There is a new type of asphalt being researched and tested in the Pavement Engineering and Science program at the University of Nevada in Reno, Nevada. Peter Sebaaly, University of Nevada Department of Civil and Environmental Engineering professor and director of the Western Regional Superpave Center, stated the program’s researchers have been conducting research on various types of material of asphalt for the last 33 years.
“Recycling is a hot topic,” Sebaaly mentioned. “We can recycle other products, such as used tires from cars and trucks. We recently looked into recycling plastics since we generate millions of tons of plastic each year.”
Graduate students dedicated to the research of materials and enhancing asphalt then collaborated with the companies that fund the research and had a brainstorming session discussing the use of recycled plastics. These private funding partners wished to further the research into post-consumer product plastics and asphalt, which led to the graduate students’ examination to test whether it was possible to use these plastics to enhance asphalt pavements. Post-consumer plastics include a wide range of plastics, such as toner cartridges, cups, water bottles, etc. It is plastic with a structure.
Asphalt consists of a mixture of gravel, sand and asphalt binder. These plastics are primarily used to replace the asphalt binder since the asphalt binder is the most expensive part of the road mixture. Traditional asphalt binder typically costs between $500 and $600 per ton.
“Anything we can find to replace the binder is actually a cost savings,” Sebaaly explained, “especially if the product is going to waste like used plastics and tires.”
Through its research, the University of Nevada has determined that post-consumer plastics can replace between 10-20% of the asphalt binder. This is tested in the university’s laboratories with both temperature and load on a variety of asphalt mixtures. These laboratory tests help to accurately simulate the different seasons as well as moisture levels.
“When you put asphalt pavement on the road, temperature and traffic loads are very important,” Sebaaly emphasized. In the heat of the summer, when the air is 100 degrees, the surface of the asphalt can reach 150 degrees. In the winter months, temperatures can dip down to 0 degrees and the asphalt can freeze. “It needs to be strong in the heat of summer as well as other extremes and be flexible when it freezes. Anything we put into asphalt needs to make sure it doesn’t rut in the summer and crack in the fall and winter.”
Laboratory testing typically takes approximately 18 months before the correct variants are determined. Following lab testing, the data is then published, and the research moves on to field testing. The pilot test with the asphalt using post-consumer plastics is on a California highway. This stretch of highway was chosen since one of the contractor sponsors funding the testing was constructing a road there. The collaboration and approval of the California Department of Transportation was critical to both the inception and success of the pilot test section. The stretch of highway tested is approximately 1,000 feet.
“There’s lots of traffic on that road, so it was an ideal location to test the binder,” Sebaaly stated.
The asphalt binder using post-consumer plastics was placed two years ago. In this pilot test, the asphalt binder was replaced with 10% post-consumer plastics. The university checks the stretch of road every few months to see how the binder is holding up and monitors the results.
“So far it has survived a couple of winters and summers. It has also dealt with a lot of rain and flooding,” Sebaaly said.
As the field testing goes on, the laboratory testing continues as graduate students work with various products and various combinations of products that could be used on the roadways.
More companies have shown interest in using this research and testing plastics as a replacement for asphalt binder on their roads and highways, and the university continues to receive inquiries. In order to begin testing on another stretch of road, the university must have a funding sponsor who wants a road in that area and has a contract for a stretch of road as well as finding road agencies that are receptive to the idea of using alternative asphalt binder. Currently, the university is following up with a potential lead with a new company on the East Coast. The university works with a wide range of sponsors at all levels of government. For any product to be evaluated on a stretch of road, the university must work with the state Department of Transportation, Federal Highway Administration, county transportation departments and city departments.