By Mark Rea

The National Asphalt Pavement Association is ready to embark upon a research program that could revolutionize the hot mix industry enough to eliminate "hot" from the mix.

Following a 2002 study tour of European research facilities, NAPA has given its blessing to the National Center for Asphalt Technology at Auburn University to research methods for reducing asphalt mixture temperatures by as much as 20 percent.

According to most experts, "warm mix asphalt" could improve paving performance as well as reduce emissions and odors while improving cost efficiency at asphalt plants.
"If a 50- or 60-degree reduction is achievable, there is going to be a significant reduction in energy consumption," said NAPA President Mike Acott. "Naturally, that would translate into increased cost efficiency for asphalt-producing plants."
The savings for asphalt plants would come in terms of emission control costs, which typically account for 30 to 50 percent of plant overhead. Typical temperatures for hot mix asphalt range from 300 to 325 degrees Fahrenheit, with warm mixes dropping to around 240 degrees.

Wayne Evans, senior vice president of asphalt operations for Florida-based Hubbard Construction Co. recently told Engineering News-Record that warm mixes would also make asphalt easier to install. "The material is more fluid, so we may be able to achieve density easier and using more static rollers instead of more expensive vibratory rollers," he said.

Once the research program begins, NCAT will look at two separate warm mix technologies. Aspha-Min was developed in France in 2001 as a fine admixture powder. It is a synthetic zeolite substance comprised of natrium aluminum silicate, which is introduced into liquid asphalt and aggregate along with other binding agents at the plant.

The other test material is WAM-Foam, developed in 1995 by a joint venture of Shell Global Solutions and companies from France and Norway. It is a process that blends hard and soft binders to make asphalt workable at lower temperatures.
Both methods were on display for the study tour, which included NAPA Chairman Peter Wilson, Asphalt Paving Environmental Council Co-chairman Michael Mangum, Dr. Mary Stroup-Gardiner of NCAT and Acott.

"We were extremely impressed with what we saw," Acott said of the tour that took the group through asphalt plants, paving sites and completed roadways in Germany and Norway. "The early results seem to show the mixes performed as well as conventional hot mix.

"Therefore, NAPA has taken the position that we are going to evaluate these different technologies. And there may be others. There is another technology that uses a wax ingredient to change the viscosity of the binder at mixing. There may also be other technologies that we will want to evaluate. So we are initiating this program at NCAT to evaluate these technologies in the lab, to look at how they do against conventional hot mix, to look at their rut resistance and then to put them into service and evaluate their performance. I would expect that this program will be up and running by later this summer."

"This certainly sounds like it has promise," said Harold Mullen, executive vice president of the Texas Asphalt Paving Association. "The benefit of warm mix is something we'd definitely be interested in here in Texas.

"Obviously, though, the proof will be in the research. What will the quality be like? Will these mixes be durable? Will they be readily available? Then we have to be patient enough to see if it they can prove themselves. But we're encouraged but what we have heard so far and very encouraged that NCAT and NAPA are stepping up to the plate to research warm mix."