Cold In Place Recycling (CIR) Research

Study examines 24 CIR asphalt roads constructed in Iowa from 1986 to 2004. Research finds that sample roads with good subgrade support have 36% longer service lives than roads with poor subgrade support in addition to revelations in varying factors affecting performance in CIR between high and low traffic roads.

Arizona studies 17 CIR projects constructed from 1981 to 2001, finds improved IRI, better resistance to cracking, lower post-construction maintenance costs, and “significant improvements in performance.”

FHWA report includes summary of performance seen by multiple agencies, confirms CIR has better results than mill & fill; And the same or longer pavement life, with equal or lower NPV than conventional HMA. Report recommends an AASHTO structural layer coefficient of 0.32-0.34 for CIR mixes.

University of Illinois study that examined CIR, FDR and HMA projects. Study concluded/recommended CIR and FDR with Asphalt Products be considered a “standard procedures.”

During the 2011 construction season, the Virginia Department of Transportation (VDOT) completed an in-place pavement recycling project to rehabilitate a 3.66-mile section of pavement on I-81 near Staunton, Virginia. VDOT employed three in-place pavement recycling techniques, full-depth reclamation (FDR), cold in-place recycling (CIR), and cold central-plant recycling (CCPR). Materials for both the CIR and CCPR were produced using foamed asphalt with cement as an additive. A combination of cement and lime kiln dust was chosen for the FDR process.

 From the results of this study, the combined structural layer coefficient for the CCPR and FDR materials was calculated as 0.37. The structural layer coefficient for the CIR material was calculated as 0.39. The structural layer coefficient for the CCPR material was calculated to have a likely range of 0.37 to 0.44. Laboratory testing showed that the performance of the CCPR and CIR materials is expected to be similar. The field performance tests demonstrated that the section of pavement rehabilitated by the three in-place recycling methods continues to perform well after nearly 3 years of high-volume interstate traffic.

This is the final report for NCHRP 9-62 project where the authors developed a short pin raveling test to determine when a CIR pavement has sufficiently cured to allow opening to traffic and a long pin test to determine when the pavement has cured sufficiently to place the wearing surface. The authors have recommended additional field verification of the proposed test methods and threshold values. 

Comparison of the environmental benefits of CIR with a thin HMA overlay to mill and overlay for 9 resurfacing projects in Wisconsin. Results showed average environmental savings of 23% in energy consumption and carbon dioxide emissions, 20% reduction in water consumption and reduced virgin aggregate consumption of 37% when using CIR with a thin HMA overlay instead of a comparable mill and overlay.

This study evaluated the effect of emulsion content reduction during the CIR process in the field on mix properties. Three laboratory CIR mix designs were performed using the same RAP material and emulsion at three different mixing temperatures. The mix design results showed that as the mixing temperature increased, the optimum emulsion content decreased significantly. Also, increasing the mixing temperature improved the mixture compaction. Both the dry and retained stabilities were also higher for the high-temperature mixtures. The critical low temperatures of high-temperature mixtures were higher than the room-temperature mixture (indicative of a worse performance) but still lower than the -20°C requirement. From the results of this study, it appears that reducing the emulsion content of CIR mixtures during the heat of the day does not necessarily deteriorate mixture properties. This could result in substantial savings for agencies that use this process without sacrificing long-term performance.

This report fully documents the research findings from the NCHRP 9-51 study determining material properties for cold-recycled asphalt mixtures for input to structural design and analysis programs and suggested Level 3 dynamic modulus values for these materials for use in pavement structural analysis using Pavement ME Design.

The Ontario Ministry of Transportation (MTO) has been using CIR with emulsified asphalt since 1990. In 2003 they placed their first trial section of CIR using foamed or expanded asphalt (CIREAM) on Highway 7 east of Perth. A 5 km trial section of CIR with foamed asphalt was constructed adjacent to a 7 km section of CIR with emulsified asphalt. The test sections were monitored for performance over the next 10 years using the MTO's Automated Road Analyzer. The results indicated that both treatments are providing excellent long term performance and have been shown to significantly reduce or eliminate reflective cracking.

This paper is a summary of the sustainability benefits derived from two in-place recycled pavements in Virginia that used CIR, CCPR and FDR. The paper reports cost savings, reduced construction times and reductions in green house gasses and energy consumption for projects on I-81 and I-64.