Estimated critical cracking temperature, as determined by this practice, is a criterion for specifying the low-temperature properties of asphalt binder in accordance with Specification D6373.

This practice is designed to identify the temperature region where the induced thermal stress in a typical HMA subjected to rapid cooling (1°C/h) exceeds the fracture stress of the HMA.

For evaluating an asphalt binder for conformance to Specification D6373, the test temperature for the BBR and DTT data is selected from Table 1 of Specification D6373 according to the grade of asphalt binder.

Note 3—Other rates of elongation and test temperatures may be used to test asphalt binders for research purposes.

1.1 This practice covers the calculation of low-temperature properties of asphalt binders using data from the bending beam rheometer (see Test Method D6648) (BBR) and the direct tension tester (see Test Method D6723) (DTT). It can be used on data from unaged material or from material aged using Test Method D2872 (RTFOT), Practice D6521 (PAV), or Test Method D2872 (RTFOT) and Practice D6521 (PAV). It can be used on data generated within the temperature range from +6°C to -36°C. This practice generates data suitable for use in binder specifications such as Specification D6373.

1.2 This practice is only valid for data on materials that fall within the scope of suitability for both Test Method D6648 and Test Method D6723.

1.3 This practice can be used to determine the following:

1.3.1 Critical cracking temperature of an asphalt binder, and

1.3.2 Whether or not the failure stress exceeds the thermal stress in a binder at a given temperature.

1.4 This practice determines the critical cracking temperature for a typical asphalt binder based on the determination of the temperature where the asphalt binder's strength equals its thermal stress as calculated by this practice. The temperature so determined is intended to yield a low temperature PG Grade of the sample being tested. The low temperature PG grade is intended for use in purchase specifications and is not intended to be a performance prediction of the HMA (Hot Mix Asphalt) in which the asphalt binder is used.

1.5 The development of this standard was based on SI units. In cases where units have been omitted, SI units are implied.

1.6 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Note 1—The algorithms contained in this standard require implementation by a person trained in the subject of numerical methods and viscoelasticity. However, due to the complexity of the calculations they must, of necessity, be performed on a computer. Software to perform the calculation may be written, purchased as a spreadsheet, or as a stand-alone program.