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41.
Over a four year period, six phases of testing were performed to observe the influence of age at loading, applied stress level, mix composition and relative humidity on the tensile creep of concrete. From these investigations it was possible to develop a model which allowed the prediction of tensile creep based on a knowledge of the compressive strength of the concrete (determined at the age of loading), the applied stress level and the relative humidity. Subsequently, this model was validated using the results from three independent investigations. Compressive creep as well as tensile creep was also obtained. This allowed a comparison of compressive creep with tensile creep and illustrated that on the basis of equal stresses, tensile creep is on average between 2 and 3 times greater than compressive creep (the maximum ratio is in excess of 8). For this investigation, however, on the basis of stress/strength ratio the difference between tensile and compressive creep is less significant. Considering a simply supported flexural reinforced concrete element, the investigation suggests that it is unwise to consider actual compressive creep equal to actual tensile creep as is often the case in design practice. 相似文献
42.
Metakaolin-based geopolymers were synthesized at Si/Al ratios of 1:1, 1.5:1, 2:1, 3:1, 4:1, and 5:1 by using silica fume as silica corrector to alter Si ratios. The microstructure and strength of these geopolymers were characterized through XRD, SEM, NMR and compressive strength measurements. The dissolving rates of Al and Si species in geopolymerization were measured, and freeze-dried N-A-S-H gel was characterized by FTIR spectra. Modelling and simulation were employed to calculate the binding energy of one Si atom and the total energy of geopolymers formed at various Si/Al ratios. At Si/Al ratio of 2:1, high concentrations of Si and Al species are dissolved from precursors, high contents of Si-O-T linkages are formed and the geopolymer is of high compressive strength. The mechanical strength of geopolymers at various Si/Al ratios is dependent on the formation of N-A-S-H gel, rather than the zeolitic nuclei or silicate derivatives. This study might provide fundamentals for the geopolymerization of mine tailings, which usually possess high Si/Al ratios. 相似文献
43.
Krystian Janiszewski 《国际钢铁研究》2013,84(3):288-296
We propose in this publication the introduction of new, additional definition describing the multiple orifice ceramic filters used in research works on the liquid steel filtrations, calling this the filter slenderness ratio. In order to confirm the theoretical assumptions we have performed a series of the laboratory scale experiments (for the filter slenderness ratio SF1 λ = 1.67 and SF2 λ = 3.34). The influence of the filter slenderness on the filtration process efficiency has been determined through variations in quantities and surface shares of the non‐metallic inclusions in the filtrated steel in relation to the non‐filtered steel. We present also the results of researches on the separating surfaces between the liquid steel and the ceramic filter material, which in form of photos and scanning microscope microanalyses are put together in the publication. 相似文献
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Wouter van Riel Johan Post Jeroen Langeveld Paulien Herder 《Structure and Infrastructure Engineering》2017,13(7):855-868
Operational decision-making processes for networked infrastructure management often occur as a multi-actor planning problem, implying these are based on negotiations between different stakeholders in addition to available system quality information. As such, does more accurate data about actual structural condition lead to other or better decision-making? A serious game is introduced, Maintenance in Motion, aiming at investigating the influence of information quality on rehabilitation decisions, for single- and multi-actor decision-making. Players manage drinking water, gas, sewer and street infrastructures. They are to balance their individual goal, cost-effectiveness, with their team utility, increasing overall infrastructure quality to minimise failure while minimising overall public costs. The game design, calibration and solution space are presented. 相似文献
46.
为实现换流变压器故障诊断,研究交流与直流电压比例对油纸绝缘放电特性的影响对换流变压器的故障诊断判据选取具有实际工程意义。因此该文搭建了一套交直流复合电压作用下油纸绝缘气隙缺陷局部放电测量平台,通过多次试验得到了局部放电特征与交直流复合比例的试验关系;另外建立了油纸绝缘气隙缺陷的物理模型,从理论上分析了比例与放电特征关系的仿真结果。试验测量和理论仿真结果相同:随着交流和直流叠加电压中直流成分的增大,脉冲重复率和放电量不断减小;交流时的放电起始电压低于交直流复合电压作用时的起始电压,而且直流比例越高,起始电压越高;随着交流中直流成分的增加,放电起始相位从交流正负半周过零点附近向负半周期峰值附近移动,换流变压器不同位置的绝缘问题应该采用不同的诊断依据。 相似文献
47.
采用两级A/O-海绵填料工艺处理DMF废水,探究一级A/O缺氧池(A1)和二级A/O缺氧池(A2)分段进水比(8∶2、7∶3、6∶4、5∶5)对系统脱氮除碳效能影响。结果表明,两级A/O-海绵填料工艺在不同分段进水比条件下均能实现对COD的高效去除,COD平均去除率均达到95%以上,而系统对TN、NO;-N和NH;-N的去除受分段进水比影响较大。在较高(8∶2和7∶3)分段进水比条件下,系统TN去除率为81.39%~89.03%,此时TN主要以NH4+-N和NO3--N形式存在;当分段进水比减小为6∶4时,系统TN去除率达到最优值91.33%,出水NH4+-N和NO3--N均明显低于其余进水比工况,分别降至8.04 mg/L和7.06 mg/L。因此通过优化两级A/O-海绵填料工艺分段进水比,可提升高浓度有机氮废水中难降解碳源的利用率与控制氨化反应进程,实现DMF废水有机氮的高效去除。 相似文献
48.
Copolymerization is a useful way of modifying the physical properties of a material to meet specific needs, but it can result in a significant light scattering loss due to dielectric fluctuations in the material. Ideal random copolymers are known to be more transparent; however, the light-scattering properties of such copolymers in bulk have not been fully studied. In this paper, two representative ideal random copolymers were synthesized: methyl methacrylate (MMA)/benzyl methacrylate (BzMA) and MMA/2,2,2-trifluoroethyl methacrylate (TFEMA). The effects of copolymer composition and polymerization temperature on the light-scattering properties were investigated. Polarized light scattering (VV) in copolymers was more sensitive to the polymerization temperature. Higher temperatures were necessary to homogenize the dielectric fluctuations and minimize excess light scattering. However, once the heterogeneous structures vanished, the copolymer bulk exhibited low scattering losses, which are comparable with homopolymers, over the entire range of copolymer compositions. 相似文献
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50.
《Journal of the European Ceramic Society》2020,40(10):3608-3617
This work focuses on a novel, co-sintered, all-ceramic solid oxide fuel cell (SOFC) concept. The objective is the understanding of interaction and degradation mechanisms of the cathode and current collector layers within the design during co-sintering. Half cells consisting of silicate mechanical support, lanthanum strontium manganite (LSM) current collector, LSM mixed with 8 mol% yttria-stabilized zirconia (8YSZ) composite cathode and 8YSZ electrolyte were co-sintered at 1150 °C < T < 1250 °C. Crystallographically stable LSM compositions within the design were identified. However, the cathode and silicate/electrolyte interacted by interdiffusion of Zn (gas diffusion) and Mn (solid diffusion), and by the formation of several reaction phases (between silicate and cathode only). Introducing silicate poisoning decreased the electrochemical performance of the cell by around 40%. This is likely due to the formation of the Zn- and Mn-rich phase in the cathode, but may also be caused by a higher ohmic resistance of the current collector. 相似文献