Cold-in-place recycling (CIR) has emerged as a powerful pavement rehabilitation strategy that combines cost efficiency with environmental responsibility. When road surfaces develop cracks, potholes, and structural defects, traditional reconstruction methods often involve removing old material, hauling it to landfills, and importing new hot mix asphalt. CIR eliminates much of that waste by reusing the existing pavement in place. A compelling example of this technology in action comes from the Cold in Place Asphalt Recycling Around the U, where Coughlin Company applied the latest CIR equipment and techniques on a district maintenance contract across four sites in Nevada. This approach not only restored pavement integrity but did so with significantly reduced material costs and environmental impact.
Understanding Cold In-Place Recycling and the Crack Barrier Method
Cold-in-place recycling is a pavement rehabilitation process that mills up the existing asphalt surface, processes the reclaimed asphalt pavement (RAP) to meet specification, mixes it with recycling additives, and places it back on the road as a revitalized base layer. Unlike hot recycling methods that require heating the material, CIR operates at ambient temperatures, reducing energy consumption and emissions.
How the Crack Barrier Works
On the Nevada project, Coughlin Company used CIR specifically to create a crack barrier between the existing roadbed and the new surface. Reflective cracking is one of the most persistent problems in pavement maintenance. When cracks form in underlying layers of a road, they can propagate upward through new overlays, undoing the benefits of resurfacing within months.
The crack barrier approach addresses this by milling the existing roadbed partially, mixing it with stabilizing additives, and placing it back as a flexible intermediate layer. This recycled subbase absorbs stresses that would otherwise cause reflective cracks to migrate to the surface. After a curing period of approximately two weeks, a final overlay of traditional hot mix asphalt (HMA) completes the rehabilitation.
The four Nevada sites selected for this method were located on:
- U.S. Highway 93
- State Route 447
- State Route 757
- U.S. Highway 50
Each of these roads exhibited surface defects requiring reconstruction, and the Nevada Department of Transportation specified a CIR-based solution to create the crack barrier. For more on how CIR performs in different environments, see Cold in Place Asphalt Recycling in Dense Urban.
The CIR Recycling Train: Equipment and Process
Coughlin employed the CIR recycling train concept, a synchronized line of equipment designed to perform milling, crushing, screening, mixing, and paving in a single continuous operation. The train consisted of tanker trucks, milling machines, crushing and screening units, mixers, pavers, and rollers working together as one integrated system.
The Roadtec RX-900 Cold Planer
The heart of Coughlin’s CIR train was a Roadtec 950-horsepower RX-900 cold planer. This machine provided propulsion for the entire train while towing the RT-500 cold recycler and a nurse tank for emulsions. It also pushed a water truck and a slurry tanker that remained attached to the train throughout operation.
A 12-foot 6-inch-wide cutter drum was used on the RX-900, operating in downcut mode. Downcutting produces a finer gradation of milled material, which Coughlin preferred for this application. The RX-900 is also capable of upcutting in the same rear-loading configuration, a bi-directional milling feature unique to Roadtec cold planers. MOBA sonar grade and slope controls ensured the surface was cut to the required profile.
The RT-500 Cold Recycler
Following behind the cold planer was the Roadtec RT-500 cold recycler. At the time of the Nevada project, this unit was part of Roadtec’s prototyping program and could handle up to 600 tons per hour of material. The RT-500 performs three critical functions:
- Crushing and screening: A JCI-brand double-deck screen receives milled material from the RX-900 conveyor. Oversized material passes through a Telsmith 3048 impact crusher and returns to the screen via a two-conveyor return circuit with cleated belts for maximum production. A water spray system prevents dust buildup on rollers.
- Weighing and blending: Material that passes the screen drops onto a 48-inch weigh belt equipped with an electronic scale accurate to within plus or minus 1 percent. The scale communicates with a blending computer that adjusts the flow of additives proportionally.
- Mixing: The weighed material enters a JCI/KPI Model 52 pugmill mixer, a twin-shaft unit with a capacity of 600 tph. After thorough mixing, the recycled material discharges as a windrow onto the roadway. The entire RT-500 system runs on electric motors powered by a Caterpillar C-9 generator set.
Behind the recycler, a windrow loader picks up the material and feeds it to a conventional paver. Heavy pneumatic vibratory rollers then compact the material to the required density.
Material Transport and Logistics
Efficient material logistics were essential to keeping the train productive. The RX-900 also pushed additional emulsion and slurry tankers that replenished the tankers hooked directly to the train. These replenishing tankers would attach just long enough to pump off their products, then return to a staging area for refilling. Darren Coughlin reported that refilling typically took place five to eight times in a workday, making careful planning and timing a direct factor in overall productivity.
