Don Rooney, owner of Pioneer Paving & Grading, was introduced to the idea of warm mix asphalt (WMA) at National Pavement Expo in 2009. The idea of a cooler paving mix that could be hauled farther, was still workable when delivered to the jobsite, and was easier on the crew and equipment intrigued him, so he tucked it in the back of his mind to look into further.
This spring he attended a WMA introduction presented by his local hot mix supplier, LaFarge Asphalt, and began to watch for a job where he could try the new environmentally friendly product. Before long the Albuquerque, N.M., contractor bid a large project for Christus St. Vincent Regional Medical Center in Santa Fe that included pulverizing and paving two roads on the hospital grounds, constructing a new parking lot and repair and overlay of nine others. One caught Rooney's eye.
"As you enter the hospital grounds on the left side is the medical dental parking lot, and I thought it would be a great place to try out the warm mix asphalt. So I approached Larry Dennis, the head engineer, and asked him, 'What would you think if the hospital parking lot went green?' He liked the idea right away but was concerned about the cost," Rooney says, adding that warm mix asphalt can cost up to $2 per ton more than traditional hot mix.
He contacted Ken Kugler at LaFarge and the supplier agreed to work with Pioneer Paving on price for that one parking lot. "They wanted to get warm mix asphalt out in the market and get it down so more people know about it and could come and take a look at it," Rooney says.
Warm mix breaking in
Warm mix asphalt is not only one of the newest U.S. paving technologies (it's been in use in Europe for years), it's the paving industry's main effort to "go green." Kugler says it's considered a "green" product because it takes less energy to produce and because it results in less fumes than traditional hot mix.
Warm mix asphalt is produced at temperatures between cold mix and hot mix, generally 50°F to 100°F below traditional hot mix temperatures. Warm mix requires foaming of the asphalt cement using either water or additives. Foaming reduces the viscosity of the asphalt cement, coating the aggregate at lower temperatures.
"We use a water-injection system that foams the oil and then coats the aggregate so it has a ball-bearing effect making it easier to move around," Kugler says.
LaFarge has been producing warm mix since March and didn't have to add any capacity to its Gencor Industries 500 ton-per-hour plant to do it. He says the 70-person plant, which supplies concrete, asphalt, and aggregate within a two-hour radius of Albuquerque, has been producing 1,500 tons of WMA a day. Kugler says LaFarge has supplied warm mix for more than 25 jobs including a parking lot four hours away − a job the plant couldn't have supplied with traditional hot mix.
"Travel time can be increased with warm mix because it cools slower than regular hot mix would so you can travel farther. We wouldn't have wanted to send normal mix that far," he says, adding that three hours is about the most they will send normal hot mix. "The warm mix will open a number of markets for us."
Proponents say that in addition to increasing haul times and distances, WMA offers a number of advantages, including:
- Fuel savings for the mix producer
- Fewer emissions at the plant and on the jobsite
- Improved worksite conditions
- Paving in colder weather
- Acts as an aid in compaction
But all those were only of marginal interest to Rooney, a member of the Pavement Advisory Board, who simply wanted to see how the mix performed.
Planning the warm mix job
The hospital required the work be done on a Friday. On the first Friday it rained and the second Friday the temperature was 57°F. Rooney rescheduled the job again because he was concerned about cold joints.