Of the cracking tests gaining popularity for their correlation to field results, the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) scores near the top of the class. If your department of transportation (DOT) requires you perform this test on your balanced mix designs (BMD) or other mixes, here’s how to do it.
First, create in the Superpave gyratory compactor six asphalt mix specimens of 150 mm in diameter, 62 mm in height, with 7 percent air voids (+/- 0.5 percent). Do not notch, cut or otherwise distress the puck.
Next, age the specimens for two hours at 25 degrees Celsius.
To run the test, begin by entering salient information in the computer software’s required fields.
Next, place the specimen on its side in the load frame. The test will be conducted at room temperature. Load the specimen at a constant deformation rate of 50 mm per minute of cross-headed displacement until fracture failure occurs.
The instrumentation feeds data to the computer software, which continuously records the load and vertical deformation. It automatically calculates the cracking tolerance index (CTIndex) using the software provided with the system.
This tests at least three replicates for each sample and generates a CTIndex for each sample in five minutes or less (after the two-hour aging of the sample). FHWA states the test meets ASTM D8225 standards and specifications.
The larger the CTIndex value, the better the cracking resistance.