Better Roads

February 2014

Better Roads Digital Magazine

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Page 24 of 39

Better Roads February 2014 23 HighwayContractor Missouri, located and bought a shingle grinder that will produce RAS ground to 1/10-inch minus. The fi ne grind will produce more effective liquid binder to coat the aggre- gates, says Jack Neel, asphalt division manager at Ideker. "Chances are that 3/8-inch chip is not getting completely melted down to be 100-percent effective oil," Neel says. "The PG grade of those shingles is extremely high. It takes a lot of heat to melt them down. It's much like sticking a frozen pie in the oven versus a tater tot." Neel says shingles ground to 3/8-inch minus have little chunks of binder that don't get completely melted in the asphalt plant. The outside layer of the little chunks heats up and melts and leaves a particle of oil inside. And if you leave that particle in the asphalt mixture in a silo, or in a truck, for an extended time, the remaining little particle will continue to melt. That, Neel says, will change the volu- metrics of your mixture. You'll get a higher percentage of effective binder and a lower air voids content. Ideker's Quality Control Manager David Wilson concurs, and says he has learned at asphalt industry conferences that the effec- tive binder content in 3/8-inch RAS is time-sensitive. On a paving project with an hour-long haul, asphalt sam- ples with 3/8-inch RAS taken close to the plant turned out to match the mix design properly. The mix would test at, say, 4 percent air voids, as planned. "But when they took sam- ples from the far end of a project, by the time they got back to the lab, the mix was cold," Wilson says. "So they had to put it in the oven and heat it back to compaction temperature, and they were fi nding that the extra time and heat in the oven was giving them a larger amount of effective oil. At the higher temperature, they found that they were getting 2, or 2.5 percent air voids, because the extra oil was melting. "We have found that it's in our best interest to do a fi ner grind, which is a little bit harder to handle at the plant," Wilson says. "You cannot just run it through a cold-feed bin." The tinier particles of RAS will tend to block up in a cold-feed bin and not feed properly. And if the one-tenth size particles are exposed to the wind on a weigh-belt, some of the RAS might blow away. Ideker has found the way to handle one-tenth-size RAS particles is to use specially designed weigh depletion bins. The company has two ALmix dual-drum asphalt plants located in the greater Kansas City area. One plant has been equipped with a special RAS bin, designed by Astec, that has a load cell in it. As RAS is fed out to the plant, the load cell weighs the remaining material. In turn, the plant controls receive a stream of informa- tion, in real time, telling the plant how much RAS is going into the mix. Control software is designed to treat the RAS as the primary source of binder. And the controls, in turn, increase or decrease the amount of virgin binder needed to make up the differ- ence between the mix design and the RAS binder content. With Ideker's new weigh depletion system, if a block- age occurs, the new software automatically knows that it's feeding less RAS in, and Ideker located and bought this shingle grinder to grind the material to 1/10-inch minus. The company is working to increase its production. The recycled asphalt shingles on the left are ground to 3/8-inch minus, and the RAS on the right are ground to 1/10-inch minus. Photo courtesy of Ideker Construction Photo courtesy of Ideker Construction

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