To determine the cracking temperature of asphalt binders, the Asphalt Binder Cracking Device (ABCD) uses the dissimilar coefficients of thermal expansion/contraction (CTE) of asphalt binders and metals. As shown in Figure 1, an ABCD ring consists of a hollow cylindrical metal (invar) tube with a uniform thickness and an electrical strain gauge glued to the inside. A surface-mounted resistance temperature detector is also installed inside of the tube to closely monitor the specimen temperature.
Asphalt binders have much larger CTE than metals. As the temperature drops, the differential thermal contraction (more rapid contraction of an asphalt binder than that of metals) will cause thermal stress to develop and will eventually lead to thermal cracks. When the specimen cracks, the accumulated thermal stress is released and will be shown as a sudden drop in the strain measurement. Accordingly, the cracking temperature of the asphalt binder is directly determined as the temperature where the sudden drop of measured strain occurs. The strain of the ring measured by the electrical strain gauge can also be used to calculate the tensile strength of the asphalt binder at that temperature. Figure 2 illustrates typical ABCD test results obtained in this study.
