Subcontractor E.J. Breneman's cold in-place recycling train starts with a down-cutting milling machine and follows with conveyors that deliver recycled pavement to an asphalt paver. Photo: E.J. Breneman, LP
Cold-recycling also provides the city with a ready, inexpensive source of aggregate. Imported aggregates are expensive to procure in Los Angeles, says Nazario Sauceda, the street bureau's assistant director. Commonly, aggregates are imported to Los Angeles from Orange County, northern California, or San Bernardino County.
Besides, says Sauceda, the best materials are already in the streets. “The aggregate we used 25 years ago is top-quality material,” he says.Significant Savings
Last year, Harford County, Md., completed its largest cold-recycling project since it started using the technique in the early 1990s: 8.2 miles of asphalt roadway ranging in width from 24 to 36 feet.
The county compared the costs of milling and resurfacing versus cold-recycling before beginning. Milling out 4 inches of asphalt, placing 4 inches of asphalt base course, and resurfacing with a 2-inch overlay would have been $2.37 million. Cold-recycling the road and adding a 2-inch hot mix overlay was $1.64 million—a 31% savings.
“We like cold recycling,” says Glen Hebel, civil engineer with the county. “It works well on open roads with few or no utilities.”
Harford County outsourced the project to Gray and Son Inc., Butler, Md., which subcontracted out the cold-recycling to E.J. Breneman LP of West Lawn, Pa. Breneman uses a Caterpillar 750C milling machine to downcut the pavement so the asphalt is sized to 2-inch minus particles (all pulverized particles are 2 inches or less in diameter). By contrast, says Breneman recycling manager Michael Polak, some recyclers upcut the pavement and leave it in chunks.
Compaction is critical to the success of cold in-place recycling. Breneman uses a 25- to 30-ton pneumatic-tired roller as well as a steel drum roller for static and vibratory passes. “If you don't have the pneumatic roller, you can't compact the recycle enough to get the air void count down and meet specs,” says Polak.Reducing drop-off
Recycling onsite saves an Illinois county half the cost of new asphalt.
Christian County, Ill., engineer Cliff Frye wanted to rehabilitate a 2½-mile county road and pave its shoulders to improve safety. Because of heavy truck traffic and relatively narrow 11-foot-wide lanes, the aggregate shoulders tended to erode downward from the edge of the pavement.
By recycling the existing pavement onsite, the county cut its costs in half: $51,920 per shoulder mile for hot-mix asphalt versus $26,535 per recycled shoulder mile.
The two-stage recycling process, completed by contractor Dunn Co., Decatur, Ill., involved conveying millings from the asphalt pavement directly into a 10-inch-deep widening trench on either side of the road. The millings were then shaped and compacted.
Then two Wirtgen 2500 S reclaimer/ stabilizers, operating in tandem, pulverized and recycled the road for its full depth and across the new shoulders as one section. Finally, the pavement and shoulders were resurfaced with hot-mix asphalt.
For more information, contact the Asphalt Recycling & Reclaiming Association at www.arra.org.
—Brown is a freelance writer in Des Plaines, Ill.