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Designing better asphalt

The Aberdeen Times of Aberdeen, Idaho

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Rock Doc

Dr. Haifang Wen grew up in a rural area of Shandong province, in eastern China. In his youth there were not many paved highways in the Chinese countryside.

"Lots of the roads were gravel," he told me recently. "They were muddy when it rained. I remember riding a cow on them, or going along in a wagon pulled by a donkey."

Living in those conditions, Wen could see quite a bit of room for improvement in road materials.

"I thought, we can do better," he said with a smile.

Thus was bom Wen's interest in asphalt, the cheapest material that can be used to pave highways.

Now a professor in Civil and Environmental Engineering at Washington State University, Wen uses his education to research new ways of making asphalt better and cheaper.

The asphalt used in roads has traditionally been made from aggregate - small particles of rock - and products made from crude oil. When crude oil is refined, it produces a variety of products including light fuels like gasoline, heavier plastics, and also dense asphalt.

"But the price of asphalt made from crude oil is pretty high, about $700 to $800 per ton," Wen told me. "That really adds up. One lane of a highway, paved for one mile, costs about $1 million. Now you know where your taxes go!"

One alternative to traditional asphalt that Wen and the people in his lab are looking into is bio-asphalt. Instead of using petroleum, waste cooking oil can be processed into asphalt. Restaurants can be spared having to pay to have their waste fat hauled away, and with free raw materials the asphalt made from the waste oil can'be more economical.

Bioasphalt is grey, rather than black, and after sticking my nose into a little jar of it, I can testify that it smells better than asphalt made from crude oil.

The name of the game when it comes to designing asphalt is to balance the properties of the material so that it's not too stiff (or rigid) but also not too soft (or ductile). If it's too stiff, the material will crack in the cold of winter. If it's too soft, a truck driving over the asphalt on a hot summer day will make ruts in the pavement.

"We fine-tune our recipes," Wen said.

Another research area Wen's group is looking into uses solid waste in place of rock aggregate. Sometimes crushed glass can be used as aggregate, as can broken-up concrete. Even crushed steel slag is being tested. By recycling these solids, large volumes of materials can be diverted from the nation's waste stream.

Using different mixtures, Wen's group is researching materials that need only be heated to 200 or 220 degrees. That's a significantly lower temperature that allows for real energy savings. As an added bonus, the blue smoke isn't produced at those lower temperatures.

Wen's research is funded both by government agencies and industry. And although he's glad to be working in this country, he still goes back to China to collaborate with engineers there.

"They are doing a lot of paving in China now," he said. "The economy is booming."

Dr. E, Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human, and Natural Resource Sciences at Washington State University.



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Original Publication Date: February 26, 2014



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