Aggregate Industries’ Northeast Region recently placed 25,952 tons of warm mix asphalt on Runway 4R/22L at Boston Logan International Airport, the first airport in the nation to use the environmentally friendly asphalt on a runway repaving project, according to the Massachusetts Port Authority. This article originally appeared in Asphalt Contractor, a Cygnus sister publication.
When the Massachusetts Port Authority (Massport) awarded a $6.3-million contract this past summer to repave Runway 4R/22L at Boston Logan International Airport, the priority was to clearly reduce greenhouse emissions and energy during construction.
For the project’s general contractor, McCourt Construction, and its paving subcontractor, Aggregate Industries’ Northeast Region, that mission was accomplished this fall.
With a warm mix design, that is produced at approximately 50 to 75 degrees F lower than hot mix, Massport projected a significant reduction in carbon dioxide and heating fuel, and achieved energy savings and Btus. Along with the lower production temperature benefits, the project was projected to generate additional savings by incorporating 18 percent reclaimed asphalt pavement (RAP) back into the warm mix.
In a statement released earlier, Massport CEO and Executive Director Tomas J. Kinton Jr. said, “Warm mix uses 20 percent less energy to make, produces 20 percent fewer greenhouse emissions when applied, and allows us to use a higher percentage of recycled asphalt pavement in the final product. This project is another example of Massport leading the way as an airport operator to reduce our impact on the environment wherever we can do so in a financially responsible way.”
Since runway paving projects in the United States must meet stringent Federal Aviation Administration standards, Massport tested warm mix at Logan on a taxiway and apron areas last year with the technical support provided by Stantec, one of Massport’s consultants.
The contract called for milling and filling the outer 37.5 feet of each side of the 10,005-foot-long runway. The center 75-foot-wide portion of Runway 4R/22L had been repaved in 2006. Success of the project will ultimately determine whether or not warm mix will be used for all future paving projects at Logan.
On the 4R/22L project, Aggregate’s crews milled off the top 8 inches of the outer runway surface, and then replaced it with an FAA P-401 mix design. The warm mix design contained 18 percent RAP, along with a lime additive to prevent stripping and a latex additive which helps prevent rutting of the mix. All of the mix was produced at Aggregate’s Saugus plant, located eight miles from Logan. The mix was placed in two lifts — a 5 1/2-inch course and 2 1/2-inch course of P-401 3/4-inch Max Lime Latex RAP Warm Mix. Both mix designs utilized a high percentage of ½-inch aggregate.
Aggregate used the Sasobit Wax organic additive to produce the warm mix for the project. The organic additive has a melting point of more than 208 degrees F and provides higher viscosity than asphalt when below the melting point, and lower viscosity than asphalt when the temperature is above the melting point. This means the wax solidifies in asphalt when the temperature is between 149 and 239 degrees F.
Aggregate blended the Sasobit with a PG 64-28 liquid AC binder at its Everett AC terminal and then transported the mixture to the Saugus plant. The company installed a custom-designed blender at the Everett facility a year and half ago for purpose of mixing all warm mix binders just prior to delivery at any plant. It’s more cost-effective than customizing each plant to accommodate the production of warm mixes.
At the Saugus facility, a lime silo was added to meet the specs of the Logan project mix design.
“We found that Sasobit is really the best warm mix additive, and that proved to be the case on the Logan project,” says Mark Nikitas, Aggregate Industries’ Northeast Region marketing manager. “With the high level of RAP and the latex additive used in the mix, the Sasobit significantly improved the workability of the mix.”
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