Influence of residual SB di-block in SBS on the thermo–oxidative aging behaviors of SBS and SBS modified asphalt

In this study, four types of SBS copolymers with different residual SB di-block content were selected and incorporated into base asphalt to prepare SBSMA. Aging samples of each group were prepared by Rolling Thin Film Oven Test (RTFOT) and Pressure Aging Vessel (PAV). The Gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR) were utilized to determine the molecular weight and analyze the chemical structure evolution of the SBS polymers and SBSMA, respectively. Besides, thermal stability and rheological properties of all asphalt binders pre and post aging were studied by Thermo gravimetric (TG) and Dynamic shear rheological (DSR), respectively. In GPC test, the Mn and Mw of SBS and the Mw of SBSMA showed a decreased trend after aging; whereas the trend of Mn of SBSMA was opposite to that of Mw. The reduction extent of molecular weight (∆T,Mn, ∆P,Mn, ∆T,Mw and ∆P,Mw) of SBS and SBSMA grew with the increase of residual SB content. As to FTIR tests of SBS and SBSMA, the CI, ∆T,IC=C and ∆P,IC=C exhibited an upward trend with the increasing residual SB content. These findings implied that the –C=C– bond in SBS broken and generated C=O bond during aging. In TG test, the T0 and TDTG max values of SBSMA decreased with the increase of residual SB content, which indicated that high residual SB in SBS reduced the thermal stability of SBSMA. The data in DSR illustrated that modified asphalt with lower residual SB content had higher (G*/sinδ) and (G*), indicating that low residual SB content had positive effect on the high temperature performance of asphalt. The result of MSCR showed the same conclusion. In addition, it was found that there was a strong correlation between the 1/(G*/sinδ), Jnr-3.2 kPa and 1/R3.2 kPa and the butadiene index reduction rate (ΔT,IC=C and ΔP,IC=C) under different aging conditions.