Street-level Cool

Blacktop is getting greener.

UMD civil and environmental engineering faculty have been researching a technique for recycling pavement rather than laying new asphalt. Known as “cold mix,” the technique can reduce emissions 40% to 80%—and even speed up the repaving process.

“You don’t need to heat all the aggregates to 300 degrees; you can mix them at room temperature,” says Associate Professor Qingbin Cui, project lead. “You can touch it even when you’re paving the roadway.”

The process uses less energy, and therefore emits less CO2. Cold recycling takes milled-up pavement and sprays it with a foamed asphalt to bind and expand the material. It can even be done on site, with no need for carbon-emitting truck transport.

“We want to really accelerate the construction process,” Cui says. “With the recycled materials, you can do that overnight easily.”

Depending on the project, it’s up to 50% cheaper than new asphalt, says Chuck Schwartz, professor and chair of the department.

Drivers won’t notice the difference, they say; recycled pavement is currently only in the lower layers of roads, and the top layer is still traditional pavement.

The technique is already hitting roadways. To test it, the Maryland State Highway Administration added a lane on Interstate 295 South. The pavement has also been rolled out on parking lots and residential streets.

“It’s only a matter of time before somebody says to the secretary of transportation, ‘We have to reduce our greenhouse gas emissions as part of a concerted effort to deal with climate change,’” Schwartz says. “And this is going to be one of the tools that transportation agencies will be able to use to do that.”