Al-Qadi, IDOT pave the way for 100% sustainable pavements

Illinois has 15,969 miles of state highways, so finding efficient ways to maintain and repair its roadways is critical.

One solution? Recycling and repaving roadways without transporting materials or using heat.

Illinois Center for Transportation and Illinois Department of Transportation examine cold recycling in their joint project, “R27-227: Moisture Content and In-Place Density of Cold Recycle Treatments.”

Imad Al-Qadi, ICT director and University of Illinois Urbana-Champaign Bliss Professor of Engineering, leads the project with John Senger, IDOT Engineer of Pavement Technology.

Cold recycling of pavements, a technique used by transportation agencies since the 1970s, can occur in place or at a plant and is usually done using 100% recycled materials.

“(Cold in-place) recycling is a fairly fast and effective treatment,” Senger said. “A recycler goes through, mills up the old pavement, sprays in the emulsion and then paves it right back down.”

The challenge?

Cold recycling uses water in the engineered emulsion, which makes the recycled material workable while binding it back together. Moving forward with construction while there’s too much water trapped in the pavement can lead to long-term problems and shorten the pavement’s life span.

To better control the quality of cold-recycled pavements, the researchers aimed to develop a technique to measure water in pavement.

“Illinois has been using cold recycling,” Al-Qadi said. “But to make it more effective and reduce potential premature pavement failure, we want to ensure that the performance of this recycled pavement is the same if not better than other pavements.”

Al-Qadi’s team turned to a technique he and colleagues have pioneered over the past 30 years: ground-penetrating radar.

GPR is a nondestructive test that sends electromagnetic waves into pavements. The reflected waves can be used to calculate dielectric properties related to material composition.

Al-Qadi’s team used the technology to quickly monitor the moisture of an entire stretch of recycled pavement, a departure from measuring localized small spots with a nuclear gauge.

Using advanced signal analysis techniques along with electromagnetic theories, they were able to correlate data processed from the GPR with field moisture measurements.

Al-Qadi’s team found that GPR accurately predicted moisture content in the recycled pavement and is a promising technology for transportation agencies looking to implement cold-recycling practices.

Key to the project is a user-friendly tool the researchers developed for IDOT engineers looking to adopt their technique.

The tool relies on the theoretical Al-Qadi-Cao-Abufares model to estimate moisture in recycled pavements, developed by Al-Qadi along with Qingqing Cao and Lama Abufares, UIUC graduate research assistants.

Their tool presents “sophisticated analyses in a very simple way,” according to Al-Qadi, and will help transportation agencies to know when to move on to the next step of the construction process safely.

Effectively implementing cold-recycling methods will help support the use of 100% recycled pavements as well as use fewer natural resources, helping combat climate change and protect the environment.

The technique is also expected to save taxpayers’ money by reducing potential damage to roadways and the time needed for work zones.

“(Cold in-place) recycling is more environmentally friendly than other methods,” Senger said. “We can affect more roads and improve them at a higher percentage than what we can with our normal rehabilitation methods as well as reduce carbon emissions by up to 30%.”

Al-Qadi noted that the effort would not have been possible without the support and assistance of his students, ICT engineers, as well as various IDOT engineers and industry members.

“I am very pleased with all the help that we got from ICT and IDOT engineers, several contractors and Heritage Group, the industry consultant on the project,” Al-Qadi said. “They all worked together as a team to accomplish this work, and their support and excitement for a new technology was amazing.”