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Frequently Asked Soil-Cement Questions
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FAQs > FDR Sample Collection and Preparation
Q: How do you collect and prepare samples for FDR
projects?
By Tim McConnell, Cement Stabilization Specialist, Southeast Cement
Association The success of any full-depth reclamation
(FDR) with cement project begins with the proper sampling and preparation
of pavement, base and/or subgrade materials to be used in lab tests.
Lab data from the sampled materials will ultimately provide the
basis for an appropriate FDR mix design. If field samples are not
obtained, and a mix design is not performed, it can lead to premature
failure of the reclaimed layer and ultimately lead to costs that
could have been avoided by following some simple procedures.
Materials that will be used in the FDR process can be sampled in
two ways:
- Field pulverization (using a special drill bit) and collection
of materials to the expected reclamation depths.
- Collection of materials by auger or manual methods (i.e. shovel,
post hole digger, pick, etc.). No field pulverization is performed.
 Method
1
Field pulverization and sample collection using a specialized drill
bit mimics the pulverization done by reclaiming equipment used in
FDR construction, and reduces lab preparation time. An example of
a sampling drill bit used by the North Carolina DOT is seen here.
Samples should be collected to the expected reclamation depth (usually
6 to 12 inches). A minimum of 100 pounds of material is needed from
each sample location to run the necessary lab tests needed for a
mix design. [Note: one 5-gal bucket will hold about 50 lbs. of material).
Method 2
If field pulverization methods are not used to obtain mix design
samples, attention to sample collection is vital. Samples should
be obtained from all layers expected to be reclaimed (asphalt, base,
and possibly subgrade). The asphalt layer can be saw cut, or in
most cases simply removed using hand tools such as picks and shovels.
Underlying base and/or subgrade materials should be sampled to the
expected reclamation depth. If the depth of reclamation is not known,
the materials should be kept separate so that blending can be done
in the lab. (For example, if it is not known if the subgrade will
be included in the reclamation, it should be bagged separately so
that the effect of including the subgrade material can be evaluated
in the lab). As with the field pulverization sampling technique,
a minimum of 100 pounds of material is needed for the necessary
lab tests.
The asphalt sample obtained for lab testing is usually collected
in large pieces. This material must be broken down to a size that
is comparable to the pulverization that occurs during FDR construction.
For instance, Summit Engineering (located in Charlotte, NC) places
sampled asphalt in a drying oven and heats the material to approximately
110° F. By using just hand manipulation, the softened asphalt
can be reduced to an appropriate size similar to that obtained during
field pulverization.
 Once
a lab has prepared the material, testing will proceed using ASTM
D558, “Standard Test Methods for Moisture Density (Unit Weight)
Relationships of Soil-Cement Mixtures” and if unconfined compressive
strength data is desired, ASTM D1633, “Test Method for Compressive
Strength of Molded Soil-Cement Cylinders” is recommended.
The road to success with full-depth reclamation begins with proper
sampling and preparation of materials for lab tests. With a few
simple procedures in sampling and material preparation, an optimized
mix design can be obtained that will contribute in part to the success
of a full-depth reclamation project.
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