In partnership with the Missouri Department of Transportation (MoDOT), researchers from the University of Missouri (MU) Mizzou Asphalt Pavement and Innovation Lab (MAPIL) recently created a real-world test road using recycled materials such as scrap tires and plastic waste along a portion of Interstate 155 in the Missouri Bootheel.

By increasing the sustainability of asphalt mixes, this innovative method can help reduce the number of items going into landfills or leaking into the environment, said Bill Buttlar, director of MAPIL.

The I-155 project takes the group’s previous test road, installed along a stretch of Stadium Boulevard in Columbia, Missouri, one step further. Instead of just testing four different types of recycled materials, the I-155 project will evaluate the real-world effectiveness of nine different types of recycled materials in the creation of asphalt pavement. This includes three different types of polyethylene (PE)—a material commonly found in plastic grocery bags—and ground tire rubber, which is a newer way of disposing scrap tires.

The pavement mixture using recycled plastic is being applied to a deteriorating section of Stadium Boulevard in Columbia near US Highway 63.

We don’t just live in the laboratory. In the field of transportation material research, we need to see how all the various materials used to construct a road—the rock, the asphalt and the recycled materials — behave in the real world and gel together to build a road. Asphalt is liquified with heat, and when you put an additive in like a plastic or rubber material, you must get everything to bond together with good adhesion. But we’re only going to know if that happens successfully when we produce it on a full-scale level and then expose it to elements, such as different weather conditions and heavy traffic.

—Bill Buttlar

MAPIL specializes in a dry process, which allows the researchers to add the recyclables directly into the mixture before it’s applied to a road surface.

An asphalt pavement test mixture sample designed by the Mizzou Asphalt Pavement and Innovation Lab is ready for further lab testing to determine its strength and durability.

The form, shape and size of the plastics bring different challenges in how the material flows, how it behaves and how it mixes. So, we did extensive small-scale testing for almost an entire year before we moved to a larger scale out in the field with contractors.

—Punya Rath, an assistant research professor in the Department of Civil and Environmental Engineering

One advantage of this process is that the researchers can test the mixtures in the field using a mobile research lab, which they developed and used for both the Stadium Boulevard and I-155 projects.

Citing environmental concerns, Buttlar said the team makes sure everything they do is within the current limits as established by the Environmental Protection Agency (EPA).

We are designing the material to be able to hold or capture the environmental by-products at the highest percentage for the longest amount of time. It’s not going to be a 100% containment. Everything built in a natural environment will degrade over time, so that’s why EPA has standards for everything, and we make sure we are safely within those standards.

—Bill Buttlar