Evaluation of resistance of asphalt mixtures to load-induced fatigue cracking is important for design and analysis of flexible pavements. There are numerous cracking tests used by roadway agencies, academia, and industry. Some of the cracking tests are practical and quick; however they are not suited for providing parameters for rigorous analysis and modeling of pavement structures because of their empirical nature. Other tests are more fundamental, but sample preparation and testing protocol can be cumbersome in those tests. This research project developed a robust and practical fatigue test system called the Three-Point Bending Cylinder (3PBC) test. The 3PBC setup possesses the most advantages of uniaxial push-pull tests along with additional advantages, such as not requiring a saw to cut the ends of the sample and gluing operation (and the gluing jig). The proposed 3PBC approach was evaluated through laboratory tests on various asphalt mixtures with varying binder types, mix components and volumetric properties. The study showed the applicability of Timoshenko-Ehrenfest beam theory formulations to the 3PBC geometry, and it was validated via 3D Viscoelastic Finite Element simulations run at different temperatures and frequencies. In addition, it was shown that the viscoelastic continuum damage (VECD) formulations can be used to analyze the 3PBC data and a single pseudo stiffness (C) versus damage parameter (S) can be obtained from tests at different strain levels, temperatures, and frequencies. The C versus S curve obtained from a single test, along with the linear viscoelastic dynamic modulus (|E*|) master curve can be used to predict the fatigue life (Nf) values at different temperatures, frequencies and strain levels. As a result, phenomenological fatigue life formulation used in Mechanistic-Empirical Pavement Design approaches (e.g., Pavement ME and MEAPA) can be calibrated using a single 3PBC test. As part of the study, the research team developed a test data analysis software. The software is named 3PBC-VECD. It is based on the viscoelastic continuum damage (VECD) formulations which reduces the experimental burden in calculating the Nf at different strain levels and temperatures. Furthermore, a new testing protocol was programmed in the AMPT user programmable software to conduct 3PBC tests in the AMPT machine. The research team also conducted ruggedness tests to identify the major test factors that may influence the 3PBC test.
The final report is available.