Cold in-place recycling (CIR) is gradually winning the favor of the agencies compared to conventional methods of rehabilitation and maintenance. As we always emphasize the importance of implementing green practices, in that way CIR is a better option than hot in-place recycling.  CIR is the better option since it helps reduce the carbon footprint as no heat is applied through the construction, despite both methods recycling 100% of the roadway. CIR is not just cost effective, but also effective in preventing cracking and other distresses from reflecting through, which has been a major concern for most overlay/mill and overlay projects.   

What is CIR? 

CIR is a pavement rehabilitation method that involves the removal of the existing asphalt pavement and treating it with a bituminous recycling agent and additives, as required. The whole recycling process is performed on-site using a train of equipment that consists of tankers, cold planers, screening/crushing units, mixers, a paver, and rollers. CIR trains have different equipment configurations: single-unit, two-unit, and multi-unit (as shown in image below). 

Midstate Reclamation and Trucking multi-unit CIR train (Schellhammer 2017)

How is it done? 

The flow chart below summarizes the process of CIR in multi-unit trains. The process is then followed by laydown and compaction.

CIR Best Practices

The CIR product is coarse graded and sensitive (Schellhammer, personal communication, June 23, 2017).  Due to the larger voids, cold mix cannot survive the harsh winter weather so a surface course is typically placed over the mix. For low volume traffic roadways, surface treatments such as micro-surfacing and chip sealing can be placed over the CIR. However, bituminous overlays should be placed over CIR for high volume traffic roadways. The ideal depth of CIR is three to four inches. When the CIR depth is reduced to less than three inches, the resistance to reflective cracking is reduced as well, thus lowering the effectiveness of CIR. 

While CIR seems to be the best choice for pavement rehabilitation, there are some factors to be taken into consideration. Cold central plant recycling will be a better option compared to CIR in an urban environment since there will be too much traffic for the CIR trains to perform. CIR is also not a good candidate if inconsistent core depths are found on the project. Though CIR provides many benefits, careful preliminary assessment shall be done; that applies to all other different rehabilitation methods. To ensure that the rehabilitation or maintenance technique achieves its full purpose, it must be performed at the right time and at the appropriate location.

Please refer to the following link for video regarding CIR.

Information Source:

Asphalt Recycling and Reclaiming Association (2015). Basic Asphalt Recycling Manual (2nd ed.).

Annapolis, MD: U.S. Department of Transportation Federal Highway Administration.

Schellhammer, D. (2017). Cold In-Place Recycling (PDF Document). Retrieved from Midstate Reclamation and Trucking.