A Comparative Study of the Static and Dynamic Mechanical Properties of High-Loaded Red Mud–Epoxy Resin Composites Prepared with Various Mixing Methods

Red mud (RM) poses a critical environmental problem because its high alkalinity restricts direct utilisation and landfilling remains the dominant disposal method. In this study, composites with a high RM concentration (40 wt.%) in an epoxy resin matrix were prepared using three fabrication techniques: mechanical stirring with an overhead mixer (OM) and hand mixing (HM), both followed by degassing, and vibration-assisted vacuum mixing (VM). Samples fabricated with VM exhibited improved structural properties and enhanced mechanical performance, with tensile and compressive strengths of 17.3 MPa and 92.5 MPa, respectively, approximately twice those of samples prepared with OM or HM. Porosity measurements and microstructural analysis revealed that VM composites had the lowest pore volume and the most uniform filler distribution. Both pore content and the presence of agglomerates influence crack propagation and thereby reduce mechanical properties. Dynamic mechanical analysis (DMA) results showed higher storage modulus (3.41 GPa) and loss modulus (319 MPa) for VM composites compared to samples mixed with OM (1.26 GPa and 120 MPa). Water ageing demonstrated that VM composites retained the highest moduli even after 4 weeks in water, making them a preferred material when improved impact resistance is required.