结构型钢纤维对混凝土单裂缝渗透特性的影响

为研究纤维对裂隙混凝土渗透性能的影响,借鉴圆盘劈裂试验引入可控裂缝,并采用Supereyes数码显微镜和Image Pro Plus(IPP)图像分析软件对裂缝形态进行了分析。对于带裂缝试件,分别利用变水压和恒定水压渗透试验研究了其抗渗性能;参照达西定律及平板渗流模型,提出了在考虑纤维影响后单裂隙混凝土渗透性能的分析方法。研究表明:在圆盘劈裂试验中素混凝土试件发生脆性破坏、无法控制裂缝的发展速率,而掺入结构型钢纤维后,试件不仅表现出良好的韧性和变形能力,而且可实现裂缝扩展速率的有效控制;结构型钢纤维可提高裂缝曲折度,降低裂缝修正系数和渗透介质通过混凝土的能力。与传统变水压渗透系数相比,恒水压渗透试验得出的修正单裂隙渗透系数可较敏感地反映内部裂缝对混凝土渗透性的影响,定量分析裂缝与混凝土渗透性之间的关系。     

黏土砖再生混凝土抗氯离子渗透性试验研究

试验研究了再生黏土砖粗骨料取代率、骨料强化、搅拌工艺、粉煤灰和硅灰单掺与复掺对黏土砖再生粗骨料混凝土抗氯离子渗透性能的影响。结果表明,随着再生骨料替代率的增加,再生混凝土抗氯离子渗透性能降低,替代率为0,30%,50%,70%,100%时,6 h通电量分别为2 090,2 596,3 207,3 989,5 182 C,氯离子渗透等级由适中过渡到高;骨料强化处理和改善搅拌工艺能够提高再生混凝土抗氯离子渗透性能,再生骨料取代率在50%以下,经过二次包裹强化或者采用改良的搅拌工艺后,再生混凝土的抗氯离子渗透性能与普通混凝土已经接近;粉煤灰和硅灰单掺或复掺可以较大幅度改善再生混凝抗氯离子的渗透性能,硅灰效果优于粉煤灰,20%粉煤灰和10%硅灰复掺可以作为最佳掺量,6 h通电量为171 C,可以用来配置较高抗氯离子渗透性能的再生混凝土。试验结果为再生混凝土推广应用提供了有力依据。     

基于渗透性能的混凝土耐久性预测模型

通过不同配合比混凝土试件的气体渗透性测试、吸水性测试及氯离子侵蚀试验,分析了混凝土氯离子扩散系数与渗透性能之间的关系,建立了基于渗透性能的混凝土耐久性预测模型,并以某临海水闸工程为例对所建模型进行验证。结果表明:空气渗透性系数、吸水性系数及氯离子扩散系数均随着水灰比的增大而增大;不同水灰比情况下,氯离子扩散系数均随空气渗透性系数、吸水性系数的增大而增大,且呈现一定的相关性;建立的基于渗透性能的混凝土耐久性预测模型,只需进行混凝土结构渗透性能的试验,即可预测混凝土结构的使用寿命;以某临海水闸工程为例对所建模型进行验证,认为该模型是可行的。建立基于渗透性能的混凝土耐久性预测模型对在氯离子环境下的混凝土结构工程直接利用渗透性能预测其使用寿命具有重要意义。     

纤维素纤维混凝土早期抗裂与抗渗性能试验

渠道衬砌混凝土极易开裂渗透,严重影响渠道的正常使用和混凝土耐久性。纤维可以在混凝土中发挥阻裂作用。通过对比试验,研究了纤维素纤维混凝土与聚丙烯纤维混凝土的早期抗裂和抗渗性能,分析纤维素纤维掺量对混凝土抗裂性和抗渗性的影响规律,探讨纤维改善混凝土抗裂和抗渗性能的机理,提出经济合理的纤维掺量。试验结果表明:纤维素纤维的掺入显著改善了混凝土的抗裂和抗渗性能,且改善效果明显优于聚丙烯纤维。     

