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Abstract:The Florida Department of Transportation (FDOT) has traditionally required that all sampling
and testing of asphalt mixtures be at the Contractor’s production facility. With recent staffing cuts, as
well as budget reductions, FDOT has been considering alternative sampling methods which will
provide greater staffing flexibility, while at the same time provide assurance that a quality product is
placed on the roadway. One of the methods being considered is sampling the asphalt mixture at the
roadway.
The first objective of this study was to conduct a literature review and survey which included
interviewing various transportation engineers to determine which agencies require, or allow, field
sampling for acceptance and whether those efforts have been successful. The second objective of this
study was to evaluate the sampling and testing variability of samples taken at the plant compared to
those taken from the roadway mat and from the paver auger. A statistical evaluation was performed
to compare results from this study to the specification limits currently being used. Superpave 9.5 mm
and 12.5 mm mixes were sampled on 11 dense-graded projects, and two FC-5 projects (Open-Graded
mix) were sampled and tested.
The survey showed as many agencies require sampling from the roadway as require sampling
from the plant; but when agencies allow either location, samples are most often taken from a loaded
truck at the plant. When roadway samples are taken, most often those samples are taken from the
mat behind the paver.
For dense-graded mixes, individual test tolerances for air voids, and Gmm and Gmb values of
limestone mixes will need to be increased if roadway samples are to be used for acceptance or
comparison with contractor results. The differences for percent passing the No. 200 sieve were
statistically significant for auger samples, but deviations were within current tolerances. Asphalt
content was significantly affected by roadway mat samples, but deviations were within current
tolerances. Roadway samples of FC-5 mix from both the mat and auger were statistically different
than the contractor and FDOT samples taken at the plant. Roadway sampling is not recommended for
FC-5 mixes.
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