To enhance the anti-ageing properties of asphalt binder, multiwalled carbon nanotubes (MWCNTs) and styrene-ethylene-butylene-styrene (SEBS) were used to create a composite-modified asphalt (CMA). The ageing resistance was assessed through rheological property changes, using a dynamic shear rheometer (DSR) for various tests. FTIR spectroscopy analyzed the ageing mechanism. The results showed that CMA exhibited significantly better rutting resistance than matrix and SBS asphalt. Although the fatigue life of CMA was lower than SBS asphalt, ist was still dramatically higher than matrix asphalt. MWCNTs reduced the low-temperature relaxation performance of unaged asphalt. Notably, CMA showed superior ageing resistance against both thermal oxygen and UV ageing, with decreases of about 30% and 28% in the UV ageing index and long-term ageing index, respectively, compared to matrix asphalt. The carbonyl and sulfoxide indices increased after ageing, with the composite containing 3% SEBS demonstrating optimal ageing resistance and road performance.
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