Do Asphalt Mixtures Correlate Better with Mastics or Binders in Evaluating Permanent Deformation?

Researchers have often looked for relationships between mechanical properties of asphalt mixtures and rheological properties of binders when assessing the resistance of mixtures and binders to permanent deformation. When mixtures are subjected to deformation on application of a stress, aggregates act as load-bearing entities, and binders deform in response to applied stress. Intuitively, a correlation must exist between the properties of mixtures and binders. However, a good correlation usually is not observed. There could be a number of reasons for the observed poor correlations, including (a) variability in the data or a possible change in the microstructure of two-phase, polymer-modified asphalt in the presence of aggregates, or (b) strong interactions between the aggregate and the binder that, of course, are not reflected in the binder properties. In such cases, there are reasons to believe asphalt mastics might provide a better correlation because they would account for at least the physicochemical aspects of the aggregate–binder interaction. The present work compared asphalt mixture data initially with mastic data and then separately with binder data. The mastic and binder rheological data were generated with the same equipment under identical conditions of measurement to identify which one correlates better with the mixture data. A good correlation was obtained in only one case when Superpave® shear tester data for mixtures were compared with the dynamic shear rheometer data for binders. In all cases analyzed in this work, no correlation was found between the permanent deformation for mixtures and the rheological properties of the mastics.