Performance Characteristics and Rheological Behavior of RAP Binder Containing Nanoclay: Laboratory Evaluation, Statistical Analysis, and Multiobjective Optimization

This study evaluates the rutting resistance, fatigue performance, and rheological behavior of nanoclay modified reclaimed asphalt pavement (RAP) binder from laboratory, statistical, and optimization perspectives. The research utilized 3% and 6% nanoclay, along with 20%, 40%, and 60% artificial RAP binder, combined with a soft binder derived from a vacuum bottom with a performance grade (PG) grade of PG52-28. High-temperature grading, temperature sweep, and multiple stress creep recovery (MSCR) tests were conducted to assess the creep resistance of the binders. Additionally, bending beam rheometer (BBR) and linear amplitude sweep (LAS) tests were performed to evaluate cracking resistance at low and intermediate temperatures. The results from the temperature sweep and MSCR tests indicated that nanoclay significantly improved temperature sensitivity and reduced the rutting rate in RAP binder samples, likely due to its high thermal stability modulus and the development of a more stable structure with binder functional groups. The interaction between clay particles and binder functional groups, along with the stress transfer from the bituminous matrix to the nanoparticles, enhanced the fatigue resistance and high-temperature performance of the modified binders compared to those of other samples. However, the low-temperature performance of the binders was somewhat compromised by the addition of nanoclay and RAP binder. Consequently, higher percentages of nanoclay are recommended for hot climates and heavy traffic conditions, whereas in colder regions, the content of clay nanoparticles and RAP should be limited. Finally, response surface methodology (RSM) analysis revealed that a combination of 53.7% RAP binder and 4.07% nanoclay represents an optimal balance of technical, economic, and environmental factors. For tropical regions with heavy and medium traffic, combinations R60/Nc4.81 and R60/Nc4.42 are suggested, respectively. In contrast, for cold areas with heavy and medium traffic, combinations R49.2/Nc1.61 and R43.1/Nc3.74 are recommended.