Multiscale Characterization of Asphalt Binders and Mixtures with High Reclaimed Asphalt Pavement Content

Abstract

As the cost of virgin asphalt materials continues to rise, transportation agencies are moving towards using higher amounts of recycled asphalt pavement (RAP) in the construction of asphalt mixtures. The use of RAP provides many environmental and economic benefits; however, RAP is a stiff and brittle material and thus at high contents, concerns arise over cracking resistance. To mitigate the high stiffness of RAP, transportation agencies use recycling agents, warm mix additives, or softer virgin binders to restore the rheological properties of aged materials. Recycling agents have gained the most interest due to their ability to mitigate the high stiffness of asphalt mixtures at high RAP contents. Numerous studies investigated the performance of rejuvenated asphalt binders; however, the mechanisms of recycling agents are still not well explored. This study investigated the effect of various types of recycling agents on the properties of asphalt binders with high RAP content. The effect of recycling agent dose selection method was also evaluated. Rejuvenation mechanisms were evaluated by employing multiscale characterization techniques including rheological, microscopic, thermal, and chemical methods. The results were used to develop a method for engineers to design rejuvenated asphalt binders and assess their effects on properties of asphalt binders with RAP.

To properly design recycled asphalt mixtures, it is also important to evaluate the factors affecting their performance. One of these factors is recycled binder activity. Previous studies reported that RAP binders are only partially active to blend with virgin materials; however, most departments of transportation assume full activity. Overestimation of recycled binder activity might result in dry asphalt mixtures and increased cracking susceptibility. This study addressed this issue by reviewing the available literature on recycled binder activity quantification methods and by performing detailed analysis on two of the methods to recommend the most feasible approach.

The findings of this project will help engineers in the selection of recycling agents that enhance the use of RAP and improve the performance of asphalt mixtures. Consequently, the findings contribute to the construction of sustainable asphalt pavements with high amounts of recycled materials.