Modelling of water permeability in cementitious materials

This paper presents a network model to predict the permeability of cement paste from a numerical simulation of its microstructure. Based on a linked list pore network structure, the effective hydraulic conductivity is estimated and the fluid flow is calculated according to the Hagen–Poiseuille law. The pressure gradient at all nodes is calculated with the Gauss elimination method and the absolute permeability of the pore network is calculated directly from Darcy’s law. Finally, the permeability model is validated by comparison with direct water permeability measurements. According to this model, the predicted permeability of hydrating cement pastes is extremely sensitive to the particle size distribution of the cement and especially to the minimum size of the cement particles. Both in simulations and experiments, the permeability of cement pastes is mainly determined by the critical diameter and by the connectivity of the pore structure, regardless of w/c ratio and curing age. The permeability of cement pastes could be predicted reasonably well when a minimum particle size 1 μm was chosen for the cement.

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Résumé Cet article présente un modèle de réseau visant à prédire la perméabilité de la pate de ciment à l’aide d’une simulation numérique de sa microstructure. Sur la base d’une liste liée de la structure du réseau de pores, la conductivité hydraulique efficace est estimée et le flux de fluide est calculé selon la loi de Hagen–Poiseuille. Le gradient de pression est calculé à tous les nœuds par la méthode d’élimination de Gauss et la perméabilité absolue du réseau de pores est directement calculée à partir de la loi de Darcy. En conclusion, le modèle de perméabilité est validé par comparaison avec des mesures de perméabilité à l’eau. Selon ce modèle, la perméabilité prévue des pates d’hydratation de ciment est extrêmement sensible à la distribution des dimensions des particules du ciment et particulièrement à la taille minimale. Dans les simulations ainsi que dans les expériences, la perméabilité des pates de ciment est principalement déterminée par le diamètre critique et par la connectivité de la structure de pore, indépendante du rapport de l’eau au ciment et de la période de traitement. La perméabilité des pates de ciment pourrait être raisonnablement bien prédite lorsque l’on choisit 1 μm comme dimension de grain minimale du ciment.

     

X-ray photoelectron spectroscopy characterization of the interface between Ag electrode and PVDF film treated by electric poling

Interface changes induced by electric poling treatment between an Ag electrode deposited by vacuum thermal evaporation and a polymer thin film have been investigated. The polymer film poly (vinylidene fluoride) (PVDF), a fluoropolymer of repeat unit (–CH₂–CF₂–) was treated under electric poling at high temperature of 90°C. The characterization was accomplished using X-ray photoelectron spectroscopy (XPS) as a primary tool. The results indicate that the piezoelectricity of PVDF thin films and adhesion force between polymer thin film and metallic electrode are improved by electric poling and chemical bond joint.     

Reproducibility and stability of N–Al codoped p-type ZnO thin films

Reproducible and stable p-type ZnO thin films have been prepared by the N–Al codoping method. Secondary ion mass spectroscopy measurements demonstrate that N and Al are incorporated into ZnO. The resistivity, carrier concentration, and Hall mobility are typically of 50–100 Ωcm, 1×10¹⁷–8×10¹⁷ cm⁻³, and 0.1–0.6 cm²/Vs, respectively, for the N–Al codoped p-type ZnO films. Hall measurement, X-ray diffraction, and optical transmission were carried out to investigate the changes of the properties with the storage period. Results show that the p-type characteristics of the N–Al codoped ZnO films are of acceptable reproducibility and stability. In addition, the N–Al codoped p-type ZnO films have good crystallinity and optical quality. The properties are time independent.     

Effects of Y concentration on luminescence properties of PbWO4 single crystals

The effects of Y³⁺ doping at different concentration on the luminescnece properties of PbWO₄ crystals have been investigated by means of Fourier transform infrared (FT-IR) spectrum, optical transmission, thermoluminescence (TL), X-ray excited luminescence (XEL), photoluminescence (PL) under excitation of UV light and light yield measurements. The series PbWO₄:Y crystal samples were grown by modified Bridgman method and the concentration of Y³⁺ in the melt was in the range of 0–1.0 mol%. The slight blue-shift and evident red-shift of the absorption edge in PbWO₄ crystal were observed at low and heavy doping concentration, respectively. TL peaks in the range of from room temperature to 250 °C disappeared after the doping with Y³⁺. With the increase of doping concentration, the luminescence intensity in the XEL and PL spectra was found to decrease accordingly, especially in the case of heavy doping. The measuring results demonstrate that Y³⁺ doping concentration below 100 ppm in the crystal seems to be the best for optimizing the optical and scintillation properties of the material. The mechanism of Y³⁺ doping concentration influence on luminescence was also discussed in this paper.     

基于小波分解的径流预报非线性模型

径流时间序列中包含了大量的信息,从频率域上来看,这些信息包括变化平稳的低频信息和变化相对剧烈的高频信息。本文利用小波分解,将径流时间序列分解为低频项和高频项,低频项采用逐步回归法预报,高频项采用基于自组织法求解的Volterra滤波器预报,两者结果综合,最终实现径流预报。实例计算表明,该模型具有足够高的计算精度。     

力控组态软件下的设备驱动程序开发

本文简要介绍了三维力控组态软件I／O驱动程序接口开发工具包（FIOS SDK），然后以力控组态软件与C8051单片机的RS-485异步串行通信为例，给出了如何运用FIOS SDK在Visual C＋＋ 6．0中开发设备驱动程序的步骤，包括界面的设计和代码的编写。     

安徽省发展核电的必要性和重要性

从安徽省作为煤炭大省和华东地区重要的能源基地出发,分析了核电作为安全能源、清洁能源、经济能源的优越性,讨论了安徽发展核电的必要性和重要性,提出应抓住安徽发展核电的优势,积极准备,早日立项,促进安徽省整个经济和社会加快发展。     

现场局部放电试验中干扰源的识别和采取的对策

局部放电试验是检测固体绝缘中存在气泡和裂纹等缺陷最有效的手段,局部放电又是个弱电现象,现场进行局部放电试验极易受各种干扰的影响。文章详细分析了常见的干扰源类型和形成途径以及各种干扰波形放电特征、显示位置和随施加电压变化规律,并对各种干扰采取有效对策,将干扰抑制在合理的数值范围内,以保证局部放电试验顺利进行。     

公路泥石流防治结构内泥石流体运动规律研究

泥石流是一种典型的公路水毁病害,也是公路水毁时主要破坏动荷载,遵循泥石流的运动规律和道路破坏特点,建立泥石流防治技术是治理公路水毁病害的关键。文章通过分析泥石流体的运动特点,提出了合理的速流槽泥石流防治结构剖面形状,根据能量守恒原理建立的泥石流体运动方程和根据平抛理论建立的泥石流体抛程计算公式,解决了泥石流防治结构受泥石流体作用力大小的计算和泥石流防治与公路水毁病害治理效果的理论判断问题,为同类型的特大型公路泥石流防治结构设计与公路水毁病害治理提供了理论依据。     

预应力锚索与土钉墙在某基坑支护与加固工程中的应用

为了更好地解决基坑支护与加固的问题,采用预应力锚索与土钉墙的方法对广州华锐大厦基坑进行支护与加固的施工.通过对预应力锚索与土钉墙的设计、施工及监测等,分析阐述了该种方法在基坑加固工程中的实际应用.工程实践表明,预应力锚索与土钉墙是解决基坑支护与加固的好方法,具有相当广泛的应用前景.