Low-Temperature and Microscopic Properties of Warm-Mix Recycled Styrene–Butadiene–Styrene-Modified Asphalt Binder

In this study, the warm-mix regeneration mechanism of an asphalt binder modified with styrene–butadiene–styrene (SBS) copolymers under simulated complex aging conditions, along with the performance of the recycled binder, were investigated. Bending beam rheometer tests were conducted to assess the low-temperature properties of the asphalt binder, and Fourier transform infrared spectroscopy and atomic force microscopy were employed for mechanistic analysis. The asphalt binder with the same degree of aging and warm-mix recycled binder recovered their low-temperature performance indicators and microscopic morphologies more efficiently than the hot-mix recycled binder. The addition of the regenerant and warm-mix agents to aged and original binders was a physical blending process that did not produce new functional groups. The regenerant was critical in adjusting the component proportions, whereas the warm-mix agent dispersed asphaltene clusters. However, neither additive restored the original molecular structure of SBS. An exponential function model was utilized to quantitatively characterize the relationship between the nanoscale microstructural properties and macroscopic rheological performance of the recycled binder. Furthermore, the butadiene index confirmed that the aged SBS-modified asphalt binder did not recover and that the performance of the recycled binder was inferior to that of the original binder.