Tweaking the System: Modifications to the Superpave Mix Design System

A recent survey by the Association of Modified Asphalt Producers showed that a majority of states now use some form of PG+ specifications, meaning that they have added tests or requirements to the Performance Graded (PG) binder specification. The situation for the Superpave mix design system is analogous. States have added requirements, changed various parameters, and implemented or declined to implement revisions to the AASHTO specifications. In 2004 and 2005, the National Asphalt Pavement Association and Federal Highway Administration sponsored a series of regional workshops across the country to assess the current state of the practice with Superpave and hot mix asphalt in general. Four workshops were held in conjunction with the regional asphalt user producer group meetings. At these workshops, industry and agency personnel shared their experiences with Superpave. One key objective of the workshops was to determine what changes had been made to the mix design system and the rationale for those changes. This paper summarizes the changes that have been made to the system across the country, giving a snapshot of the current state of the practice.