Synergic effects between vacuum residue and polymers for preparing high-performance bitumens

This research presents a laboratory study on a polymer-modified bitumens (PMBs) made with a vacuum residue (VR) as a bitumen extender. Two different PMBs were prepared, one with a plastomeric Elvaloy and the other one with an elastomeric styrene-butadiene-styrene SBS. The mechanical properties of the samples were determined by means Multi Stress Creep Recovery tests (MSCR) and temperature sweep test. The results show that polymers can improve the mechanical properties of bitumen, and the vacuum residue can be used as softening bitumen extender. However, their simultaneous presence highlights non-additive effects giving optimal mechanical properties with a lowered temperature dependence of the viscoelastic properties and a high extension of the usage temperature range. The peculiar effect of the combined action of polymers and vacuum residue was also confirmed by chemical-physical analyses. In fact, Atomic Force Microscopy (AFM) and Nuclear Magnetic Resonance (NMR) relaxometry have shown that vacuum residue and polymers are able to effectively interact with the inner structures of the bitumen to give enhanced performances, with an increased stability upon temperature changes.