Synergistic enhancement of the mechanical properties and microstructural mechanisms of earthen building materials by xanthan gum and jute fiber

Earthen construction materials offer a sustainable alternative to cement yet are limited by low strength and brittle failure. This study proposes a fully bio-based stabilization strategy using xanthan gum (XG) at 0.0–3.0% and jute fiber (JF) at 0.00–1.00% to enhance the mechanical performance of poorly graded sand (SP) as a representative granular earthen material. An integrated experimental-numerical framework was established, combining unconfined compressive strength (UCS) tests, particle image velocimetry (PIV) for full-field displacement monitoring, and discrete element method (DEM) simulations for internal force-chain analysis, to systematically investigate the combined reinforcement effects. Results demonstrate that the optimal combination of 1.0% XG and 1.0% JF increases UCS by nearly eightfold (from 86.92 kPa to 694.94 kPa) and transitions the failure pattern from brittle strain-softening to ductile strain-hardening. The PIV-DEM cross-validation reveals the underlying synergistic mechanism: XG enhances inter-particle cohesion and increases force-chain density from approximately 24.5 × 10 ³ to 27.5 × 10 ³ , while JF suppresses strain localization and reduces post-peak strength decay from 12.2% to 5.5%, collectively transforming localized force-chain buckling into distributed network restructuring that inhibits microcrack propagation and achieves more uniform energy dissipation. This integrated quantitative approach elucidates the coupled effects of cohesive bonding and fiber bridging, establishing XG-JF as an effective and sustainable stabilizer for poorly graded sand and providing a diagnostic framework for future low-carbon building practices involving similar sandy soils.