Compressive and flexural properties of engineered geopolymer composites incorporating dune sands

The integration of dune sand (DS) into engineered geopolymer composites (EGCs) has been shown to enhance their mechanical properties while simultaneously reducing dependence on ultrafine silica sand (SS), thereby contributing to cost-effective production. The study analyzes the effects of DS replacement ratios on EGC compressive and flexural properties across varying NaOH concentrations. Microstructural analysis, conducted using scanning electron microscopy (SEM), provides insights into the mechanisms underlying these improvements. Incorporating DS significantly boosts compressive and flexural strengths as well as toughness. The improvements stem from DS's pozzolanic activation at optimal NaOH levels, fostering secondary hydration and densifying the matrix. Maximum performance is recorded at 20 % NaOH, where DS addition enhances compressive strength by 18.18 %, flexural strength by 35.19 %, and midspan deflection to 105.27 mm. DS improves the fiber-matrix bond, enabling multiple cracking and strain-hardening. This enhanced fiber-matrix interaction contributes to superior energy absorption and improved ductility. To further characterize the mechanical behavior of EGCs, a refined stress-strain model is proposed, offering an accurate representation of both pre-peak and post-peak responses under uniaxial compression.