Significance and Use
5.1 The ideal rutting test (IRT) is used to determine asphalt mixture rutting resistance at high temperature in the range of 50 ± 15 °C, depending on local climate. The specimens are readily obtained from Superpave Gyratory Compactor (SGC) compacted cylinders with a diameter of 150 ± 2 mm, with no cutting, gluing, drilling, or instrumentation required. Similarly, field cores with a diameter of 150 ± 2 mm can be tested to measure rutting resistance of in-place asphalt mixtures.
NOTE 1: Field cores may need cutting to a right thickness ranging from 38 mm to 95 mm. This test standard is not applicable to the specimens with a diameter other than 150 ± 2 mm, regardless of laboratory-compacted specimens or field cores.
5.2 The RTIndex of an asphalt mixture is calculated from the peak load (or shear strength). The RTIndex is a performance indicator of the rutting resistance of asphalt mixtures containing various asphalt binders, asphalt binder modifiers and additives, aggregate blends, fibers, and recycled materials. Generally, the higher the RTIndex value, the better the rutting resistance and consequently the smaller the rut depth in the field. Users can employ the RTIndex and associated criteria to identify rutting-prone mixtures during mix design and production quality control/assurance.
NOTE 2: 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 rutting resistance at high temperatures using cylindrical laboratory-prepared asphalt mix samples or pavement cores. The test method describes the determination of the rutting tolerance index, RTIndex, and other parameters determined from the load-displacement curve. These parameters can be used to evaluate the resistance of asphalt mixtures to rutting.
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 The within-laboratory repeatability standard deviation of rutting tolerance index has been determined to be 2.42, based on two labs, 30 test replicates, and ten different samples. The between-laboratory reproducibility of this test method is being determined and will be available on or before December 31, 2026. Therefore, this standard should not be used for acceptance or rejection of a material for purchasing purpose.
1.5 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.
1.6 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.