accompanied by evidence of polymer agglomeration and spatial heterogeneity. Based on quantitative metrics and microstructural observations, three structural stages were identified: discrete particle stage, bridged stage, and matrix-dominated stage. The findings demonstrate that xanthan gum dosage significantly influences soil microstructure in a nonlinear manner. This SEM-based approach provides a systematic framework for identifying microstructural transitions in biopolymer-modified soils.