Public defence, Building Technology, MSc Yuxuan Sun

Title of the thesis: Performance-based multiple recycling of asphalt materials – A multiscale assessment across five aging-rejuvenation cycles

Thesis defender: Yuxuan Sun
Opponent: Prof. Zhanping You, Michigan Technological University
Custos: Prof. Weiwei Lin, Aalto University School of Engineering

High contents of reclaimed asphalt pavement (RAP) are increasingly used in asphalt paving to reduce the need for virgin materials and support circular road construction. However, when asphalt is recycled repeatedly, aging products continue to accumulate, and it remains unclear how many recycling cycles can be achieved before rejuvenation becomes insufficient and durability risks increase. This doctoral thesis studied asphalt materials containing 60% RAP and examined how asphalt binders and mixtures change during several aging-rejuvenation cycles. The aim was to compare the effectiveness of different rejuvenators, identify practical limits for repeated recycling, and evaluate durability under conditions relevant to Nordic road pavements.

The results showed that rejuvenator type had a strong influence on long-term performance. Bio-based rejuvenators provided more stable recovery over repeated cycles than the wax-based alternative. With optimized dosage, the 60% RAP binder system remained practically manageable through four recycling cycles, while the fifth cycle approached performance-related limits. Overall, three recycling cycles provided the most balanced response. The thesis also showed that repeated recycling cannot be evaluated only by binder stiffness or RAP content. Chemical, molecular, rheological, and microscale analyses revealed that early-cycle rejuvenation was more effective, whereas later cycles showed reduced recovery in material structure and cracking-related performance. At the mixture level, moisture durability showed a clear threshold, with acceptable performance in early cycles but clear deterioration at higher recycling levels.

These findings provide practical support for rejuvenator selection, dosage adjustment, and durability evaluation of high-RAP asphalt materials. The thesis concludes that repeated recycling of high-RAP asphalt is a promising approach for more sustainable road construction, but it should be guided by performance-based evaluation and clear recycling limits.

Key words: reclaimed asphalt pavement (RAP), multiple recycling, rejuvenation, multiscale characterization, dynamic water damage

Thesis available for public display 7 days prior to the defence at Aalto University's public display page. 

Contact information: yuxuan.sun@aalto.fi