Balanced Mix Design Plus for Mixtures that Contain Recycled Asphalt Pavement

Abstract

Recent efforts have been made to include mixture performance tests at the mix design stage using so-called “balanced” mix design (BMD). This paper evaluates the use of two mixtures that contain intermediate and high recycled asphalt pavement contents in the context of a BMD approach referred to as balanced mix design plus (BMD+). BMD+ utilizes the dynamic modulus, cyclic fatigue, and stress sweep rutting tests and mechanistic models and has three tiers of design based on the amount of performance testing required. As part of the BMD+ approach, index–volumetrics relationships (IVRs) and performance–volumetrics relationships (PVRs) based on the four-corner concept were developed for the two mixtures and verified using the performance data from seven other volumetric conditions. The developed PVRs were used to perform BMD+ Tier 3 analysis of the two mixtures, whereas the IVRs based on two points at the target air void content of 4% were used to conduct BMD+ Tier 2 analysis. The results indicate that the use of BMD+ Tier 2, which requires performance tests at only two conditions and without pavement simulations, yields longer lasting mixtures compared with Tier 1, which follows the Superpave volumetric mix design method. It was also found that Tier 3 requires more testing and pavement simulations but leads to even further gains in predicted life duration compared with Tier 2.