Monitoring the evolution of the structural properties of warm recycled pavements with Falling Weight Deflectometer and laboratory tests

In pavement engineering, the use of warm mix asphalt (WMA) technologies can ensure important environmental and technical benefits. However, several uncertainties about WMA still exist, such as long-term field performance and full compatibility with reclaimed asphalt pavement (RAP) or polymer modified bitumen (PMB). In this regard, a full-scale trial section (including three test fields with warm recycled mixtures prepared with different WMA chemical additives and a reference test field with hot recycled mixtures, all containing PMB) was constructed along an Italian motorway and monitored for several years of service life. The evolution of the structural properties was assessed with in-situ Falling Weight Deflectometer (FWD) tests and laboratory tests on extracted cores, both immediately after the construction of the trial section and after more than three years under actual traffic loading. It was found that the reduced working temperatures adopted for the WMA mixes (40°C lower than hot mix asphalt (HMA)) did not penalise the workability and the stiffness immediately after the trial section construction, whereas the HMA mixture experienced higher structural damage (likely due to more severe aging) during the in-service life. The WMA mixes exhibited better stiffness homogeneity and, overall, superior performance and potentially longer service life with respect to the reference HMA mixture.