Evaluation of Aging Effects in Polymer-Modified Bitumen Using Rheological, Chemical, and Morphological Analyses

The growing use of reclaimed asphalt pavement (RAP) in sustainable pavement construction raises important challenges related to the presence and activity of polymers in aged binders. In particular, the long-term performance of mixtures depends on whether polymer-modified binders in RAP retain their functionality after aging. This study investigates the evolution of styrene–butadiene–styrene (SBS) modified binders during aging, with comparisons to a RAP binder and an unmodified binder. The SBS binders were subjected to laboratory aging, and their response was evaluated using a combination of rheological, chemical, and morphological analyses. Dynamic Shear Rheometry (DSR) assessed changes in dynamic modulus, phase angle, and creep-recovery behavior, while Fourier Transform Infrared Spectroscopy (FTIR) provided insights into chemical modifications in the polymer–bitumen matrix. Fluorescence Microscopy (FM) enabled quantitative evaluation of the polymer network, including particle density, size distribution, and morphology. The results demonstrate that aging causes significant restructuring in PMBs, as evidenced by reduced polymer peak magnitudes in FTIR, disintegration of the polymer network observed in FM, and diminished polymer network activity in the phase angle master curve.