Comparative Performance Analysis of Superpave4 and Superpave5 Asphalt Mixtures in Massachusetts: Cracking Resistance, Permeability, and Mechanistic-Emperical Evaluation

This study presents Phase II of a research study for the Massachusetts Department of Transportation (MassDOT) comparing Superpave mix design (Superpave4) and Superpave5 through laboratory testing and performance modeling. Currently, MassDOT develops mix designs with the Superpave4 method, but targets 5% field air voids; however, Superpave4, when placed in the field, typically achieves 6%–8% air voids. As a result, MassDOT increased their effective binder content by raising minimum VMA specifications, yet there were issues achieving the target voids. Therefore, Superpave5, which targets 5% air voids in both laboratory and field applications, was explored as a potential solution. Four 12.5 mm nominal maximum aggregate size mixtures were evaluated: Superpave4 with 14% and 15% VMA, and Superpave5 with 15% and 16% VMA. Building on Phase I findings that revealed inconsistent cracking tolerance index (CT Index ) behaviors between mix types, Phase II focused on intermediate-temperature cracking using Texas Overlay Test, low temperature cracking using the Thermal Stress Restrained Specimen Test (TSRST), permeability with a falling head permeability test, and performance prediction using FlexPAVE ™ . The Texas Overlay Test results aligned with Phase I CT Index results. TSRST results showed no significant differences between mixture types, indicating that binder rheological characteristics influence low temperature performance rather than mix design methods. Superpave5 mixtures exhibited higher permeability than Superpave4 at equivalent air void content but remained within acceptable thresholds. FlexPAVE ™ modeling confirmed superior rutting resistance for Superpave5 mixtures, while cracking simulations aligned with the CT Index and Texas Overlay results, suggesting mixture characteristics affect cracking susceptibility along with air void levels.