Significance and Use
5.1 The indirect tensile cracking test is used to determine asphalt mixture cracking resistance at an intermediate temperature which could range from 5 °C to 35 °C, depending on local climate. The specimens are readily obtained from Superpave gyratory compactor compacted cylinders with a diameter of 150 ± 2 mm, with no cutting, gluing, notching, drilling, or instrumentation required. Similarly, field cores can be tested to measure remaining cracking resistance of in-place asphalt mixtures.
5.2 The CTIndex of an asphalt mixture is calculated from the failure energy, the post-peak slope of the load-displacement curve, and deformation tolerance at 75 % of the peak load. The CTIndex is a performance indicator of the cracking resistance of asphalt mixtures containing various asphalt binders, asphalt binder modifiers, aggregate blends, fibers, and recycled materials. Generally, the higher the CTIndex value, the better the cracking resistance and, consequently, the less the cracking amount in the field. The range for an acceptable CTIndex will vary with mix types and associated specific applications.4 Users can employ the CTIndex and associated criteria to identify crack-prone mixtures during mix design and production quality control/assurance.
NOTE 1: The quality of the results produced by this standard 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 standard are cautioned that compliance with Specification D3666 alone does not completely ensure reliable results. Reliable results depend on many factors; following the suggestions of Specification D3666 or some similar acceptable guideline provides a means of evaluating and controlling some of those factors.
Scope
1.1 This test method covers the procedures for preparing, testing, and measuring asphalt mixture cracking resistance using cylindrical laboratory-prepared asphalt mix samples or pavement cores. Testing temperatures are selected from the long-term pavement performance (LTPP) database intermediate temperatures. The test method describes the determination of the cracking tolerance index, CTIndex, and other parameters determined from the load-displacement curve. These parameters can be used to evaluate the resistance of asphalt mixtures to cracking.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 The text of this standard 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 standard.
1.4 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.
1.5 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.