On the mathematics of time-dependent apparent chloride diffusion coefficient in concrete

This paper provides an improved mathematical analysis of chloride penetration into concrete employing a time-dependent diffusion coefficient for the solution of Fick's second law of diffusion. In the paper the possible errors caused by the application of oversimplified mathematical expressions used in some models for the evaluation of service life of reinforced concrete structures are discussed. The results from this mathematical analysis demonstrate that some models based on the oversimplified error function complement (ERFC) solutions may easily overestimate the service life by orders of magnitude, especially when the age factor is high. Some chloride profiles after up to 10 years' field exposure were used to compare the oversimplified with the improved models. The results show that both the oversimplified and the improved models fairly well predict the 10 years' chloride ingress in Portland cement concrete, but the oversimplified ERFC model significantly underestimates the chloride ingress in concrete with fly ash.     

Comprehensive modeling of chloride ion and water ingress into concrete considering thermal and carbonation state for real climate

This article presents a comprehensive modeling of temperature, carbonation, water and chloride ions transport in cover concrete using the transport model “TransChlor”. The TransChlor transport model employs weather data and chloride ion concentrations present on the concrete surface to predict the temporal and spatial evolution of the presence of chloride ion concentrations in the cover concrete pores. The main features of the TransChlor model are presented and validated.The TransChlor model has been calibrated using experimental data on liquid water movement in concrete of different permeabilities under realistic microclimatic conditions. Chloride ion transport is validated by means of experimental results obtained from a newly developed chloride ion optical fiber based sensor.     

Effect of chloride salt, freeze–thaw cycling and externally applied load on the performance of the concrete

The effect of sodium chloride solution, freeze–thaw cycling and externally applied load on the performance of concrete was experimentally investigated. The results show that the concrete specimens subjected to freeze–thaw cycling scaled more severely in chloride salt solution than those in water, and weight losses of the specimens tested in chloride salt solution were twice as much as those tested in water. However, dynamic modulus of elasticity of the concrete specimens decreased more slowly in chloride salt solution than in water due to the decline in the freezing point of the chloride salt solution compared with water. It is also shown that the performance deterioration in the concrete subjected to multidamaging processes was significantly accelerated. The larger the stress ratios, the fewer freeze–thaw cycles the concrete could bear. When steel fiber is incorporated, performance degradation in the steel fiber-reinforced concrete exposed to the multidamaging processes could be considerably retarded.     

Durability properties of micro-cracked ECC containing high volumes fly ash

This paper presents the durability of Engineered Cementitious Composites (ECC) that contain high percentages of Class-F fly ash (FA). ECC is a newly developed high performance fiber reinforced cementitious composite with substantial benefit in both high ductility in excess of 3% under uniaxial tensile loading and improved durability due to intrinsically tight crack width. Composites containing two different contents of FA as a replacement of cement (55 and 70% by weight of total cementitious material) are examined after 28 days of curing. Accelerated aging (exposure to continuous sodium hydroxide at 38 °C and sodium chloride solutions at room temperature) and tests of transport properties (salt ponding, rapid chloride permeability and sorptivity tests) are used to study the effect of FA on the durability of the ECC. After accelerated aging, direct tensile tests are performed to evaluate the effect of deterioration on the tensile strength, tensile strain capacity and crack width of ECCs. In addition to virgin specimens, the durability performances of mechanically loaded specimens are also tested. Test results show that both mechanically pre-loaded and virgin (without pre-loading) ECC mixtures with high volumes of FA remain durable in terms of mechanical performances after accelerated aging period, and show a tensile strain capacity of more than 2%. In terms of transport properties, micro-cracks induced by mechanical pre-loading increase the chloride transport and the sorptivity values of ECC. Moreover, increasing FA content is shown to have a negative effect especially on the transport properties of ECC tested in this study. However, the risk of water transport by capillary suction and chloride transport by diffusion in ECC, cracked or uncracked, is found to be comparable with that in normal sound concrete.     

Preparation and characterization of new photoactive polyamides containing 4‐(4‐dimethylaminophenyl)urazole units

4‐(4‐dimethylaminophenyl)‐1,2,4‐triazolidine‐3,5‐dione ( DAPTD ) was prepared from 4‐dimethylaminobenzoic acid in five steps. The compound DAPTD was reacted with excess acetyl chloride in N,N‐dimethylacetamide (DMAc) solution and gave 1,2‐bisacetyl‐4‐[4‐(dimethylaminophenyl)]‐1,2,4‐triazolidine‐3,5‐dione as a model compound. Solution polycondensation reactions of monomer with succinyl chloride (SucC), suberoyl chloride (SubC), and sebacoyl chloride (SebC) were performed under conventional solution polymerization techniques in the presence of triethylamine and pyridine as a catalyst in N‐methylpyrrolidone (NMP) and led to the formation of novel aliphatic polyamides. These novel polyamides have inherent viscosities in the range of 0.09–0.21 dL/g in N,N‐dimethylformamide (DMF) at 25°C. Fluorimetric studies of the model compound as well as polymers were performed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 947–954, 2007     

