Papers by Author: Wei Sun

Abstract: In this paper, sample of Eu-doped SrTiO₃ was synthesized using hydrothermal method, in which the Eu (NO₃)₃ and Sr (OH)₂ were as the Eu and Sr source. X-ray diffraction (XRD), scanning electron microscope (SEM) were used to characterize the structure and ingredient of the as-prepared samples. The results show that high-purity of SrTiO₃ was prepared and structure of SrTiO₃ without change with Eu doping. Also, performance of cathodic protection of stainless steel was tested in the photoelectricity cell. Furthermore, the mechanism of the improvement by the rare earth was also detected.

Abstract: To evaluate the bending performance of a steel fiber-reinforced concrete shield segment, bending testing was conducted on prism specimens and full-scale segments with 30 kg/m³ and 40 kg/m³ steel fiber. The results show that, with increasing fiber content, the ultimate and equivalent flexural strengths increase, while the flexural toughness of the prism concrete specimen increases by approximately 15%. With increasing fiber content, the flexural capacity of the shield tunnel segment increases, the peak load increases by 24%, the crack number increases, and the average crack width decreases. During bending tests, the steel fiber-reinforced concrete segment shows remarkable characteristics of strain hardening and multiple cracking. The embedded parts reduce the cross-sectional area and cause stress concentration in the mid-span; therefore, the main crack form in this region.

Abstract: Photovoltaic grid-connected power generation is the inevitable development trend of solar photovoltaic systems,grid inverter is an essential part of photovoltaic grid-connected power generation. With the developed three phase current type PWM inverter device as the research object, and symmetry rules sampling method is applied to the inverter, through the method combined by the computer simulation and experiment research, the device was verified by simulation and experimental .The results show that: This method could not only effectively reduce the DC side inductance volume of the current-mode PWM inverter , and it could make output AC currents sinusoidal and in phase with grid voltages, but also improve the efficiency of the system, it will be more suitable for photovoltaic grid-connected.

Abstract: Pseudo-ductile cementitious composites (PDCC) are a new type of special discontinuous random-fibers reinforced cementitious composites with high tensile ductility achieved by the uniform formation of multiple cracks along the length of the specimen. In the present study, rubber particle was introduced into the cementitious composites as the artificial flaw. The tensile properties, compressive strength, water permeability and shrinkage of PDCC with various volume contents and size of rubber particles were measured. The test results show that incorporation of rubber particle will reduce the compressive strength and first cracking strength of PDCC. With increased size and volume of rubber particles, the compressive strength is increased. To achieve maximum tensile ductility, optimum rubber content and size should be employed. Water permeability is found to be similar for various PDCC mixes with or without rubber addition. The content of rubber particle plays a significant role on the dry shrinkage of PDCC, while the particle size only has a slight effect.

Abstract: Ultrahigh performance concretes (UHPC) are promising materials for the next generation infrastructures due to their superior mechanical properties and durability. In this paper, comparison studies were conducted to show the potential of UHPC for sustainable constructions in chloride environments in view of service life. For reinforced concrete, the service life was calculated with analytical solution of Ficks second law on diffusion. And for reinforced concrete with nonlinear initial chloride profiles and depth-dependent chloride diffusion coefficient, a numerical method based on the Crank-Nicholson numerical scheme was adopted to predict the service life. The results show that the reinforced concrete structures constructed and repaired with UHPC have much longer service life than that of normal concrete (NC) and high performance concrete (HPC). It hence needs less cost for maintenance and reconstruction, which fulfills the requirements of sustainable construction.

Abstract: This paper studies how polymer alters the flexural toughness of concrete. By selecting five different types of polymer mixing into concrete; results indicate that polymer has obvious effect to enhance toughness of concrete evaluated by toughness index T. Microstructure of polymer-modified concrete were studied through environment scanning electron microscope, digital micro-hardness tester and nanoindentor, results indicate that polymer form the ionic compounds and reduce the crystallization of Ca (OH) ₂, acting as a flexible filler and reinforcement in concrete. Polymer also alters the microstructure at the aggregatecement interfacial transition zone.

Abstract: XRD-Rietveld method has been adopted for quantitative analysis of phases in cement powder, phases in mixed samples of cement and pure calcium hydroxide, and sulfate attack products in cement pastes, based on the TOPAS software. The results show that, Rietveld analysis values show good agreement with the actual levels of mixed samples, and the accuracy degree of Rietveld method is at least as well as that of TG/DSC method which is commonly used in quantitative analysis of calcium hydroxide. By adding appropriate internal standard substance, XRD-Rietveld analysis method can be effectively used in quantitative analysis of sulfate attack products in cement-based materials. This work has practical significance on the study of sulfate attack of cement-based material.

Abstract: In this study three-dimensional X-ray computed tomography (X-ray CT) is used to investigate the testing results differences of cement paste and mortar before and after drying. It can be found that the mean gray values of paste and mortar before drying are bigger than after drying, and the impact of drying on cement paste is more serious than mortar. In addition, the porosity of non-drying cement paste and mortar is 1.10% and 0.43%, while that of drying cement paste and mortar is 1.55% and 0.70%, respectively. So, the porosity of paste and mortar markedly increases after drying process. The numbers of pores of paste and mortar sharply increase after drying process in particular between 0.01mm3 and 0.1mm3. The impact of drying on smaller pores is more serious than bigger pores.

Abstract: A type of small-scale fibers with dumbbells on two ends and notches in the middle was first designed to improve the workability and crack resistance of fresh high performance steel fiber reinforced concrete (HPSFRC). By using the fiber, the HPSFRC was continuously pumped to 306 meter high Sutong bridge tower. To ensure crack resistance of HPSFRC, tests concerning both non-loaded crack and structural crack were systematically performed, respectively. Then, the mechanisms behind the macro-behaviors were explored. Finally, life assessment method of HPSFRC that focused on the fatigue loading coupled with chloride and carbonation environment was presented by considering the effects of different fatigue degree on concrete durability. The results demonstrate that the steel fiber has the remarkable ability to restrain shrinkage and resist structural crack. It was also shown that the small-scale steel fiber can greatly improve the fracture toughness and fatigue property. In addition, the increased degree of damage due to fatigue loading would shorten the service life of concrete and the service life of HPSFRC under the multi-damage of fatigue loading and environmental loading would be longer than that of plain concrete.

Abstract: In this paper, high-performance concrete (HPC) incorporated organic fibers, i.e., polyvinyl alcohol fiber (PVA fiber), polypropylene fiber (PP fiber), cellulose fiber (UF fiber), polyethylene fiber (PETF) was produced. The properties measured included strength, crack resistance performance and water permeation of the concrete. The effect of organic fibers on the shrinkage and water permeation properties was investigated. Test results indicated that the organic fibers of different types could reduce the size and amount of crack source; organic fibers provided better enhancement for shrinkage resistance and impermeability of HPC; the improvement of the shrinkage resistance and the impermeability of the concrete resulted from the use of organic fiber, which was dependent on the types, total volume fraction and of fibers, proportions of organic fiber.