Short Term Aging - Influence of Mixing Time at Laboratory Specimen Production

The viscoelastic behavior of hot mix asphalt (HMA) is influenced by several factors, e.g. by the binder behavior, which has crucial impact on the pavement performance. The behavior changes due to aging during its in-service life within years, as well as during HMA production and compaction processes within a few hours. Therefore, aging processes are classified into long-term aging (LTA) and short-term aging (STA). This paper presents a study, analyzing STA processes at laboratory productions of HMA slabs. Six production cycles, with up to three slabs each were analyzed. The mix of binder and aggregates were prepared at once. This requires storing the hot and prepared mix inside the laboratory mixer while the first and the second slab are compacted, respectively. Bitumen was recovered for each produced slab. |G*| stiffness tests (DSR) are carried out afterwards at 52–82°C and 1.592 Hz. The results show that mixing times lead to a stiffness increase of 1.5 compared to the virgin bitumen, what is slightly below RTFO aging level. Recovered binder from Slab 2 and Slab 3 show increases of |G*| of 1.9 and 2.5. Therefore, for the used binder, longer mixing times have a significant impact on STA. The results can be used to back-calculate STA levels for specimens that are used for LTA aging studies. Furthermore, both binder and additional HMA stiffness results can serve as basis for multi-scale stiffness modelling by coupling the results.