Advanced Materials Research Vols. 168-170

Abstract: Based on different direct tensile test methods of concrete in the present studies, the effects of specimen shape and grip method on the stress distribution in specimen were discussed and a series of tests were carried out by using epoxy adhesive method. Influences of fiber content and fiber type on tensile strength, tensile strain and residual strength of concrete have been studied. The specimen dimension was 100mm×100mm×200mm and the content of Macro-PP fiber was 6 kg/m3, 7 kg/m3, 8 kg/m3, 9 kg/m3 and 10 kg/m3, respectively. The content of steel fiber used in the contrast test was 30 kg/m3 and 40 kg/m3. The test results indicate that Macro-PP fiber can enhance the tensile strength and tensile strain at peak load effectively. Compared with plain concrete, it was found that the tensile strength and tensile strain at peak load of concrete with 9 kg/m3 macro-PP fiber increased by 43 % and 41% respectively.

Abstract: Dispersion of gaseous pollutant emissions in different street canyons was studied using two dimensional sections of canyon models airflow. Effects of building size, street width wind velocity and different turbulent model on the pollutant transport were examined. Depending on wind speed, building height, and street width, it was found that large recirculation regions in canyons may form. Under certain conditions, gaseous pollutants emitted from vehicle exhaust may trap inside the street canyon. It was shown that the amount of pollutants in street canyons reduces when the wind speed increases. The simulation results were compared with the available wind tunnel experiments and favorable agreement was found.

Abstract: For exactly analyzing the course of the coupling impact of auto and protective guard pillar, it’s especially important to get the analytical solution of the coefficient of horizontal subgrade reaction of the horizontal column of protective guard pillar. Using the reaction relationship of soil density and horizontal load ,we build up the estimate theory of the coefficient of horizontal subgrade reaction, with a simple form, describing the relationship of horizontal subgrade reaction and horizontal displacement. Using the Mohr-coulomb yield criterion and the finite element numerical simulation result of ABAQUS, we found that during the column rotary deformation, the coefficient of horizontal subgrade reaction is not a constant ,but it will be smaller and smaller with the development of the deformation. Plastic yield of protective guard pillar and earth coupling model soil caused by horizontal load depends on the difference in value of the max stress component and the min stress component, at the same time raising a theoretical formula of the coefficient of horizontal subgrade reaction and ultimate bearing capacity of soil and setting the theoretical model of coefficient of horizontal subgrade reaction under the horizontal load ,to provide a reference of design and analyze for the practical project.

Abstract: Mechanical properties of fiber reinforced concrete with polypropylene fiber, alkali-resistant glass fiber and basalt fiber separately were studied in this paper. The internal structure of fiber reinforced concrete was researched by testing chloride ion diffusion coefficient and scanning electron microscope (SEM) analysis. The results show that adding a certain amount of three fibers separately into concrete have all increased splitting strength. Compared with referenced concrete, compressive strength of alkali-resistant glass fiber reinforced concrete and basalt fiber reinforced concrete are both improved. According to analysis, the effect of srengthening and toughening for basalt fiber is particularly significant. The order of chloride ion diffusion coefficient from lower to higher is alkali-resistant glass fiber reinforced concrete, referenced concrete, basalt fiber reinforced concrete, polypropylene fiber reinforced concrete. This result indicates that alkali-resistant glass fiber bonds cement paste best and makes internal structure densest by SEM analysis.

Abstract: The photo-catalytic efficiency and durability of nano-TiO2 photo-catalytic cementitious materials for oxidizing nitrogen dioxide were investigated under simulated sunlight irradiation. The experimental results showed that the photo-catalytic efficiency increased with increase of the content of nano-TiO2. When 15wt% nano-TiO2 was added, the photo-catalytic efficiency was equal to 223% of that of standard cement. When activated carbon was used as the carrier of nano-TiO2, the photo-catalytic efficiency of cementitious nano-TiO2 could be enhanced markedly. For example, the photo-catalytic efficiency could reach to 85.7%, which was as much as 359% of that of standard cement when the contents of activated carbon and nano-TiO2 were both 10wt%. Compared with nano-TiO2 powder, the photo-catalysis durability of cementitious nano-TiO2 supported by activated carbon could be improved clearly for that activated carbon could absorb nitrogen dioxide effectively, which was favored to the photo-oxidation of nano-TiO2 on nitrogen dioxide.

