Cold Central Plant Recycling Research

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 where the authors developed a short pin raveling test to determine when a CCPR 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.

This report summarizes the findings from the second round of testing during the 2015-2017 research cycle at the NCAT Test Track for VDOT's three CCPR test sections. The study found that the performance of the three CCPR sections continues to be excellent after 20 million ESALs of loading. This was evidenced by the following examples of functional performance: no observable cracking at the pavement surface, rut depths less than 0.3 inch, steady measurements of ride quality and steady or increasing modulus values.

The Virginia Transportation Research Council performed a laboratory investigation to evaluate whether stockpiling a CCPR mixture using foamed asphalt and cement as an active filler had any negative consequences with respect to the mechanical properties of the mixture. The mechanical properties included indirect tensile strength and dynamic modulus. The study recommended allowing stockpiling of CCPR mixtures using foamed asphalt and cement as the active filler for up to 24 hours. The study recommended verification of the findings and recommendations through follow-up studies.

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.

This paper is a summary of the sustainability benefits derived from two in-place recycled pavements in Virginia that used CCPR, CIR 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.