Green asphalt? A plant-based compound may undo aging, boost recycling

Workers resurfaced a residential driveway. A Wilmington firm has created a plant-based compound that could replace traditional asphalt.
Workers resurfaced a residential driveway. A Wilmington firm has created a plant-based compound that could replace traditional asphalt.

There’s nothing green about asphalt, unless you can make less of the stuff by more efficiently reusing the pavement we’ve already got.

The Warner Babcock Institute for Green Chemistry in Wilmington says it’s found a way. The institute’s new plant-based compound, Delta-S, rejuvenates worn-out asphalt so it mixes better with new paving material. With Delta-S, road builders can add a higher percentage of old asphalt to their new roads, which means lower cost and reduced consumption of the heavy, toxic petroleum found in fresh asphalt.

“The road to sustainability has to be paved with superior quality, superior cost, and oh, by the way, it has to be better for the environment,” Warner Babcock cofounder John Warner said.

As a chemistry professor at the University of Massachusetts, Warner was a leader of the “green chemistry” movement, which trains chemists to consider environmental safety when developing compounds.

Warner earned his doctorate from Princeton University in 1988. At the time, he said, “not one university on the planet ever required any one to take a test on toxicity or environmental impact. That’s why I started the field of green chemistry — to change the way people do chemistry.”

In 1998, Warner coauthored a college textbook on the principles of green chemistry. In 2007, he and corporate attorney James Babcock launched the institute, a chemical think tank with about 30 doctoral researchers on staff. They develop effective, environmentally safe compounds for a multitude of uses. For instance, in April the company unveiled Hairprint, a new product for restoring natural color to gray hair. Hairprint contains no dye and is designed to supplant popular gray-hair treatments that contain potentially harmful lead compounds.

Warner Babcock plans to license Hairprint to cosmetics companies. But the institute has spun off a for-profit company, Collaborative Aggregates LLC of Wilmington, to bring the asphalt rejuvenator to market.

According to the National Asphalt Pavement Association, asphalt is already America’s most recycled substance. More than 76 million tons of it was scraped and chopped from the nation’s roads in 2013, with 1.3 million tons of it coming from Massachusetts. But only a 10th of the total ended up in landfills. Most was reused or stockpiled for future use.

Peter Montenegro, a marketing consultant for Collaborative, said that it isn’t rain, snow, or cold that’s mainly responsible for worn-out asphalt; it’s oxidization. The petroleum compounds in the pavement combine with oxygen from the air, making the road surface dry, brittle and subject to cracking and crumbling.

Delta-S, which is made for Collaborative by an outside contractor, reverses the process. “It softens it, and reverses the oxidization that has occurred,” Montenegro said. In addition, Delta-S allows pavers to mix the asphalt at a much lower temperature than usual — around 180 degrees compared to about 380 degrees. This means less of the oil evaporates, so there’s less air pollution and less wasted petroleum.

Lots of paving companies already recycle old asphalt by simply adding it to new material during the mixing process. But the finished product can contain no more than 25 percent recycled material. If more is added, the oxidized asphalt will weaken the pavement. But when Delta-S is added, “we can have recycled asphalt content up to 50 percent of the weight of the mix,” Montenegro said. Since old asphalt costs next to nothing, adding more of it to the mix lowers the price of paving.

Other companies make asphalt recycling products, but these often contain highly toxic substances such as hydrolene, a petroleum extract that has been linked to cancer, birth defects, and organ damage. By contrast, Delta-S is nontoxic.

Asphalt mixed with Delta-S has been used only in a few places, so its durability is still an open question. Dave Hickey, a town engineer in Wellesley, has used it to pave the city’s recycling facility. “The jury is still out a little bit for it,” said Hickey, who noted some cracking along seams in the pavement. But he said that the problem might be due to incorrect application by the contractor, who had never worked with Delta-S before.

Hickey said that it’ll be good news for taxpayers if Delta-S lives up to Warner Babcock’s promises. “If this becomes more mainstream technology,” Hickey said, “I would expect costs would go down, and that would be a great thing for municipalities.”

Hiawatha Bray is a technology reporter for the Boston Globe. E-mail him at
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