Experimental and Analytical Procedures to Characterize Mechanical Properties of Asphalt Concrete Materials for Airfield Pavement Applications
University of Kansas
Civil, Environmental & Architectural Engineering
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In the past two decades, the pavement mechanics community have made a significant progress in developing mechanistic-based constitutive relationships for asphalt concrete materials, flexible airfield pavements, and roadways. However, a number of factors have caused the community not to properly adopt and implement these sophisticated constitutive relationships in design and refined analysis of asphalt concrete pavements. The lack of straightforward experimental and/or analytical procedures to extract the material properties associated with these models is the main reason for the community to avoid adopting these sophisticated mechanistic-based models. Available characterization methods either are over-simplified or require extensive laboratory tests and analyses procedures to extract the material properties associated with asphalt concrete materials. Furthermore, the immergence of next generation heavy aircraft and heavy trucks require such characterization methods to design the experiments and analysis procedures to account for high tire contact stresses. This dissertation aims to develop straightforward experimental and analytical procedures to characterize coupled viscoelastic, viscoplastic, and hardening-relaxation viscoplastic properties of asphalt concrete pavements while maintaining the required level of accuracy by incorporating the important factors affecting these mechanisms. Therefore, this dissertation proposes laboratory tests and analysis procedures to systematically calibrate and validate a comprehensive constitutive material model for asphalt concrete materials. The proposed method accounts for multi-axial state of stresses; deviatoric, confinement, and shear stress levels; and time-, temperature-, and rate-dependent response of asphalt concrete when subjected to high tire pressures. Separate laboratory tests were required to measure and calibrate the individual response of asphalt concrete materials at appropriate temperatures and loading rates. The proposed characterization methods are then applied to four different asphalt mixtures used in Federal Aviation Administration (FAA)’s National Airport Pavement and Materials Research Center (NAPMRC) test sections to evaluate the efficacy of the methods. This dissertation presents a straightforward procedure that allows for identification of nonlinear viscoelastic response of asphalt concrete. This procedure incorporates the effect of confinement and deviatoric stress levels into the analysis procedure along with a laboratory test that can be used systematically to extract nonlinear viscoelastic parameters. Furthermore, a straightforward procedure that allows for identification of viscoplastic and hardening-relaxation viscoplastic response of asphalt concrete materials were proposed. This procedure incorporates the genetic algorithms into the analysis procedure to extract viscoplastic and hardening-relaxation viscoplastic properties of asphalt concrete materials as one of many engineering optimization problems along with a laboratory test that can be used systematically to extract viscoplastic and hardening-relaxation viscoplastic response of asphalt concrete materials. The presented tests are mimicking the realistic general multi-axial state of stresses observed in a pavement structure. Moreover, rheological properties and stress-dependent behavior of modified/unmodified asphalt binders plus Evotherm–M1 additive were evaluated using multiple stress creep-recovery tests and strain controlled frequency sweep tests in different ranges of interest frequencies, temperatures and strains. The test data is analyzed to improve the Pavement Analysis using Non‐linear Damage Approach – Airfield Pavements (PANDA‐AP) calibration protocol and extract the material properties of asphalt concrete pavements.
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