Rheological analysis and optimisation of Wanol-based polyurethane and SBS hybrid modified asphalt binders

High-temperature stability and rutting resistance of asphalt binders are important challenges especially under heavy traffic and long-term loading. Polyurethane-based modifiers are promising thanks to their reactivity and network-forming ability, but their hybrid use with styrene-butadiene-styrene (SBS) has not been sufficiently investigated. In the present study, the rheological behavior of modified asphalt binders was studied with Wanol-based polyurethane modifier alone and in combination with SBS. Frequency sweep tests were carried out with a dynamic shear rheometer. The experimental results were evaluated by master curve construction, rheological modeling, and response surface optimization. Results showed that polyurethane modification increased binder stiffness and resistance to low frequency deformation. The hybrid binder with 2% SBS and 6% Wanol-based polyurethane (2S6W) showed the best overall performance, the highest complex modulus, the lowest crossover frequency of 16.81 rad/s and about 20% higher rheological index than the neat binder. The zero-shear viscosity of the blend at 40 °C was 1.66 × 106 Pa·s indicating the improved rutting resistance. The RSM analysis identified a model-predicted optimum formulation of 3.43% SBS and 3.73% Wanol for rutting performance within the investigated design space.