Coughlin Provides Cold In-Place Recycling Solution

With highways and paved roads around the world exhibiting surface defects in need of repair, utilizing an innovative road reconstruction process such as cold-in-place recycling (CIR) is a cost-effective and environmentally friendly alternative to more conventional methods of rebuilding asphalt roadways.

Coughlin Company, a Utah-based company providing milling, CIR, heavy hauling, pulverizing, and soil stabilization services throughout the Western United States, recently used the latest in CIR technology on a district maintenance contract project involving four different sites throughout the state of Nevada.

All four sites required the creation of a "crack barrier" between the existing roadbed and the new surface, and specifications stipulated that the existing roadbed was to be partially milled up, mixed with additives and placed back on the road.

The subbase created in this way has the ability to keep underlying base cracks from migrating to the surface. A final overlay of traditional hot mix was then applied after a curing period of approximately two weeks. The four Nevada sites were located on U.S. 93, S.R. 447, S.R.757, and U.S. 50.

CIR train

Coughlin employed the CIR "recycling train concept" consisting of tanker trucks, milling machines, crushing and screening units, mixers, pavers and rollers - all designed and integrated into one comprehensive operation.

In Coughlin's CIR train, a Roadtec 950-hp RX-900 cold planer provided the train's propulsion, towing a RT-500 cold recycler and a nurse tank for the emulsions. It also pushed a water truck and a slurry tanker that are always with the train.

The RX-900 also pushed another emulsion tanker and slurry tank when present to replenish the tankers hooked to the train. Those two replenishing tankers are attached to the train just long enough to pump off their products and then go to a staging area where they are refilled to return to the train.

Darren Coughlin says the refilling typically took place five to eight times in a workday. Careful planning and timing of these material transports has a positive impact on the productivity of the train.

Roadway grade and slope

A 12-foot 6-inch-wide cutter drum was used on Coughlin's RX-900 in this train and operated in the downcut mode. Coughlin preferred the gradation produced with the downcutting process. The RX-900 is also capable of upcutting in this same rear-loading configuration. Bi-directional milling capability is a unique feature of Roadtec cold planers.

MOBA brand sonar grade and slope controls were used with the RX-900 milling machine to cut the surface to the required profile. The pavers that followed also used automated grade and slope devices to hold spec.

Width and depth

Maximum width that can be handled in one path with this process depends on the amount of material put through the RT-500, which is designed for maximum throughput of about 600 tons per hour; as well as the paver production rate. A practical maximum width estimate would be 20 feet. A 13-foot 4-inch-wide cut was made on the Hwy. 93 portion of the project.

Coughlin "precut" a narrow path using a Roadtec RX-60 cold planer and had it deposit the material to one side. The RX-900 in the CIR train then walked over that material and incorporated it into the final milling pass.

Compaction specs are among the variables that influence the depth of cut. A typical depth of cut would be between 2 and 5 inches. Coughlin cut 3 inches deep on this project. The resultant 3-inch thickness of the CIR base layer provided sufficient stress-absorbing characteristics to keep any underlying reflective cracking from coming through to the top layer of HMA, according to Coughlin.

Following behind the cold planer was the Roadtec RT-500 cold recycler. The unit, which Roadtec says was being used on the job as part of the machine's prototyping program, can handle up to 600 tph of material. The RT-500 cold recycler is designed to crush and screen the RAP produced by the RX-900, while its pugmill mixes the emulsion with the recycled materials.