Figure 13-5.—Sample data sheet, calibration of sand-cone density apparatus.
will also need a baking pan, moisture content canisters,
a paintbrush with moderately long bristles, and some
modeling clay.
CALIBRATION.— The sand-displacement method
includes three calibration procedures that must be
completed before you conduct the test.
The first of the calibration procedures is the
apparatus calibration that determines the volume of
the jar and connecting cone (up through the cone valve).
To perform the calibration, you first weigh the
assembled apparatus (jar and cone) when it is empty,
clean, and dry. Record this weight on a data sheet similar
to figure 13-5. Then you weigh the apparatus when the
jar and the smaller end of the cone is filled with water
(making sure that no air is entrapped in the water).
Record this weight on the data sheet and then empty the
water from the apparatus. After repeating these steps at
least three times, you can then determine the average
weight of the water and compute the volume of the
apparatus, using the formulas shown in figure 13-5.
The second calibration that you must make before
performing the sand-cone test is sand calibration.
The sand that you use in the sand-cone test must be
clean, dry, and free-flowing with a constant moisture
content while the test is performed. Uniformly graded
and well-rounded sand passing the No. 20 sieve and
retained on the No. 40 sieve is most suitable for the test.
Almost no material finer than the No. 200 sieve should
be in the sand. This sand is usually purchased in bulk
quantities that can be used for many sand-cone tests
performed over extended lengths of time. The density
of the sand may be determined soon after the sand is
received; however, since the bulk density of the sand is
affected by changes in temperature and humidity, you
must recalibrate the sand before each test.
To calibrate (or recalibrate) the sand, you first weigh
the assembled apparatus when it is empty, clean, and dry.
This weight is recorded on line 2 of DD Form 1215 (fig.
13-6A). Next, the apparatus is filled with air-dried sand
by pouring the sand into the apparatus through the large
end of the cone. When the jar and lower end of the cone
is filled and all excess sand is removed, weigh the
sand-filled apparatus. Record that weight on line 1. Then
by subtracting these weights, you can determine the
weight of the sand (in grams). Finally, to determine the
calibrated density of the sand, you convert the weight of
the sand to pounds and divide by the volume of the
apparatus.
13-6
