The mechanical behavior and failure mechanism of recycled semi-flexible pavement material were investigated by different scales method. The macroscopic mechanical behavior of samples was studied by static and dynamic splitting tensile tests on mechanics testing system (MTS). The mechanical analysis in micro scale was carried out by material image analysis method and finite element analysis system. The strains of recycled semi-flexible pavement material on samples surface and in each phase materials were obtained. The test results reveal that the performance of recovered asphalt binder was the major determinant on the structural stability of recycled semi-flexible pavement material. The asphalt binder with high viscoelasticity could delay the initial cracking time and reduce the residual strain under cyclic loading conditions. The failure possibility order of each phase in recycled semi-flexible pavement material was asphalt binder, reclaimed aggregate, cement paste and virgin aggregate.
Polymer-modified rejuvenator has a different composition and dispersion behavior to traditional rejuvenators. The objective of this study was to investigate the micromechanism of polymer-modified rejuvenators on the behavior of aged asphalt binder. Firstly, gel permeation chromatography (GPC) analysis was conducted to determine the dispersion effectiveness. Secondly, the dispersal behavior of polymer-modified rejuvenators was studied by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Rheological, toughness-tenacity, and force–ductility analyses of the rejuvenated asphalt binder were additionally performed. The results indicate that the contacted asphaltenic micelles in aged asphalt binder were dispersed by dispersion agent in the polymer-modified rejuvenator, and that the dispersion ability of the polymer-modified rejuvenator was promoted to the commercial rejuvenator level. Additionally, the polymer-modified rejuvenator was found to improve the rejuvenated asphalt binder’s resistance to deformation, through the formation of polymeric network structures in the asphalt binder. The results may be used to improve the performance of rejuvenated asphalt binder in recycled-pavement engineering.
Abstract. TA15 (Ti-6.5Al-2Zr-1Mo-1V) and BTi-6431S (Ti-6.5Al-3Sn-3Zr-3Mo-3Nb-1W-0.2Si) titanium alloy plates were welded through gas tungsten arc welding (TIG) and different ultrasonic impact treatment (UIT) were conducted on the weldment. The effects of ultrasonic impact treatment (UIT) on the microstructure and residual stress distribution and mechanical properties for the welding joint were investigated through optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and tensile tests. After TIG welding, the structure of welding joint is composed of fusion zone (FZ), heat-affected zone (HAZ) and base metal. The FZ is widmannstatten structure with coarse β grains and a large number of acicular α due to the fast cooling rate. The microstructure in the HAZ shows a gradual change because of the presence of temperature gradients during welding. The residual stress after TIG is mainly tensile stress and the maximum longitudinal stress appears in the centerline of welding joint. The UIT process shows dramatic influence on residual stress distribution. After employing UIT twice, the residual stress near the welding joint shows a uniform distribution and the maximum tensile stress changes to compressive stress. However, the tensile properties at room temperature almost remain unchanged after UIT.
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