Issue link: http://read.dmtmag.com/i/266311
HOT-MIX MAGAZINE 34 VOLUME 19 NUMBER 1 A number of contractors in Texas are successfully run- ning reclaimed asphalt pave- ment (RAP) and recycled asphalt shingles (RAS) and warm mix all at the same time. However, these con- tractors have faced challenges in running all three at once, and they have climbed the learning curve to do so. "When you're running RAP and RAS, you're doing it for a couple of reasons," said Mike Brown, vice president of construction, Wheeler/ Oldcastle, Round Rock, Texas. "One reason is to reduce the amount of virgin asphalt cement, and the other is to reduce or eliminate modifying the virgin asphalt cement with a polymer. So we're able in a lot of cases to get high-temperature and low-temperature properties—and eliminate the polymers—by using RAP, RAS, and warm mix." The maximum amount of RAP allowed by the Texas Department of Transportation (TxDOT) in sur- face mixes is 20 percent. In base courses, the limit is 30 percent. And the maximum shingles content is 5 percent. But if a contractor runs 5 percent shingles, the maximum RAP content gets reduced by that 5 percent, to 15 percent. But hold on, it gets more compli- cated. "We only allow 20 percent recycled binder in the surface course," said Dale Rand, director, Flexible Pavements Branch, TxDOT. "However, if they make a binder grade adjustment where they go with a softer, what we call our allowable substitute binder, they have to lower the high-temperature grade and the low-temperature grade of the binder. Then we'll allow them to go up to 30 percent recycled binder in the surface. And in that case, they could probably use, depending on how the num- bers come out, 15 percent RAP and 5 percent shingles. We have a table on how much total recycled binder they can use." That said, Rand noted that more experienced asphalt producers do not run the maximum allowable percentages of RAP and RAS. For example, they may use 3 percent shingles and 10 percent RAP together. "They know that if they try to go much above that, that may not get good mixing, and could have other problems," said Rand. "Whereas a less experienced asphalt producer will tend to maxi- mize the specification because it gives him the lowest bid," Rand continued. "In my experience, the more experienced people tend NOT to maximize the specification. They tend to find that spot where they operate the most efficiently." TRANSFERRING HEAT One challenge is to transfer enough heat—by conduction through the superheated aggregate in a The lessons learned from seasoned asphalt producers pave the way for more usage of recycled materials. Meeting the Challenges: RAP, RAS & WMA 13609_Astec_HotMixV19N1.indd 34 2/18/14 11:25 AM