Mechanistic–empirical pavement design has received significant attention from the pavement community as the method for designing asphalt pavements in the future. Currently available software for mechanistic–empirical pavement design includes the AASHTOWare Pavement ME Design (Pavement ME) program. The Pavement ME program allows users to predict pavement distresses by applying layered elastic theory for the mechanical responses and using empirical models for the distress predictions. The layered viscoelastic pavement design for critical distresses (LVECD) program, which employs three-dimensional viscoelastic finite element analysis with moving loads, can also be used to predict the fatigue and rutting performance of pavements. The LVECD program employs the simplified viscoelastic continuum damage (S-VECD) model as the material model for the fatigue performance predictions of asphalt mixtures under complex loading and environmental conditions. This paper examines and compares the performance of 33 pavement sections from five research projects located in the United States, Canada, and South Korea by using both the Pavement ME and LVECD computer programs. To verify the results obtained from these two programs, the simulations were compared with the field performance data. In terms of ranking, the LVECD simulations provided better agreement with the field performance data than did the Pavement ME simulations. One of the main reasons for the better predictions obtained by the LVECD program is that its fatigue performance predictions depend on the mixture properties of all the layers, whereas the Pavement ME program considers the fatigue properties of only the bottom layer mixture.
Deep separation of low concentrations of molybdenum from tungstate solution has been a technical bottleneck in tungsten metallurgy and subsequent value-added utilization of tungsten products. A feasible strategy, named microbubble floating-extraction, was proposed and employed to achieve the highefficiency and deep separation of molybdenum from tungstate solutions in this work. It was demonstrated that reagent mineralization is crucial for the formation of MoS 4 2− −N263 hydrophobic complexes, which is the rate-determining step of microbubble floating-extraction. Owing to the higher bubble and interface mass transfer rates, microbubble floating-extraction can achieve high-efficiency enrichment and deep separation of MoS 4 2− −N263 complexes with a large aqueous-to-oil phase ratio. The separation mechanisms of microbubble floating-extraction include the attachment process of MoS 4 2− −N263 hydrophobic complexes on the surface of rising microbubbles and the mass transfer process at the oil−water interface.Compared with solvent extraction, the flotation efficiency of molybdenum increases from 98.61 to 99.14%, while the loss rate of tungsten decreases from 3.31 to 2.12% under the optimal conditions. The microbubble floating-extraction exhibits significant advantages of high separation efficiency, a high enrichment coefficient, and low consumption of organic solvents.
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