Investigation of Different Design Methods for Determining the Appropriate Binder Ratio on Recycled Asphalt Mixtures

With the current concern about environmental issues and scarcity of raw materials, the production of recycled asphalt mixtures with high contents of reclaimed asphalt pavement (RAP) has been established as a sustainable and cost-effective solution. However, the increase of RAP content in recycled mixtures without loss in field performance is still a challenge. Among the reasons for that is the lack of a well-accepted and recognized mix design method to calculate the appropriate blending ratio between virgin binder and RAP binder. Blending charts are usually applied to determine this ratio, but different parameters can be used to construct them. In Europe, binder penetration is traditionally used, while performance-based parameters are preferred in the United States. In the present paper, different methods are applied to determine the appropriate ratio between RAP binder and virgin binder in different asphalt mixtures, for different types of RAP. The objective was to determine how the use of different parameters in the blending charts affects the blend design for the recycled mixture. Results showed that using penetration may promote the use of higher RAP contents in recycled mixtures, while using the performance grade parameters may result in lower RAP contents. The Jnr parameter of the MSCR test was also applied, and showed mixed results depending on the material analyzed. The results highlight the need for studies that correlate blend design and field performance, in order to improve mix design methods and ensure adequate performance for high-RAP mixtures.