Rock doc: Designing better asphalt
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 born Wen’s interest in asphalt, the cheapest material that can be used to pave highways. That interest propelled him through a university education and a Ph.D. Now a professor in Civil and Environmental Engineering at Washington State University, Wen researches new ways of making asphalt better and cheaper.
Asphalt has traditionally been made from aggregate — small particles of rock — and products of crude oil.
“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 alterative to traditional asphalt that Wen and the people in his lab are looking into is bioasphalt. Instead of using petroleum, waste cooking oil can be processed into asphalt.
Bioasphalt is grey, rather than a 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.
“Sometimes you can even smell what the restaurant was frying in the oil,” Wen said with a laugh.
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.
Another part of Wen’s research involves the temperature to which asphalt must be heated to be used in paving roads. Traditionally, the material has been heated to 300 degrees. That’s very hot, and accounts for the blue smoke you can see wafting up from paving operations along a road in the summertime.
“That means a lot of energy is required for major paving operations. And the smoke is not good for the environment or the workers,” Wen told me.
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 and doesn’t produce the blue smoke.
Although Wen is 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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