1. Scope

1.1 This test method provides a procedure to determine the fatigue life (number of cycles to failure--Nf) of asphalt mixtures and also the reduction in dynamic modulus (E*) with loading cycles using cylindrical samples subjected to three-point cyclic bending. The results obtained from this test can be used to calibrate viscoelastic continuum damage (VECD) models to obtain a damage characteristic curve, which in turn can be used to obtain fatigue lives (Nf) at a variety of temperatures, strain levels, and frequencies (a separate standard practice is being drafted for this procedure). Even though this test method is intended primarily for displacement- (strain-) controlled fatigue testing, certain sections may provide useful information for force-controlled tests. 1.2 This test method describes the testing apparatus, instrumentation, specimen fabrication, and analysis procedures required to determine the number of cycles to failure of asphalt concrete. 1.3 The text of this test method references notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the test method. 1.4 Units--The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. 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 and health practices and determine the applicability of regulatory limitations prior to use.

Keywords

asphalt concrete fatigue; asphalt concrete dynamic modulus; asphalt concrete tensile testing; fatigue life; flexural bending; shear bending; Timoshenko beam theory

Rationale

Fatigue cracking is one of the critical distress modes in asphalt pavements. Accurate prediction and evaluation of fatigue performance are crucial to extending the service life of asphalt mixtures. Naturally, laboratory testing methods for fatigue characterization are time-consuming and require sophisticated procedures. Any effort to improve the speed and quality of the information gained from laboratory fatigue tests is valuable. This test method introduces a cyclic test run on cylindrical asphalt specimens in three-point beam mode, herein referred to as the three-point bending cylinder (3PBC) test. The 3PBC setup possesses the most advantages of available tests and includes more advantages such as not requiring a saw to cut the ends of the sample and not requiring gluing operation (and the gluing jig), drilling, or notching. This level of practicality and ease of testing implementation is also important for use in performance-based mix design and construction acceptance.

The title and scope are in draft form and are under development within this ASTM Committee.