Determination of usable residual asphalt binder in RAP.

ICT-R27-11For current recycled mix designs, the Illinois Department of Transportation (IDOT) assumes 100% contribution ofworking binder from Recycled Asphalt Pavement (RAP) materials when added to Hot Mix Asphalt (HMA). However, it isunclear if this assumption is correct and whether some binder may potentially be acting as \u201cblack rock,\u201d and notparticipating in the blending process with the new binder. Furthermore, it is also unclear whether binder modificationsshould be considered in the mix design for recycled HMA. The goal of this research was to determine if the current IDOTmix design practice required modification with respect to the use of RAP.A set of mixtures was prepared using RAP in accordance with current practice. Additional sets were preparedusing recovered binder and recovered aggregate to simulate the effect of RAP binder blending with virgin binder. Mixescontaining 0, 20, and 40%RAP were prepared and the dynamic modulus testing results of these mixtures were compared toillustrate the effect of RAP on HMA. Tests on recovered, virgin, and blended binders were also conducted using theDynamic Shear rheometer (DSR).This study found that up to 20% RAP in HMA does not require a change in binder grade. However, at 40% RAP inHMA, a binder grade bump at high temperature and possibly at low temperature is needed; more tests are required to verifythe need for low temperature binder grade bumping. In addition, this study recommends RAP fractionation in thepreparation of laboratory specimens