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Figure 19. MDTS gluing apparatus.
resolve the deficiencies. Substantial effort was expended by
both the research team and MDTS to resolve the deficiencies.
All of the deficiencies were addressed, and the upgraded
device was accepted in January, 2007.
3.2.4 IPC Global Production Unit
The IPC Global production unit is shown in Figure 20.
This unit is very similar to the first article device evaluated in
Phase II of the project. The machine is slightly larger than the
first article to accommodate the larger refrigeration unit
needed for testing at 39ºC and a second acrylic cell was added
around the test chamber to provide insulation. IPC Global
also made a modification to improve the holders for the
Figure 17. Test chamber lift mechanism for the MDTS
LVDTs for the specimen mounted deformation measuring
SPT. system used in the dynamic modulus test.
The IPC Global SPT is relatively small. It consists of (1) a
cabinet (44 in. wide by 53 in. high by 25 in. deep) that in-
cludes the test chamber, the hydraulic pump and actuator,
the heating and refrigeration unit, and associated power and
control electronics; and (2) a desktop computer for control-
ling the machine and collecting and analyzing test data. The
system operates on single phase 208230 V AC power.
Figure 21 shows the IPC Global SPT with the test chamber
open and a specimen inserted for unconfined testing. The test
chamber is relatively small, only 8.5 in. in diameter by 14 in.
high. Since temperature control is provided by conditioned
air circulated through the test cell, there are no heat ex-
changers inside the test cell to interfere with test specimen in-
stallation and instrumentation. The test chamber is opened
and closed by pneumatic actuators. Two hand switches are
provided as a safety feature. Hand contact must be made with
Figure 18. MDTS specimen mounted deformation both of these switches for the test chamber to close. The test
measuring system. chamber is insulated by a second acrylic cell that hangs on the
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Table 11. MDTS deficiencies and solutions.
Deficiency Solution
Specimen mounted deformation Reduced glued contact size.
measuring system glued contact
size exceeded specification.
Moment on glued gage points too Revised specimen mounted deformation measuring system by removing
high resulting in gage point failure LVDT spring and modifying the connection to decrease distance from the
at high temperatures. specimen.
Temperature control is difficult to Removed manufacturer supplied offsets. User must develop a table of
use to manufacturer supplied offsets.
offsets.
Confining pressure control did not Modified the software to properly control the confining pressure during
function properly in the flow these tests.
number and flow time tests.
Auto strain control in the dynamic Modified auto strain control algorithm.
modulus test does not function
correctly.
Incorrect computation of some Modified the software to correctly compute the data quality statistics.
dynamic modulus data quality
statistics
Some data quality statistics not Modified the software to include all data quality statistics in the reports.
included in dynamic modulus
reports.
Raw data, not normalized data, Modified the software to use the normalized data in the report plots.
used in the plots in the dynamic
modulus reports.
Summary report not provided. Modified the software to include the summary report.
Strain rate computations for the Modified the software to correctly report the strain rate
flow number are shifted forward by
one line.
Strain not set to zero at the Modified the software to set the strain to zero at the time specified in the
beginning of the flow time test. software.
Strain rate computations for the Modified the software to correctly report the strain rate
flow time are shifted forward by
one line.
automated test chamber. The specimen mounted deforma- shown in Figure 24. This system has pneumatic actuators that
tion system consists of three spring-loaded LVDTs mounted press the gage points against the specimen at the correct gage
120° apart as shown in Figure 22. IPC Global designed a length at the center of the specimen. It also includes a mem-
unique holder for the LVDTs that can be used for unconfined brane stretcher to assist with membrane installation for
and confined testing. Each holder has a stiff spring that grips confined tests.
the glued gage points. The spring was designed to highly com- Final design, fabrication, and shop testing of the IPC
press the latex membranes to minimize errors during con- Global SPT required approximately 6 months. IPC Global
fined testing. was given authorization to proceed with the machine on
The ruggedness testing revealed that at high temperatures, February 6, 2004. The machine was delivered on July 29,
creep of the LVDT gauge points can occur, and when this hap- 2004. Upon delivery, the specification compliance testing
pens, erroneous dynamic modulus data are obtained. The summarized in Table 9 was performed. The specification
spring force for the IPC Global LVDTs is the highest of compliance testing revealed a small temperature effect on the
the three machines tested, and this machine was the only device LVDTs used in the dynamic modulus testing over the tem-
to exhibit gauge point creep at the temperatures used in the perature range of 39 to 140ºF. IPC Global investigated this
ruggedness testing. IPC Global designed springs to counter the problem and determined that the temperature effect was
LVDT spring force and minimize gauge point creep. Figure 23 caused by an incorrect excitation frequency being used with
shows the counter springs on the IPC Global LVDT holders. the LVDTs. Apparently the LVDT manufacturer provided
These counter springs should be used when LVDT gauge point IPC Global an incorrect optimum excitation frequency. IPC
creep is detected in high temperature dynamic modulus tests. Global subsequently replaced the LVDT conditioners to
Gauge point creep occurred in the ruggedness testing at 95°F resolve this problem. The machine was accepted in October,
when testing specimens made with PG 64-22 binder. 2004 and delivered to the Turner-Fairbank Highway
To quickly and accurately mount the glued gage points to Research Center, where it has been used extensively on sev-
the specimen, IPC Global designed the gluing apparatus eral research projects.
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Figure 20. Overall view of the IPC Global SPT.
Figure 21. Open test chamber for the IPC Global SPT.
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Figure 23. Additional springs to minimize gauge
point creep at high temperatures.
Figure 22. IPC Global specimen mounted
deformation measuring system.
Figure 24. IPC Global gluing apparatus and
membrane stretcher
