Cluster phenomenon and partial differential aging in RAP mixtures

The present study defines a procedure for gaining a better understanding of the interaction between the aged and the virgin binders and what actually occurs during a mix process. Indeed, the authors propose a methodology to determine and quantify the cluster phenomenon in mixtures containing RAP, defining how the aged binder interacts in the mix. Rheology, in particular the complex modulus, becomes the tool thanks to which it is possible to support the hypothesis of the composition of clusters of RAP particles surrounded by the virgin binder during the new mix production, considering different percentages of RAP. Moreover, the authors aim to establish the basis for the hypothesis of the existence of a partial differential aging: the RAP binder on the external surface (i.e. the crust around the aggregate) is more exposed to external factors and oxidation and is over-aged with respect to the binder under the crust that is more protected and less oxidated.