Significance and Use
4.1 The test method was developed for determining the fracture resistance of asphalt mixtures. The fracture resistance can help differentiate asphalt mixtures whose service life might be compromised by cracking. The test method is generally valid for specimens that are tested at temperatures of 10 °C or below (see Note 1). The specimen geometry is readily adapted to 150 mm diameter specimens, such as fabricated from Superpave (trademark) gyratory compactors (Test Method D6925), which are used for the asphalt mixture design process. The specimen geometry can also be adapted for forensic investigations using field cores of pavements where thin lifts are present. This geometry has been found to produce satisfactory results for asphalt mixtures with nominal maximum aggregates size ranging from 4.75 to 19 mm (2).
NOTE 1: The stiffness of the asphalt binder tends to influence the assessment of a valid test as described in 7.4. For instance, a soft asphalt binder which may be required for a very cold climate might not lead to a mixture that would produce valid results at +10 °C and, conversely, a hard asphalt binder utilized in hot climates may require higher temperatures to provide any meaningful information.
NOTE 2: The quality of the results produced by this test method are dependent on the competence of the personnel performing the procedure and the capability, calibration, and maintenance of the equipment used. Agencies that meet the criteria of Specification D3666 are generally considered capable of competent and objective testing, sampling, inspection, etc. Users of this test method are cautioned that compliance with Specification D3666 alone does not completely ensure reliable results. Reliable results may depend on many factors; following the suggestions of Specification D3666 or some similar acceptable guidelines provides a means of evaluating and controlling some of those factors.
NOTE 3: The failure mechanism experienced in this test is influenced by the aggregate type due to the interactive effect of asphalt binder stiffness and aggregate quality on the fracture path and, therefore, fracture energy values. At high values of asphalt binder stiffness, similar to those experienced near the low-temperature performance grade of the asphalt binder, the crack will travel around the aggregate when the mixture includes hard, non-absorptive (for example, granite, trap rock) aggregates resulting in a longer crack path and higher values of fracture energy. For softer, more absorptive aggregates, the crack will travel through the aggregate, shortening the crack path and leading to lower values of fracture energy (3). Due to the influence of aggregate type on fracture energy, mixture design and/or binder grade adjustments in mixes that use softer aggregates may not be sufficient in improving fracture energy to meet a target value.
Scope
1.1 This test method covers the determination of fracture energy (Gf) of asphalt mixtures using the disk-shaped compact tension geometry. The disk-shaped compact tension geometry is a circular specimen with a single edge notch loaded in tension. The fracture energy can be utilized as a parameter to describe the fracture resistance of asphalt mixtures. The fracture energy parameter is particularly useful in the evaluation of asphalt mixtures with ductile asphalt binders, such as polymer-modified asphalt mixture, and has been shown to discriminate between these materials more broadly than the indirect tensile strength parameter (AASHTO T 322, Ref (1)).2 The test is generally valid at temperatures of 10 °C and below, or for material and temperature combinations which produce valid material fracture, as outlined in 7.4.
1.2 The specimen geometry and terminology (disk-shaped compact tension, DC(T)) is modeled after Test Method E399 for Plane-Strain Fracture Toughness of Metallic Materials, Appendix A6, with modifications to allow fracture testing of asphalt mix.
1.3 The test method describes the testing apparatus, instrumentation, specimen fabrication, and analysis procedures required to determine fracture energy of asphalt mixture and similar quasi-brittle materials.
1.4 The text of this test method references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the test method.
1.5 The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.
1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.