Mix design and volumetric analysis of hot recycled bituminous mixtures using a bio-additive

Nowadays, the use of reclaimed asphalt (RA) as a constituent material for hot asphalt concretes (AC), is gain-ing increasing interest because of the important technical and environmental advantages. In addition, the reuse of the old bitumen from the RA, allows the required amount of new bitumen to be reduced with clear eco-nomic returns. However, only a small percentage of RA can be recycled in new ACs (typically less than 30%), as the excess of oxidized aged bitumen may lead to a brittle behavior of the pavement layer. In order to avoid this issue, when high amount of RA are used, specific additives are recommended in order to restore the bi-tumen characteristics leading to a mixture with the expected mechanical properties. The present paper deals with the use of a bio-based additive (A) for the production of AC for binder layer containing high quantities of RA. In particular, the study focuses on the mix design phase, highlighting the effects of RA and A on the volumetric properties of the mixtures. The experimental program included four ACs with no RA, 40% of RA, 40% of RA and additive A, 50% RA and additive A respectively. Results showed that the optimum bitumen content decreased when decreasing RA content or when adding A. Moreover, the use of A allowed obtaining the desired volumetric properties even with a significantly lower amount of virgin bitumen to be added to the mixture without penalizing its mechanical response.