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Performance testing of asphalt mixtures is an important aspect of performance engineered
mixture design of asphalt.
It helps improve performance and prolong service life of flexible pavements.
This video is part two in a series of four videos on asphalt testing using the
Asphalt Mixture Performance Tester or AMPT.
This video demonstrates the Dynamic Modulus for Small Specimen Test based on AASHTO TP 132.
All AASHTO and ASTM standards mentioned in this video are private, voluntary standards
and are not required under Federal law.
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Before beginning this test, prepare your test specimen as recommended in AASHTO PP 99.
Refer to video one in this series for more information.
Before beginning the Dynamic Modulus test on the AMPT,
attach gauge points to the test specimen using a Fixing Jig.
Supplies and materials are shown here and include:
Glue Mixing stick
Mixing palette Gauge points
and 38-mm diameter by 110-mm tall specimen.
Start by installing gauge points on the setting arms for the fixing jig.
Place the specimen on the stage to test alignment.
Make certain the stage is horizontal and the gauge points will be attached in the middle
of the test specimen.
Adjust the bottom pedestal and/or setting arm, if necessary.
Apply glue to the mixing palette and mix thoroughly according to manufacturer's recommendations.
Apply glue evenly to the installed studs.
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Place the specimen on the center of the stage making sure it's aligned correctly.
Gently stabilize the specimen with one hand and activate the jig to close the setting arms.
Refer to the manufacturer's instructions for recommended mixing and curing time.
Once appropriate time has elapsed, unseat the gauge points from the setting arms.
Remove the test specimen from the fixing jig.
Visually inspect for proper stud attachment and then place it in an external environmental
chamber for temperature conditioning.
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Supplies and materials for the Dynamic Modulus test are shown here and include:
Small Scale Dynamic Modulus fixture with steel ball;
LVDT sensors or specimen-mounted deformation-measuring system;
LVDT clamps; 0.25 mm thick and 40 mm diameter PTFE sheet;
38 mm diameter by 110-mm tall specimen; Dummy specimen with thermocouple/thermal probe
installed in the middle of the test specimen.
Place both the testing and dummy specimens in the external environmental chamber until
the dummy specimen reaches the test temperature.
Verify the calibration of the AMPT using a proving ring before beginning this test.
Prepare the AMPT conditioning chamber.
Open the AMPT conditioning chamber and install the LVDT sensors and fixtures required for
small-scale specimen testing.
Place the bottom platen, PTFE sheets, and the top platen with steel ball in the chamber.
Close the chamber and set the temperature control to the desired testing temperature.
Allow the testing chamber to equilibrate for at least one hour at the testing temperature.
Once the dummy specimen has reached the designated testing temperature, remove the test specimen
from the external environmental chamber and attach the LVDT clamps.
If multiple sets of LVDT clamps are available, they can be installed before placing the specimen
in the external environmental chamber.
Open the AMPT conditioning chamber and setup the test specimen.
Remove the top platen and a PTFE sheet.
Place the PTFE sheet on the top of the specimen and then place the top platen with steel ball.
Carefully center the specimen on the contact surface of the bottom platen with PTFE sheet
and install the LVDTs between the LVDT clamps.
Once the LVDTs are installed, ensure the LVDT readings are adjusted to accommodate the deformation
range of the test.
It is typically set to zero to accommodate displacements due to compression and tension.
Close the AMPT conditioning chamber.
Allow the chamber and the specimen to return to the test temperature.
According to the standard, setting up the test specimen in the AMPT conditioning chamber
and returning the chamber to test temperature should not take more than 5 minutes.
Select the appropriate test template.
Enter the specimen identification and control information into the dynamic modulus test template.
The information may include: Project name;
Operator name; Specimen identification;
Specimen dimension;
Specimen conditioning time; and comments like air voids.
Check the target test temperature and initial modulus on the test control software.
The initial modulus should be representative of the regions' typical values of asphalt
mixture use at test temperature.
Verify the average dynamic strain range is between 50 and 75 micro-strain
and the contact stress is 5 percent.
Wait for the contact pressure and temperature to stabilize.
The temperature should register within plus or minus .5 degrees Celsius of target temperature.
Check 'confirm' and then start the test.
Begin testing at the lowest temperature and highest frequency.
Test all frequencies from 10 Hz to 1 Hz to 0.1 Hz before moving to the next higher temperature.
Follow the recommended test temperatures in the standard.
Accept only test data meeting the Data Quality Statistics Requirements.
If excessive amount of permanent deformation has accumulated,
discard the specimen, and use a new specimen.
When the test is complete, export the data.
Once acceptable data has been collected, open the AMPT conditioning chamber
and remove the tested specimen.
Repeat this process for the remaining test specimens.
For more information about Asphalt Mixture Performance Tester procedures or other pavement
testing resources, contact the Federal Highway Administration.
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