Influence of electroosmotic treatment on the hydro-mechanical behaviour of clayey silts: preliminary experimental results

Preliminary results of an investigation focused on the influence of electrokinetic treatment on the mechanical and hydraulic behaviour of clayey soils are presented. The experimental programme aims at providing a contribution to the sustainability of contaminant extraction or containment via electroosmosis. Changes in the hydraulic and mechanical properties of two illitic clayey soils, subjected to a DC electric field, were investigated. Samples of the two soils were subjected to electrokinetic filtration, for different periods of time, and under different constant loads. Afterwards, they were tested under one-dimensional compression to detect changes in stiffness and hydraulic conductivity due to the electrical treatment. After the application of a DC field for a few hours, a small reversible increment in the average soil stiffness was observed, with respect to the untreated soil, while the hydraulic conductivity was not affected substantially. Dramatic changes of the mechanical and hydraulic soil properties, correlated to changes of the soil pH, were observed following non-conditioned electrokinetic treatment with duration of the order of days.     

Influence of silica fume on the desiccation cracks of compacted clayey soils

Clayey soils containing smectites are widely used for construction of liner and cover systems to reduce the hydraulic conductivity in geotechnical applications because of their low permeability and high cation exchange capacity. However, the compacted clayey soils crack on drying because of their high swelling potential, and their hydraulic conductivities increase. To solve this problem, it is essential to stabilize the clayey soils using additive materials. The aim of this study is to examine the suitability of silica fume as a stabilization material to reduce the development of desiccation cracks in compacted clayey liner and cover systems. Natural clayey soil and clayey soil–silica fume mixtures were compacted at the optimum moisture content and subjected to laboratory tests. The results show that silica fume decreases the development of desiccation cracks on the surface of compacted samples. We concluded that silica fume waste material can be successfully used to reduce the development of desiccation cracks in compacted clayey liner and cover systems.     

Indenter studies of the swelling, creep and pressure solution of Bure argillite

Experimental deformation of Bure argillites was performed by indenter techniques in order to investigate the kinetics of pressure solution processes. Various parameters included in pressure solution laws were tested: solubility of the mineral in solution (calcite), diameter of the indenter, temperature and stress. None of the observed effects confirm the contribution of pressure solution. In long duration experiments, a stabilized linear relation was found between displacement rate and stress, at least after 2 months. However, wide scattering of the data was observed, associated with unstable microfracturing around the indenter that may be linked to the swelling that always occurs before the indenting and that weakens the strength of the rocks (especially when using water). Argillite deformation is likely to be linked to the deformation of clay minerals acting as potential weak zones. The study does not exclude the possibility that pressure solution mechanisms may be of some importance for the long-term behavior of the natural barrier. This work just underlines the difficulty of studying this mechanism in weak rocks where several mechanism of deformation may competes and the faster strain rate hide the slower one at human time scale, whereas the slower one may be predominant on long-term duration.     

Creep behavior identification of an environmental barrier coating using full-field measurements

For the use of thermal and environmental barrier coating (T/EBC) with ceramic matrix composites, it is crucial to master the behavior under (extreme) environments representative of the hot section of engine turbines. An experimental setup to simulate such thermal loading has been developed with various diagnostics enabling for kinematic and thermal field measurements, which are used to drive a finite element model and estimate thermomechanical properties such as creep parameters of the coating.     

紫外光对PP蠕变行为的影响

通过对聚丙烯(PP)施加紫外光的方法研究了紫外光对其蠕变行为的影响,利用蠕变性能测试、GPC、XPS、PALS、SEM等手段考察了紫外光作用下的PP蠕变行为及其失效机理。实验结果表明:紫外光能加速PP的蠕变失效,其失效机理与辐照强度有关;短时间失效主要是由紫外光引起的分子链段的活性变化所致,长时间作用下的失效,主要是紫外光引起的老化导致材料强度的削弱所致;另外,对不同种类的PP,在相同的外部条件(下温度、应力和紫外光,)其失效速率与结构和分子量无关,只与该温度下材料的屈服强度有关,屈服强度越高抗,蠕变能力越好。     

A new method for remedial treatment of contaminated clayey soils by electrokinetics coupled with permeable reactive barriers

This paper presents the results of preliminary investigations into the potential application of a remediation system that couples the electrokinetic (EK) remediation with the permeable reactive barrier (PRB) concept. Atomizing slag was adopted as a PRB reactive material for freshing groundwater contaminated with either inorganic or organic substances. Laboratory experiments were performed with variable conditions including (i) type of pollutant, (ii) processing time, and (iii) the application of PRB system during the EK processing. From the results of the preliminary investigations, the coupled technology of EK with PRB system could effectively remediate contaminated groundwater in situ without extracting pollutants from subsurface through the effectiveness of the reactions between the reactive materials and contaminants.     