堆石混凝土层面渗透性能影响因素试验研究

堆石混凝土层面情况直接关系到层间施工缝的渗透性能,进而影响工程质量。设计了12组不同层面特性及层面处理工艺的堆石混凝土和1组不含层面堆石混凝土试件,开展了13组试件的室内渗透试验,研究层面不同堆石高度、堆石面积、凿毛工艺、石粉含量对层间渗透性能的影响,并与不含层面试件进行对比分析。试验结果表明：含层面施工缝的堆石混凝土试件渗透呈端面未渗水和端面渗水2种渗水形式,其中层面堆石高度、堆石面积会不同程度影响层面施工缝的相对渗透性系数及渗水形式;而层面石粉含量、凿毛工艺对其渗透性能有着显著影响。为提高层面防渗性能,堆石混凝土施工应尽可能将层面凿毛至露石,石粉含量控制在440 g/m~2以下。     

塑性混凝土渗透性能试验研究

采用水工混凝土抗渗仪法和土工渗透仪法对蝮性混凝土的渗透性能进行了试验,分析了水胶比、膨润土用量、黏土用量、水泥用量、砂率等对渗透性能的影响.结果表明:塑性混凝土的抗渗性能随着水胶比的减小和砂率的减小而增大,适当增加膨润土和黏土用量可以提高其抗渗性能,水泥用量对渗透性能影响不明显.     

土工织物垂直渗透性能规律及取值方法探讨

本文比较了国内外几种主要的土工织物渗透性能测试标准成果取值方法，通过理论分析及试验数据，得出渗透性能中水头差及流速的关系式，并对将来国内标准的可能修订提出建议。     

同轴套管间涡旋流动及强化传热数值模拟

相对旋转两同轴套管间的涡旋流动,能够带来二次流强化传热传质作用,在航空、水处理、生态保护、生物工程和膜分离等领域都具有广泛的应用价值。本文使用Fluent软件,对同轴套管间涡旋流动及传热特性进行数值模拟,考察了内管转速、内外管壁面温差等操作参数变化对同轴套管间流体传热性能的影响,分析了涡旋流动与传热效率之间的关联关系。模拟结果表明:内管转速增加在流场中形成泰勒涡,涡流扰动增大了高温壁面与流体间的热流密度,增强了流体传热效率。增大内外管壁面温差,也可加强流体传热性能,但其强化作用不及内管转速的强化作用显著。受流场中泰勒涡影响,流体速度、温度及热流密度沿轴向的分布都呈正弦状周期性波动,在相邻两涡交界面处,流体传热性能最好,在涡中心处的传热性能最差。     

冻融损伤条件下水工混凝土渗透性能试验

氯离子扩散系数是评定混凝土渗透性能的一个重要指标。对水工C30引气混凝土先后进行冻融循环试验和渗透性试验,基于不同冻融损伤程度开展氯离子扩散系数试验,用理论和试验相结合的方式分析冻融损伤对水工混凝土渗透性能的影响。试验结果表明:随着冻融循环次数的增加,损伤程度随之加深,混凝土的密实性逐渐下降,氯离子扩散系数呈线性增长,混凝土抗渗透性能明显下降。     

旋转流膜生物反应器膜透水特性研究

对旋转流膜生物反应器与一体式膜生物反应器透水性能进行了对比试验研究,结果表明,前者的膜平均透水量是后者的1.3-1.8倍,当旋转流膜分离器垂直安装、膜纤维呈环状布置、曝气点位于纤维膜环中心底部时膜透水量达最大值。交替切向进水和膜分离器底部曝气可增大膜束振动频率,提高膜抗污染能力。     

Reuse of carwash wastewater with hollow fiber membrane aided by enhanced coagulation and activated carbon treatments.

