Effect of hyper-modified asphalt binder and steel slags on cracking and rutting behaviour of wearing course mixtures

This paper presents a laboratory investigation aimed at evaluating the effect of employing hyper-modified asphalt binders in surface asphalt courses. Two different Hot Mix Asphalt (HMA) surface layers were investigated: an Open Graded Friction Course (OGFC) and a dense-graded blend. Two different asphalt binders were employed: a highly modified binder and an experimental hyper-modified binder. Both natural aggregates and steel slags were used for asphalt mixture design. The cracking behaviour of the mixtures were evaluated using a visco-elastic fracture mechanics-based cracking model. The cracking behaviour of the mastics was investigated using a Modified Direct Tension Test (MDTT), together with a Digital Image Correlation (DIC) system. The results showed that the hyper-modified binder provides better performance than the traditional hard modified one when used in the OGFC mix. Conversely, it does not bring great improvements in terms of fracture resistance for the dense-graded blend, but helps to resist more to rutting.