Fundamental Binder and Practical Mixture Evaluation of Polymer Modified Bituminous Materials

Conventional bituminous materials have tended to perform satisfactorily in most highway pavement and airfield runway applications. However, in recent years, increased traffic levels, larger and heavier loads, new axle designs and increased tyre pressures have added to the already severe demands of load and environment on the pavement system. This has facilitated the need to enhance the properties of existing asphalt material with bitumen modification, particular polymer modification, offering one solution to overcome the limitations of bitumen and, thereby, improve the performance of these asphalt mixtures. This paper evaluates the relative performance of a series of ethylene vinyl acetate (EVA) and styrene butadiene styrene (SBS) polymer modified bitumens (PMBs) in terms of the two main distress modes associated with flexible asphalt pavements of permanent deformation and fatigue damage. The study makes use of fundamental rheological binder testing using a dynamic shear rheometer (DSR), pavement performance prediction by means of the Superpave binder parameters and the zero shear viscosity (ZSV) concept, and practical, mechanical asphalt mixture testing using the Nottingham Asphalt Tester (NAT). These binder and asphalt mixture procedures have been used to quantify the fatigue and permanent deformation performance of a series of polymer modified bituminous materials. The relative permanent deformation and fatigue cracking performance of the various PMBs and control penetration grade binders have then been ranked as a function of their binder rheological properties and actual asphalt mixture performance. The fundamental rheological data together with the permanent deformation and fatigue testing in the NAT all indicate an improved rutting and fatigue performance for the EVA and SBS PMBs compared to the unmodified penetration grade bitumens. However, based on the Superpave binder parameters and the ZSV, determined by means of the low frequency oscillation method, no unique correlation was found between actual mixture performance and predicted binder performance.