Pennsylvania Gets Out Front With Rubberized Asphalt

The Pennsylvania Department of Transportation (Penn DOT) launched a project last month to evaluate the long term performance of a warm mix asphalt rubber gap-graded (AR-GG) mix on the surface pavement layer of a high volume traffic road.

The project drew interest from stakeholders from across several disciplines including asphalt, engineering, tire recycling, pavement research and testing who joined Penn DOT officials for a project briefing and tour hosted by project contractor All States Materials Group (ASMG).

The September 24 briefing included a tour of the asphalt rubber blending operation and mix production at Lebanon Materials in Annville and placement and compaction of the rubberized asphalt mix on I-78 in Berks County, PA.

DOT officials from neighboring Maryland, Delaware and New Jersey also participated in the tour. Delaware and New Jersey are using rubberized asphalt and Massachusetts has been incorporating recycled tire rubber in its paving mix for the last two years, Mark Belshe, Executive Director of the Rubber Pavements Association and an attendee at the project briefing said.

“The PennDOT project is significant because it marks a continuation of the use of asphalt rubber in the eastern region of the U.S.,” Belshe said.

For the project, PennDOT placed a warm mix asphalt rubber gap-graded (AR-GG) mix on the wearing course of a five-mile section of I-78 in Annville. Two layers of 1.5 inch of AR-GG surface course material were placed on the eastbound lanes of the high volume road.

The heavily traveled road has an average daily traffic volume of 18, 438 vehicles. Thirty-eight percent of which is truck traffic, according to Penn DOT.

“The result of this research project and follow up testing is to document, observe and quantify the long term performance benefits of asphalt rubber,” Mark Edsall of ASMG’s Technical Marketing Division said.

A ten-year formal evaluation of the AR-GG wearing course will be conducted. A decision on approval or disapproval of the use of AR-GG will be made three years after final placement of the asphalt mix; sooner if the evaluation warrants, Edsall said. The project includes a control section paved with a conventional warm mix asphalt (no crumb rubber) material.

Warm mix asphalt (WMA) reduces the high mixing temperatures of regular hot mix asphalt. Its benefits are reduction in energy consumption during production and reduced emissions during production and placement. WMA also offers contractors the ability to pave at lower temperatures, extending the paving season.

Materials testing will be conducted at the conclusion of the project, Edsall said. Three different research universities (UMASS Dartmouth, Rutgers University and Arizona State University ) have already requested test quantities of both the AR-GG surface mix and the control mix to do their own lab testing, Edsall said.

On another note, Edsall said the Transportation Research Board is also recognizing the interest in rubberized asphalt and is devoting a session solely to rubberized asphalt at its annual meeting in Washington, D.C. in January.

The project used about 17,000 tons of AR-GG mix including 500,000 pounds of crumb rubber produced by Pittsburgh, PA-based Liberty Tire Recycling. According to ASMG, the addition of 15 to 20 percent of crumb rubber material to a warm mix asphalt can improve resistance to rutting and cracking and increase long-term durability of the pavement overall.

© Scrap Tire News, October 2012