Stockpiling Cold Central Plant Recycling Mixtures

About the report:

The Virginia Department of Transportation (VDOT) contracted to reconstruct and add new lanes to a portion of Interstate 64 near Williamsburg.  As the work progressed, the contractor requested permission to produce and stockpile the cold central plant recycling (CCPR) mixture that was being used on the project.  Since VDOT’s specifications did not address this issue, VDOT asked the Virginia Transportation Research Council to investigate whether stockpiling a CCPR mixture had any negative consequences with respect to the mechanical properties of the mixture. 

The purpose of this study was to assess the mechanical properties of a CCPR mixture subjected to a laboratory stockpiling procedure.  The mechanical properties assessed included the indirect tensile strength and dynamic modulus of the CCPR mixture. 

The study found that the laboratory stockpiling procedure was effective at retaining moisture within the mixture over a period of 41 days.  The study also found that the CCPR mixture became less workable, as defined by the number of gyrations required to compact a CCPR test specimen in a gyratory compactor, as curing time progressed.  The study showed that the indirect tensile strength and dynamic modulus decreased exponentially within the first 3 days of stockpiling and then reached a steady value. 

The study recommends that VDOT consider allowing stockpiling of a CCPR mixture produced using foamed asphalt as the recycling agent and cement as the active filler for up to 24 hours, following verification of these findings from a future study that examines field stockpiling from additional projects. Further, the Virginia Transportation Research Council should conduct a follow-up study investigating the stockpiling of CCPR mixtures having different recycling agents and/or active fillers and investigate the ability to store produced CCPR material in a field stockpile.

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