This report describes
the selection and implementation of a shadow project conducted by the North
Carolina Department of Transportation (NCDOT) for the Federal Highway
Administration’s asphalt mixture performance-related specifications (PRS).
The
overall shadow project process started with the NCDOT selecting a field project
to serve as the shadow project. The selected project uses RS9.5C, RI19.0C,
RB25.0C mixtures as the surface, intermediate, and base layers, respectively. The
North Carolina State University research team acquired 27 mixture samples from the
three asphalt layers of the project. The team performance-tested the RS9.5C and
RI19.0C mixture samples (using the ‘four corners’ procedure) for calibration and
verification of the performance-volumetric relationships (PVRs) that were
developed for the selected mixtures. Once the PVRs were developed, pavement
performance was predicted using the mixtures’ volumetric properties that were measured
in accordance with typical acceptance practices.
The verification results
revealed that the PVR functions developed for the tested mixtures worked
reasonably well to predict pavement performance under the volumetric conditions
of the verification samples. The PVRs also were used to evaluate the effects of
field construction variability on pavement performance by applying the
developed PVRs to measured acceptance quality characteristics. Reasonable
trends were found between pavement performance and in-place density.
However,
the effects of binder content were not captured well by the PVRs due to the
narrow range of binder contents in the tested samples that were used to develop
the PVRs. Overall, the shadow project’s test results were found to predict
pavement performance as a function of acceptance quality characteristics in the
context of PRS reasonably well.