The particles from carwash wastewater were separated by a hollow fiber membrane aided by a enhanced coagulation and activated carbon. This study demonstrated that the addition of KMnO(4) to coagulant (PAC) could enhance the efficiency of coagulation, which helped reduce clogging of the ultrafiltration membrane and activated carbon. The existence of LAS can loosen the gel layer on the membrane and improve the flux. Adsorption of particles such as organic matter and oil is the main reason causing membrane flux decrease. When carwash wastewater was pretreated, the permeation flux of membrane showed a higher value. LAS, odour and colour are removed by GAC adsorption treatment at last. The COD, BOD, LAS and oil of reuse water was 33.4 mg/L, 4.8 mg/L, 0.06 mg/L and 0.95 mg/L, respectively.     

Pervaporative removal of acrylonitrile from aqueous streams through polydimethylsiloxane membrane

This study describes the successful separation of acrylonitrile (ACN) from dilute aqueous streams using pervaporation process. The influences of ACN feed concentration, permeate pressure, operating temperature, feed flow rate and membrane thickness on the membrane separation performance were investigated. The results showed that with an increase in ACN concentration in the feed solution, the permeation flux of ACN increased while the enrichment factor decreased. It was also indicated that increasing the permeate pressure reduced the driving force for mass transfer and consequently the permeation flux dropped while the enrichment factor enhanced. Polydimethylsiloxane membranes used in this study showed very good properties in the separation process, leading to enrichment factors in the range of 70-140. Furthermore, the activation energy for pervaporation of both ACN and water calculated from Arrhenius plot indicated that the permeation of water through the membrane was more temperature dependant than ACN.     

Preparation of three-bore hollow fiber charged nanofiltration membrane for separation of organics and salts

Three-bore hollow fiber charged nanofiltration (NF) membrane was prepared by interfacial polymerization (IP). The results showed that the flux and rejection of NF membrane prepared in this study increased with the increasing in the operating pressure. The water flux decreased and rejection for obvious dyes increased as the solute concentration increased. The separation factor for mixture of Xylenol orange/NaCl decreased when NaCl concentration in solution increased and could reach to as high as 18. In addition, three-bore hollow fiber charged nanofiltration membrane prepared in this study has excellent stability for strong acid (pH = 3), strong alkali (pH = 11) and high temperature solution (80 °C).     

Antibacterial properties of PES/CuCl(2) three-bore hollow fiber UF membrane

In this study, a three-bore polyethersulfone (PES) hollow fiber ultrafiltration (UF) membrane with antibacterial properties was prepared by phase inversion, using PES as the membrane material, N,N-dimethylacetamide (DMAC) as solvent, polyvinylpyrrolidone (PVP) and CuCl(2) as additives. The effect of CuCl(2) content on the water flux and rejection was studied and the antibacterial properties of PES hollow fiber UF membrane were also investigated. The water flux results indicated that the hydrophilic properties of PES UF membranes were improved after adding CuCl(2). The rejection of PVA-50000 was expected to drop slightly but remain high above 96%. The membranes showed good antibacterial activity against Escherichia coli (E. coli) after adding CuCl(2) and the antibacterial rate of PES/CuCl(2) UF membranes was close to 100% after running for 48 h. PES hollow fiber UF membranes with antibacterial properties were prepared through the formation of the water-soluble PVP/Cu(2+) complex with spatial network structure, which have good antibacterial and hydrophilic properties. Therefore, this study could provide an effective method for membrane antifouling.     

Comparison of treatment efficiency of submerged nanofiltration membrane bioreactors using cellulose triacetate and polyamide membrane.

This study evaluates the performance of nanofiltration membrane bioreactor (NF MBR) systems using cellulose triacetate (CA) and polyamide (PA) membranes. The results indicated that both NF membranes could produce high quality permeate in the submerged NF MBR system. In addition, hollow fiber CA membranes exhibited the capability of higher permeate productivity than PA membranes. However, to obtain high quality permeate for a long-term operation, CA membranes should be maintained using an appropriate method, such as chlorine disinfection, in order to control the membrane biodegradation. The results demonstrated that PA membranes were capable of producing higher quality permeate for a long period than CA membranes. In order to enhance the practicability of PA membranes in submerged NF MBR systems, it is required that the membranes should have the lowest possible intrinsic salt rejection.     

