Effect of Sawdust Content on Mechanical and Durability Performance of Expanded Polystyrene (EPS)-Based Lightweight Geopolymer Composites

This study explores the effect of sawdust incorporation on the mechanical and durability properties of expanded polystyrene (EPS)-based lightweight geopolymer composites (LGCs) cured under ambient conditions. The mixtures were formulated with 10% EPS (by volume) while varying sawdust content at 10%, 20%, and 30% as partial replacement for natural fine aggregates. Physical, mechanical, and durability characteristics were evaluated through workability, density, ultrasonic pulse velocity (UPV), compressive, splitting tensile, flexural, and impact strength, alongside sorptivity tests. Results indicated a progressive reduction in workability and density with increasing sawdust, with density decreasing from 2203.89 kg/m³ (SD0) to 1017.91 kg/m³ (SD30), confirming the lightweight potential of the composites. Compressive, tensile, and flexural strengths decreased significantly at higher sawdust levels due to its low stiffness, high porosity, and weak interfacial bonding with the geopolymer matrix. Nonetheless, the mix containing 20% sawdust exhibited improved impact resistance, reflecting enhanced energy absorption and ductility. Sorptivity increased from 0.88 to 1.30 mm/min⁰·⁵, suggesting higher permeability and moisture ingress at elevated replacement levels. A strong correlation (R² = 0.97) between UPV and compressive strength confirmed UPV as an effective non-destructive indicator of mechanical performance. Overall, limited substitution (≤ 15%) of sawdust is recommended for structural-grade LGCs, while higher contents may be appropriate for non-structural or insulation applications emphasizing sustainability and reduced self-weight.