Innovative Modified Stone Mastic Asphalt Concretes Containing Composite Poly-functional Fibres for Eco-friendly Paving Applications

In the present research, a complete study was carried out investigating the effectiveness of novel cellulose-based poly-functional fibres in enhancing the mechanical and performance properties of a virgin and 25% RAP containing Stone Mastic Asphalt (SMA). Therefore, there could be a significant economic advantage and a well-balanced solution between eco sustainability and technology in using RAP in SMA, if it could be used without sacrificing the excellent performance of SMA mixtures. The fibres modification was carried out by adding mineral (glass) fibre, a type of Plastomeric polymer and/or powdered tire rubber. The mix of mineral fibres and rubber with polymeric component was supposed to perform similarly to the regular bitumen modifiers improving the dynamic/mechanical performance of the bituminous binders. The fibrous component contributes to further improving the rheological and thixotropic behaviour of the bituminous mastic. The test program included numerous tests in both binder and mixture-scale in addition to primary microscopic analysis providing a wide range of data to achieve a complete understanding of fibre interaction with binder and its performance in asphalt mixtures. For this purpose, four different cellulose-based fibres (with and without powdered crumb inside), a 50/70 penetration graded neat bitumen, and a 10/40-70 SBS PmB were used to produce the bituminous compounds and mixtures to be investigated through the experimental works. Overall, the results indicate the possibility of modifying asphalt mixtures via modified fibres and the superiority of rubberized fibres in comparison to those of non-rubberized. However, the rubberized mixtures needed enough digestion and interaction temperature and time. In addition, it has been found that while the substitution of 25% virgin materials with RAP could enhance some of the dynamic mechanical properties of SMA, the low-temperature thermal cracking sensitivity increased for all the tested RAP containing mixtures with different fibres rather than the type of modification.