Papers by Keyword: Environmental Effect

Abstract: High demand for new asphalt pavements often requires that paving is to be done in an unfavourable condition such as low air temperatures, high wind speeds, and night construction that will affect the Time Available for Compaction (TAC). In local practice, the asphalt paving compaction control mechanisms quoted from the locally used specifications are normally based on the limits of the delivery and laying completion temperatures. This study was conducted which aim to determine the appropriate TAC of Warm Mix Asphalt (WMA) with the effect of different wind velocity using laboratory tests. It focused on WMA Asphaltic Concrete (AC)14 of mix type for wearing course and AC28 of mix type for binder course. Sample of WMA was prepared in a slab mould instead of typical round mould, which was used to resemble the shape of actual pavement. The different wind velocity was simulated by the fan located at different distance from the sample. The results indicated that the cooling rate of WMA is significantly affected by the wind velocity thus influencing the Time Available for Compaction (TAC), which decrease in average by 10-50% during windy days.

Abstract: The 7000 series alloys have the highest strength in the aluminum alloys, but lower fatigue properties than 2000 series alloys. Thus, 7000 series alloys are not applied to a large proportion of the aircraft components. However, the mechanism for this has not been elucidated yet. In humid air, hydrogen embrittlement based on intergranular cracking has been known to occur in 7000 series alloys. To date, in order to explain the difference in the fatigue crack growth behavior in the two series alloys, the effect of the test environment on the fatigue crack growth of the two series alloys has been investigated in this study. A 7075-type as well as 2024-type alloy with relatively coarse equi-axed grains was T6-tempered and subjected to fatigue crack growth test in humid and dry environments. Crack growth rate at low ΔK level seemed to be larger in the 7075-type alloy than the 2024-type alloy in the humid air, when assessed by means of gradually decreasing K method. In order to clarify this result, crack growth rate of the two alloys was assessed by means of gradually increasing K method as well as decreasing K method. Crack growth rate of the 7075-type alloy in moist air was concluded to be the largest in consistent with the previous study. Thus, the large fatigue crack growth rate of the 7075-type alloy is attributable to hydrogen embrittlement.

Abstract: Load-bearing joints of glass structures belong to the one of new applications of adhesive connections in civil engineering. They provide several important benefits particularly even stress distribution along the contact depending on geometry and stiffness of the glue joint, which is crucial for brittle glass. There is a lack of knowledge about semi-flexible or semi-rigid adhesive connections in the structural glass field and durability is one of the essential properties that have to be assessed during design-process of bonded connection. An extensive research focused on shear glued joints in glass structures was performed at CTU in Prague, which also comprised environmental effect simulation on the glued specimens in laboratory accelerated conditions. The paper is dedicated to impact of ageing to the specimens and their mechanical properties together with brief overview of available laboratory ageing methods.

Abstract: Displacement is a good descriptor of the structural behavior and safety status. However, measuring displacement of structures under dynamic excitations is still a challenging task. Videogrammetry shows great potential for dynamic displacement measurement, benefiting from its non-contact and long-distance characteristics. Nevertheless, its all-weather performance has to be fully evaluated before gaining wide applications. This study therefore carried out an investigation into the environmental effects of the all-weather videogrammetry for structural dynamic displacement monitoring. First, long-term outdoor dynamic displacement monitoring tests were carried out. Virtual structural displacement was generated by a motion simulation device and monitored by a commercialized industrial digital camera. The adaptive filter was then employed to filter out noises, which had the primary input of the major displacement component and the reference input of the minor displacement component. The results show that the adaptive filter is well capable of filtering out noises and the measurement accuracy of videogrammetry is significantly enhanced.

Abstract: Legacy 7XXX series aluminum alloys were developed primarily for their high strength with less regard for their fatigue properties, corrosion resistance and fracture toughness. The constituent alloying elements in these materials (used to achieve high strengths) markedly increased their corrosion susceptibility. Consequently, aircraft structures made from these alloys have exhibited fatigue and corrosion damage. In the present work, we have investigated a crack finding in a fuselage skin of AA7XXX series alloy. This investigation revealed the crack propagated by a combination of fatigue and corrosion. Through the use of extensive metallography, mechanical analysis and laboratory experiments, we have separated the contributions to the damage growth due to corrosion and fatigue. We have also confirmed that in-service mixed-mode failures like this, observed in these alloys, can be reproduced reliably in the laboratory. Furthermore, it was observed that the presence of corrosion can actually change the propagation of a fatigue crack from mode I, the preferable orientation for fatigue crack propagation, to mode II, the preferable orientation for corrosion propagation. Even though the mechanical driving force is enough to grow the crack in mode I, the presence of corrosion can change it to mode II by electrochemical degradation of the material. Using electrochemical measurements, we relate the change in failure mode to the frequency of cyclic loading. At slow enough cyclic frequency the electrochemical energy released due to galvanic corrosion degrades the material such that the crack turns and propagates in the orientation which has only one third the mechanical driving force as compared to the original crack propagation path. This is the first time such phenomenon has been successfully replicated in the laboratory and modeled with finite element analysis.

