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How a bioindustrial additive makes old asphalt young again

August 27, 2018

For most asphalt, there’s no such thing as retirement. But there is something like an elixir of youth.

Asphalt is the most recycled product in the United States. Nearly all of the old pavement scraped up when roads are repaved can be put back to work.

But it becomes brittle as it ages, limiting how much can be recycled at one time. The rest is stockpiled faster than we can reuse it. In some places, the piles get so big that they’re fitted with signal lights to alert low-flying aircraft.

Cargill is working to change that, incorporating an engineered plant-based additive into asphalt mixes that pushes the limits of how much reclaimed pavement can go back onto the road.

Cargill’s Anova rejuvenator rebalances the chemical composition of bitumen, asphalt’s petroleum-based liquid binder.

Over time, bitumen degrades. That limits the amount of recycled pavement that can be used in new roads without sacrificing performance. Surface repaving, which makes up most road work in big cities, typically uses only about 20 percent recycled asphalt.

But asphalt mixed with Anova rejuvenator can perform as well or better than standard mixes while using a far greater percentage of recycled content. The result is pavement that’s more sustainable and cost-effective.

Putting it to the test

Anova mixes have already been adopted for many roads around the world. In the last year, a million-plus tons of asphalt pavement used Anova. In the Netherlands, mixes use as much as 85 percent recycled asphalt. In New York and New Jersey, where repaving is a near-constant process, it can be as high as 100 percent.

In other places, local partners want a closer look at how it performs under their own road conditions. In Hopkins, Minnesota, for instance, it’s getting a side-by-side test starting this summer in which the county’s standard blend of asphalt – about 30 percent recycled content – is laid alongside an Anova mix that used 45 percent.

It’s a golden opportunity to see how the different mixes compare when everything else— the weather, the traffic, the underlying road bed — are the same, said Hassan Tabatabaee, global technical manager for Cargill Bioindustrial’s Anova Asphalt Solutions.

“This is a lane-to-lane comparison,” he said. “It’s really important to see how it performs under the same conditions.”

The project is small – the mix with more recycled content covered one of four lanes in a 1.1-mile stretch of road. Even that was enough to put 125 tons of additional reclaimed asphalt back onto the road — the equivalent of six full dump trucks. That’s in place of more resource-intensive new asphalt.

Had the Anova mix been used to pave the entire project, it would have put more than 500 tons asphalt back onto the road.

The potential to be able to use more recycled asphalt is attractive to Hennepin County Public Works, the local government agency responsible for the project.

“We’re always looking at ways to be innovative in maintaining our infrastructure,” said Colin Cox, a county spokesman. “This was a great opportunity to look at the mix’s longevity, sustainability and how it hold ups over time.”

Anova blends will also be put to the paces this year in two high-profile test sites — Minnesota’s MnROAD test track and the National Center for Asphalt Technology track at Auburn University in Alabama.

The one-two punch of warm, humid Alabama and punishing winter in Minnesota will give the mixes exposure to the range of conditions recycled asphalt needs to endure, said Susan Listberger, the Cargill product manager for the project.

“If it can make it there, it can make it anywhere,” she said.