Characterisation of the performance of binders is increasingly complicated due to growing use of modified bitumens. Polymers are incorporated to improve viscoelastic properties of asphalt by increasing temperature range over which it retains its integrity to resist rutting and thermal cracking, and lengthening fatigue life. While conventional methods can adequately compare bitumens, they are not accurate enough for modified materials. SHRP has developed specifications and test methods for more accurate prediction of field behaviour of all binders. Dynamic Oscillatory Shear Rheometer is used to characterise viscoelastic behaviour at high and intermediate pavement temperatures. A minimum binder modulus is needed at highest temperature for rut resistance, and a maximum modulus for intermediate range where fatigue damage is most likely. Bending Beam Rheometer predicts low temperature where binder becomes sensitive to thermal cracking. Direct Tension simulates fracture under low temperature conditions where binder has insufficient tensile strain tolerance to withstand movement. In this study, binder test methods developed by SHRP were used to evaluate elastomer modified bitumens and grade them according to expected performance in rutting and thermal cracking. A plastomer modified bitumen and some partially air blown bitumens were also evaluated and graded. Some of these binders were compared in a field trial under specific traffic and climatic conditions. (This paper was also published in the Proceedings of the Eurasphalt & Eurobitume Congress, 7-10 May 1996, at Strasbourg (IRRD 887507), Vol 2).
Samenvatting