The effect of Selenice Natural Bitumen on un-modified and polymer-modified bitumen rheological properties

Selenice Natural Bitumen (SNB) is a natural bitumen with specific properties, which make it a valuable additive in asphalt mixtures in order to reduce the dosage of virgin bitumen, thus reducing the environmental footprint. The current state of the art validated its use in unmodified bituminous blends, highlighting the positive influence as an ageing inhibitor only at low dosages (≤ 10 %). In order to consider higher dosages of SNB in asphalt pavement materials, the objective of this study is to investigate the rheological properties of bituminous blends composed of SBS polymer-modified bitumen and SNB. The experimental program evaluated the addition of SNB in different dosages in an un-modified bitumen and an SBS polymer-modified bitumen. The analysis involved empirical and rheological properties at different ageing conditions. The main rheological characterization consisted in complex modulus tests, Multiple Stress-Creep Recovery (MSCR) tests and Linear Amplitude Sweep (LAS) tests. Overall, the results related to un-modified bituminous blends are consistent with findings reported in previous studies, confirming that a maximum SNB content of 10 % by weight is recommended to limit performance loss. Conversely, the experimental data did not support the feasibility of increasing the SNB dosage beyond 10 % when using SBS polymer-modified bitumen. The presence of SBS polymers in the modified blends did not mitigate the fatigue performance loss associated with SNB use. Therefore, the use of SNB at dosages exceeding 10 % by weight of the total bituminous blend is not ecommended, regardless of whether unmodified or SBS-modified bitumen is employed.