What happens to road construction waste?

In every corner of the metro, and across Minnesota, you'll find construction crews ripping up roads and rebuilding bridges.

Work being done along Interstate 494 in Bloomington is just one of 200 projects the Minnesota Department of Transportation has scheduled this summer to fix up highways, bridges and other infrastructure. That's a lot of asphalt, concrete and steel being removed and replaced.

"We build out specifications with the anticipation that the material that's already on the job is going to get reused either on that job or another job," said Curt Turgeon, MnDOT's director of the office of materials and road research. "We really don't in the industry use the term 'waste.' What you'll hear is 'recycled.'"

According to the Environmental Protection Agency, about 95% of asphalt concrete waste from road and bridge projects is reused. How that happens is up to the contractor, according to Turgeon. 

"We write the specifications so that the contractor owns the material when we say remove it, and it's up to them to find the most cost-effective way to reuse it," said Turgeon.

Often the materials are crushed, milled, then reused directly on-site at the job where they were removed. If not, they're trucked to a contractor's home base, like Valley Paving in Monticello, to be used on future projects.

Brent Carron is Valley Paving's president. He looked over a chunky pile of concrete, asphalt and sand on his property, telling WCCO it came from Interstate 94 and neighboring Highway 25.

"Asphalt is the easiest [to recycle] because we can introduce that back into our asphalt plant to make new asphalt, but also we can crush it down to make road base, shouldering material," said Carron. 

When it comes to recycled concrete, Carron said they'll crush it to be used as an aggregate base for a road. It's then covered by asphalt. 

"Roads are the best source of materials for us right now," said Carron.

While asphalt concrete is highly reusable, it only makes up a portion of a new road. For MnDOT, Turgeon said about 20% to 30% of a new road is made from recycled material, while the rest is what they call "virgin" material. 

"We've had projects where we've done special things to allow over 40% recycled pavement back into the new pavement," added Turgeon.

At Valley Paving, crews harvest the raw materials from the land, a mix of sand and gravel. They're blended with recycled asphalt and oil to make new asphalt.

But Carron happily pointed to a pile of recycled asphalt that has a different plan. It will instead be used to make a road's shoulder, meaning the shoulder will be 100% recycled material. 

"The cool thing with this is it's just like normal asphalt. Once the sun hits it, Minnesota 90-degree weather comes, it kind of melts into place," said Carron.

That shoulder project has another benefit: saving taxpayer money. Turgeon said new asphalt is about $100 a ton, and it's heavily impacted by the price of oil. 

"With every ton we can recycle, we're saving $100 that would have cost us to come up with a brand-new virgin mix [of asphalt]," said Turgeon.

Another MNDOT project handled by Valley Paving cut down costs for taxpayers. 

"The original plan of the Highway 25 job was to use imported aggregate base, and we went to MnDOT and we said we could reuse the aggregate base on-site," said Carron. 

By reusing the same aggregate base, Carron said the project's price dropped by $250,000. It also saved them time by keeping all the materials on-site.

MNDOT previously told WCCO that an interstate's lifespan is 20 years for asphalt and 35 years for concrete. But thanks to recycling, those roads technically have several lives ahead of them.

"There's probably an infinite number of times we can recycle these materials," said Turgeon. "We haven't run into an issue with recycling asphalt pavement yet where the material we've taken up has been too brittle or too hard to reuse."

Steel is primarily found in bridges. According to the American Institute of Steel Construction, 98% of structural steel can be recycled for new uses. Reinforcing bar, or rebar, has a recycle rate of 72%.