In the 1970s, the oil shock caused by the Arab Oil Embargo led to petroleum shortages and long lines of drivers hoping to fill their tanks. Although less visible to the general public, the asphalt pavement industry also had to adjust its practices to manage tightened supplies of asphalt binder. Even though the practice of reactivating binder from old pavements had been used since the early 1900s, the oil shock spurred new investment in R&D, and the development and routine use of cold milling machines and drum mix plants has helped spur the use of recycling.
Over the past 40 years, the asphalt pavement industry has made significant advances in the use of reclaimed asphalt pavement (RAP), as well as expanded its use of other reclaimed and recycled materials. These efforts have mitigated the rising costs of raw materials, helping states and municipalities complete more road improvement and maintenance work than would have been possible with all-virgin material, and they have put millions of tons of construction and demolition waste to productive use every year. The asphalt pavement industry has earned a reputation as the most diligent recycler in the nation with more than 99% of all RAP being put back to use in building new pavements.
Across the U.S., the availability of RAP affects how much is put to use in different places. Densely populated urban areas with an abundance of paved surfaces tend to generate and use more RAP than less developed rural areas. Since 2009, NAPA has conducted an annual survey of the industry’s use of recycled materials. During the 2014 construction season, the average RAP percentage used in projects nationwide was 20.4%, although reported RAP content percentages for states ranged from 13-33%. Over the years, we have seen the number of states reporting average RAP percentages of greater than 20% from 14 states in 2009 to 27 states in 2014.
Although RAP usage has always been highest in mixes produced for the commercial and residential sector, the percentage of RAP in mixes for state departments of transportation and other public agencies has increased steadily over the years from just over 12% in 2009 to just under 20% in 2014. Clearly the industry sees the value in sustainable asphalt pavements.
While the increase in the use of RAP is encouraging, there is more that can be done in this arena. More than 94% of roadways in the U.S. are surfaced with asphalt, and every time maintenance is performed to restore smoothness and drivability to one of those roads, new RAP is generated; effectively, old pavements are mined for materials that will be used to build new pavements. In Japan, an average of 47% RAP is used in dense-graded asphalt pavements, and in some areas, the average RAP percentage is as high as 73%.
In December 2014, the National Asphalt Paving Association (NAPA) led a delegation of asphalt pavement producers and state department of transportation officials to Japan to learn about the success achieved in that nation with high RAP content mixes. Although differences in practices and equipment were noted, for the most part the delegation saw little that could not be applied in the U.S. to help achieve successful asphalt mixtures with increased levels of RAP. Japanese asphalt producers attributed their success with RAP to three key points:
An overall focus on quality and reducing variability through processing/fractionating RAP and covering stockpiles;
Heating the RAP to dry out the moisture and soften the RAP binder; and
Using a softening or rejuvenating agent along with other mixing best practices to ensure the desired mix characteristics.
NAPA and the delegation are working to disseminate the findings of this scan tour at various meetings and through a publication released by NAPA in January: High RAP Asphalt Pavements: Japan Practice — Lessons Learned (IS 139).
In Japan, a culture of sustainability has helped drive the advancement of high RAP content mixes. In the U.S., we are seeing an increasing emphasis on sustainability for project design. While green ratings systems, such as LEED, have encouraged many in the commercial sector to consider the use of recycled materials and other sustainable practices in parking lots and business parks, this same drive is now reaching state agencies.
Federal rules encourage the consideration of project sustainability, and this is reaching the highways and pavement market through efforts like the Federal Highway Administration’s (FHWA) Sustainable Pavements Technical Working Group, in which NAPA is a participant. In the coming years, we expect states to begin considering how to apply life-cycle assessment methodologies to projects, alongside the life-cycle cost analysis methodologies already being used. Use of recycled materials, along with other sustainable practices like warm-mix asphalt, is an important part of meeting these demands, and NAPA’s forthcoming Environmental Product Declaration program will help producers and owners alike quantify the sustainability of the materials used in projects.
But to be truly sustainable, these sorts of advances must meet the need for long-lasting, high-performing roads. While we have steadily increased the use of recycled materials over the decades, we have been guided by two principals: 1) Mixtures containing recycled materials should meet the same requirements as mixes produced with all-virgin materials, and 2) mixes containing recycled materials should perform equal to or better than virgin mixes. For these reasons, the industry invests heavily in research and education and continues to work to make a proven, sustainable product even better.
NAPA, working through FHWA’s Accelerated Implementation and Deployment of Pavement Technologies Program, is releasing in the first quarter of 2016 Best Practices for RAP and RAS Management (QIP 129). This new publication covers the latest knowledge regarding RAP management—milling, processing and storage through testing and mix design—and outlines steps that can help ensure the greatest economic benefit is achieved from the use of RAP.
Every time an asphalt pavement is built or maintained, the materials needed for future roads are being stored. Ensuring drivability and performance for today’s road users begins with smooth, well-maintained asphalt pavements, but thanks to advances in technologies and best practices, asphalt pavements also ensure that future generations can continue to use and reuse these materials well into the future. AT
