Effect of Long-Term Aging on Polymer Degradation and Fatigue Resistance of Hybrid Polymer-Modified Bitumen

Binder aging significantly affects the overall performance of asphalt pavements. For polymer-modified bitumen (PMB), this complex phenomenon is attributed to both polymer degradation and bitumen aging. This study aims to analyze whether the aging of hybrid PMB—combining styrene-butadiene-styrene (SBS) and recycled linear low-density polyethylene (RLLDPE) from waste plastic—is a result of bitumen aging, polymer degradation, or both aspects simultaneously. To further understand the aging process as a function of time, five different PMBs were subjected to long-term aging simulation using a pressure aging vessel (PAV) at three different durations (20, 40, and 60 h). SBS and RLLDPE (polymers only) were also aged under similar conditions, in order to isolate the polymer degradation from the bitumen aging. Tensile strength tests revealed that SBS is susceptible to polymer degradation and improves its elastic response as a result of aging. However, the tensile test results did not indicate whether RLLDPE underwent degradation. Results from the thermal analysis showed that RLLDPE did not significantly change the thermal events as the aging progressed. Hence, RLLDPE is assumed to have minimal degradation when subjected to long-term aging. Infrared spectroscopy results indicated that SBS underwent degradation, with aging promoting carbonyl formation, which is associated with bitumen hardening. Rheological results indicate that bitumen aging, due to thermal oxidation, is dominant compared to polymer degradation; as such, polymer degradation has minimal effects upon bitumen hardening.