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The above cases clearly show that there is a need to identify a mechanical parameter measured from standardized tes that is sensitive to polymer or CRM modification of binder and mixture performance. Presence of such parameters would enable an empirical evaluation of the impact of modification of the binder on mixture and eventually on pavement performance.

Superpave specifications were primarily designed for neat binders. Researchers have determined that the tests specified in Superpave are not suitable for characterization of polymer modified binders. Asphalts modified with different polymers can behave very differently even when they have the same performance grade, as determined by the Superpave specifications.

Currently, the state of New Jersey requires the use of styrene-butadiene or styrene-butadiene-styrene formulations. In-lieu of the polymer shortages, the state of New Jersey would like to expand the use of polymers and rubber in the binder. The state of New Jersey has adopted specification limits from the Elastic Recovery test to evaluate modified binders. However, since then, the binder Expert Task Group has recommended the use of MSCR (Table 3 - AASHTO TP 70) to evaluate modified binders. Before the state of New Jersey can allow the use of other modifiers, there is a need to first determine whether parameters such as the Jnr and the recoveries determined from MSCR and ER are sensitive to the polymer or rubber modification of the binder. This will be a critical step in identifying whether these parameters can be effectively utilized in the selection of modified binder specification.