Better Roads Digital Magazine
Issue link: http://read.dmtmag.com/i/276457
Better Roads March 2014 15 T he number of transportation agencies that use recycled tire rubber in asphalt has increased steadily in recent years. Several states have speciﬁ cations for adding recycled tire rubber to asphalt binder, including Florida, Georgia, Louisiana, Texas, Arizona and California. As prices for asphalt cement (AC) and polymer have shot up dramatically, agencies and contractors are looking for ways to hold the line on the cost of asphalt pavements. Cur- rently, almost 20 percent of the asphalt binder sold in the United States for paving is polymer modiﬁ ed. This makes rubber an economically attractive extender of asphalt, since it contains both polymer and oil. Also, the price of recycled tire rubber is stable, unlike the price of AC and polymer. Recycled tire rubber can be added to asphalt in three ways, says Doug Carlson, vice president of asphalt products for Lib- erty Tire Recycling, a Pittsburgh-based rubber provider. The classic method, speciﬁ ed by ASTM D6114, is called asphalt rubber, or the Arizona method. It is a wet process. Recycled tire rubber is added at close to 20 percent by weight of the liquid AC. The rubber particles are fairly large – up to 2 milli- meters in size. The process requires special blenders that can be used in the ﬁ eld to react the rubber with AC. Asphalt rubber has found its place in heavy-duty chip seals and in surface mixes that are gap graded to have space for the rubber particles. Open-graded friction courses (OGFC) and stone-matrix asphalt (SMA) can make good use of as- phalt rubber. The material is comparable to an asphalt modi- ﬁ ed with 7 percent polymer, says Carlson. He calls the second method the "Polymer Switch Binder." The Magic of The Magic of This rubber blending equipment is set up on an asphalt plant owned by Diamond B in Louisiana. The blending equipment was built by D&H Equipment Ltd. HighwayContractor By Daniel C. Brown As prices for asphalt cement (AC) and polymer have shot up dramatically, agencies and contractors are looking for ways to hold the line on the cost of asphalt pavements.