Kentuckians generate 4.1 million scrap tires per year, or the equivalent of 5.6 million passenger tires when considering the weight of larger truck tires. We recycle 81 percent into various products such as playground mulch, or tire derived fuel which is burned in industrial boilers or used in cement kilns. Still, 17.5 percent of waste tires are disposed in landfills. (Division of Waste Management 2012). Is there a better destination?
The Kentucky Transportation Cabinet (KYTC), in conjunction with the Energy and Environment Cabinet (EEC), reports the completion of the first rubber modified asphalt project in almost 20 years. The Department of Highways District 6, headquartered in Covington, is the construction manager for the paving of a 2.2 mile stretch of KY 8 running from I-471 to Dayton, Ky., on Sept. 25-29. I-471 connects downtown Cincinnati near Great American Ball Park, the home of the baseball Reds, and Paul Brown Stadium, the home of the football Bengals, with northern Kentucky. KY 8 runs by the Newport Aquarium and its surrounding shopping district. It is parallel to the Ohio River and includes many turn of the (last) century neighborhoods and shops. One contractor reports even uncovering the original street cobblestones while recovering the overlying asphalt!
Why pursue rubber modified asphalt? From the transportation sector, the use of rubber modified asphalt may help overcome any future shortages of polymer. Allen Myers, director of the Division of Materials in the Transportation Cabinet, says, “In 2008 we suffered a shortage of polymer used in premium-grade asphalt binder. Because of this scarcity and other economic factors, Kentucky used unmodified binders on major highways for a time. These materials could potentially result in higher rutting susceptibility and lesser pavement durability. We want to investigate the use of rubber modified asphalt as a possible replacement for polymers in case the situation reoccurs.”
From the side of the environment, the rubberized asphalt consumes about 2,000 waste tires per lane-mile according to CAL Recycle. Also, the crumb rubber market represents a higher end-use. The sale price for tire derived fuel is about $20-40/ton while crumb rubber for asphalt brings $100-400/ton for the scrap tire processor. Development of the fine rubber market in Kentucky would mean more profit for the shredding companies and consequently would attract more scrap tires. Tony Hatton, director of the Division of Waste Management which is co-sponsoring the project, says, “Rubber modified asphalt, extruded rubber automotive parts, and athletic field crumb rubber infills are examples of crumb rubber markets. Kentucky will not have these better uses unless we develop the markets.”
Eaton Asphalt Paving Company is the first contractor to propose the crumb rubber asphalt project to the Department of Highways, District 6. Eaton President Tony Ogle says, “Our parent company has done several rubber modified asphalt projects around Dayton and Toledo, Ohio. We have the know-how and ability to do similar jobs in Kentucky, which is part of our service area.” Brian Donnelly, District 6 materials engineer, likes what he hears: “If the use of rubber modified asphalt meets specifications and keeps waste tires out of landfills, I’m all for it.”
The planning meeting was held July 24 at District 6. The group decision was that it is easier to modify an existing project rather than bidding a completely new one. The KY 8 endeavor, with an original price tag of $651,000, fills the bill. The agreement calls for paving one lane and its parking spaces with polymer-modified asphalt as a control, and the other side with rubber-modified asphalt. Both types of asphalt binder satisfy the applicable specification. The EEC is paying the additional $70,000 costs for the polymer and rubber modified asphalt as well as the $15,000 for long-term testing by the Kentucky Transportation Center at the University of Kentucky.
Paving began on a temperate fall evening in downtown Dayton, Ky., near the Ohio River floodwall. The contactor used an additive to make the rubber modified asphalt handle similar to regular asphalt. The ingredient decreases the “stickiness” and rubber smell that normally come from rubberized asphalt. The use of warm-mix also decreases the temperature and assists with the odor.
The density tests completed soon after the project revealed that the contractor met the 100 percent pay standard set by KYTC. There was some settlement of rubber particles during construction, but KYTC believes that this may be minimized by controlling the distance from the plant and continually stirring the tanks. Mark Belshe, the observing engineer EEC contractor from the Rubber Pavement Association, says that it handles similar to regular asphalt.
The Kentucky Transportation Center is conducting long-term testing on the durability of the rubber modified asphalt as compared to the control section.
The pilot is considered a success so far. “With the test results, contractors in other parts of the state using regional aggregate can modify their asphalt mix design and proceed with confidence in the final product,” said Brian Donnelly of District 6. “I believe that the Transportation Cabinet will be better prepared if another polymer shortage occurs,” said Myers.
Here are sources of more information on rubber modified asphalt:
The Rubber Pavements Association (RPA): http://rubberpavements.org/
The Rubberized Asphalt Foundation (RAF): http://www.ra-foundation.org/
The Asphalt Rubber Technology Service (ARTS): http://www.clemson.edu/ces/arts/
National Center for Asphalt Testing at Auburn (NCAT): http://www.ncat.us/
Florida DOT: http://www.dot.state.fl.us/
“Waste Tire Program CY 2012: A Report to the General Assembly”, Kentucky Division of Waste Management, Jan. 14, 2013, http://waste.ky.gov/RLA/Waste%20Tires/Documents/WasteTireRevisedReport129102.pdf