The inclusion of a percentage of RAP in the production of bituminous mixtures is now unanimously accepted practice. The asphalt plants are able to produce with even higher percentages of recycling than those provided for by the Technical Specifications of the main Highway Admnistrations. However, are the performance of mixtures packaged with higher RAP percentages, overall, at least equal to those of mixtures currently used on motorway pavements and commonly accepted?
The aim of this task (hot recycling) is to investigate, with an innovative approach, the performance of bituminous mixtures produced with hard polymer-modified bitumen with high RAP content.
It starts with an in-depth analysis of the binder phase (how does the bitumen contained in the RAP behave? Can it still be considered a modified bitumen? At what level is it reactivated and participates in the binder phase with virgin bitumen?), to move on to the selection and processing of milled materials, to the best practice for the execution of the mix design phase, and finally to the performance analysis of mixtures on real scale trial sections. The hot recycling process takes place at high temperatures, as the virgin aggregates and the recycled aggregates from the milling of existing pavements are heated during premixing and mixing.
When mixing, the use of high temperatures implies that the bitumen present in the RAP is reactivated and will “merge” with the virgin bitumen, forming a new binding phase with different properties than virgin bitumen. In addition, it should not be neglected that exposure to high temperatures causes an extra oxidative process, in addition to that already suffered during the service life, of the bitumen coming from the milled material (RAP).
This further alters the chemical and mechanical properties of the bitumen contained in the RAP. It follows, therefore, the need to study the properties of aged bitumen from recycled material and its possible combinations with virgin bitumen, with particular attention to its chemical and rheological characterization.