Abstract
The ductilometer is currently being used by the asphalt pavement community for determination of elastic recovery of asphalt materials. Briquet specimens are pulled apart at 5 cm/min, held after a specified elongation, then severed at the center and allowed to recover undisturbed for 1 h with the idea of getting a measure of the ability of the asphalt material to recover after imposing a deformation. Materials with poor ability to recover are known to lend themselves to permanent deformation resulting in rutting of pavements. The Superpave specification parameter |G*|/sinδ recommended by the Strategic Highway Research Program was found not to relate well with observed rutting of mixtures that used polymer-modified asphalts with increased elastic behavior. This led researchers to seek methods to refine this parameter. While refinement efforts have been ongoing, there has been an inclination on the part of a number of State Departments of Transportation to use the elastic recovery test to complement the Superpave specification tests. However, the elastic recovery test is truly not very elegant and accurate, and often fails to discriminate between the behaviors of differently modified binders. The present work suggests a dynamic oscillatory test using the dynamic shear rheometer DSR that would fulfill the objectives of the elastic recovery test. The elastic recovery term and the condition under which it is determined from DSR data are selected by observation of master plots of a wide variety of asphalt binders. The criterion is developed by observing the ability of the selected term in best discriminating asphalt binders for their elastic recovery behavior. It is recommended that the term cosδ determined at a temperature T = 82°C and frequency ω = 1 radian/s be used to assess the elastic recovery of asphalt materials. Cosδ (T = 82°C, ω = 1) > 0.04 is recommended as the criterion for acceptance of required elastic recovery behavior.
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