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Assessing the Use of Blending Charts to Estimate the Allowable Reclaimed Asphalt Pavement (RAP) Binder Content for Mixes Containing RAP from Different Sources

UCD-ITS-RP-20-23

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Suggested Citation:
Elkashef, Mohamed, Shawn S. Hung, John T. Harvey, David Jones (2020) Assessing the Use of Blending Charts to Estimate the Allowable Reclaimed Asphalt Pavement (RAP) Binder Content for Mixes Containing RAP from Different Sources. Journal of Testing and Evaluation 49 (5)

Blending charts are used by many agencies to design mixes with high-content reclaimed asphalt pavement (RAP). They are typically used with mixes containing more than 25 % RAP to determine the performance grade of the virgin binder or to obtain the maximum allowable RAP content. The aging condition of the RAP binders extracted from RAP can vary greatly based on years of service, climatic conditions, and traffic loading. The current specifications do not consider the stiffness of the RAP in determining the cutoff RAP percentage above which blending charts should be used. According to the current specifications, mixes containing less than 15 % RAP do not require a change to their virgin binder grade regardless of the RAP source. In this paper, extracted and recovered RAP binder from two sources representing different climatic conditions is blended with two virgin binders at different proportions. The rheological properties of the virgin and RAP binders and the resulting binder blends were compared using master curves and Black diagrams, and changes in the rheological parameters such as the crossover frequency and rheological index were noted. The blending chart procedure was used to determine the maximum allowable RAP binder ratio (RAPBR) for different mixes. The results show that the 25 % limit, currently specified, appears appropriate for the not very stiff RAP binder having a performance grade of PG94-4. However, for the stiff RAP binder (PG106+2), blending charts should be used for blends containing more than 18–20 % RAPBR. It was also shown that a change to the virgin binder is required for blends with as low as 6 % RAPBR, when the stiff RAP binder was used.

Keywords: reclaimed asphalt pavement, blending charts, Black diagrams, asphalt binder rheology