Nevada Project Details: Materials, Specifications, and Results
The Nevada maintenance contract required distinct specifications for the CIR process. Every aspect from cut depth to additive proportions was precisely controlled to meet the project’s crack barrier requirements. Cold in Place Recycling Delivers Cost Savings and highlights similar quality outcomes on comparable projects.
Width and Depth Parameters
The maximum width handled in one pass depends on the RT-500’s throughput capacity of 600 tph and the paver’s production rate. A practical maximum width is approximately 20 feet. On the Highway 93 portion, Coughlin made a 13-foot 4-inch-wide cut. To achieve this width efficiently, the crew precut a narrow path using a Roadtec RX-60 cold planer, depositing material to one side. The RX-900 in the main train then walked over that material and incorporated it into the final pass.
Compaction specifications influence the depth of cut. Typical depths range between 2 and 5 inches. On this project, Coughlin cut 3 inches deep. The resulting 3-inch CIR base layer provided sufficient stress-absorbing characteristics to prevent reflective cracking from reaching the top HMA layer.
Additive Mix Design
Coughlin recycled 100 percent of the existing material for the crack barrier. The specific mix design for this project included:
| Component | Percentage by Weight | Function |
|---|---|---|
| Reclaimed Asphalt Pavement (RAP) | 100% of recycled material | Base structural layer |
| PASS Emulsion (Western Emulsions) | 2.5% | Binding and rejuvenation |
| Lime Slurry | 1.5% | Anti-strip and stabilization |
The lime slurry was approximately 35 percent solids to water by weight and was prepared by a nearby slaking plant. Roadtec developed calibration routines for the RT-500 cold recycler to achieve the correct proportions of liquids and solids per specification. A BearCat 1,000-gallon liquid calibration trailer was used to calibrate the RT-500’s emulsion pump.
Curing and Overlay
After placement and compaction, the CIR base underwent a curing period of approximately two weeks. During this time, the emulsion broke and the water content evaporated, allowing the recycled layer to gain strength and stability. Following the curing period, Frehner Construction placed a 3-inch hot-mix asphalt overlay on top of the 3-inch CIR base, completing the pavement structure.
Cost and Environmental Benefits of Cold In-Place Recycling
The advantages of CIR extend well beyond the performance of the finished pavement. Coughlin emphasized three primary categories of benefit that make this technology attractive to both contractors and roadway agencies. Urban Cold in Place Recycling How Streator Saved demonstrates similar savings realized by municipalities adopting CIR.
Time Savings
With a single recycling train, the entire reconstruction process is completed in hours rather than days. Conventional methods require multiple separate operations: milling, hauling, crushing off-site, importing new material, and paving. CIR collapses these steps into one continuous pass, dramatically reducing lane closure times and traffic disruption. For heavily traveled routes like U.S. 93 and U.S. 50, minimizing road closure duration is a significant advantage for both the contractor and the traveling public.
Material and Energy Cost Reduction
By recycling 100 percent of the existing pavement in place, CIR eliminates the need to import virgin aggregate and binder for the base layer. The savings in raw materials are substantial. Additionally, since the process operates at ambient temperature, there is no energy cost for heating the material, unlike hot mix production which requires fuel for drying and heating. Manpower costs are also reduced because fewer haul trucks and support personnel are needed when material does not need to travel to and from the job site.
Extended Pavement Service Life
The crack barrier created by the CIR layer extends the service life of the new overlay by preventing reflective cracking. This means road agencies and taxpayers get longer performance from their rehabilitation investment. When the full lifecycle costs are considered, CIR often proves more economical than conventional mill-and-fill approaches, even when the initial unit costs appear comparable.
Environmental Savings
The environmental case for CIR is equally compelling:
- Natural resource conservation: Reusing 100 percent of the existing HMA layer preserves virgin aggregate and asphalt binder for other uses.
- Landfill reduction: No old pavement material is hauled to landfills, eliminating disposal costs and extending landfill life.
- Reduced emissions: Fewer truck trips to and from the construction zone lower fuel consumption and exhaust emissions. The single-pass recycling train further reduces the carbon footprint compared to multi-stage reconstruction.
- Greenroads credits: The CIR process qualifies for credits under the Greenroads rating system, which awards points for sustainable practices in new construction, reconstruction, and rehabilitation of roads.
The Nevada project demonstrated that CIR is not merely an alternative to conventional rehabilitation but often a superior choice on technical, economic, and environmental grounds. Contractors like Coughlin Company continue to refine the process, and equipment manufacturers such as Roadtec keep advancing the technology through prototyping programs and real-world field testing. As roadway agencies increasingly prioritize sustainable practices and lifecycle cost efficiency, cold-in-place recycling is positioned to become an even more common specification for pavement rehabilitation across the United States.