Influence of SBS type and base bitumen composition on the chemical response of polymer modified bitumen to short-term overheating

The article examined how styrene-butadiene-styrene (SBS) copolymer type, polymer content, and base bitumen composition affect the chemical response, as assessed by FTIR spectroscopy, of polymer-modified bitumens (PMB) to short-term technological overheating. Two paving-grade bitumens, 160/220 and 50/70, differing in colloidal instability index, were modified with four commercial SBS copolymers at 3 and 8 wt.%. Part of each binder was additionally conditioned at 240°C for 1 h to simulate accidental overheating during production or storage. Binders were analysed by Fourier-transform infrared spectroscopy (FTIR), supported by thermogravimetric analysis (TGA) of neat SBS copolymers and differential scanning calorimetry (DSC) of non-overheated PMBs. The SBS index depended mainly on polymer content, but its response to overheating was strongly influenced by SBS type and base bitumen composition. TGA showed neat SBS copolymers did not undergo major bulk decomposition at 240°C under nitrogen, while DSC on non-overheated PMBs showed strong effects of base bitumen composition on phase organization. Overall, PMB response to overheating is governed mainly by polymer-bitumen compatibility, SBS architecture, and phase structure, not by copolymer thermal decomposition.