Comparison of Linear Viscoelastic Properties of Crumb Rubber–Modified Binders Measured Using Parallel-Plate and Concentric Cylinder Geometries with Asphalt Mixture Dynamic Modulus

Abstract

Rubber particles can become compressed during testing of asphalt binders modified with crumb rubber (CR) in dynamic shear rheometer (DSR) parallel-plate geometry. This is especially true at high concentrations and/or large CR sizes. There have been claims in the literature that this compressed condition does not represent the true properties of CR-binder suspension rheology. This has resulted in questioning the applicability of the Superpave performance grading (PG) procedure to these binders. An alternative test geometry commonly used in the food industry, concentric cylinder geometry, was proposed to allow for better suspension of CR during testing. However, because CR particles are compressed within an asphalt mixture, binder properties measured using parallel plates may correlate better to mixture properties than those obtained by the concentric cylinder. In this study, a comparative analysis was conducted for the dynamic shear moduli of CR-modified binders measured using these two DSR geometries. The modified binders were produced with different CR concentrations and sizes. Comparisons were also made with dynamic moduli of mixtures produced with these different binders. It was observed that parallel plates correlate to mixture properties as good as or better than the concentric cylinder geometry.