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Table 14. Dimensions of specimens prepared using the FlexPrepTM system.
Specimen Characteristics Diameter Height Flatness Perpendicularity
Gyratory Air Standard
Mix Size, Aggregate Binder Height, Voids, Average, Deviation, Average, Top, Bottom, Top, Bottom,
No. mm Type Grade mm % mm mm mm mm mm mm mm
1 9.5 Limestone 58 165 7 101.3 0.1 149.5 0.25 0.05 0.05 0.05
2 9.5 Limestone 58 165 7 100.7 0.2 148.3 0.30 0.05 0.10 0.05
3 19 Granite 58 175 7 100.8 0.1 149.5 0.30 0.10 0.05 0.30
4 9.5 Limestone 64 165 7 101.3 0.1 149.8 0.45 0.05 0.15 0.05
5 9.5 Limestone 64 165 7 101.1 0.1 149.9 0.45 0.05 0.15 0.05
6 9.5 Limestone 64 165 4 101.3 0.0 149.8 0.20 0.05 0.15 0.05
7 9.5 Limestone 64 165 4 101.1 0.1 149.7 0.25 0.10 0.10 0.05
8 9.5 Limestone 64 165 7 101.0 0.1 149.9 0.15 0.05 0.05 0.15
9 9.5 Limestone 58 165 7 101.0 0.1 148.0 0.10 0.05 0.05 0.30
10 19 Granite 64 165 7 101.4 0.1 149.3 0.30 0.25 0.10 0.10
11 19 Granite 64 165 7 101.3 0.1 150.0 0.30 0.30 0.15 0.10
12 19 Granite 64 175 4 101.1 0.1 150.3 1.00 0.15 0.15 0.15
13 19 Granite 64 165 4 101.0 0.1 150.5 0.85 0.05 0.50 0.10
14 9.5 Limestone 64 165 4 101.2 0.1 150.6 0.90 0.10 0.50 0.10
15 9.5 Limestone 58 165 4 101.0 0.0 149.8 0.90 0.05 0.40 0.30
16 9.5 Limestone 64 175 4 101.2 0.1 150.5 0.45 0.05 0.30 0.10
17 9.5 Limestone 64 175 7 101.3 0.1 150.5 1.45 0.45 0.40 0.10
18 19 Granite 64 175 7 101.2 0.1 150.6 1.25 0.15 0.30 0.05
19 19 Granite 58 165 7 100.8 0.1 149.9 0.80 0.15 0.25 0.20
20 19 Granite 58 165 4 101.1 0.0 150.7 1.25 0.20 0.30 0.20
created as shown in Figure 34. None of the variables included produced by the Interlaken compactor used to fabricate the
in the experiment affected the top end flatness failure rate. gyratory specimens for this study. The Interlaken compactor
Although both the top and bottom cutoff blades have produces high air voids at the top of the specimens and low
the same shape, the failures only occurred on the top of the air voids at the bottom. It is likely that the higher air voids at
specimen. This is likely the result of the air void gradient the top are the reason the failures always occurred at that end
during the specification compliance testing.
The effect of not meeting the specimen end tolerance on
the measured properties of the specimens was not evaluated
in this study. The defects may not significantly affect the
measured properties because the instrumentation is located
far from the specimen end and aggregate interlock, and the
resulting redistribution of stress and strain likely produces
more uniform conditions at the center of the specimen.
Additionally, it may be possible to fill the defects with plaster
or some other material without significantly affecting the
measured material properties.
4.2.4 Needed Improvements
The FlexPrepTM System was found to be in substantial com-
pliance with the first article equipment specification and was
accepted by the research team. The machine complies with
the physical size and power requirements. It can produce
specimens meeting the dimensional tolerances for specimens
for the SPT. The cycle time for cutting and coring test speci-
mens is less than the specified 15 minutes.
Figure 34. Divot in top of specimens created by the Although the FlexPrepTM System was accepted under
FlexPrepTM system. NCHRP Project 9-29, the specification compliance testing
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identified several improvements that should be made in · Water circulation system. The settling tank is undersized and
future production units. These are summarized below: requires frequent cleaning. Additionally the cooling water
heats-up after several specimens are cut in succession. The
· Cutoff blade. Shedworks should perform additional devel- water heats sufficiently that specimens made with soft
opment work to improve the cutoff blades and their con- binders and high air void contents may creep beyond the
trol to minimize the potential for aggregate being torn range of the self-tightening chuck or break while being cored.
from the specimen. · Test specimen removal. It is difficult to remove the cap on
· Controls. The control system requires further improve- the core barrel to remove the test specimen. A different
ment. In some cases, the limit switches that detect the type of core barrel cap is needed.
completion of the cutting or the coring failed to trip. · Front doors. The machine has a wide front door that pro-
When this occurs, there is no manual override that allows vides access for removing the test specimen and cleaning
the program to continue from its current point. The only the system. This door is made from a polycarbonate mate-
alternative is to reset the machine and restart the cutting rial. It is relatively wide and split horizontally in the middle.
and coring operation from the beginning. Restarting A spring loaded pin-type latch is included in the top half of
from the beginning wastes time and increases the possi- the door to close it. This door is difficult to use particularly
bility that the test specimen will not meet the dimensional when coring grit builds up on the door. Additionally, the
tolerances. door leaks at the bottom as shown in Figure 33.
