准确检测混凝土抗渗性能的思考

本文是以渗水法手段检测混凝土抗渗性能为基础进行研究，以不同的密封材料作为试验对比，以找出合理的封闭材料配方，保证试验结果不受密封材料原因造成边缘透水影响判断混凝土抗渗性能。同时，讨论其它方法检测混凝土渗透性能有利于高性能混凝土耐久性的测试技术。     

氯离子在混凝土中扩散传输的有限体积法模拟分析

基于氯离子在混凝土结构中的扩散传输理论,建立了氯离子扩散传输偏微分方程,讨论了边界与初始条件。根据因变量在有限大小的控制体积中满足守恒定理,建立了氯离子在混凝土中扩散传输的离散方程,编制了计算程序。算例分析表明,有限体积法可以很好地模拟氯离子在混凝土中的扩散传输,可以分析计算复杂边界条件下的混凝土内的氯离子分布,并对受氯离子侵蚀混凝土结构的使用寿命进行预测分析。     

Ag/AgCl氯离子传感器在混凝土中的应用

尝试将试验室制作的Ag/AgCl氯离子传感器用于混凝土中测试,验证该传感器应用于混凝土结构中的可行性。测试了传感器在混凝土试件中的长期稳定性,建立了传感器在混凝土中的线性响应方程,并通过加速氯离子渗透的方式对建立的线性方程进行了验证。试验结果表明,传感器在混凝土试件中可以长期稳定有效地工作,85d电位波动25mV,传感器在氯离子掺量相同的试件中电位响应一致性良好;通过建立的线性方程计算得到的电位响应值与实测电位响应值符合得很好,所建立的方程与试件水胶比水平无关,与氯离子的引入方式无关,是适用于混凝土结构的比较准确的线性方程。通过该方程的建立即可实现使用该传感器监测混凝土结构中的氯离子分布,达到钢筋锈蚀提前预警的目的。     

氯离子导体及其应用开发

本文围绕有希望实现实用化的PbCl_2基氯离子导体,着重从材料研制、应用探索及应用前景这三个方面概述了氯离子导体研究的状况和今后动向。     

饱和钢纤维再生混凝土氯离子扩散特性研究

利用废弃骨料制作再生混凝土是建筑固废弃物的再生资源利用途径之一,其在氯盐侵蚀环境条件下的耐久性规律与普通混凝土不同。本文以模拟海洋侵蚀环境,通过改变水灰比及NaCl溶液浓度,分析各因素对钢纤维再生混凝土氯离子扩散行为的影响规律。结果表明:浸泡液浓度越大,进入混凝土内部的氯离子越多,随着深度的增加氯离子含量逐渐减少;较低的水灰比与适量钢纤维的掺入均可以有效降低氯离子扩散系数,提升钢纤维再生混凝土的抗氯盐侵蚀能力;氯离子扩散系数随着NaCl溶液浓度的增加而增大。     

多壁碳纳米管增强混凝土的抗氯离子渗透性能

采用快速氯离子迁移系数(RCM)法和自然浸泡法对多壁碳纳米管(MWCNTs)增强混凝土的抗氯离子渗透性能进行研究,测量混凝土试件纵向断面上的氯离子扩散深度,据此计算氯离子扩散系数。试验结果表明：当MWCNTs掺量为0.15wt%时,混凝土28天的氯离子扩散深度、氯离子扩散系数分别降低了25.7%、19.1%;在4种不同侵蚀龄期的自然浸泡下,掺入MWCNTs的混凝土,内部氯离子浓度始终低于对照组。结合两种方法分析得出：混凝土内部各深度的自由氯离子浓度随着MWCNTs掺量的增加而降低,致使氯离子扩散系数随着MWCNTs掺量的增加而变小,MWCNTs的掺入提高了混凝土的抗氯离子渗透性能。此外,通过SEM和压汞(MIP)测试进一步探究MWCNTs对混凝土抗氯离子渗透性能的微观增强机制,分析结果表明,MWCNTs具有一定的桥接和填充效应,这可能使混凝土裂缝扩展受到抑制、孔隙更加细化,从而改善混凝土的微观结构,提高混凝土的抗氯离子渗透性能。     

DY-2501B型氯离子测试仪计量性能检测探讨

DY-2501B氯离子测试仪可用来精确测定混凝土中氯离子的总含量,本文主要介绍了该原理,校准及测量方法,同时对该仪器进行计量性能检测实验并对结果进行分析讨论,从而提出进一步展望。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。