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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 one in a series of four videos on asphalt testing using the
Asphalt Mixture Performance Tester or AMPT.
Part one demonstrates the Compaction of Superpave Gyratory Compactor (SGC) Samples as well as
the fabrication of small and large specimens based on AASHTO PP 99.
All AASHTO and ASTM standards mentioned in this video are private, voluntary standards
and are not required under Federal law.
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Prepare an asphalt mixture to fabricate a compacted SGC sample with 150 mm diameter
and a height of 180 mm or higher.
The mass of asphalt mixture for each SGC sample depends on the specimen height,
the theoretical maximum specific gravity of the mixture, and target air void content of the test specimen.
For Stress Sweep Rutting, or SSR test, compact the SGC samples as recommended by AASHTO T 312
Place a paper disk in the bottom of the mold.
Place the asphalt mixture at compaction temperature into the mold in one lift.
While placing the mixture, care should be taken to avoid segregation.
Next, level the mixture in the mold.
Place another paper disk and upper plate, if required, on top of the leveled material.
Load the charged mold into the compactor and allow the compaction to proceed until the
target height is achieved.
Extrude the compacted sample from the mold.
Allow the compacted SGC sample to cool to atmospheric temperature,
then core a 100 mm nominal diameter test specimen from the center of the SGC sample.
Next, saw both ends of the core to obtain a test specimen with a nominal height of 150 mm.
Both the coring and saw equipment should be adequately supported and secured
to ensure the resulting test specimens are cylindrical with smooth parallel sides,
and they meet the tolerances for height, end flatness, and end perpendicularity.
Check the perpendicularity of each end of the specimen using a precision square and
a 1 mm carbon steel wire at two locations approximately 90 degrees apart.
Trim or grind the specimen to meet the specifications for flatness, perpendicularity, and height.
If the specimen meets the height, perpendicularity, and flatness requirements, proceed to the
air void determination as recommended in AASHTO T166 or T331.
Store the test specimen, until tested, on its end at room temperature, 59° to 81°F.
Ensure the specimen is dry before proceeding to further testing.
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For the small-scale test specimen, prepare the SGC sample in accordance with AASHTO PP 99:
Standard Practice for Preparation of Small Cylindrical Performance Test Specimens
Using the Superpave Gyratory Compactor, or SGC, or Field Cores.
The SGC specimen compaction procedure recommended in AASHTO PP 99
is in accordance with AASHTO T 312 with the following exceptions:
1: Pour the asphalt mixture at compaction temperature into the center of the mold to minimize air
void variation within the sample.
2: Charge the mold in two equal lifts.
After each lift, scrape the walls of the mold by inserting a spatula 8 to 10 times.
Insert the spatula 10 to 12 times in the center of the mixture in an evenly distributed pattern.
Allow the compacted SGC sample to cool to atmospheric temperature.
Mark the SGC sample where the cores will be taken.
All cores must be taken within the center 100 mm diameter of the SGC sample.
Core a test specimen with a nominal diameter of 38 mm.
Four test specimens can be cored from one SGC sample.
Next, saw both ends of the core to obtain a test specimen with a nominal height of 110 mm.
Check the flatness of each end at three locations approximately 120 degrees apart.
Using the blade of the precision square as a straightedge, check the maximum departure
of the test specimen using a 0.5-millimeter diameter carbon steel wire.
Check the perpendicularity of each end of the specimen using a precision square and
a 1 mm carbon steel wire at two locations approximately 90 degrees apart.
Measure the height of the test specimen as recommended in ASTM D3549/D3549M.
Trim/grind the specimen to meet the specifications for flatness, perpendicularity, and height.
If the specimen meets the height, perpendicularity and flatness requirements, proceed to the
air void determination as recommended in AASHTO T166 or T331.
Store the test specimen, until tested, on its end at room temperature, 59° to 81°F.
Ensure the specimen is dry before proceeding to further testing.
For more information about Asphalt Mixture Performance Tester procedures or other pavement
testing resources, visit fhwa.dot.gov/pavement.
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