-Farm News photo by Lori Berglund
Buffalo Center farmer Brad Matson and 7-year-old son Monroe get an up-close look at the soy asphalt floor in the Varied Industries Tent at the Farm Progress Show.

Iowans may soon be walking, biking, parking and even driving on asphalt roads made from the fields of soybeans that pass like an ocean of green out the window as one drives across the state.

A renewable resource, grown in the United States, far more cost effective than traditional asphalt, and a new market for soybean growers was on display at the Farm Progress Show recently.

In a joint effort with the Iowa Soybean Association, Iowa State University researchers poured nearly an acre of 100 percent recycled asphalt that served as the floor of the huge Varied Industries Tent at the Central Iowa Expo Grounds near Boone.

For show visitors, it gave tired feet a more comfortable walking surface, but the greater goal is in increased demand for soybean growers, and more affordable paving options for all.

“This all started with a materials discovery dating back to 2010,” said Eric Cochran, professor of chemical and biological engineering at ISU. “What we figured out is how to convert soybean oil into a material called a polymer. It was unique in that, even though soy molecules have been used to make things like mattress foam and upholstery cushions and the like, formulating them into a polymer that could be dissolved into other materials was totally new.”

Asphalt has traditionally been made with crude oil. Like fuel prices, the cost of asphalt has been rising at a fast pace. And, like most industries, the asphalt industry has also been hard hit with supply chain issues. But the supply chain for soybeans is right here in the Midwest, and the cost is nothing close to crude oil.

While there are several ways to formulate soy polymers for asphalt-related applications, the project at the Farm Progress Show used 100 percent recycled asphalt, according to Cochran.

It all begins with an old asphalt road that has reached the end of the road.

“The way recycled pavement comes into being is at the end of a road’s life they are going to drive a milling truck over that old pavement,” Cochran explained. “It’s going to generate big chunks of pavement that are then hauled to a quarry or mix plant where it will be further ground into a gravel-like consistency.”

Such crushed asphalt is plentiful across the United States. And more of it is always being generated as old roads are torn out and new roads are constructed.

“There’s 130 million tons of this type of material currently stockpiled throughout the U.S. that is waiting for a home,” Cochran said.

The challenge has long been that it’s difficult to work with and compact on its own.

Asphalt requires a hot mix and a temperature of 350 degrees to be put down as a new road surface. The simple logistics of hauling and reheating old asphalt has been prohibitive.

“So, what you need is something other than heat to provide the softening, and that’s the first aspect of what the soy product does when it’s sprayed onto crushed asphalt,” Cochran explained. “It temporarily softens it, so that instead of heat, you are using chemistry to create a pave-able mix, so then you can drive the compactor over that while it’s in that temporarily softened stage. The result is that you get a very densely compacted paved surface.”

Cochran compared the chemical process to a child who sprays water into a sand box. The water lands on the surface of the sand and then soaks in and saturates all the sand in the box. The soy polymer acts as the moisturizer, the glue, that makes old asphalt usable again.

Potential uses are readily identifiable and quickly growing. Residential streets, driveways, golf cart paths, machine shed floors, parking lots, even reducing the number of gravel roads are all likely markets.

Secondary roads are an even bigger untapped potential market. “It’s a great choice for a sublayer on a county road,” Cochran says. “Even county roads are 12 inches thick. The top 3 inches is the surface course that interacts with the tires. Beneath that is another 9 inches of pavement, and there’s no need for that lower 9 inches to be the top quality, virgin asphalt hot mix. You can use these cold mixes as the sub-grade on fairly regularly traveled county roads.”

As a finished product, the soybean component is only about 5 percent of the overall product, according to Cochran. The greatest share is reclaimed rock and recycled asphalt binder.

These factors work together to make a more environmentally friendly, renewable product at a cost that is substantially less.

“The cost savings are pretty significant,” Cochran said. “An acre of pavement, like we had out at the Farm Progress Show, if that was all virgin pavement, you’re looking at about a quarter of a million dollars — and this year it’s even worse with the supply tightening of asphalt binder. A couple years ago, virgin asphalt was about $300 per ton, and this year there are places where it’s pushing $1,000 per ton.”

By contrast, the entire project with recycled soy asphalt came in far under that budget.

The project consumed roughly 2,000 pounds of soybean oil, the equivalent of about 200 bushels.

Depending on yields, that’s “including all the contractors, the dirt work, the dump trucks and everything, it came to $170,000,” Cochran said.

The work was funded by the Iowa Soybean Association to showcase the technology and promote this burgeoning new market for growers. It’s an example of check-off dollars at work for the good of agriculture.

Cochran is anxious to see recycled soy asphalt products hit the road in wide-spread use.

“The sooner the better,” he said. “We’re working with a couple of companies to get this on the market. We should be seeing website and glossy mailers and the like becoming available later this year or early next year.”

For Iowa State researchers such as Cochran, it’s gratifying to continue the Land Grant mission of helping move agriculture forward through real life applications.

“For Iowa State, I think it just continues a pretty long legacy of innovation in the ag space and putting science into practice,” he said.