Boston Logan's Warm Mix

Airport is first in the U.S. to use environmentally friendly asphalt

The mix would usually leave the plant at 270 to 280 degrees F and would only drop to about 260 degrees F directly behind the paver screed.

Using a Cat AP-1055D paver and a Blaw Knox material transfer vehicle, Aggregate’s paving crews placed approximately 4,700 tons per day.

“We didn’t use a material transfer vehicle the first day and realized the paver was idle for about 90 seconds between each truck, and when you’re placing a 5 1/2-inch lift it doesn’t take long to run through a truckload,” notes Dennis Horan, project superintendent. “So we brought out an MTV and that helped to increase our daily production rate.”

Paving the 37.5-foot-wide areas in three pulls, the paving crew would place 2,200 feet before backing up to lay the adjacent lift.

“With the MTV we managed to put down approximately 580 tons per hour,” says Horan. “We used four vibratory rollers (IR DD-130) and changed our rolling pattern (rolling) from cold to hot, to (rolling) from hot to cold in order to achieve better joint densities. We were able to achieve density a lot quicker with the warm mix, with the exception of the longitudinal joints, which required a little more work.”

Mat density specs called for compaction between 93 and 97 percent. Core samples and field density checks validated that Aggregate’s paving crew averaged 95 percent mat density throughout the project. The grade requirement for the project allowed for a ½-inch variance. Again, Aggregate’s paving crew met that spec 100 percent.

According to Horan, the Logan warm mix project was a “basic job” with few challenges other than weather related issues.

“We had some taxiway issues when the wind shifted and the airport had to shift over to a different runway that crossed the one we were working on,” he notes. “When that happened we had to shut down our operation. “We adjusted to that situation by working both nights and days, and in some cases 16-hour days to complete the project on schedule.”

Promoting the benefits
While the Logan project was not Aggregate’s first major warm mix job, it provided significant validation that a high-RAP, warm mix design not only performs as well as hot mix, but also saves energy, materials and provides customers like Massport with an environmentally-friendly solution to its paving needs.

“We produced 55,000 tons of warm mix this year for the Rte. 93 project through Boston, and we’ve produced and placed a substantial amount of warm mix for commercial customers as well as municipalities,” Nikitas says. “We’re able to produce quality warm mix with or without latex and with high or low amounts of RAP. Using Sasobit helps improve the viscosity of the mix, which allows us to achieve better compaction at a lower temperature.”

For the Logan project, it was simply a matter of providing a warm mix that could meet the stringent FAA specification requirements used on hot mix.

“The requirements are performance-based percent within limits that define air voids, stability, compaction and grade standards that need to be achieved,” says Mike Nichols, Asphalt Quality Control manager for Aggregate Industries’ Northeast Region. “Performance-based specifications on this job allows the contractor to offset any penalties with bonuses achieved in meeting the outlined requirements monitored by quality control and the Massport consultants. As a result, it is possible to achieve 100 percent payment allowed by the FAA specification.”

For Massport, proving that warm mix can provide a quality pavement that withstands the rigors of heavy planes was important in charting future repaving projects at Logan.

But more importantly, the project provided another way for Massport to continue its environmental stewardship commitment to reduce emissions and recycle valuable resources.

As Kinton noted earlier when announcing the Logan project, “We have a lot to be proud of, but we have much more work to do. We must do what we can to limit the environmental impacts of the aviation and maritime industries.”

You can be sure that warm mix asphalt projects designed with high RAP will be part of the solution.

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