低氧诱导因子-1α和上皮间质转化相关蛋白在甲状腺滤泡状癌组织中的表达及其临床意义

目的探讨低氧诱导因子-1α(Hypoxia-inducible factor-1α,HIF-1α)和上皮间质转化(Epithelial-mesenchymaltransition,EMT)相关蛋白在甲状腺滤泡状癌(Follicular thyroid carcinoma,FTC)组织中的表达及临床意义。方法采用免疫组化SP法检测42份FTC组织中HIF-1α、锌指转录因子(Snail)、波形蛋白(Vimentin)和钙黏蛋白E(E-cadherin)的表达;MTT法检测不同浓度CoCl2对FTC WRO细胞增殖活力的影响;RT-PCR法检测不同浓度CoCl2对WRO细胞HIF-1α基因mRNA转录水平的影响;免疫荧光法观察150μmol/L CoCl2处理24 h的WRO细胞中HIF-1α蛋白的核定位;Western blot检测150μmol/LCoCl2处理不同时间对WRO细胞中HIF-1α、Snail、Vimentin和E-cadherin蛋白表达的影响;Transwell小室试验检测150μmol/LCoCl2处理24 h对WRO细胞中侵袭及迁移能力的影响。结果在42份FTC组织中,HIF-1α、Snail、Vimentin和E-cadherin蛋白的表达与多项临床指标相关,且4者表达显著相关(P<0.05);CoCl2可抑制WRO细胞的增殖活力;随着CoCl2浓度的增高,WRO细胞中HIF-1α基因mRNA的转录水平先增高然后趋于平稳;150μmol/L CoCl2处理24 h的WRO细胞内HIF-1α蛋白发生核转位;CoCl2处理的WRO细胞中随着HIF-1α蛋白表达的增多,Snail和Vimentin蛋白的表达逐渐增多,E-cadherin蛋白的表达逐渐减少(P<0.05);150μmol/L CoCl2处理24 h后,侵袭、迁移细胞数目较对照组明显增加。结论 HIF-1α能够通过上调Snail与Vimentin的表达,下调E-cadherin的表达,进而促进FTC EMT的发生。     

Mechanical characterization and modeling stress relaxation behavior of acrylic–polyurethane-based graft-interpenetrating polymer networks

The stress relaxation behavior of acrylic–polyurethane (PU)-based graft-interpenetrating polymer networks (IPNs) was characterized via dynamic mechanical analysis (DMA) and modeled using finite element method (FEM) analysis. Stress relaxation of glassy IPN specimens was experimentally studied under flexural testing, while rubbery IPN specimens were tested in tension. The effects of varying the styrene content in the acrylic copolymer phase, compatibility of the two phases in IPNs, and changing the concentration of acrylic copolymer and PU were studied. A higher percentage of styrene content resulted in higher homogeneity of IPN specimens, and decrease in initial modulus for acrylic copolymer specimens. Additionally, glassy IPN specimens with 90% styrene shows resistance to relaxation as high as acrylic copolymer samples. Experimental results were used to develop a numerical model to study stress relaxation response of specimens. While polymer systems have been studied computationally, numerical modeling of IPN systems is still in its infancy. A three-dimensional FEM model was developed using the Generalized Maxwell model and four-term Prony series constants, which were extracted from the stress relaxation experiments. With four terms in the Prony series, a good match was observed between experimental observations and results from the FEM model.     

Novel conventional and chelating anion exchange resins with amino ligands for sorption of silver

ABSTRACT

The polymeric resins containing diethylenetriamine, tetraethylenepentamine, 2-(diethylamino)ethanol, 1-methylimidazole, and 1,2-dimethylimidazole ligands have been synthesized from vinylbenzyl chloride-divinylbenzene copolymers and used in the removal of Ag(I) from chloride solution. The best Ag(I) sorption was reached in the case of 1-methylimidazole resin. Resins retain their capacity towards Ag(I) in five consecutive sorption/desorption cycles. The resins with imidazole ligands were highly selective for Ag(I) from synthetic chloride solution and they did not sorb chloride complexes of Cu(II). Additionally, the recovery of Ag(I) was tested from real chloride solution coming from leaching of the copper concentrate from Lubin Concentrator (KGHM Polska Mied? S.A.).     

