Road testing: Research team studies potholes in quest for better asphalt sustainability

A Missouri S&T research team is studying asphalt binders, the materials that hold road materials together, to better understand how they perform and help improve the durability of Missouri's roads. Because roads are constantly exposed to sunlight, changing weather and the stress of daily traffic, these binders can break down over time, making reliable testing essential.

The team is evaluating the unaltered chemical microstructure of road aggregate mixtures before and after use to test how well the materials perform over time.

"Where you see a pothole, I see a research opportunity," says Dr. Klaus Woelk, professor of chemistry at Missouri S&T. "We are measuring how to best treat asphalt so that we can fix roadways more efficiently and more cost-effectively."

Woelk and his research team are conducting relaxometry analysis of asphalt samples, looking at how rejuvenation treatments change the microstructure of the asphalt over time. He uses nuclear magnetic resonance (NMR) excitation to measure the performance of asphalt.

"It's like an MRI for early cancer detection, but for asphalt failure," says Woelk. "We excite the asphalt materials through NMR and then measure how soon they return to their normal state."

Asphalt binder is a tar byproduct of the crude oil refining process. To make road pavement, it is mixed with aggregates such as crushed rock and limestone. These materials were underground for millions to hundreds of millions of years without exposure to the sun and air. Once exposed to sunlight and air, Woelk says, asphalt changes in its molecular structure, becomes more brittle, loses its elasticity and cracks more often.

"Right now, it is the Wild West of research and development because there is not a firm definition of rejuvenation for asphalt," says Dr. Rebecca Herndon, a research collaborator in Woelk's lab and a university alumna who earned a bachelor's degree and Ph.D. in civil engineering. "Measuring the microstructure in asphalt core samples with NMR is useful because we can detect the difference between new, aged and rejuvenated sections."

Herndon says the research addresses a need for rapid quality testing of asphalt before and after it is laid.

The researchers are sharing their findings with experts at the Missouri Department of Transportation (MoDOT).

"Our results can help develop standards for asphalt rejuvenation materials," Woelk says. "That would be a huge selling point for companies that mass-produce these rejuvenation oils and contract with various transportation departments throughout the country."

Woelk's research team also includes two undergraduate students: Rosalee Brown, a senior in chemical engineering, and Catherine Skaggs, a junior in chemistry.

"Asphalt ages from things like ultraviolet (UV) light, oxygen exposure and the freeze-thaw cycle, so we try to get samples from a wide range of areas," says Skaggs. "For example, the needs for roads in Minnesota will be very different from those in Louisiana because the local climate has a huge impact."

Woelk's research team has collaborated with Corrective Asphalt Materials and MoDOT to get road samples.