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Structural Study of Cold Central Plant Recycling Sections at the National Center for Asphalt Technology (NCAT) Test Track: Phase III
Brian K. Diefenderfer, Ph.D., P.E., David H. Timm, Ph.D., P.E., Ilker Boz, Ph.D., and Benjamin F. Bowers, Ph.D., P.E.
Ilker Boz
Ilker Boz
Brian K. Diefenderfer
Brian K. Diefenderfer
Year: 2019
VTRC No.: 21-R22

The Virginia Department of Transportation (VDOT) contracted with the National Center for Asphalt Technology (NCAT) in 2012 to install, instrument, and monitor three pavement test sections at the NCAT Test Track.  The purpose of this current study was to assess the performance of two of the original three test sections after approximately 30 million 18-kip single equivalent axle loads (ESALs).  Both of these test sections, Sections N4 and S12, included a 5-in-thick cold central plant recycling (CCPR) layer placed on top of either a compacted aggregate base (Section N4) or a cement-stabilized foundation(Section S12) produced using equipment and procedures used in full depth reclamation (FDR).  The test sections were assessed using pavement instrumentation and periodic performance monitoring to capture the response and any distresses developing from truck loading. 

The study concluded that the two test sections are examples of new or reconstructed pavement structures that include CCPR or CCPR and a stabilized base layer (similar to FDR) that can achieve a long service life under heavy truck traffic.  Section S12, containing the stabilized base layer (similar to FDR), was found to have very low strain levels and no deterioration evident at the surface after 30 million ESALs.  The superior performance of this section was attributed to the use of the stabilized base layer.  Section N4, having an aggregate base, was found to have cracking that was evident at the surface at approximately 29.6million ESALs.  This was expected at some point during the testing given the evidence of reduced moduli values for the asphalt/CCPR layer; greater and more erratic strain values; and increasing vertical base and subgrade pressures noted during the 2015-2018 NCAT Test Track cycle.  Further trafficking of Section N4is expected to provide additional information that might be used to determine a suitable design approach for similar pavement sections.  Following trafficking, a forensic investigation of the test sections should be conducted to identify the specific layers in which any deterioration occurred. 

The study recommends that VDOT modify their design manuals to include using a stabilized base layer (similar to FDR) beneath a CCPR layer when CCPR is included on pavement sections having high traffic volumes.  It is also recommended that VDOT investigate if designing a pavement section consisting of both CCPR and a stabilized base layer (similar to FDR) is more appropriate using a flexible or a semi-rigid approach.  The study further recommends that VDOT continue to sponsor trafficking on Section N4 for the 2021 NCAT Test Track cycle to understand better the behavior of the CCPR material in terms of its eventual deterioration.  Following completion of testing on these sections, a forensic study should be conducted to help identify the specific layers in which any deterioration occurred.

The benefits to VDOT of implementing the study recommendations include the anticipated longer service life of a pavement section built using pavement recycling techniques where CCPR and a stabilized base layer (similar to FDR) are included.  Determination of an appropriate design methodology; additional trafficking of Section N4 containing the aggregate base layer; and a forensic study of both sections following trafficking will provide VDOT a better understanding of the behavior of the CCPR material in terms of its eventual deterioration.