Performance Evaluation of High-content RAP Asphalt Mixtures with Recycling Additives

The reuse of reclaimed asphalt pavement (RAP) is a key strategy to reduce the consumption of virgin materials and the environmental impact of road infrastructure. When RAP content becomes high, however, the stiff aged binder strongly influences mixture behavior and recycling agents are often needed to restore an adequate balance between stiffness, durability and workability. This thesis evaluates the effect of a liquid rejuvenating additive, referred to as Experimental Product (EP), on the performance of a dense-graded asphalt mixture containing about 40% RAP. Four mixtures were produced at an industrial asphalt plant and laid in an experimental field, differing only in the rejuvenator dosage with respect to the RAP binder: 0%, 3%, 4% and 5% (Mix_0%, Mix_3%, Mix_4% and Mix_5%). After several months of service under heavy traffic, cores were extracted for laboratory testing. The study combines in-situ functional measurements (skid resistance and macrotexture) with volumetric analyses (binder content, aggregate gradation, maximum and bulk density, air-void content) and mechanical tests on cores (indirect tensile strength at 25 °C, indirect tensile stiffness modulus at 20 °C and Hamburg Wheel Tracking in water at 50 °C). The results show that almost all mixtures guarantee adequate functional performance, while EP mainly affects volumetric and mechanical behavior. Increasing EP dosage generally increases soluble binder content and bulk density and reduces air-void content, especially for Mix_5%. At the same time, tensile strength, stiffness and rutting resistance decrease as EP dosage rises, with Mix_0% showing the best mechanical performance and Mix_5% the highest rut depths. Overall, moderate EP dosages (about 3–4% on RAP binder) may provide a compromise between improved compactability and acceptable mechanical properties, whereas higher dosages are not recommended under the investigated conditions.