Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85926
The cold-in-place recycling train features a milling machine followed by a recycler, which crushes the RAP, screens it, mixes it with emulsion and lays the material down in a windrow. been sized to specification, it passes over a belt scale that weighs it before the asphalt hits a pug mill. "In the pug mill, a consistent 1.6 percent emulsion was added by a computerized injection system. The flow of emulsion is automatically regulated according to the weight of the material crossing the belt scale. If needed, the operator can add a bit of water to help the movement of the material," says Rogers. "Much of the time, we just go with the water that's added at the milling cutter, which is around 1.5 to 2.0 per- cent," he says. Once the emulsion was mixed in with the RAP, the recycler deposited the recycled asphalt in a windrow. From there, Granite Construction used a Cedarapids windrow elevator to pick up the material and place it into a paver hopper. Working one lane wide, the paver spread the material and compaction followed. Microsurfacing came next – over all the entire 9 miles. Pavement Coatings used three microsurfacing machines, all truck-mounted VSS Macropaver 12B units, to apply a Type II micro- surface. The application rate was 18 pounds per square yard. The micro- surfacing machine uses a pug mill to mix fine aggregates, emulsion, and 0.5 to 1.0 percent portland cement as a setting agent, to control the break of the liquid. The final microsurface is one-quarter to three-eighths of an inch thick. "The project was completed in just eight days. The CIR process required very few trucks for material delivery during construction," Ford notes. "Using hot mix would have been difficult, because the nearest hot mix plant was 55 miles away. Plus, access to the site was difficult." By using the CIR and microsurfac- ing, the county was able to save ap- proximately 25 percent compared to a conventional cold mill and overlay with 1.5 inches of hot mix. Pavement Recycling Systems estimates the CIR process saved 334 offsite truck trips, eliminated more than 12,523 truck miles, saved 4,420 tons of virgin ag- gregates and almost 200 barrels of oil. The energy savings was at least 32 percent compared to a hot mix alternative. "When we can fix the cause of the problem, but still save money and minimize the impact to the environ- ment, that's what I call a perfect green solution," says Diaz. "One of the things that made this project so fantastically successful was the teamwork between the county, the suppliers, and the contractors," says Ford. Write 142 on Reader Service Card or visit www.betterroads.com/info Better Roads July 2012 29