Comparison between surface and bulk hydrophobic treatment against corrosion of galvanized reinforcing steel in concrete

The effectiveness of bulk hydrophobic treatment against corrosion of galvanized steel reinforcement in concrete specimens with w/c = 0.45 and w/c = 0.75 was compared with that of surface treatment, even in the presence of cracks 0.5 and 1 mm wide in the concrete cover. In this case surface hydrophobic treatments were applied both before and after cracking as a preventive and a restorative method against reinforced concrete deterioration, respectively. The obtained results in terms of water absorption, electrochemical measurements, chlorides penetration, and visual observations carried out on reinforced concrete specimens during the exposure to wet–dry cycles in 10% NaCl solution showed that bulk hydrophobization is the most effective treatment in improving the corrosion resistance of galvanized steel reinforcements in concrete also in the presence of cracks. Surface hydrophobization is very effective just in the first few exposure cycles to the aggressive environment and when used as a restorative method which is able to cancel the deleterious effect of cracks only 0.5 mm wide.     

室温固相法制备氢氧化镁及其对水溶液中Ni(Ⅱ)的吸附

以氯化镁、氢氧化钠、氯化钠为原料,利用室温固相反应制备了氢氧化镁.采用X射线粉末衍射(XRD)、扫描电镜( SEM)等方法对样品的物相、形貌进行了表征.对氢氧化镁吸附处理含Ni(Ⅱ)废水进行了研究,考察了pH值、吸附时间和吸附温度等因素对氢氧化镁吸附Ni(Ⅱ)过程的影响,使用准一级动力学模型、准二级动力学模型对动力学数据进行了拟合,结果表明氢氧化镁对Ni(Ⅱ)的吸附过程符合准二级动力学模型,并且吸附量随温度的增加而增大.     

Thermal and structural characterization of nanofibers of poly(vinyl alcohol) produced by electrospinning

Poly(vinyl alcohol) (PVOH) was obtained from the alkaline hydrolysis of poly(vinyl acetate) (PVAc). Nonwoven membranes (mats) of PVOH nanofibers were produced by electrospinning of solutions of PVOH in water with and without aluminum chloride. The concentration of the PVOH/water solution was 12.4% w/v. The morphology of the mats was analyzed by scanning electron microscopy (SEM). The thermal properties and the degree of crystallinity of the nanofibers were measured by differential scanning calorimetry (DSC); the crystal structure of the mats was evaluated by wide‐angle X‐ray diffraction. The best nanofibers were obtained by electrospinning the PVOH/water solution with aluminum chloride (45% w/v) in which an electrical field of 3.0 kV/cm was applied. It was observed that the addition of the aluminum chloride and the increase in the applied electrical field decreased the number‐average nanofibers diameters. The mats without aluminum chloride had higher melting temperatures and higher degrees of crystallinity than the mats with the salt. The crystal structure of the mats was found to be monoclinic; however, the mats were neither highly oriented nor have a high degree of crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Chemical alteration of calcium silicate hydrate (C-S-H) in sodium chloride solution

The effect of sodium chloride on the chemical alteration of calcium silicate hydrate (C-S-H) was measured and discussed. The release of calcium from C-S-H was increased as the concentration of sodium chloride in the solution increased. It was observed that sodium sorbed onto the C-S-H phases and some sodium replaced calcium in C-S-H so that the release of calcium was enhanced. An integrated modelling approach employing an ion-exchange model and an incongruent dissolution model of C-S-H is developed. It reasonably and accurately predicted the release of calcium from C-S-H in sodium chloride solution by considering cation exchange and the effect of the ionic strength on the solubility of C-S-H.     

Theoretical and experimental studies of free convection and stratification of electrolyte in a lead-acid cell during recharge

Free convection and stratification of the electrolyte in a lead-acid cell with porous electrodes and during recharge were studied theoretically and experimentally. The concentration field was measured by means of Holographic Laser Interferometry (HLI) and the velocity field by means of Laser Doppler Velocimetry (LDV). A two-dimensional mathematical model was also developed for mass transfer and electrolyte motion during the process. It was assumed for simplicity that the electric current density and porosities of the electrodes were constant and uniformly distributed in the electrodes. The results from the experiments were compared with numerical results obtained from the mathematical model. The agreement was found to be good. A simplified mathematical model, as an alternative to the full numerical problem, was also developed. The results of the simplified model proposed here proved to be in good agreement with the results from the full numerical solution, albeit for sufficiently large times.     

