Physicochemical Rejuvenation of Aged Styrene-Butadiene-Styrene-Modified Bitumen through Joint Use of Polyurethane Prepolymer and Tall Oil for Maintaining High-Temperature Property

Conventional rejuvenation techniques, such as adding oil-based substances, are proved very effective to improve some properties of aged styrene-butadiene-styrene modified asphalt (SBSMA), including low-temperature cracking resistance and fatigue characteristic. However, its significant reduction of high-temperature properties needs to be closely focused on because it is related to the deformation resistance to rut. The major reason is that these rejuvenators play as viscosity-reducing agents to physically soften the aged SBSMA binder, whereas it does not work to repair the molecular structure and properties of aged SBS. Therefore, this study adopted polyurethane (PU) prepolymer as reactive chemical together with tall oil (TO) as common asphalt rejuvenator for the physicochemical rejuvenation of aged SBSMA. A series of tests including Fourier transform infrared (FTIR) spectra, softening point, viscosity, dynamic shear rheology (DSR), and multiple stress creep recovery (MSCR) were carried out to identify the above-mentioned issues. The results obtained showed that the chemical rejuvenation of PU contributes to fix the molecular structure of SBS degradation products in the aged binder, which is able to improve the high-temperature deformation resistance and elastic recovery of aged SBSMA binder. TO can help supplement partial loss of light components for a better workability of PU rejuvenated binder. Surprisingly, limited use of TO will not significantly decrease the elastic recovery of PU rejuvenated SBSMA at high temperature based on the physicochemical rejuvenation effects. The research achievements can address the worrying issues, especially the early-stage rutting deformation resistance, in terms of fresh rejuvenated SBSMA mixtures.