Chemo-morphological evaluation of the blending behaviour of PMB and polymer-modified RAP binder

Polymer-modified reclaimed asphalt pavement (PM-RAP) is increasingly available for recycling, but the complex ageing and degradation of styrene-butadiene-styrene (SBS)-modified binders hinder its effective reuse in surface layers. This paper aims to understand the chemo-morphological blending behaviour between aged PM-RAP binders and fresh polymer-modified bitumen (PMB) at recycling ratios of 30% and 60%. Three PMBs from different geographical locations were combined with PM-RAP binders originating from the same respective regions. In total, three PMBs and three corresponding PM-RAP sources were used. Chemical characterisation was performed using Fourier-Transform Infrared (FTIR) spectroscopy, SARA fractionation, and FTIR analysis of the individual fractions. Morphological analysis was carried out using fluorescence microscopy. Results show that the addition of PM-RAP binder increases the ageing index and alters SBS-related signals depending on the RAP source. SARA analysis revealed a shift toward higher resin and asphaltene content with increasing PM-RAP content, while FTIR of the fractions indicated that a majority of the SBS remains in the n-heptane-insoluble phase, together with the asphaltenes. Blending occurred primarily through physical mixing, and strong agreement between experimental and calculated blend compositions (R ² > 0.9 relative to the X = Y parity line) suggests potential for predictive recycling. Fluorescence microscopy confirmed morphological changes reflected by a reduction in fluorescence intensity and polymer domain size upon increased PM-RAP binder percentages, highlighting limitations of chemical analysis alone. These findings provide new insights into the interaction mechanisms between aged and virgin SBS-modified binders and act as a foundation for more targeted recycling strategies.