Performance Degradation during Elevated Storage Temperature of SBS-Modified Binders and Asphalt Mixes: Impact of SBS Molecular Structure

Styrene-butadiene-styrene-modified binders (SBS-MBs) are susceptible to property erosion even in the absence of air at elevated storage temperatures. The current study focused on monitoring the properties of SBS-MBs prepared using four different types of polymers: linear SBS (L-SBS), branched SBS (B-SBS), high vinyl SBS (HV-SBS), and diblock SBS (DB-SB). The four modified binders were stored at 180°C and 150°C for 14 days. The result shows significant property deterioration in L-SBS and B-SBS polymer-modified binders during storage at 180°C, while only marginal erosion in HV-SBS and DB-SB modified binders due to the higher vinyl content in the polymer structure. As the C═C bond in the butadiene segments is highly susceptible to thermal degradation, shifting the C═C bond to the side group protects the primary polymer chain from thermal scission during storage at 180°C. Asphalt mixes were prepared using unstored and stored modified binders, and their performance was scrutinized through Marshall stability, resilient modulus, water susceptibility, permanent deformation, and fatigue cracking behavior. The results showed that, similar to the deterioration in binder properties, asphalt mixes prepared with stored (7 days at 180°C) L-SBS and B-SBS modified binders exhibited a substantial drop in performance, while HV-SBS and DB-SB polymer-modified binders demonstrated only marginal property reduction (≈5%–10%). Moreover, irrespective of different SBS molecular structures, the performance properties of the binders were stable due to storage at 150°C. Therefore, in actual practice, if an SBS polymer with a vinyl content ≥30% is used, no significant deterioration in binder properties due to thermal degradation should occur when stored for 7 days at 180°C.