Incorporating High Percentages of Recycled Asphalt Pavement and Warm-Mix Asphalt Technology into Thin Hot-Mix Asphalt Overlays as Pavement Preservation Strategy

In order to address the national and municipal demands for increased recycling and environmentally friendly asphalt mixtures, thin-lift Hot Mix Asphalt (HMA) overlays were developed that incorporated high percentages of Recycled Asphalt Pavement (RAP) and Warm Mix Asphalt (WMA) technology (Sasobit). These mixtures were defined as mixtures placed between 3/4" to 1-1/4”. A Superpave 4.75mm and a Mass Highway Surface Treatment mixture with 0%, 15%, 30%, and 50% RAP were designed. Each mixture was developed with two binders, a PG64-28 and a PG52-33. These mixtures were evaluated for stiffness and workability. Mix design data showed that most of the mixtures with high percentages of RAP could be designed to meet specification requirements, for gradation and volumetrics. Dynamic modulus testing was utilized to develop Master Curves for each mixture. These curves indicated that there was a degree of blending between the virgin binder added and the aged binder in the RAP. Additionally, the data indicated the softer binder (PG52-33) did not have a significant reduction in the stiffness of the mixtures incorporating 30% and 50% RAP when compared to the mixtures prepared with the PG64-28. Workability data showed that higher RAP contents decreased the workability of the mixture. This indicated that with higher percentages of RAP, the dose of WMA additive may need to be increased. Finally, a field trial of the Superpave 4.75mm with 30% RAP was placed in Wellesley, Massachusetts in October 2007. To date there are no visible distresses.