Evaluating the Intermediate Temperature Properties of SB Modified Asphalt Binders: Influence of SB Copolymer Structure

Asphalt pavements are prone to fatigue cracking at intermediate service temperatures (0–30 °C). This study evaluates the impact of styrene–butadiene (SB) copolymer structure (linear, branched, high vinyl, and diblock) on the intermediate temperature rheological properties of the SB modified binders (SB-MBs). Temperature sweep (0–80 °C) and frequency sweep at 15 °C (100–0.1 rad/s) were performed in the linear viscoelastic region (LVE). Asphalt mixes were prepared using SB-MBs with different SB copolymers, and their fatigue performance at 15 °C was determined. The result illustrates that the structure of the SB copolymer significantly affects the elevated temperature (145–170 °C) and upper service temperature (60 °C) rheological properties of the SB-MBs. Radial branches, triblock architecture, and higher molecular weight in branched SB copolymer result in the highest viscosity and performance properties at elevated and upper service temperatures. In contrast, the influence of SB structure on the rheological properties of modified binders diminishes below 25 °C due to the exponential increase in stiffness (| G *|) of the base binder. The rheological imprint of the SB copolymer structure on the rheological properties of SB-MBs in the LVE region becomes negligible owing to lower SB copolymer content (≤ 7 wt%) compared to the highly stiff base binder (≥ 93 wt%). Notably, a significant difference in the fatigue performance of the asphalt mixes was observed, with the branched SB copolymer resulting in the best-performing asphalt mix. The results demonstrate the inadequacy of LVE region rheological measurements in forecasting the fatigue performance of asphalt mixes.