[FHWA logo]
♫ music ♫
Asphalt mixture performance tests help agencies, contractors, and researchers
improve asphalt performance and prolong service life of flexible pavements.
This video is part of a series on asphalt performance testing and demonstrates the Indirect Tensile Cracking test or ITCT.
The ITCT also sometimes is referred to as the IDEAL-CT.
See ASTM D8225-19: Standard Test Method for Determination of Cracking Tolerance Index
of Asphalt Mixture Using the Indirect Tensile Cracking Test at Intermediate Temperature.
All AASHTO and ASTM standards mentioned in this video
are voluntary standards and are not required under Federal law.
For the ITCT, load is applied to a cylindrical asphalt specimen until fracture failure.
This data is used to determine the asphalt’s cracking tolerance index, or CTIndex.
The CTIndex is an index performance indicator of cracking resistance of asphalt.
Typically, the higher the CTIndex value, the greater the cracking resistance of the mixture.
[truck passing]
Supplies and equipment for this test include:
Axial loading device;
Load cell;
Data acquisition system with a sampling rate of 40 Hertz or more;
Internal or external displacement measuring device;
Steel loading strips;
Masonry saw for cutting field cores;
A caliper accurate to 0.1 millimeter;
Water bath or environmental chamber capable of maintaining specimen temperature;
Three 150 millimeter diameter by 62 millimeter or 95 millimeter thick test specimens.
The ITCT test can be performed on laboratory prepared test specimens or cores taken from the field.
For the mixtures with a NMAS of 19 millimeter or smaller, the specimens should be 150 millimeter in diameter by 62 millimeter thick.
For the mixtures with a NMAS of 25 millimeter or larger,
specimens should be 150 millimeter in diameter by 95 millimeter thick.
For laboratory prepared specimens, short-term condition the asphalt mixture according to
AASHTO R30 and fabricate three 150 millimeter diameter specimens at the target air void and target height
using a Superpave gyratory compactor or SGC.
Allow the specimens to cool.
Determine the test temperature based on the climatic intermediate performance
grade temperature as described in the suggested standard.
Condition test specimens in an environmental conditioning chamber or water bath
at the target test temperature for two hours plus or minus 10 minutes.
If water bath is used, use a sealed bag to prevent moisture ingress to the test specimen.
Inspect the fixture to ensure all contact surfaces are clean and free of debris.
Before starting the test, enter the specimen and test information in the control software.
Remove the specimen from the environmental chamber and quickly mount the specimen in the fixture.
Visually inspect the specimen to ensure it is centered and
making uniform contact on the support strip.
Begin the test.
The test should be completed within 4 minutes of removing the specimen from
the environmental chamber to maintain the specimen's specified test temperature.
Apply load to the specimen in load line displacement or LLD control
at a constant rate of 50 millimeter per minute.
Stop the test when fracture failure occurs or the load drops below 100 N.
During testing, record the time, load, and displacement at a minimum
sampling rate of 40 data points per second to obtain a smooth load LLD curve.
The curve should have a clear peak and smooth increasing and decreasing slopes before and after the peak respectively.
After testing is complete, remove the specimen and clean the equipment.
Analyze the test data and calculate the cracking tolerance index, or CTIndex, as described in the standard.
An ITCT data report may include the following parameters for each test specimen:
Asphalt mixture type;
Test temperature in Celsius;
Specimen preparation method and aging condition;
Specimen air void percentage;
Specimen thickness in millimeters;
Specimen diameter in millimeters;
Displacement at 75% of the peak load after the peak in millimeters;
Post-peak slope;
Failure energy in Joules per meters squared;
Work of failure;
Cracking tolerance index or CT Index;
and average and coefficient of variation in percent of CT Index values.
For more information about asphalt testing procedures
or other pavement testing resources, visit fhwa.dot.gov.
♫ music ♫