Mechanical Strengthening and Microstructural Evolution of Bentonite–Chitosan Mixtures During Pre-Compaction Curing

Abstract

Bentonite–chitosan mixtures are promising clay–biopolymer composites for sustainable barrier applications; however, their response may depend on moisture conditioning before compaction. This study investigates mechanical strengthening and microstructural evolution during pre-compaction curing in a mixture containing 98% bentonite and 2% chitosan. The dry composite was moistened to 10% water content, sealed, and cured for 1, 7, 14, 28, and 60 days before static compaction to 16 kN/m³. Unconfined compression tests were performed on compacted specimens, while FTIR, XRD, and SEM were used to examine uncompacted cured mixtures. The highest strength and stiffness were obtained after 60 days, with unconfined compressive strength ( ) reaching approximately 310 kPa and the stiffness modulus reaching 2100–2200 kPa. FTIR and SEM results indicated changes in water-related bands, particle arrangement, and clay–biopolymer interaction, while XRD showed no major mineralogical transformation. These findings demonstrate that pre-compaction curing is an important preparation stage for improving bentonite–chitosan mixtures for compacted clay liner applications.