Abstract

This study evaluated the effect of biochars derived from European hazelnut shells as modifiers of the antioxidant, physical, and rheological properties of asphalt binders used in road construction. Two types of biochar (BH) were produced via slow pyrolysis at 300 degrees C (BH1) and 550 degrees C (BH2) with a residence time of 1 h, and were incorporated into unaged, short-term aged (RTFO), and long-term aged (PAV) asphalt binders. Phenolic compounds of the BHs were identified by liquid chromatography, while their antioxidant effect on asphalt binders was assessed using spectroscopic analyses. Physical properties (rotational viscosity, penetration, softening point, Fraass breaking point) and rheological properties (rutting parameter G*/sin(delta), Rheological Ageing Index, multiple stress creep recovery (MSCR), fatigue parameter (G*center dot sin(delta), crossover temperature, and complex modulus |G*|) were measured in all ageing states. The results revealed that both BHs mitigated binder ageing, as evidenced by reductions in ageing indices and oxygenated structures. BH1's antioxidant effect was attributed to its phenolic compounds, whereas BH2's effect was attributed to its porous morphology, which facilitated the adsorption of volatiles. Physically, BH reduced viscosity by up to 16 % after PAV ageing, maintained penetration, and lowered the softening point, although Fraass breaking points increased due to particle stiffening. Rheologically, BH improved rutting resistance by up to 8 % during the early ageing stages. After PAV ageing, it mitigated stiffness gain, preserved viscoelastic behaviour, and reduced |G*| at low temperatures compared with the controls. Overall, recycled hazelnut shell BH enhanced the ageing resistance and thermal stability of bituminous binders through distinct mechanisms, offering a potentially viable option to extend the service life of road pavement materials.