Sustainable Modification of Bitumen Using Waste Toner and Lignin

Integrating waste materials into road infrastructure is essential for environmental sustainability and resource efficiency. This study addresses the modification of short-term-aged 50/70-penetration-grade bitumen using two sustainable additives: waste toner powder and lignin. Waste toner was added at weight percentages of 4%, 8%, 12%, and 16%, while lignin was added at 15% and 20%. Since these modifiers have individual uses, this study examines how they may strengthen the oxidized binder. It focuses on extending the lifespan of the mixture by combining industrial and bio-based polymers. The main aim was to delineate the impact of these modifiers on the physical consistency, low-temperature flexibility, and microstructural morphology of the binder. The results show that both modifiers increase binder stiffness by reducing penetration at all modification rates. The resins in the waste toner enhance the polymer matrix, and the lignin’s aromatic structure increases the elastic components, improving high-temperature stability. However, ductility tests showed a reduction in elongation capability, suggesting a brittle state at lower temperatures. Also, waste toner additive is identified as the ideal modifier for high-temperature applications. SEM analysis illuminated the mechanisms underlying these performance modifications. Both additives had homogeneous distribution and good bitumen matrix interfacial bonding at lower concentrations.