While fatigue distress is still of major concern relative to the performance of asphalt pavements, permanent deformation in the form of rutting is assuming more significance for heavy duty highway pavements because of increased number of repetitions of heavy axle loads and increased tire pressures resulting from the use of radial tires (as compared to bias ply tires). In recent years, asphalt modifiers have found increasing use in mitigating excessive permanent deformation in the asphalt concrete pavements. However, questions arise as to what methodology should be used in comparing modifiers and in selecting the amount of modifier which should be used for a particular application.
This paper presents results of a study in which the applicability of dynamic testing is evaluated for assessing rutting potential for mixtures containing modified asphalt binders. Particular emphasis is placed on the rheologic properties of the modified asphalt binders and the binder-aggregate mixtures. Watsonville granite and an AR-2000 California Valley asphalt, and the same asphalt modified with Microfil 8 and K4460 modifiers were used in this investigation.
While the rheologic properties of modified binders may suggest improved performance over the same asphalt in the unmodified state, it is still necessary to define the performance characteristics of the mixture since the aggregate exerts a significant influence on mixture performance.
Mixture stiffness by itself does not appear to provide a measure for assessing the propensity for rutting in mixtures containing modified asphalt binders. Accumulated plastic deformation obtained under dynamic loading seems to represent better, the potential for rutting in mixtures containing modified asphalt binders. These dynamic tests provide results which are sensitive to asphalt type, temperature, degree of compaction and binder content.