Methodologies for Estimating Effective Performance Grade of Asphalt Binders in Mixtures with High Recycled Asphalt Pavement Content Case Study

In 2009, hot-mix asphalt pavement sections containing 0%, 15%, and 50% recycled asphalt pavement (RAP) were built in a collaborative effort between Manitoba Infrastructure and Transportation and the Asphalt Research Consortium. Two types of 50% RAP mixtures were evaluated: one with no grade change in asphalt binder (PG 58-28) from mixtures with lower RAP content and one with a grade change in asphalt binder (PG 52-34). The following methodologies were used to determine the effective binder properties of the evaluated field-produced mixtures: grading of the recovered binders, blending chart process, mortar procedure, and backcalculation of binder properties from the measured dynamic modulus of mixtures with the Hirsch model and the modified Huet-Sayegh model. Overall, good correlations were observed between the estimated critical temperatures from the blending chart process and the measured ones from the recovered asphalt binders. Of the various evaluated methods, the mortar procedure provided promising results when used to estimate the mixture binder properties at critical pavement temperatures. The findings from the mortar procedure were consistent with the mixtures' resistance to thermal cracking and their current field performance. The procedure indicated that a partial blending was occurring between the virgin and RAP binders of the evaluated mixtures. Although some difficulties arose with the use of the Hirsch model, the backcalculated binder shear moduli were reasonable. The modified Huet-Sayegh model requires further evaluation to assess the true relationship between the characteristic times of the binders and mixtures.