Equipment World Digital Magazine
Issue link: https://read.dmtmag.com/i/473140
A pproximately 93 per- cent of the more than 2.6 million miles of paved roads and high- ways in the United States are surfaced with asphalt. As- phalt surfaces range from full-depth pavements to thin asphalt over- lays, but all are quick and easy to build and maintain. These factors, coupled with refi nements in asphalt technologies, have helped asphalt maintain its popularity in paving. Several asphalt mixes are also refl ecting an emphasis on sustain- ability, including energy-saving warm-mix asphalt (WMA) technolo- gies and recycled materials such as reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS). Warm-mix asphalt Dr. Heather Dylla, director of sustainable engineering at the Na- tional Asphalt Pavement Association (NAPA), points to several trends revealed in the association's annual survey on the use of recycled mate- rials and warm-mix asphalt. Since being introduced in the United States in 2004, the use of warm-mix asphalt has seen an explosive growth. According to the NAPA survey, warm-mix asphalt usage has increased by 533 per- cent since 2009. The technologies behind warm-mix asphalt improve the workability of the mix, leading to better performance of the asphalt mixture in the pavement. "In 2012, approximately 25 per- cent of the total asphalt tonnage was warm-mix asphalt," Dylla says, adding that, by the 2013 construc- tion season, 30 percent of total tonnage is warm-mix asphalt. "We are pretty proud of how successful we've been at its deployment. The technology came from Europe, but Europe hasn't been as aggressive in deploying warm-mix technologies as the United States has been." When the asphalt doesn't have to be heated to as high a temperature, less energy is used, which means fewer emissions. Low emissions are important for keeping things "green" on the construction site. Worker comfort is also greatly im- proved, since they aren't exposed to high temperatures. Improvements are still in the works for this successful product. According to Dylla, other technolo- gies are being explored to get the temperatures even lower than they are now. Reclaimed asphalt pavement The asphalt paving industry is now recycling at a rate of more than 99 percent, says Dylla, pointing out that the NAPA survey shows only 100,000 tons of RAP made it to landfi lls. "A majority of RAP is being used in hot-mix and warm-mix as- phalt, which means we not only get the value of the aggregate, but we get the value of the binder as well, and that's a good thing," she says. "That trend has been increasing, as only 64 million tons were used fi ve years ago." On average, departments of transportation (DOTs) use nearly 20 percent RAP in their mixes, which is almost double what it was fi ve years ago when they only allowed approximately 10 percent. Some DOTs use as much as 30 percent now, and these percentages are expected to increase. Late last year, a group of 11 people made up NAPA represen- tatives, asphalt contractors, state asphalt pavement association representatives, and four state DOT representatives made a trip to Japan to explore how Japan has been able to use 50, 60, and even 70 percent RAP in its asphalt mixes. Dr. Randy West. P.E., director at the National Center for Asphalt March 2015 | EquipmentWorld.com 58 Refi ned technologies are helping to keep asphalt pavements in the headlights highway contractor | by Kerry Clines Jason Nelson, a National Center for Asphalt Technologies engineer, takes a core sample from an asphalt pave- ment to check crack depth.