Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder

More than 90 percent of highways and roads in the United States are built using hot-mix asphalt (HMA) or warm-mix asphalt mixtures, and these mixtures now recycle more than 99 percent of some 76.2 million tons of reclaimed asphalt pavement (RAP) and about 1 million tons of recycled asphalt shingles (RAS). According to the National Asphalt Pavement Association, cost savings in 2017 totaled approximately $2.2 billion with these recycled materials replacing virgin materials.

The use of RAP in HMA dates back to the early 1900s, with renewed focus on research and implementation in the 1970s and 1980s and again in 2008 with significant increases in the cost of petroleum products including asphalt binders. Thus, highway agencies and the paving industry have developed a renewed interest in utilizing larger quantities of recycled materials (RAP and RAS) to maximize economic and environmental benefits that include conservation of natural resources (aggregate, binder, fuel, etc.), reduction in energy consumption, and reduction in emissions (including greenhouse gases).

In spite of these symbiotic benefits, state departments of transportation limit the use of RAP and RAS in asphalt mixtures for reasons that include variability of the recycled materials and concerns about long-term mixture performance. In addition, mix design is more complicated and more time consuming, particularly with large quantities of recycled materials identified by high recycled binder ratios (RBRs).

This pre-publication draft of NCHRP (National Cooperative Highway Research Program) Research Report 927: Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder focuses on using recycling agents to facilitate increasing RBR.