Application of sequencing batch membrane bioreactors (SB-MBR) for the treatment of municipal wastewater

Sequencing batch membrane bioreactors can be a good option in up-grading small municipal plant and for industrial applications, maintaining some of the advantages of both original technologies (effluent quality improvement, flexibility and simplicity of realization, operation and control). In this study, the effects of volumetric exchange ratio (VER) and aeration/filtration strategy have been evaluated. Moreover, with the adoption of cycles shorter than 8 h, the opportunity of further simplification of the membrane operation has been tested by choosing a continuous filtration mode instead of the usual short cycle of permeation/relaxation. Two lab-scales MBR equipped with Zenon hollow fiber modules were fed on real primary effluent. For all tests, hydraulic retention time of 10 h and sludge retention time of 60 days have been adopted. Different cycles have been investigated, lasting between 1 and 8 h and all comprising an anoxic phase to allow for denitrification. Operation at low VER resulted in better effluent quality with no limitations to the denitrification phase. For VER >33% a pre-aeration step was required before effluent withdrawal for optimal ammonium removal. Moreover, VER appeared to have limited negative effect on sludge concentration and yield, while the membrane cleaning frequency slightly increased for increasing VER.     

Preparation, characterization and performance of a novel PVDF/PMMA/TPU blend hollow fiber membrane for wastewater treatment

Polyvinylidene fluoride (PVDF)/polymethylmethacrylate (PMMA)/thermoplastic polyurethane (TPU) blend hollow fiber membranes were successfully prepared by the wet-spinning method with the loading of PMMA and TPU in a range of polymer concentrations varying from 0 to 20 wt% and at a total polymer concentration of 16 wt%. The influence of the addition of PMMA and TPU on the morphologies and the properties of such prepared membranes was investigated through FTIR-ATR, SEM, viscosity measurements, UF experiments and mechanical strength tests. Based on the experimental results, the compatibility of the PVDF, PMMA and TPU blend was best under the conditions of the PVDF-rich phase. The elongation at break of the membrane increased to a maximum of 146% with increase in the TPU concentration to 20 wt% in dope solution. The addition of PMMA increased the water permeation flux from 120 to 195 L/(m(2) h) initially. The flux then decreased when PMMA concentration was increased to over 10 wt%. The membranes obtained at optimized blending ratio were applied to the dyeing process wastewater filtration. During continuous filtration for 8 h, the flux was stabilized at about 20 L/(m(2) h) at 0.1 MPa. The reduction in COD(Cr), turbidity and color were about 63, 84 and 63% respectively.     

Strategies for chemical cleaning in large scale membrane bioreactors.

Systematically testing alternative cleaning agents and cleaning procedures on a large scale municipal membrane bioreactor, the Erftverband optimized the cleaning strategies and refined the original cleaning procedures for the hollow fiber membranes in use. A time-consuming, intensive ex-situ membrane cleaning twice a year was initially the regular routine. By introducing the effective means of cleaning in place in use today, which employs several acidic and oxidative/alkaline cleaning steps, intensive membrane cleaning could be delayed for years. An overview and an assessment of various cleaning strategies for large scale plants are given.     

Membrane-based gas transfer: an environmental engineering laboratory.

We propose an educational experience in which students design a membrane gas transfer reactor, construct a bench-scale version in the laboratory, and employ the reactor to measure mass transfer coefficients. The membrane reactor is useful for teaching mass transfer principles because the mass transfer interface is well defined and easily observed. The system can be modeled successfully using straightforward mathematics. The reactor can be designed and constructed by students, using the mathematical model as a basis, providing insight into the physical meaning of model parameters. The proposed membrane system can be readily operated to obtain data that can be employed to develop or modify existing mass transfer correlations. This can provide students with significant insight into the development of mass transfer correlations and how the constants in such correlations are typically determined. These features help promote a deeper understanding of mass transfer principles.