Abstract: In the present study, the tensile and fatigue properties of extruded 7075 Al alloys subjected to re-solution treatment and then T6, T73 and retrogression-reaging (RRA) tempers were reassessed based upon the microstructural analyses by means of electron backscattering diffraction (EBSD) and X-ray diffraction (XRD). The microstructural analyses indicated that fibrous grains having orientations close to <111> and <001> were preferentially aligned in the extrusion direction and that re-solution treatment increased the fraction of <111> grains. Further the as-received T6 specimens had very high dislocation density as well as fine subgrains, while the re-solution treatment decreased dislocation density considerably and increased grain size. These characteristics explained tensile properties well, by taking into account the effect of precipitates formed by tempers. On the other hand, fatigue strength decreased prominently in all of the specimens, as the relative humidity (RH) was increased from 25% to 85%. T73 and RRA treatments which improve the resistance to stress corrosion cracking (SCC) in static loading were not effective in the humidity-enhanced deterioration in fatigue strength.

Abstract: Fiber reinforced polymer ( FRP) rods have a broad application in civil eng ineering field used as a material substiting steelbars. Based on the domestic and abroad research, the durability of the fiber reinforced polymer (FRP) rods undermultifarious environmental conditions is summarized in this paper, and the effect of environments such as temperature, humidity, corrosion from acid, alkaline and salt solutions on durability performance of FRP materials as well as the degradation of the bond characteristics between FRP rods and the interface of concrete caused by the acceleration environment test are mainly discussed. The results indicate that the environmenta lconditionsm entioned above affect FRP rods and bond characteristics between FRP rods and the in terface of concrete.In addition, a relatedmodel predicting the influence on durability of FRP rods in alkaline solutions is given and future study trend on durability of FRP rods is presented

Abstract: Natural water cycle is of river-basin characteristic, with obvious river-basin regularity in formation, movement and change. The development and utilization of river-basin water resources are of important significance to solve the shortage of water resources. Dagujia river is the second largest river in Yantai. But with fast development of social economy and population growth of Yantai city, Dagujia river resources have been overexploited, resulting in corresponding environmental effects. Based on the thorough investigation of the current water resources utilization, the paper analyses the production and the change trend of environmental effects and discusses projects and management mode in order to achieve efficient utilization of water resources.

Abstract: Industrialization process cause a huge material input, waste discharge and environmental impact. To realize the sustainable development of society and reduce environmental pressures are caused by economic and social activities, process simulation of industrial metabolism and its environmental effect analysis have become a hot issues in the international research field. Around the key scientific issues of regional material metabolism, this project fully learn and absorb domestic and international research results. The empirical study focus on energy (coal) and chemical industry base in china, starting from material metabolism analysis of regional industrial system, analyze the relationship between industrial system material metabolic processes and environmental effects, establishing the environmental effects index model of industrial metabolic with the environmental effects analysis; eventually propose the approaches and countermeasures to reduce environmental effect of industrial system material metabolic.

Abstract: The action of freeze-thaw is one of the important influence factors which can cause the changes of soil physicochemical and biological characteristics. During the freeze-thaw period the variations of active organic matters in cropland black soil were studied through the in-situ monitoring and determining methods. The surface soil experienced a series of repeated freeze-thaw actions during the alternate from autumn to winter and from winter to spring. The soil active organic matter was in the trend of fluctuation increase from 8.68 mg kg^-1 to 9.81 mg kg-1 during the seasonal freeze-thaw period. The soil water soluble organic matter was also in a gradually increasing trend, which could increase 33.95% for the surface layer in early April of the next year when compared with that of January. The soil microorganism carbon content increased firstly and then decreased during the seasonal freeze-thaw period, which fluctuated at 912.51-1137.91 mg kg^-1. The research showed that the freeze-thaw action could improve the active organic matter and strengthen the adaptability and activity of microorganism, which could promote the mineralization of organic matter.