ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 337

Direct Tension Test The direct tension test system consists of a displacement-
controlled tensile loading machine with gripping system, a temperature
controlled chamber, measuring devices, and a data acquisition system, as
shown in Figure 9.18 (ASTM D6723). In this test, an asphalt binder speci-
men, conditioned in the rolling thin-film oven and pressure-aging vessel, is
pulled at a constant rate of deformation of 1 mm/min. The test temperature
equals the low temperature rating plus 10°C. A noncontact extensometer
measures the elongation of the specimen. The maximum load developed dur-
ing the test is monitored. The tensile strain and stress in the specimen when
the load reaches a maximum is reported as the failure strain and failure stress,
respectively.
The strain at failure is a measure of the amount of elongation that the
asphalt binder can sustain without cracking. Strain at failure is used as a
criterion for specifying the low-temperature properties of the binder.

FIGURE 9.18 Direct tension test apparatus.