Published: Jun 4, 2008 1:00:00 AM
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Source: Austin American-Statesman (TX)
State road projects may soon warm up to the green movement if a new method to produce asphalt with fewer greenhouse gas emissions proves successful.
The Texas Department of Transportation is using "warm" asphalt for a three-mile-long paving project on Texas 71 near Austin-Bergstrom International Airport this week.
Warm asphalt is mixed at 240 degrees, compared with 330 degrees for traditionally used hot asphalt. The lower temperature reduces the amount of chemicals released into the air.
"Very few industries in this country have the opportunity to reduce their environmental footprint by 50 percent, so to have the sort of emission reductions as dramatic as we are seeing for this process is very significant," said Jonathan Maclver, a business development manager for MeadWestvaco Corp., the company that came up with the process.
Contractors and manufacturers say the so-called green asphalt is more expensive than traditional asphalt but is faster to mix and just as durable.
Joe Jackson, owner of Asphalt Paving Co. and a contractor for the Texas 71 project, said mixing the warm asphalt costs $53 a ton, $3 a ton more than the traditional method.
The pavement project on Texas 71 requires 8,500 tons of asphalt, and Jackson said his company can make 200 tons of asphalt an hour.
"With conventional hot asphalt, you have to get it heated to 300-plus degrees first, but with the warm asphalt, it cuts about an hour off the time for you to start producing the asphalt," Jackson said.
Myles McKemie, vice president of marketing for Ergon Asphalt and Emulsions Inc., a co-partner in developing the warm asphalt process, said warm asphalt has the same durability as hot asphalt. He said some preliminary tests at the National Center for Asphalt Technology at Auburn University show that the process may even slow down the "aging" of asphalt, extending its life.
"Asphalt lasts eight to 12 years before it needs repairs, so we estimate that with this process, it can extend the life to 10 to 15 years, possibly," McKemie said. "We can't say conclusively yet — only time will tell — but our testing so far indicates that."
Transportation Department spokesman Marcus Cooper said the agency will be monitoring the section of Texas 71 that was paved before deciding whether to use the warm asphalt process in future projects in Austin.
The key to the warm asphalt process, considered to be more environmentally friendly because it releases fewer chemicals into the air, is an additive called Evotherm, a compound that helps bind the asphalt at a cooler temperature and that South Carolina-based MeadWestvaco Corp. developed in 2004. Warm asphalt was first used in a pavement project in downtown San Antonio in 2005.
According to a study by Pinchin Environmental Ltd., an agency based in Ontario, Canada, carbon monoxide emissions decreased from 70.2 percent to 25.9 percent using the warm asphalt process compared with conventional methods, and carbon dioxide emissions dropped from 4.8 percent to 2.6 percent. The study also concluded that sulphur dioxide emissions were reduced to 2.9 from 14.9 parts per million, and nitrogen oxides decreased to 26.1 from 62.2 parts per million.
Levels of methane tripled in the study, but researchers attributed it to an error in collecting the sample.