Chemical and Morphological Evolution of Polymer Networks in Bitumen during Aging: Insights from FTIR and Fluorescence Microscopy

Modified binders are evaluated for rutting and fatigue resistance after short and long-term aging. While short-term aged tests such as the Multiple Stress Creep and Recovery (MSCR) test, can indicate polymer network integrity through parameters like percent recovery and Jnrdiff, the persistence of these networks after long-term aging remains unclear. This uncertainty is critical when reclaimed asphalt pavement (RAP) contains residual polymer-modified binders. Since conventional rheological tests cannot quantify polymer degradation, advanced techniques are required. In this study, an unmodified binder, three SBS-modified binders (with dosages of 3.5% and 6.5% both produced at the laboratory, and a commercial one), and three RAP binders were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) and Fluorescence Microscopy (FM). FTIR showed butadiene loss with aging and strong oxidation in RAP binders, while FM revealed dispersed domains (PMB-3.5%), crosslinked networks (PMB-6.5%), and degraded remnants in RAP. Together, FTIR and FM confirm the loss of functional polymer networks in RAP, highlighting the need for improved rejuvenation strategies.