Cold recycling consists of recycling reclaimed asphalt pavement (RAP) without the use of heat to create a bound pavement layer. The two categories of cold recycling that are becoming more prevalent in the road building industry include: Cold In-place Recycling (CIR) and Cold Central Plant Recycling (CCPR). CIR occurs in situ where a portion of the existing asphalt pavement is milled, crushed, blended with recycling agents and paved. A typical thickness for a CIR layer is 3 to 5 inches. The CIR process occurs in the roadway without the RAP material leaving the road. The CCPR process produces a product that is similar to CIR but the recycling occurs at a mobile plant. The RAP used for CCPR may either come directly from a paving project by milling or be found in existing RAP stockpiles. An advantage to removing the RAP from the roadway is that the underlying material can be stabilized if needed. An advantage to using existing RAP stockpiles is that recycling can be used to build new or widened lanes. The RAP is processed, blended with recycling agents at the mobile plant, and paved. Typical recycling agents used for CIR and CCPR are emulsified asphalt or foamed asphalt.
Both CIR and CCPR have advantages to owner agencies and users. According to Asphalt Recycling and Reclaiming Association (ARRA), CIR can save agencies from 30 to 50% of total expenditure when compared to conventional construction methods. Likewise, significant savings can be realized by agencies using CCPR mixes in lieu of traditional HMA materials, in the range of 25 to 45%. Additional benefits include reduced greenhouse emissions and reduction in user delays.
CIR and CCPR have not been widely adopted despite economic and environmental benefits, successful performance experience and technological advances in equipment and stabilizers. Reasons for limited adoption range from a lack of familiarity on behalf of contractors and agencies, a lack of uniform specifications across agencies for assessing quality, and a lack of documented long-term performance of recycled pavement sections.
The objective of this synthesis is to document how CIR and CCPR technologies are selected, implemented and evaluated by state DOTs. This information will compare the results of the 2011 NCRHP 421 Synthesis to determine if usage is growing. The information for CCPR would also be an initial look at the quantity of RAP that are going back into roads rather than into growing stockpiles or landfills.
Information to be gathered will include:
• DOT experience with CIR and CCPR as part of rehabilitation strategies (e.g. number of projects and tons or lanes miles per year)
• Structural design inputs
• Stabilizing agents and active filler selection
• Mixture design
• Acceptance requirements and evaluation methods
• Selection criteria for recycling projects
• Barriers for adoption of CIR or CCPR
• Recurring issues and solutions
• Performance data on pavement management system level and/or project-based level
Information will be gathered through a literature review, a survey of state DOTs and, based on the results of the survey, five agencies will be selected for case examples of CIR and CCPR. Of these, two agencies should have more than 10 years of experience and/or greater than 50 lane miles of each year in their annual program. Other agencies should have 3 to 10 years of experience to determine how implementation was initiated along with data on cost savings, lessons learned and initial performance. The last agency in the case example should be one with limited experience (at least one project) and has not developed a CIR or CCPR program. The objective of the case examples is to identify implementation barriers or knowledge gaps for agencies to implement these technologies in their rehabilitation strategies.
• Stroup-Gardiner, Mary. NCHRP Synthesis 421: Recycling and Reclamation of Asphalt Pavements Using In-Place Methods. Synthesis 421, National Cooperative Highway Research Program, Washington, DC, 2011.
• Asphalt Recycling and Reclaiming Association. Basic Asphalt Recycling Manual, 2nd Ed. Annapolis, MD, 2015.
• Schwartz, Charles, Brian Diefenderfer, and Benjamin Bowers. Material Properties of Cold In-Place Recycled and Full-Depth Reclamation Asphalt Concrete. Report 863, National Cooperative Highway Research Program, Washington, DC, 2017.
• Federal Highway Administration. Overview of Project Selection Guidelines for Cold In-place and Cold Central Plant Pavement Recycling, Publication FHWA-HIF-17-042, Washington, DC, August 2017.
• Ma, Wagyu, Randy West, Nam Tran, Brian Diefenderfer, and C. Chen “Effects of Mineral Additives on Cold Recycled Foamed Asphalt Mixtures in Laboratory- and Field-Curing Conditions.” Accepted for Publication to Transportation Research Record, 2018.
• NCHRP Project 09-62, Rapid Tests and Specifications for Construction of Asphalt-Treated Cold Recycled Pavements.