Investigating the Multiple Stress Creep Recovery bitumen characterisation test

Zero shear and Low shear viscosity test protocols were shown to be perfectly adequate for characterising high temperature creep behaviour of selected penetration grade bitumens but the tests were less satisfactory with respect to a proprietary SBS-modified bitumen tested in this investigation. Furthermore, Multiple Stress Creep Recovery (MSCR) tests conducted at a pre-determined temperature were argued to provide more satisfactory comparisons across a number of bitumen types compared to MSCR runs at a pre-determined target viscosity.Results show that varying the grade of unmodified bitumen did not result in a dramatic effect on the MSCR shear stress levels at failure when all testing were conducted at 70 °C. Increasing the bitumen viscosity by blending in a micro-sized calcium carbonate filler or a nano-sized organo-clay filler were shown to affect the stress sensitivity but not the actual magnitude of failure stress which remained in line with the base bitumen. On the other hand, the SBS-modified bitumen had completely altered shear stress failure criterion. When considering non-polymer-modified bitumens, simple high temperature strain sweeps have also been shown to be a potentially rapid and very useful creep performance ranking tool.

► Improved bitumen ranking obtained from MSCR tests at constant temperature compared to constant stress.
► Micro and nano sized fillers affect stress sensitivity of bitumen blends.
► SBS modification alters MSCR failure stress significantly.