Getting Warm

In the asphalt paving industry, the past two years has brought a flurry of advances in recycling practices and mix design. The elephant in the room – the development pavement engineers must understand – is the warm mix phenomenon.

Imported from Europe a decade ago on a trial basis, NAPA saw warm mix as a way to reduce fumes and enhance the working environment for paving crews. The product was demonstrated at the 2004 World of Asphalt and trialed around the country over the next several years, during which time a variety of other benefits were discovered, most notably: easier compaction, less sensitivity to ambient temperatures and haul distances, and an excellent medium for high-ratio RAP (reclaimed asphalt pavement) blending.

Not to mention: a reduction in carbon footprint of 10 percent or more based on energy savings alone. Using the greenhouse gas calculator on NAPA’s website (www.asphaltpavement.org), Howard Marks, Ph.D, JD, MPH, director of environmental and regulatory affairs for NAPA, demonstrated a conservative example of the savings.

“If a plant produces mix at 250 F rather than 300 F, the calculator shows a 10-percent fuel savings” says Marks. A 10-percent fuel savings will reduce CO2 emissions by 10 percent, from 45.5 pounds per ton mix to 41 pounds. But we’ve seen up to 15-percent fuel savings documented during field trials.”

The use of warm mix has mushroomed. “In 2009, warm mix production hit 17 million tons in the U.S., and in 2010 it went to 47 million tons,” notes Margaret Cervarich, NAPA’s vice president of marketing.

Usage is being driven by the mix’s construction virtues. “In states where contractors can use hot or warm mix, many contractors are opting for warm mix because it yields a nicer work environment and it’s easier to compact,” notes Kent Hansen, PE, NAPA’s director of engineering. “Even if there’s a slight increase in the cost of warm mix, they make it up in eliminating penalties or getting bonuses for density.”

Asphalt’s already low carbon footprint will decline even more as the warm mix marketshare grows, and it is expected to continue its rapid growth curve for the foreseeable future. NAPA forecasts that warm mix will claim 50 percent of the asphalt market in three to five years.