Applicability of time-temperature superposition for laboratory-aged neat and SBS-modified bitumens

The applicability of the time–temperature superposition principle (TTSP) can breakdown in the case of highly oxidized bitumens and polymer-modified bitumens (PMBs). This study investigates such problem in Styrene Butadiene Styrene (SBS) modified bitumens subjected to high oxidative laboratory-aging levels. The effects of aging were investigated by gel permeation chromatography (GPC), fluorescence microscopy (FM), and linear viscoelastic rheological characterization. As expected, the GPC and FM showed, respectively, an increase in the heavy fractions of bitumen and the degradation of the polymer morphology. Both the phenomena affected the rheological response provided in the form of black diagrams and isochrones of the loss tangent. Neat bitumens demonstrated thermorheologically simple behavior with some very slight symptoms of TTSP breakdown only at very high levels of aging. On the other hand, the applicability of TTSP to PMBs depends on the polymer content and the aging level. Low-medium and medium–high polymer contents PMBs produce minor concerns for TTSP irrespective of the aging level. However, high polymer contents may induce a TTSP breakdown mainly in unaged PMBs with the degradation of the polymer backbone due to oxidative aging progressively restoring a thermorheological simple configuration.