Made from the residue left behind after production of gasoline, plastics, and other materials, asphalt still commands $700-800 per ton, or half the price of gasoline at $1,500 per ton, Wen estimates.

Asphalt binder, the sticky “glue” that holds crushed stone and sand together to form pavement, only accounts for about 5% percent of the final hot mix asphalt (HMA) that is steamrolled into glossy new lanes and boulevards.

HMA has to be tough and reliable, able to withstand wear from traffic and weather. In Wen’s lab, each component of his bioasphalt is subjected to a series of rigorous stress tests, such as intense heat, freezing temperatures, compression, and loading. After four years working with a chemist and “adjusting the recipe,” Wen is confident that his green, sustainable asphalt “is as good as the old-school petroleum asphalt.”

Only in the last decade has the green asphalt industry started coming together. It’s slowly picking up—more slowly than I wish.

—Haifang Wen

In Iowa, for example, scientists are making a corn-based bioasphalt from residue left after the production of ethanol. In North Carolina, swine manure is being incorporated as a paving substitute.

Building roads is a big investment in taxpayer money. In general, a one-mile road in a rural area costs at least a million dollars to build. With the waste cooking oil technology, we can reduce the cost of asphalt binder to under $200 per ton, making road building much cheaper.

—Haifang Wen