Long-term performance assessment of a warm recycled motorway pavement

In the last decade, warm mix asphalt (WMA) technologies have undergone a strong development in the pavement sector. In fact, the reduction of the production and compaction temperatures up to 40 °C with respect to the conventional hot mix asphalt (HMA) mixtures has many environmental beneficial effects. However, the long-term field performance of WMA mixtures is still an open issue, especially when they contain reclaimed asphalt pavement (RAP) and polymer modified bitumen (PMB). In this regard, the objective of this investigation was to monitor the performance of a full-scale field trial constructed along an Italian motorway. The field trial included a section constructed with WMA mixtures (produced with a WMA chemical additive) and a reference section constructed with HMA mixtures. The WMA and HMA mixtures had the same composition (i.e., amount of RAP and PMB) and differed only for the temperatures adopted during the production of the mixtures and construction of the sections. Cored samples were taken from the binder and base courses at different times during the in-service life of the field trial (timespan of six years) and subjected to conventional testing as well as viscoelastic continuum damage (VECD) characterization. The HMA mixtures were generally stiffer than the WMA mixtures, likely due to a more marked RAP oxidation during the production and construction phases and a higher in-service ageing rate. On the contrary, the WMA mixtures always exhibited higher fatigue resistance and better homogeneity than the HMA mixtures. Based on these findings, better long-term performance is expected for the WMA section.