Structural Study of Cold Central Plant Recycling Sections at the National Center for Asphalt Technology (NCAT) Test Track

About the report:

In 2012, the Virginia Department of Transportation (VDOT) contracted with the National Center for Asphalt Technology (NCAT) to install, instrument, and monitor three pavement test sections at the NCAT Test Track during the 2012-2014 track cycle. The work consisted of constructing, instrumenting, and trafficking the test sections with heavily loaded trucks until approximately 10 million 18-kip equivalent single axle loads (ESALs) were applied. Embedded instruments were installed to capture the temperature and pavement response from truck loading. The three test sections, having a length of 200 ft each, consisted of two different asphalt overlay thicknesses placed on top of a five-in cold central-plant recycled base. One of the three sections also contained a cement-stabilized base designed to simulate a full-depth reclaimed layer.

The purpose of this study was to evaluate the performance of the three test sections constructed using cold central plant recycling (CCPR) over the initial 2-year track cycle. The performance was documented by analyzing the results of laboratory testing from collected cores, as well as deflection testing from falling weight deflectometer, temperature, pressure, and strain measurements from embedded instruments, and surface-observable deterioration of the pavement sections.

The study found that none of the three sections showed any surface-observable deterioration after 10 million ESALs of loading. Throughout the cycle, the average measured strain from Section N3 (having a 6-in asphalt overlay) was 40% less at 68°F than that of Section N4 (having a 4-in asphalt overlay). The strain from Section S12 (having a 4-in asphalt overlay and a cement-stabilized foundation) was approximately 69% and 49% less than the strain levels for Sections N3 and N4, respectively, at 68°F. The structural layer coefficient of the CCPR material was estimated to range from 0.36 to 0.39 based on falling weight deflectometer testing. The temperature-normalized asphalt mixture/CCPR modulus of Section S12 was found to increase with respect to time. This indicates that the cement-stabilized foundation is increasing in strength over time, likely attributable to continued curing of the layer.

The study recommends that VDOT continue to emphasize the use of pavement recycling methods for new pavement construction and pavement rehabilitation projects. To this end, VDOT will work to identify locations for future pavement recycling projects where performance data suggest that maintenance activities take place more often than the average. VDOT will also review existing memoranda with district pavement management and design staff that state pavement recycling should be considered for projects where it is a viable option.

This study shows that the three pavement designs used in the three test sections constructed at the NCAT Test Track to be adequate for a minimum of 10 million ESALs and likely much longer. This report is an interim report in that the test sections are still being trafficked. A final report will be prepared upon the completion of testing.

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