AASHTO TP 107:18(2020) Standard Method of Test for Determining the Damage Characteristic Curve and Failure Criterion Using the Asphalt Mixture Performance Tester (AMPT) Cyclic Fatigue Test.
4.1. An actuator displacement-controlled and repeated cyclic loading is applied to a cylindrical asphalt concrete specimen until failure. The applied stress and on-specimen axial strain response are measured and used to calculate he necessary quantities. The relationship between the damage (S) and the pseudo secant modulus (C) is determined and expressed as the damage characteristic curve. It is important to consider this document pertains to direct tension testing in an AMPT. Test procedures will differ if using other machinery and it is recommended more specialized procedures be developed for these loading machines.
5.1. The damage characteristic curve represents the fundamental relationship between damage and material integrity for asphalt concrete mixtures. This property is independent of temperature, frequency, and mode of loading. Combined with the linear viscoelastic properties of asphalt concrete, the damage characteristic curve can he used to analyze the fatigue characteristics of asphalt concrete mixtures.
5.2. Damage characteristic curves can also be combined with the failure criterion and additional pavement response models to predict the fatigue behavior of in-service asphalt concrete mixtures.
6.1. Asphalt Mixture Perfirmance Tesier—An AMPT or system meeting or exceeding the requirements of Equipment Specifications for the Simple Performance Test System, NCHRP Report 629, Appendix E, with the additional capability to conduct direct tension testing. as shown in Figure 1. The minimum requirements of the accuracy and resolution of the equipment measurement system are summarized in Table 1.
6.2. External conditioning chamber (optional,—An environmental chamber for conditioning the test specimens to the desired testing temperature. The chamber shall he capable of controlling the temperature of the specimen over a temperature range of 5 to 25°C (41 To 77°F) to within ±0.5°C (±1°F). The chamber shall he large enough to accommodate at least a single test specimen and a “dummy” specimen with a thermocouple or other calibrated temperature-measuring devices mounted at the center for temperature verification.AASHTO TP 107 pdf download.