Estimation of Blending of Rap Binder in a Recycled Asphalt Pavement Mix

Many of the recycled asphalt pavement (RAP) mix design methods assume 100% blending of the RAP binder with virgin binder to estimate the properties of the binder in the RAP mix. However, 100% blending is not practically achieved. Thus, it is essential to have procedures for determination of the degree of blending so that the properties of the blend can be estimated more accurately from the properties of RAP and virgin binders. To achieve this objective, a detailed study is conducted to evaluate the level of interaction between RAP and virgin binders. This study considers two proportions of RAP (20 and 35%) and two viscosity grades of virgin binders (VG10 and VG30). The difference in the qualities of the binders in the RAP and virgin aggregate portions is evaluated in terms of different binder properties such as ${\mathrm{G}}^{*}/\sin \delta$, penetration, and softening point. The results show that the grade of virgin binder and RAP content in the hot mix asphalt concrete governs the degree of blending achieved. Based on the results of the study, a simple approach is proposed for estimation of the properties of the combined (blended) binder in the recycled mix.