Effects of Long-Term Field Aging and Secondary Aging during Hot In-Place Recycling on Rheological, Chemical, and Mechanical Properties of SBS-Modified Asphalt

Hot in-place recycling (HIR) offers a technically and economically viable approach for the rehabilitation and reconstruction of asphalt pavements. However, a knowledge gap persists in understanding the aging mechanisms and behavior of styrene-butadiene-styrene (SBS)-modified asphalt during the HIR process compared with field aging, limiting its widespread application in SBS-modified asphalt pavements. This study aims to investigate the effects of long-term field aging and secondary aging during HIR on the rheological, chemical, and mechanical properties of SBS-modified asphalt. A comprehensive set of analyses, including elemental analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), dynamic shear rheometer (DSR), and bending beam rheometer (BBR), were performed on asphalt samples from a HIR project. The results indicate that SBS-modified asphalt undergoes significant molecular changes during the HIR process, including oxidation of the base asphalt and chain scission of the SBS polymer, with more pronounced effects than those observed in long-term field aging for nine years. Long-term field aging leads to considerable reductions in elasticity due to polymer network degradation, decreased resistance to permanent deformation, and diminished low-temperature performance. When this long-term aged binder is subjected to HIR, secondary aging exacerbates the aging process, marked by further stiffness increases by 67% and additional polymer network degradation. Additionally, the study reveals that SBS degradation becomes less significant, and base asphalt hardening predominates in HIR process compared with long-term field aging. It is therefore recommended to optimize heating strategies during HIR to minimize secondary aging and preserve the performance of recycled asphalt pavements.