Determination of Usable Residual Asphalt Binder in RAP

Abstract

For current recycled mix designs, the Illinois Department of Transportation (IDOT) assumes 100% contribution of
\nworking binder from Recycled Asphalt Pavement (RAP) materials when added to Hot Mix Asphalt (HMA). However, it is
\nunclear if this assumption is correct and whether some binder may potentially be acting as ???black rock,??? and not
\nparticipating in the blending process with the new binder. Furthermore, it is also unclear whether binder modifications
\nshould be considered in the mix design for recycled HMA. The goal of this research was to determine if the current IDOT
\nmix design practice required modification with respect to the use of RAP.
\nA set of mixtures was prepared using RAP in accordance with current practice. Additional sets were prepared
\nusing recovered binder and recovered aggregate to simulate the effect of RAP binder blending with virgin binder. Mixes
\ncontaining 0, 20, and 40%RAP were prepared and the dynamic modulus testing results of these mixtures were compared to
\nillustrate the effect of RAP on HMA. Tests on recovered, virgin, and blended binders were also conducted using the
\nDynamic Shear rheometer (DSR).
\nThis study found that up to 20% RAP in HMA does not require a change in binder grade. However, at 40% RAP in
\nHMA, a binder grade bump at high temperature and possibly at low temperature is needed; more tests are required to verify
\nthe need for low temperature binder grade bumping. In addition, this study recommends RAP fractionation in the
\npreparation of laboratory specimens.