What is Cold-in-place recycling and what are its advantages?
Cold-in-Place (CIR) recycling is a method of removing and reusing the existing asphalt surface. It involves grinding off the top 2 to 5 inches of the existing asphalt surface and mixing the crushed asphalt with an asphalt recycling agent, and placing it back down with a paver. Sometimes an additional module is included crushing this material and screening it to a specific size. Often specific sized aggregate is added to correct the deficiencies found in the existing asphalt material. Asphalt deficiencies are determined by sampling and testing the existing asphalt material prior to beginning the process.
The cold-in-place process is typically performed using a “train” of equipment which includes an emulsion tanker, milling machine, sometimes a crusher and a screen, and an asphalt paver and a combination of pneumatic and vibratory rollers. Because of the length of the train this process can be difficult on tight, windy and narrow streets.
The milling depth is determined largely on the existing depth of the asphalt material. Only the asphalt layer is to be milled in this process. Milling depth can be done up to a depth of 5 inches, however, depths greater than 4 inches tend to present compaction problems when the improved material is re-placed onto the road surface with the paver.
Cold-in-place recycling is used to restore and reuse the existing material reducing the amount of outside material required to be hauled to the site. This efficiently improves the road surface and strength while minimizing expenses typically incurred during the paving process. In addition, CIP can correct deep asphalt defects such as rutting, fatigue (alligator) cracking, and utility cuts that cannot be addressed by a surface treatment or an overlay, and allows minor corrections to the profile of a road surface, reduces reflective cracking, and results in a minor inconvenience to traffic. As its name implies, this is a cold process that requires minimal additional heat during the rejuvenation of the asphalt material, resulting in a decrease in the amount of energy required to produce the final material.
Success when using this process includes taking multiple samples along the road surface to identify any changes in the existing asphalt material which may require an adjustment to the added materials. This will allow for a more consistent and structurally sound asphalt base when the material is placed back onto the road surface. Because this is a “cold” process the material is slightly more porous than one would have from a hot mix material; it is therefore highly recommended that a surface treatment or an asphalt overlay be applied to the CIR material to protect it from water intrusion and to extend the life of the material. According to an FHWA study findings for New York State, a “CIR (4”) with a 1.5 inch overlay is expected tolast 10-15 years with little maintenance as compared to a 5-8 year life of atraditional 1.5 inch overlay”.
Asphalt Paving Principles (pdf)
CLRP workshop manual
Cold-In-Place Recycling (CIR): Current Projects and Activities; Cold-In-Place Recycling State of Practice Review
Federal Highway Administration, Pavements, 04/07/2011.