Improving the behavior of eco-friendly HMA containing high percentage of RAP with the Nano-CaO modified bitumen

The increasing traffic volume and vehicle load, combined with the impacts of climate change, have intensified common types of pavement distress such as fatigue cracking, moisture damage, and rutting in Hot Mix Asphalt (HMA). In this study, the use of reclaimed asphalt pavement (RAP) was investigated as a sustainable approach to reduce HMA production costs while minimizing environmental impact and promoting sustainable development. To enhance the performance of RAP-based mixtures, Nano-Calcium Oxide (CaO) was incorporated into HMA containing 50% RAP at three different dosages: 0.5%, 1%, and 2% by weight of bitumen. A series of laboratory tests were conducted, including fatigue tests at 5 °C and 25 °C, moisture susceptibility tests at 25 °C, and wheel tracking tests at 40 °C and 60 °C. The results indicated that incorporating 50% RAP without Nano-CaO led to an approximately 80% reduction in fatigue life, a 20% reduction in moisture resistance (TSR), and a 60-65% increase in rutting compared to the control mix without RAP. However, the inclusion of 1% Nano-CaO in the 50% RAP mixture significantly improved performance, showing an approximately 94% increase in fatigue life, a 43% improvement in moisture resistance, and a 50-55% reduction in rutting compared to the RAP mixture without Nano-CaO. When compared to the control mixture (without RAP or Nano-CaO), the modified mix containing 50% RAP and 1% Nano-CaO exhibited a 15-20% improvement in fatigue life, an 19% increase in moisture resistance, and a 20-25% reduction in rutting resistance. These findings suggest that the addition of 1% Nano-CaO to HMA with 50% RAP can effectively compensate for performance losses while reducing the demand for new aggregates by approximately 50% and the need for virgin bitumen by about 2.9%, contributing both to performance enhancement and material sustainability.