Effect of Thermal Activation and Short-Term Aging on the Physical and Rheological Properties of Bauxite Residue Bitumen Mastics

The increasing accumulation of bauxite residue (red mud), a by-product of the alumina refining industry, presents environmental and disposal challenges. The utilization of bauxite residue as a filler in bitumen mastics provides a sustainable approach to reducing industrial waste while enhancing asphalt paving materials. This research investigates the influence of untreated and thermally activated bauxite residue on the physical and rheological properties of C600 bitumen mastics under unaged and short-term aged conditions. Bauxite residue was thermally activated at 350°C and 600°C before being incorporated into C600 bitumen at 10%, 20%, and 30% by weight of the binder to produce bitumen mastics. The mastics were subsequently subjected to short-term aging using the Thin Film Oven Test (TFOT). Untreated and thermally activated bauxite residue samples were characterized using Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) to evaluate changes in morphology and mineralogical phases resulting from thermal activation. The physical properties of the unaged and aged bitumen mastics were evaluated through penetration, softening point, and rotational viscosity tests. Rheological performance was characterized using a Dynamic Shear Rheometer (DSR) through temperature sweep testing, evaluating complex shear modulus (G*), phase angle (δ), and rutting parameter (G*/sinδ). In addition, Multiple Stress Creep Recovery (MSCR) testing evaluated non-recoverable creep compliance (Jnr) and percentage recovery (R%). Results indicate that bauxite residue incorporation improved stiffness and aging resistance, with penetration values reduced by 8–28% and softening points increased by 2–3% compared with the control binder. Increased rotational viscosity confirmed enhanced filler–binder interaction. Among the investigated mastics, the 30% bauxite residue treated at 600°C demonstrated the highest rutting resistance based on G*/sinδ results. These findings highlight the potential of thermally activated bauxite residue as a sustainable filler for bitumen mastics, promoting waste utilization and supporting circular economy principles in pavement engineering.