SHEAR STRENGTH AND PERMEABILITY OF BENTONITE–CHITOSAN COMPOSITES WITH NATURALLY GRADED SANDS

Abstract

The increasing need for sustainable materials in environmental engineering has driven research on eco-friendly clay liners. This study aimed to optimize the shear strength and permeability of chitosan–bentonite–sand composites by investigating the effects of sand grain distribution. Sands from various quarries with distinct gradations were used to explore composite performance under realistic conditions. Standard Proctor compaction determined the maximum dry density (1.64 g/cm³) and optimum moisture content. Direct shear tests (ASTM D3080) showed cohesion values of 9.77–18.64 kPa and internal friction angles of 26.37°–30.36°, demonstrating significant mechanical stability comparable to commercial clay liners. Characterization analyses (FTIR, XRD, SEM, and TGA) confirmed chitosan integration into the bentonite matrix, revealing chemical interactions, partial intercalation, morphological modifications enhancing cohesion, and improved thermal stability. Permeability values under standard compaction ranged from 5.7 × 10⁻⁸ cm/s to 6.9 × 10⁻⁸ cm/s, meeting regulatory limits. However, at 90% of MDD, permeability exceeded 1 × 10⁻⁷ cm/s for some samples, indicating sensitivity to compaction effort and grain distribution. Sands with well-graded distributions, particularly from Sungai Ulin and Barito River, exhibited higher shear strength, whereas those with poorer gradation had reduced internal friction angles. These results highlight the relationship between grain distribution and mechanical properties, emphasizing the need for optimized compaction to maintain both shear strength and permeability within acceptable limits.