Determination of Usable Residual Asphalt Binder in RAP

For current recycled mix designs, the Illinois Department of Transportation (IDOT) assumes 100% contribution of working binder from Recycled Asphalt Pavement (RAP) materials when added to Hot Mix Asphalt (HMA). However, it is unclear if this assumption is correct and whether some binder may potentially be acting as ???black rock,??? and not participating in the blending process with the new binder. Furthermore, it is also unclear whether binder modifications should be considered in the mix design for recycled HMA. The goal of this research was to determine if the current IDOT mix 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 prepared using recovered binder and recovered aggregate to simulate the effect of RAP binder blending with virgin binder. Mixes containing 0, 20, and 40%RAP were prepared and the dynamic modulus testing results of these mixtures were compared to illustrate the effect of RAP on HMA. Tests on recovered, virgin, and blended binders were also conducted using the Dynamic 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 in HMA, a binder grade bump at high temperature and possibly at low temperature is needed; more tests are required to verify the need for low temperature binder grade bumping. In addition, this study recommends RAP fractionation in the preparation of laboratory specimens.ICT-R27-11published or submitted for publicationis peer reviewe