“Sometimes you can even smell what the restaurant was frying in the oil,” Wen said with a laugh. “Corn oil or peanut oil, it all works.”
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. “First we make a very small sample and measure its properties. Then we make a slab about the size of a conference table and run a wheel over it. Then we make more pavement and put it outside in the elements.”
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.
Yet another part of Wen’s research involves the temperature to which asphalt must be heated to be used for 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. As an added bonus, the blue smoke isn’t produced at those lower temperatures.