October 14, 2024
Mizzou researchers are devising a way to demonstrate how rubber-based asphalt reduces greenhouse emissions.
Oct. 15, 2024
Contact: Janese Heavin,聽heavinj@missouri.edu
Photos by Zac Anderson
Roads made with rubber-based asphalt mixtures are proving to be more durable than traditional asphalt, and they鈥檙e better for the environment by providing an effective way to recycle discarded tires.
But do they also help reduce greenhouse gas emissions? That鈥檚 what civil engineering researchers at the University of Missouri are now aiming to find out.
Bill Buttlar, a professor in Mizzou鈥檚 College of 糖心Vlog传媒, is optimistic the team鈥檚 findings could pave the way for a new era of rubberized roads across the U.S.
鈥淩ubber-based roads have been around for more than three decades, it鈥檚 just that the amount of this material has been relatively small,鈥 said Buttlar, who is the Glen Barton Chair in Flexible Pavement Technology. 鈥淚n the U.S., growth of rubber-modified asphalt has been slow. Now, the increased focus on sustainability is creating a demand for it.鈥
A recipe for success
To ensure contractors know what they鈥檙e getting when choosing which asphalt mixtures to use, Buttlar and his team are devising a way to quantify the environmental impact of rubber-modified asphalt.
This includes measuring the amount of carbon dioxide (CO2) and other greenhouse gases emitted not only when roads are built, but also during the process of grinding tires into rubber.
With a $1.2 million grant from the Environmental Protection Agency, the team is creating environmental product declarations (EPDs) for the recycled tire rubber industry. These EPDs act like nutrition labels for construction materials, said Punya Rath, an assistant research professor who works alongside Buttlar in the Mizzou Asphalt Pavement and Innovation Lab.
鈥淔ood labels are highly visible and will tell you about the product 鈥 it has this many grams of sugar, this much sodium and so on,鈥 he said. 鈥淓PDs will tell you how much CO2, nitrogen dioxide and other gases are emitted during the production of rubber-modified asphalt mixtures.鈥
That data already exists for more traditional asphalt mixtures, as well as other construction materials, and can be found in a national database. But the data has not yet been collected for roads using rubber-modified asphalt.
And that鈥檚 especially important now that the Federal Highway Administration (FHWA) 鈥 which oversees the nation鈥檚 highway systems 鈥 has allocated funding to boost the use of low-carbon construction materials.
鈥淔or the FHWA to enforce low-carbon materials, there has to be some way to quantify it,鈥 Rath said. 鈥淗ow are you going to say which asphalt is less carbon-intensive? We need a scoring system to make that comparison.鈥
To get the data, Mizzou researchers are working with the U.S. Tire Manufacturers Association, as well as Michigan Technology University, and the Scrap Tire Research and Education Foundation.
A sustainable path forward
More than 350 million tires are produced in the U.S. each year. And right now, there aren鈥檛 many uses for discarded tires.
鈥淭hey can go to landfills, but that鈥檚 not great because tires are tough and don鈥檛 degrade easily,鈥 Rath said. 鈥淭hey can be burned, which is greener than burning coal but a waste of highly engineered materials.鈥
While rubber from recycled tires has been used in products such as mulch and roof shingles, the market for these applications hasn鈥檛 been large enough to keep up with the supply. There are, however, plenty of roadway miles in need of repair.
鈥淭he transportation industry produces about 500 million tons of asphalt per year,鈥 Rath said. 鈥淲e could use a significant number of scrap tires, if not all, that the U.S. generates.鈥
To test the viability of rubber-modified asphalt, Buttlar and his team have been working on several road projects across Missouri, including a聽
In Kansas City, crews recently laid asphalt containing both rubber and recycled plastic along a municipal road. Additionally, rubber-modified asphalt has been used along interstates 44, 70 and 155, as well as U.S. Highway 63 near Rolla.
The results so far have been promising, Buttlar said. Studies have shown that rubber-modified asphalt roads can last up to two times as long as traditional asphalt surfaces, which results in less construction and fewer potholes. Rubber also makes the roads smoother, meaning less wear and tear on vehicles and tire treads.
Having sustainability data from the EPDs will also ensure these roads are environmentally friendly while still being as affordable as traditional asphalt options.
鈥淚n the past, we鈥檝e looked at what material contractors can provide at the lowest cost,鈥 Buttlar said. 鈥淣ow, we鈥檙e adding sustainability to that equation. This will allow us to choose the materials that perform well, are low cost and are better for the environment. This is a new tool to drive us toward that triple bottom line.鈥
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