Microstructural Evaluation of Bagasse Ash Stabilized Sand-Bentonite Mixtures Using XRD SEM, and EDX Techniques

The microstructure of compacted sand–bentonite mixtures (SBMs) modified with sugarcane bagasse ash (SBA) was investigated to evaluate the mechanisms responsible for improving their suitability as sustainable landfill liner materials. SBA was incorporated at replacement levels of 0%, 2.5%, 5%, 7.5%, 10%, and 12.5%, while the mixtures were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and X-ray Diffraction (XRD). XRD analysis of the control sand revealed quartz, kaolinite, and metahalloysite as the dominant mineral phases, with minor quantities of gibbsite and vermiculite. The mixture containing 10% bentonite and 12.5% SBA exhibited new diffraction peaks and peak broadening, indicating the formation of calcium silicate hydrate (C–S–H) and confirming the occurrence of pozzolanic reactions. SEM images demonstrated a progressive transformation from the loose, porous granular structure of the untreated sand to a dense, compact, and well-cemented matrix in the SBA-modified mixtures. EDX analysis of the optimum mixture recorded oxygen (61.40 wt%), silicon (17.37 wt%), aluminum (6.52 wt%), and iron (6.42 wt%), confirming the development of a silica–alumina-rich cementitious matrix. These microstructural modifications enhanced particle bonding, reduced pore spaces, and improved contaminant retention capacity. The findings demonstrate that SBA effectively induces pozzolanic reactions and pore refinement, making SBA-modified SBMs a sustainable and environmentally friendly material for engineered landfill liner systems.