TM 5-822-7/AFM 88-6, Chap. 8
b. Optimum number of rolling passes. During the
until the specified density is reached. Two nuclear
test strip construction, a nuclear gage operated in
density gages should be calibrated (using the same
holes) during the test section construction so that an
the direct transmission mode and standardized with
extra one is available during final construction.
a calibration block should be used to determine the
optimum number of passes with the vibratory roller
d. Strength tests. Ten cores and beams should be
taken from the test section after 28 days to deter-
to reach maximum density. The density should be
measured by inserting the nuclear gage probe into
mine a correlation between flexural strength and
the same hole after each pass of the vibratory roller.
splitting tensile strength and/or compressive
The hole should be made with an instrument
strength of the RCCP. This reduces the amount of
sawing necessary to obtain samples during further
specifically designed for the purpose, and should be
formed using the same method throughout the test
construction. Although both the splitting tensile
and compressive strength data would be useful for
section and main construction. This rolling and
measuring procedure should be continued until there
historical reference, only one of these tests is needed
is less than a 1 percent change in successive
for quality control testing of the RCCP construction.
readings. These data may be used in conjunction
After the correlation is determined, the appropriate
with correlation between the nuclear gage and the
splitting tensile and/or compressive strength that
laboratory density to determine the minimum
correlates to the specified design flexural strength
number of passes needed to achieve or slightly
should be used in any further quality control testing.
exceed the specified density in the RCCP construc-
tion. However, a minimum of four vibratory passes
D-8. Batching, mixing, and transporting. RCCP
should be used, and this minimum will probably
needs a vigorous mixing action to disperse the relatively
prevail in most cases.
c. Nuclear gage/laboratory density correlation.
small amount of water evenly throughout the matrix.
This action has been best achieved by using a
After a reasonable estimate is made of the optimum
number of passes needed for compaction, a correla-
twin-shaft pugmill mixer commonly used in asphaltic
tion between the value of in situ RCCP density as
concrete mixing. Batching of the concrete may be
measured with the nuclear gage and the value
accomplished successfully in either a continuous-
mixing or a weigh-batch asphalt plant. The continuous-
obtained by weighing a sample of the RCCP in air
mixing plant is recommended for batching RCC
and water should also be determined. This should be
because it is easier to transport to the site, takes less
accomplished by measuring the final compacted
time to set up, and has a greater output capacity
density (after four or more passes with the vibratory
than the weigh-batch plant. The weigh-batch plant
roller) in 10 locations with the nuclear gage, which
allows more accurate control over the proportions of
has been standardized with a calibration block. The
material in each batch, but generally does not have
measurement should be made by inserting the probe
enough output capacity for larger paving j ohs. The
the full depth of the lane. Then, at 7 days, a pair of
output of the plant should be such that the smooth,
cores should be taken on either side of the remaining
continuous operation of the paver(s) is not interrupted,
nuclear gage holes (within a 1- to 3-foot radius from
the hole) and the density of the cores measured in the
and for all but the smallest jobs (1,000 square yards
or smaller), the capacity of the plant should be no
laboratory by weighing them in air and water. For
less than 250 tons per hour. The output (or production)
each of the 10 holes, the average of the pair of the
of the plant should not be greater than the laydown
laboratory densities should be compared with their
capacity of the paver(s) nor greater than the rolling
corresponding nuclear gage density, and a constant
capacity of the rollers. The plant should be located as
relationship between the nuclear gage and laboratory
close as possible to the paving site, but in no case
densities developed by averaging the algebraic
should the haul time between the batch plant and the
differences in these readings. This difference should
paver(s) exceed 15 minutes. The RCC should be hauled
be combined with future field readings to obtain an
from the mixer to the paver(s) in dump trucks. These
adjusted reading which can be compared to the
trucks should be equipped with protective covers to
specified density. In the past a specified density of
guard against adverse environmental effects on the
96 percent of theoretical weight as defined in ASTM
RCC, such as rain, or extreme cold or heat. The truck
C 138 has been achieved. If the adjusted nuclear
should dump the concrete directly into the paver
gage density is less than the specified density,
hopper.
additional passes should be made on the fresh RCCP
D-5
Previous Page
