The Asphalt Low-Temperature Performance Tester is an advanced instrument designed to evaluate the low-temperature cracking behavior of asphalt binders and mixtures. Its primary function is based on the AASHTO T387 Asphalt Binder Cracking Device (ABCD) test method, which measures the temperature-strain curve of asphalt binders to determine their low-temperature cracking temperature directly.
During the ABCD test, the asphalt sample is placed inside a ring-shaped mold composed of silicone and INVAR steel. Inside the INVAR steel ring, strain gauges and temperature sensors are attached, with a silicone protrusion penetrating through the asphalt sample. The filled test mold is then placed inside a temperature-controlled chamber, where testing begins at 20°C. The temperature decreases at a constant rate of 40°C per hour between 0°C and 20°C, and at 20°C per hour from -60°C to 0°C.
As the temperature drops, the asphalt sample shrinks significantly, causing it to exert pressure on the INVAR steel ring, which is monitored via strain gauges. Due to stress concentration at the silicone protrusion, cracking first occurs in this ring-shaped region.
For reference, the thermal shrinkage coefficient of asphalt is approximately 200 × 10⁻⁶ /°C, whereas that of INVAR steel is 1.2 × 10⁻⁶ /°C.
When cracking occurs, the pressure exerted by the asphalt on the INVAR steel ring suddenly decreases, leading to a strain transition. This allows for precise determination of the asphalt's cracking temperature based on the temperature-strain relationship.
Compared to BBR (Bending Beam Rheometer) low-temperature flexural tests and DT (Direct Tension) tests in the Superpave PG grading system, the ABCD (Asphalt Binder Cracking Device) method provides a more direct measurement of the asphalt’s cracking temperature without requiring assumptions or calculations.
Validation of ABCD Testing Method
To verify the effectiveness of the ABCD testing method, a comprehensive evaluation was conducted during its development, involving 23 laboratories across the United States. Among them, 11 laboratories performed comparative tests with BBR results, and the method was further validated against real-world field data from experimental roads in Elk Country, Pennsylvania (USA), as well as Lamont and Highway 17 in Ontario (Canada).
During comparative tests across the 23 laboratories, asphalt samples were categorized into high (H), medium (M), and low (L) modulus levels. Overall, the consistency of test results was good. Lower modulus asphalt exhibited higher variability due to challenges in sample preparation, transportation, and handling, whereas higher modulus asphalt was less affected, leading to more stable test outcomes.
Field validation results from the three test roads indicate that ABCD test results exhibit a stronger correlation with actual field observations. In most cases, the correlation is higher than that of BBR and DT tests, demonstrating the accuracy and reliability of the ABCD method in assessing asphalt binder cracking performance.
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