Within the Superpave mix design system there are design criteria for 9.5 to 37.5 mm nominal maximum aggregate size (NMAS) mixes. Many agencies have expressed an interest in using a 4.75 mm NMAS mix because such a mix could result in an easy riding surface, be used for thin lift applications, correct surface defects (leveling), decrease construction time, provide a use for manufactured screening stockpiles, provide a very economical surface mix for low traffic volume facilities, and be used for thin lift maintenance. In February 2002, the National Center for Asphalt Technology completed a study to develop Superpave mix design criteria for a 4.75 mm NMAS mix (Cooley et al, 2002). NCAT's research was used, in part, by the Superpave Mixture/Aggregate Expert Task Group to recommend to AASHTO the addition of 4.75 mm NMAS mixes to the Superpave mix design system.

The objective of this study will be to refine and field validate design criteria for 4.75 mm NMAS Superpave mixes. Additionally, guidelines for the production, construction, and use of this mix type will be developed.

The tentative work plan will have two phases. Initially, a laboratory phase will be needed to refine the mix design criteria developed for the 4.75 mm NMAS Superpave mixes. The second phase will include a field validation of the refined mix design criteria through the construction of experimental test sections utilizing mixes designed with the refined mix design criteria.

Pooled fund participation is planned for a minimum of 8 States at $30K each. The contribution could be in two contributions of $15K over the first two years of the project.