Pig manure may pave the way to sustainable road building

Chunks of asphalt made with binders derived from pig manure, which can replace the petroleum found in traditional asphalt

Researchers from North Carolina A&T State University have developed a process that uses pig manure as a low-cost replacement for petroleum in the production of road asphalt. In searching for bio alternatives, the group discovered that swine waste is especially rich in oils very similar to petroleum, at a grade too low to make gasoline but suited for asphalt.

With funding from the National Science Foundation, the group developed a process that turns the waste into a black crude – the sticky binder that can be used to make asphalt. The cost to process the manure oil is US$0.56 a gallon, which is much cheaper and greener than current petroleum binders.

"It is different from petroleum refinery, which distills crude oil to produce mainly fuel and leave the residue for asphalt," Ellie Fini, lead researcher and assistant professor of civil engineering, told Gizmag. "Here we produce bio-adhesive from breaking bio-mass molecular structure and re-synthesizing the bio-adhesive structure. Bio-adhesive is lower in cost, requires less heat for mixing and compaction and is more durable."

For drivers concerned about the odor of their roads, the compounds that give pig manure its uniquely pungent smell – a stew of volatile fatty acids – are filtered out during processing. And the dry matter left over from the process can be used as fertilizer.

Meanwhile, the bio-asphalt is being put through rigorous testing to see how it will hold up under real world road conditions, including a simulation of truck traffic making 20,000 passes over it. The tests have so far been successful, passing Department of Transportation specifications, which led the group to form the company Bio-Adhesives to scale up their research.

"We think it's scalable and cost-wise it's profitable," says Fini. "Our vision is to help the farmer and help the construction industry, both sides. We see a win-win approach in the solution."

Asphalt made from pig manure could alleviate what's become a huge environmental issue – effluence from factory farm feedlots – especially in large swine-producing states like North Carolina.

"We generate 43 billion gallons of swine manure in the world every year," says Daniel Oldham, graduate student researcher on the project, who adds that China produces 10 times the amount of pig manure as the U.S.

At the same time there are around 2.3 million miles of asphalt paved roads in U.S., with the cost of paving an urban two-lane road with traditional petroleum asphalt costing over $800,00 per mile.

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