考虑骨料表面强化的再生混凝土内氯离子传输细观数值模拟

采用纳米强化再生骨料表面的措施来改善再生骨料性能,建立多相再生混凝土细观数值模型,进行氯离子在再生混凝土内部传输的模拟和试验验证,并预测了氯盐环境下再生骨料表面强化混凝土耐久性寿命。结果表明:数值模拟得到的氯离子在再生混凝土内的分布与试验结果吻合较好;同一深度处,越靠近骨料表面,氯离子浓度越大,其中未强化再生骨料表面的氯离子浓度要大于强化再生骨料表面的氯离子浓度;增加保护层厚度可以有效提高纳米强化再生混凝土在氯盐环境下的耐久性寿命;随纳米包裹层氯离子扩散系数的减小,再生混凝土的耐久性寿命有所增加。     

Relating rapid chloride transport parameters of concretes to microstructural features extracted from electrical impedance

The rapid chloride transport parameters such as the rapid chloride permeability (RCP) and non-steady state migration coefficient are related to the material microstructural parameters in this paper. Electrical impedance spectroscopy and associated equivalent circuit modeling are used to extract the microstructural features of the plain concrete as well as concretes modified with varying amounts of Class F fly ash or silica fume. A methodology is developed in this paper that utilizes the ratios of RCP values and the ratios of effective conductivities to pore solution conductivities of plain and modified concretes, to quantify the relative influence of pore solution conductivity and pore structure on the RCP values. The resistance attributable to the connected pores is extracted from an equivalent circuit model for the impedance spectra of concretes, which is found to relate well to the rapid chloride transport parameters as well as the microstructural parameters. Based on the experimental results and electrical circuit models, it is shown that a reduction in pore connectivity has a higher impact on the rapid chloride transport parameters than a reduction in the porosity, and reduction in pore sizes is more consequential than porosity reduction in reducing pore connectivity.     

The effect of silane-based hydrophobic admixture on corrosion of reinforcing steel in concrete

The influence of a hydrophobic admixture based on silane on the corrosion resistance of steel reinforcement in concrete was studied. Sound or deliberately pre-cracked concrete specimens were manufactured with w/c of 0.45 and 0.80, both in the presence and in the absence of silane. The specimens were fully immersed in a 3.5% NaCl aqueous solution.The results, in terms of electrochemical measurements, visual observations, and weight loss measurements of steel reinforcement, show that silane blocked corrosion process in uncracked concrete specimens. On the other hand, in cracked concrete specimens, corrosion of steel reinforcements was unexpectedly more severe in hydrophobic specimens rather than in the corresponding not hydrophobic ones. It is believed that oxygen, which is needed to feed the corrosion process, diffuses faster in a gaseous phase through the open concrete porosity in the hydrophobic concrete, whereas in concrete without silane, oxygen diffuses much more slowly through the water filling the pores of the saturated concrete.     

可逆加成-断裂链转移聚合制备聚氯乙烯-b-聚乙二醇-b-聚氯乙烯共聚物

合成了含黄原酸酯端基的聚乙二醇（X-PEG-X）大分子链转移剂,并以其为可逆加成-断裂链转移试剂调控氯乙烯（VC）溶液和悬浮聚合,合成聚氯乙烯-b-聚乙二醇-b-聚氯乙烯（PVC-b-PEG-b-PVC）三嵌段共聚物。X-PEG-X调控VC溶液聚合得到的共聚物的分子量随聚合时间增加而增大,分子量分布指数小于1.65。X-PEG-X具有水/油两相分配和可显著降低水/油界面张力的特性,以X-PEG-X为链转移剂和分散剂,通过自稳定悬浮聚合也可合成PVC-b-PEG-b-PVC共聚物,共聚物颗粒无皮膜结构,分子量随聚合时间增加而增大;由于VC悬浮聚合具有聚合物富相和单体富相两相聚合特性,共聚物分子量分布指数略大于溶液聚合共聚物。通过乙酸乙烯酯（VAc）扩链反应进一步证实了PVC-b-PEG-b-PVC的“活性”,并合成PVAc-b-PVC-b-PEG-b-PVC-b-PVAc共聚物。水接触角测试表明PVC-b-PEG-b-PVC的亲水性优于PVC。     

Performance studies of heterogeneous ion exchange membranes in the removal of bivalent metal ions in an electrodialysis stack

Heterogeneous anion and cation exchange membranes have been prepared by solution casting technique with poly(vinyl chloride) as inert binder and anion/cation exchange resins (?300 + 400 mesh) in a blend ratio of 60 : 40. The membranes were characterized with respect to their physical, mechanical, and electrochemical behavior. Anion and cation exchange membranes (10 cell pairs) were packed in an electrodialysis stack in a parallel plus series flow pattern. Desalting experiments were carried out with four different salt solutions, such as calcium chloride, magnesium chloride, cupric chloride, and nickel chloride (varying in their total dissolved solid from 500 to 1000 ppm), at different applied potentials and flow rates. The resultant current, percentage reduction in total dissolved solid, current efficiency, and energy consumption were calculated. The maximum current density in the electrodialysis stack was observed for calcium chloride solution and at any applied potential and flow rate the percentage reduction in total dissolved solid for Ca⁺⁺ > Cu⁺⁺ > Ni⁺⁺ > Mg⁺⁺. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009