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Out with the old: Recycled pavement approach brings new possibilities

7/28/2020 McCall Macomber

With all the uncertainty surrounding COVID-19, one thing remains the same: Illinois Center for Transportation and Illinois Department of Transportation are hard at work building better roads.

The two entities are studying moisture content in pavement in their joint project, “R27-227: Moisture Content and In-place Density of Cold Recycle Treatments.”

Imad L. Al-Qadi, ICT director and University of Illinois at Urbana-Champaign Bliss Professor of Engineering, and John Senger, IDOT’s engineer of pavement technology, lead the project.

The research team uses an asphalt lightweight deflectometer, a soils/granular lightweight deflectometer and ground-penetrating radar to measure pavement density near Farmington, Ill. on June 17. The researchers include, from left, Javier García Mainieri, Uthman Mohamed Ali, Qingqing Cao, Greg Renshaw, and Imad Al-Qadi.
The research team uses an asphalt lightweight deflectometer, a soils/granular lightweight deflectometer and ground-penetrating radar to measure pavement density near Farmington, Ill. on June 17. The researchers include, from left, Javier García Mainieri, Uthman Mohamed Ali, Qingqing Cao, Greg Renshaw, and Imad Al-Qadi.

Due to COVID-19, the researchers made sure to take extra precautions when kicking off the project.

“We made sure that our team was social distancing,” Al-Qadi said. “They wore masks in the field and maintained all guidelines provided at the state and national levels.”

“We were very pleased that we were able to help IDOT in an important research project like this, and, at the same time, we were very cautious and very diligent about what needs to be done to protect ourselves,” he added.

In the effort, the researchers are investigating cold in-place recycling, a recycling method in which existing pavement is milled, combined with engineered emulsified asphalt and repaved onto the road.

“This technique is cost-efficient and, most importantly, is environmentally friendly,” Al-Qadi said. “The pavement is 100 percent recycled and placed back on the road in one process, with minimal disruption to traffic and no expensive hauling of new materials.”

One of the drawbacks of this technique, however, is that moisture used in the mix needs to be dried before placing a new layer of asphalt or opening the road to traffic, or pavement failure may occur.

The team seeks to create a method to determine the amount of water left behind from cold in-place recycling, which will help regulate when the road should be opened to traffic.

Key to this issue is ground-penetrating radar — a technique similar to the radar system used to detect airplanes.

GPR sends electromagnetic waves into pavement to detect different materials, including moisture.

ICT is no stranger to this method, having pioneered its development for pavements over the past 30 years.

“(GPR) will potentially provide us the opportunity to look at the entire length of pavement that’s being recycled so we can determine if we’ve got problem areas that need a little bit more time to dry out before we place (the) wearing course,” Senger said.

The technology will also provide significant savings to researchers, as they will be able to predict the moisture level and density of pavement directly in the field at highway speeds.

As for the benefit to the public?

“We’re going to see a lot more recycle treatments (in Illinois). It’s not only cost-effective, but it’s more environmentally friendly to the public,” Senger said. “If we can increase the lifespan and improve construction practices of these treatments, we can not only make them last longer, but we can also give the public better roads going forward.”

“It’ll definitely be a game changer,” he added.