Asphalt Target of New Research Program

In the new Asphalt Research Consortium (ARC), Hussain Bahia, a University of Wisconsin-Madison civil engineering professor, is using $5 million in funding to study ways of making asphalt more environmentally sustainable.

The university is one of five institutions nationwide to participate in ARC, the Federal Highway Administration's first major consortium to improve asphalt technology since the Superpave effort of the early 1990s.

More than 90 percent of U.S. roadways are paved with asphalt, which means any modifications that boost its recycled content, lengthen its life, or cut the energy needed to manufacture it could have a big impact, says Bahia. One of his first goals is to develop so-called "cold mix" asphalts for widespread introduction into the United States. Places like Africa and India have used them for decades, and research shows they can save up to seven times the energy of their hot mix counterparts.

"This is a no-brainer," says Bahia, who has studied asphalt for more than 20 years. "If any person involved in managing our infrastructure looks at the data, why would you spend more energy and money on something else? But the challenge will be to show through advanced design of these materials that the performance is equal."

Asphalt is a byproduct of oil refining; essentially, it's the black, sticky stuff that remains after fuel and lubricating oil are extracted from crude petroleum. It's too thick, however, to be laid on roads as is. That's why in places like the United States and Europe, it is heated to temperatures as high as 300 degrees Fahrenheit, making it easy to pump and apply.

Other parts of the world have taken a different approach. In South Africa, for example, asphalt is made workable by shearing it into fine particles, and then mixing it with water and soap-like chemicals called surfactants. The surfactants keep the asphalt in solution until it's laid, after which it hardens to form the road surface.

Studies by Canada's Office of Energy Efficiency and others have found that paving with these cold mixes (also called emulsions) saves significant amounts of energy, especially when combined with recycling efforts. These asphalts also cut emissions of carbon dioxide and other gases. But a number of issues remain, and this is where Bahia hopes his research will make a difference.

"At U.S. refineries today, there are very mature, established specifications for hot binders -- our paving-grade asphalts," he says. "But for emulsions, there is no clear agreement on how to define the quality. So, we have emulsions already, but we don't produce them as much because the specifications aren't as clear."

Bahia said he'd like to experiment with adding materials to cold mixes, such as polymers or plastics, which can make pavements quieter, safer, and more durable. In fact, these "modified" asphalts are the major thrust of a new campus center he's establishing called the Modified Asphalt Research Center (MARC).

He first wants to develop quality control tests and standards that will encourage U.S. engineers, chemists, and road builders to adopt cold mix asphalts, or at least give them a try. This means first defining the critical ways in which these asphalts fail, and designing systems for detecting the failures.

"We can then determine the chemistry or physics that will give us a larger margin of safety from these failures," says Bahia. The final step will involve simulating various climate conditions in the laboratory to see how failure limits change with freezing cold or blazing heat.

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