Simplicity and accuracy are the Asphalt Binder Cracking Device's unique advantages in low-temperature binder testing technology.Low-temperature thermal cracking is one of the major asphalt pavement failure modes. Low-temperature asphalt thermal cracking results in billions of dollars spent annually for pavement repair in the United States. To minimize premature failure due to thermal cracking, it is essential to properly grade asphalt binders for the expected climatic environment.
Asphalt binders have changed considerably since the inception of the Performance-Graded (PG) Asphalt Binder specification. Wider, more varied ranges of crude oil sources are being used to produce asphalt binders, and materials such as polymers, polyphosphoric acid, re-refined REOB, bio binders, and GTR are increasingly being added to improve asphalt binders. RAP is being used in ever-increasing percentages. Today’s asphalt binders generally continue to meet the requirements of the PG specifications, but highway agencies continue to experience premature failures.
NCHRP 09-60 has looked at the shortcomings of the PG specification and made various recommendations, which include proposing the ABCD test as one which should be added to the PG specifications.The ABCD test was developed by Dr. Sang Soo Kim at Ohio University. It is a simple but very effective low-temperature asphalt binder test.
With the ABCD test a new parameter, delta Tf, is introduced
dTf = Tc(S) from the BBR – Tcr from the ABCD test
dTf correctly ranks polymer-modified asphalts and gives credit to elastomeric modifications
How it works
The field-like condition created during the ABCD test eliminates the need for measuring moduli and strength. The ABCD test also eliminates the need for lengthy calculations and assumptions used in the AASHTO specifications, such as the coefficient of thermal expansion and the time-temperature shift function. In the ABCD test, the binder sample is placed outside of a 2-inch diameter ABCD ring which has near-zero thermal contraction. The test specimen is placed in a cooling chamber where the temperature is steadily reduced. As the temperature is lowered, the binder specimen contracts and compresses the ABCD ring. The sensors installed inside the ABCD ring measure and record temperatures and strains. When the binder specimen cracks, the strain is relieved abruptly and the temperature at that moment is the ABCD cracking temperature. Cracking temperatures correlate with field tests much better than the current AASHTO methods.
After the binder samples are prepared, they are placed in a small environmental chamber that cools the samples at a pre-determined rate. At least three samples of the same specimen are recommended for each test. During the cooling and data recording process, the computer program does all of the test work. The program records the strain and temperature readings at ten-second intervals. A real-time plot of the binder strain and temperature is recorded in the data acquisition software and the test is ended when the samples crack. The cracking temperature is recorded as the temperature where a sudden strain jump appears on the strain versus temperature plot. The strength of the asphalt binder can also be determined from the magnitude of the strain jump. Again, only the ABCD can accurately and simultaneously measure the thermal stress and cracking temperature of asphalt binders.
Main applications
• To test the low temperature cracking susceptibility of the asphalt binders
• Quality Control
Key benefits
• Direct Readings：Low temperature thermal cracking can be determined directly without elaborate assumptions and complicated calculations.
• Emulates Actual Conditions：The test creates field-like conditions for the tested binders as the sample is restrained from contracting.
• Straight-forward Procedure：A set of four specimens takes about three hours to prepare and about four hours to cool in the cooling chamber to determine the cracking temperature.
• Simple Calculations：The cracking temperature is determined directly from the real-time graph of binder temperature and strain versus time.
• More Reliable：The silicone molds reduce the handling of the specimen to decrease erroneous results. The molds also maintain flexibility at lower temperatures so no excess strain is applied to the sample during testing, allowing the specimens to contract.
• Easy & Multiple Specimen Testing：The test is forgiving and the simplicity of the testing is easy to master, reducing chances for errors. The current testing chamber can hold 16 specimens at once, which allows different binder samples to be tested simultaneously.
Software
Real-time graph during ABCD test showing four specimens being tested in the cooling chamber. Temperature continuously decreases. Asphalt binder strain stays relatively constant for the first 90 minutes, then the binder begins to contract (strain drops), and the strain jumps when the binder cracks. The cracking temperature is recorded at the time the strain jumps.
After the test, the data are analyzed and presented as a graph of strain vs. temperature and in a summary table in an Excel worksheet for easy incorporation into reports and presentations. The summary table shows cracking temperatures, strain jumps, averages and standard deviations.