Assessing Superpave5 Implementation in Massachusetts: Evaluating the Impact on the Compactibility and Performance of Massachusetts Department of Transportation Mixtures

Abstract

The traditional Superpave method, called Superpave4, targets 4% air voids during laboratory compaction. However, field compaction generally results in 6%–8% air voids, which can negatively affect pavement durability. The Massachusetts Department of Transportation (MassDOT) requires a field density of 95%, equating to 5% air voids; however, achieving this density has been challenging. To address this, MassDOT increased their minimum voids in mineral aggregate (VMA) specification to increase the effective binder content and thus aid compactibility, yet density issues remained. Inspired by the Indiana Department of Transportation’s success with Superpave5, which targets 5% air voids in both the lab and field, MassDOT explored adopting Superpave5 to improve field compaction. The study in this paper compared the compactibilities, workabilities, and mixture performances of Superpave4 and Superpave5 mixtures in MassDOT projects. Four 12.5-mm nominal maximum aggregate size mixtures were evaluated: Superpave4 with VMAs of 14% and 15% and Superpave5 with VMAs of 15% and 16%. Aggregate gradations were optimized using the Bailey method. Compactibility and workability were assessed using construction densification index and workability energy index, respectively. Superpave5 mixtures showed better compactibility and workability. Performance tests, including the Hamburg wheel tracking test (HWTT) and the cracking tolerance index (CT_Index), showed that all mixtures met the MassDOT’s HWTT rutting criteria; however, Superpave5 inconsistently affected the CT_Index, suggesting differences in cracking behavior. FlexPAVE™ simulations showed that Superpave5 offers enhanced long-term rutting resistance, suggesting that it could eliminate the need for higher VMAs in current MassDOT specifications without sacrificing rutting performance.