Effects of the Combined Incorporation of ZnO and TiO2 Nanoparticles on the Mechanical, Rheological, Thermal, and Healing Properties of a Dense Polymeric Asphalt Mixture

This study evaluated the combined incorporation of zinc oxide (ZnO) and titanium dioxide (TiO₂) nanoparticles into a styrene-butadiene-styrene (SBS) copolymer-modified asphalt binder, aiming to increase thermal conductivity and healing potential while maintaining rheological performance. Nanocomposites containing ZnO + TiO₂ (50/50 wt.%) were produced at dosages of 2-12 wt.% and subjected to the Rolling Thin Film Oven Test (RTFOT), thermal conductivity measurements, viscosity testing, and rheological characterization. A dense-graded asphalt mixture with the optimized dosage was evaluated through wheel-tracking, four-point bending fatigue and healing, and internal heating rate assessment under microwave radiation. The integrated results indicated 8.5 wt.% as the optimal dosage, providing a 106.3% increase in thermal conductivity and improving the high-temperature performance grade (PGH) from 76-XX to 82-XX. Non-recoverable creep compliance (Jnr) decreased by 21.1%, and viscosity at 135 °C increased by 41.8%, remaining below 3.0 Pa·s. In the asphalt mixture, healing capacity increased by 50.7%, and the internal heating rate by 50.0%, while the wheel-tracking rut depth decreased by 13.3%. These findings demonstrate that 8.5 wt.% ZnO + TiO₂ simultaneously enhances heat conduction, healing efficiency, and resistance to permanent deformation, offering a promising solution for pavements subjected to high temperatures and heavy traffic.