Better Roads Digital Magazine
Issue link: http://read.dmtmag.com/i/276457
Better Roads March 2014 17 HighwayContractor The rubber can be blended at an asphalt terminal, or added in the fi eld with the same equipment that asphalt rubber is made with. A fi ner-grind rubber is used – particles of half a millimeter – and it is typically added at 8 to 12 percent of the weight of the AC. The AASHTO M320 spec will soon be changed to allow particulate tire rubber to be used in performance-graded binders and Superpave mixes, Carlson says. More than ever, terminal or refi nery facilities are ei- ther considering supplying rubber-modifi ed binders or do supply them, says Jeff Smith, technical direc- tor for Cactus Asphalt, an asphalt rubber binder sup- plier. "That's a change in our industry, because in the past they have been totally resistant to that," Smith says. The reason is the lower cost of recycled tire rubber. "Even if it takes three times the tire rubber percentage to do what one percent of virgin polymer will do, still, the overall cost to the manufacturer is much less to use tire rubber." The third method is a newer dry process, ap- proved by specifi cation in Georgia. "It's a very fi ne- grind rubber, less than 600 microns in size. And the dosage is only around 10 percent by weight of the binder," says Carlson. "The new dry process also will get a lot of attention here in 2014 because there are quite a few states that have specifi cations based on mix performance. Contractors and states prove the mixes based on a Hamburg rut tester or the Overlay tester. Rubber happens to do very well under those tests." PG tests Smith also points out that the movement to Performance Grade (PG)nparticulate rubber binder materials, such as asphalt rubber and polymer-modifi ed asphalt rubber, is 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. As a result, the number of transportation agencies that use recycled tire rubber in asphalt has increased steadily in recent years.