April 9, 2009

Paving industry warms up to warm-mix asphalt process

Construction Corner

Korky Koroluk

A family of technologies known collectively as warm-mix asphalt, is beginning to gain traction in the North American market.

It’s no big trend yet, but it might well become one, as the paving industry, like all others, searches for ways to become more environmentally friendly while maintaining profitability.

Warm-mix asphalt, or WMA, originated in Europe, where it is used in Belgium, France, Germany and Norway. It came to the United States in 2002, and three years later it arrived in Canada. Since then, there has been a scattering of demonstration projects, and some interest among hot-mix paving companies.

Now a technical working group has been formed in the U.S. Experts from the National Asphalt Pavement Association, several state departments of transportation, the Federal Highway Administration, and other related groups from both private and public sectors, meet periodically to talk about issues and share knowledge about WMA.

WMA allows the producers of asphalt paving to lower the temperatures at which the material is mixed and placed. Typical hot mixes range between 150 and 170C. Warm mixes range between 100C and 140C. The advantages of this are spelled out in a report written by a group of American experts who visited Europe a couple of years ago.

“Data indicate plant emissions are significantly reduced,” they said. “Typical expected reductions are 30 to 40 per cent for carbon dioxide and sulfur dioxide, 40 per cent for volatile organic compounds, 10 to 30 per cent for carbon monoxide, 60 to 70 per cent for nitrous oxides, and 20 to 25 per cent for dust.

“Burner fuel savings with WMA typically range from 11 to 35 per cent,” they wrote, and could range as high as 50 per cent with variations in the manufacturing process.

They found that the material can he hauled longer distances while remaining warm enough to be workable. It can be placed in cooler weather. It is easily compacted. And it also allows for the incorporation of higher percentages of reclaimed asphalt paving at reduced temperatures.

But there are still technical questions to be answered.

Does the lower production temperature mean that the binder does not age as much? Will the potential for thermal cracking be reduced? Will the potential for rutting be different? Will the contractor have to use a different grade of asphalt binder?

There is another question: Since most of the WMA systems are proprietary, how do you ensure that the tendering process is fair to all?

And that leads to another question: Can the technologies developed in Europe be adapted to North America, where climate conditions can be pretty severe, or will they have to be refined for North American use?

The WMA technical working group has set up a website, and posted a lot of information there, including the European practice report I’ve quoted from here. The site is solely to keep the paving community informed about research and development into WMA, so you won’t find any commercial material there.

There are things for sale, though, including good videos about WMA, and a best-practices guide.

But for a start, go to www.warmmixasphalt.com where you’ll find a link to the report on the home page. For quick information, there is a brisk little two-page summary of WMA on another website.

Works Alberta is a Calgary-based outfit that is part of the Colas Group of Companies, an international roadbuilding goliath based in France. Colas has its own labs, and has developed one of the WMA technologies that’s already on the market.

But the company has written and posted a brief summary of several warm-mix processes, not just its own. Go to www.works.alberta.ca and follow the Technical>Warm Mix Asphalt links.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com

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