Durability and Reuse Potential of Biopolymer-Stabilized Sands under Wetting–Drying Cycles

Biopolymer-amended soils have shown promise as sustainable construction materials; however, their durability and recyclability under cyclic moisture exposure, particularly in relation to soil gradation effects, remain poorly understood. This study presents, an integrated, multiscale investigation of xanthan gum (XG)–treated sands with differing particle-size distributions: less-uniform sand (Sand Type 1, ST1) and a uniform sand (Sand Type 2,ST2), amended with 0.5, 1, and 2% XG by dry mass. Mechanical performance was evaluated through unconfined compression and oedometer testing to quantify strength, stiffness, compressibility, durability, and reuse potential under wetting–drying cycles, while micro-computed tomography (μCT) was employed to directly link pore-scale evolution to macroscopic response. Unlike prior studies that primarily focus on initial strength, this work simultaneously evaluates durability degradation, recyclability through mechanical reconstitution, and microstructural mechanisms governing performance loss. All mixtures exhibited strength reduction with wetting-drying cycles; however, ST1 treated with 1% XG retained the highest fraction of its initial strength (≈40 % after two cycles), reflecting the combined benefits of moderate biopolymer dosage and enhanced particle interlocking in the less-uniform sand.. After recycling, ST1 specimens converged to similar strengths regardless of initial XG content, indicating that mechanical reprocessing disrupts the gradation-dependent bonding advantages. In contrast, ST2 specimens with 1% XG retained comparatively higher post-recycling stiffness, suggesting that the more uniform particle-size distribution promotes more homogeneous deformation and improved preservation of biopolymer bonds at moderate dosage. μCT analysis revealed progressive pore coarsening and solid-phase loss with increasing XG content, consistent with swelling–shrinkage-induced bond disruption during moisture cycling. Overall, results indicate a clear gradation–dosage trade-off: less-uniform sands achieve higher initial strength, while uniform sands exhibit improved durability and recyclability under cyclic moisture exposure. • Uniform biopolymer-amedned sand exhibits greater wetting–drying resistance than less-uniform sand • Less-uniform biopolymer-amended sand attains higher initial strength and stiffness • Optimum durability and strength occur at 1 % xanthan gum • Recycled uniform sand retains strength; graded sand shows greater losses • μCT reveals pore enlargement and solid-phase reduction with higher XG content