Towards a new mix design method for asphalt mixtures containing rap

Recycling is one of the most important aspects to conceive the new construction or rehabilitation of sustainable road infrastructures. Even if Reclaimed Asphalt Pavement (RAP) is commonly used in the practice, its presence may lead to some critical aspects due to the physical and chemical phenomena occurring during the new mix process. For instance, the formation of RAP clusters during a new mix may inhibit the uniform distribution of the virgin binder as well as cause changes in the design grading curve of the mixture. Indeed, laboratory results demonstrate that small-size RAP particles stick together forming clusters. The amount of clusters depends on different parameters observed: The percentage of RAP bitumen trapped in the small-size fractions, the dimension of the grains and the percentage of RAP. Moreover, the partial re-Activation of the aged binder and the quality of the RAP aggregates should be considered in the design of a new mixture to ensure the same performance level as for a traditional mix. Therefore with the aim of meeting these needs this study helps, together with other initiatives, to address the challenge of defining a new mix design approach for HMA including (hot) RAP by taking into account the physical phenomena occurring during a new mix.