Characterizing Compactability of High RAP and Warm Mix Asphalt Mixtures in the Superpave Gyratory Compactor

Compactability of asphalt concrete mixtures is critical for successful long-term performance in the field. Laboratory samples are necessary for volumetric analysis and performance testing during the design process, so the ability to quantify compactability during specimen production in the lab would be highly beneficial. While there has been significant work in defining compaction characteristics of asphalt concrete, most of this work has revolved around traditional Hot Mix Asphalt (HMA), and little work has been done with Warm Mix Asphalt (WMA) or high percentage Recycled Asphalt Pavement (RAP) mixtures. This research examined HMA without RAP (HMA Virgin), HMA with 35 % RAP (HMA RAP), and two WMA technologies with 35 % RAP (WMA 1 and WMA 2). Four compactability metrics were evaluated, including number of gyrations to 92 % density (N92), Construction Densification Index (CDI), the Construction Force Index (CFI), and the newly introduced Normalized Shear Index (NSI). This research found that the WMA technologies improved the compactability of asphalt concrete, as did the addition of RAP. In general, the WMA 1 showed better compactability than WMA 2, but this could be partially attributed to a softer binder grade, higher asphalt binder content, and the potential for a tender mix, as indicated by the normalized shear curve. The HMA RAP mixture also had a higher asphalt binder content compared to HMA Virgin, which could have contributed to the improved compactability. The NSI metric consistently showed the lowest Coefficient of Variation (COV) values and has the potential to distinguish tender mixtures.