Abstract: Soil improvement is one of the most important problems to be solved for shielding tunneling in the complex strata. Now the foam modifying soils technique has been widely used in shield tunneling construction. A new foaming agent used for soil properties improvement is developed and presented in this paper. This paper presents test research of soil properties improvement on sand in rich-water strata and clay soils from permeability, fluidity, compressibility and shear strength. Compared with the imported and domestic foaming agent, the basic performances of the newly developed foaming agent are obtained. Some conclusions are drawn in the paper, and it is significant to improve the engineering properties of soil and reduce the ground damage in shield tunneling construction.

Abstract: Geomembrane installed on the bottom and the side slope of a waste landfill as liner system is made of high density polyethylene or thermo plastic elastmer polyplopylene. Stress in the geotextile is caused by friction between the waste and the geotextile which is a result of the compression of the disposed waste, and the tensile force is transferred into the liner system by friction. With elapsed time, the stress relaxation will occur under certain strain conditions. If the stress of geomembrane is at high stress for a long period of time, the long time design strength of the geomembrane may be controlled by the creep at the end of the design life. So it is very important for design to determine the stress induced in the geomembrane. In this paper, the authors present a formula based three element visco-elastic model to evaluate the relation between the stress and elapsed time. Then the authors present some results of modeled tests conducted, it is shown that the relation between the material characteristic and temperature by indoor experiment.

Abstract: Based on the finite element method, the propagation of flexural vibration in a binary phononic crystal thick plate with a point defect is studied. The plate is composed of a square array of concrete cylinders embedded in the rubber matrix. Complete band structure and frequency response function of this perfect thick plate indicates the existence of low-frequency absolute band gap. Detailed investigations have been carried out to study the dependence of the width of absolute band gap on both structural and material parameters. For the point defect, the defect modes are localized around the defect, and the frequency and the number of the defect bands are significantly dependent on the filling fraction, the size and the mass density of the defect cylinder. To better support the statement of the defect band structures, we also represent the frequency response function of the propagation of flexural vibration in the thick plate with a point defect. Based on the detailed investigations, both the absolute band gap and the defect bands of a binary thick plate could be modulated with appropriate parameters. It may be useful to vibration control in engineering structure.

Abstract: Orientations distribution between grains of two high grade pipeline steels were investigated by electron back-scattered diffraction (EBSD). Then the percentage of low-angle grain boundaries was studied qualitatively to analyze the effect of low-angle grain boundaries on the yield-strength ratio of high grade pipeline steels. From the mode of coordinate deformation and the ability to resist deformation by the grain boundaries, the results show that when the effective grain size are almost the same, the pipeline steel which has the smaller percentage of low-angle grain boundaries, the larger difference between the yield strength and tensile strength, which makes the yield-strength ratio of pipeline steel lower.

Abstract: In traditional calculation method, the critical thick of water-resisting layer at foundation pit can be got by comparing the gravity of water-resisting layer and water pressure of artesian aquifer, which had not considered the influence of shear strength of soil. The result of traditional calculation method is conservative to reality. Based on force equilibrium analysis of water-resisting layer, equations for calculating safety factor of abrupt gush and critical thick of water-resisting layer is suggested in this article, which considered the influence of shear strength of soil. Some cases have been studied with those new equations. It had been found that the result of those new equations is coincident with realities. In order to ensure the security of foundation pit, it is advised that foundation pit can be adjudged safety only both the safety factor of abrupt gush and critical thick of water-resisting layer satisfied requirements.