Investigation on Mix Design of Recycled Asphalt Pavement (RAP) Materials

Project summary:

Recycled asphalt pavement (RAP) materials have been seen more increasingly with applications in construction of asphalt pavements. In 2016, the Minnesota Department of Transportation (MnDOT) published a synopsis on the use of RAP material. The synopsis identified various benefits of using the RAP materials, which include the reduction of cost and environmental impacts, and reduction of the demand of virgin aggregates and asphalt binders. MnDOT has a long history of incorporating RAP into plant mixed asphalt.

It has been widely recognized that one of the most important considerations in the design of asphalt mixtures is the gradation of aggregates. The proper choice of the gradation has important implications for the compaction performance, which in turn affects the mechanical properties and durability of the constructed pavements. Recent studies by the PI and co-PI on Superpave 5 showed that, by properly choosing the gradation according to the maximum density line, one can improve the compaction performance considerably. However, similar investigations focused on the gradation of the RAP used in mix design have not been performed. Meanwhile, previous work by the team also showed the improvements in the compaction properties and mechanical properties of the asphalt mixtures by adding graphite nanoplatelet (GNP) to the binders.

Inspired by the findings of this previous research, the team will investigate the mix design of RAP materials from two aspects: 1) design the gradation curve to study whether the concept of the maximum density line would apply to the RAP materials, and 2) study the effect of GNP on mix design of RAP, particularly on the percentage of RAP used in the mix design. The investigation will involve compaction experiments and mechanical properties experiments on different mix designs of RAP material.