Vital Role of Styrene-Butadiene-Styrene Concentration on the Property Evolution in Short-Term–Aged Styrene-Butadiene-Styrene–Modified Binders

ABSTRACT Asphalt binder aging and thermo-oxidative degradation of the styrene-butadiene-styrene (SBS) polymer molecules occur simultaneously during short-term aging of SBS-modified binders (SM-ABs). This study demonstrates that, irrespective of the base binder, the detrimental effect of short-term aging on the properties of SM-ABs is strongly dependent on the concentration of the SBS polymer in the binder. At low SBS concentrations (<3 wt.%), the SBS molecules fail to form an interconnected polymer network and are discretely dispersed within the binder. Hence, the partial degradation of the SBS macromolecules due to rolling thin film oven (RTFO) aging has only a marginal effect on the rheological properties of SM-ABs. On the contrary, at SBS concentrations above 3 wt.%, an interconnected SBS-rich network starts forming in the binder, and RTFO aging adversely affects this delicate interconnected SBS-rich network. Hence, between 3 and 5 wt.% of SBS dosage, the partial degradation of SBS molecules results in a steep decline in the performance properties of SM-ABs. Commercially, the majority of the SM-ABs are prepared with SBS content between 3 and 5 wt.%. The hardening of the base binder plays a negligible role in this concentration range. At SBS content > 5 wt.%, due to the presence of excess polymer and a stronger interconnected SBS-rich network, neither the partial rupture of the SBS macromolecules nor the hardening of the binder significantly affects the performance of SM-ABs after RTFO aging. Commercial manufacturers and users of SM-ABs should be aware that significant property deterioration in SM-ABs can occur during pavement construction. The decline in SM-ABs properties can be mitigated by strictly following quality guidelines, using the higher vinyl grade of SBS polymer, using additives that enhance the thermo-oxidative stability of SM-ABs, using a higher dosage of SBS polymer to compensate for the loss during pavement construction, etc.