热塑性高分子薄膜蠕变模型的研究

在研究热塑性高聚物变压力拉伸蠕变过程的基础上,应用Boltzmann原理对Maxwell Voigt粘弹性模型进行了改进,建立新的蠕变模型及数据处理软件。实验证明此模型可以较好地应用于PVC薄膜拉伸蠕变试验研究中     

Experiment and Simulation Study on the Creep Behavior of PMMA at Different Temperatures

In the present study, creep experiments at different stress and different temperatures were carried out to study the creep behavior of PMMA (MDYB-3). The results show that the creep behavior of PMMA is significantly dependent on temperature in the temperature range of 20–75°C. It was indicated that the duration curves of creep could be divided into three phases. The Chen theory, Norton formula and exponential expression can be used to describe three phases of creep behaviors, respectively. Furthermore, the creep constitutive model based on the experiment results was introduced and implemented into a user subroutine UMAT of software ABAQUS. The finite element analysis (FEA) results prove that the constitutive model introduced in the paper can successfully simulate the creep behavior of structure made of PMMA.     

Creep and physical aging behaviour of PA6 nanocomposites

The creep and physical aging behavior of various types of PA6 nanocomposites and unfilled PA6 are described. After annealing far above T_g the samples were quenched to room temperature and tested after various ageing times. The creep compliance shows a significant reduction with the addition of exfoliated layered silicate to the matrix polymer. The shape of the creep curves of the nanocomposites is similar to unfilled PA6 and time—ageing time superposition is possible with all materials. The shift rate for superposition is in the same range, but slightly higher in nanocomposites. The creep behavior of nanocomposites conditioned with an equilibrium amount of moisture and dry samples at elevated temperatures shows that the effect of nanofillers is much stronger under these conditions.     

Creep and recovery behaviors of a polythiophene-based electrorheological fluid

We investigate the creep response of poly(3-thiopheneacetic acid) (PTAA) particles doped with perchloric acid. With increase in applied stress, these suspensions exhibit an evolution from a linear viscoelastic response, with three components of instantaneous elastic strain, retarded elastic strain and viscous strain, to a nonlinear viscoelastic response, where the retarded elastic and viscous strains monotonically decrease and a plastic contribution to the instantaneous strain grows, followed by a viscoplastic solid behavior, with fully plastic instantaneous strain, and finally a transition from plastic solid to a plastic liquid at the yield stress. With increase in electric field strength at fixed particle concentration and applied stress, the viscoplastic response diminishes, and more elastic behavior ensues. For highly doped samples, at high-electric field strengths, a fully elastic solid response is observed in the linear viscoelastic regime. The equilibrium compliance, J_C and steady state recoverable compliance J_R, were investigated as a function of electric field strength, particle concentration and particle conductivity. The results are interpreted in terms of the field-induced formation of thick fibrillar aggregates spanning the gap between the electrodes, each consisting of bundles of particle strings. Strings, which are fully connected to both electrodes generate an elastic response to the applied stress, whereas strings which are attached at only one end or are unattached generate a viscoplastic response. The net effect of an increase of the electric field strength, particle concentration, or particle conductivity is an increase in elasticity, i.e. predominantly creation of fully connected particle strings.     

Comparative ion-exchange characterization of zeolitic and clayey materials for pedotechnical applications—Part 1: interaction with noxious cations

With the purpose to set up a convenient strategy to rehabilitate degraded soils by recovering their functionality, the possibility of using zeolitized tuff as inorganic ion-exchanger components of organo-mineral aggregates, in place of the naturally occurring clay materials was estimated. Accordingly, after the evaluation of a suitable method for measuring the cation exchange capacity of both materials (a phillipsite-rich tuff from the surroundings of Naples, Italy, and a bentonite, from Wyoming, USA), exchange kinetics and isotherms of Cu²⁺, Pb²⁺ and Zn²⁺ for Ca²⁺ at 25°C and 0.1 total normality, were determined and the related kinetic and thermodynamic quantities computed. Comparative results demonstrate that phillipsite-rich tuffs exhibit higher cation exchange capability and selectivity performances towards noxious cations than the montmorillonite clay does, and therefore that they can be considered good substitutes of clay materials to recover and/or rebuild polluted and degraded soils.     

Development of clayey ceramic membranes prepared with bio-based additives: Application in water and textile wastewater treatment

Eco-friendly ceramic membranes have been developed from clayey materials mixed with biobased additives (woodworking waste and rice husk) as pore-forming agents. Heated blends of two clayey occurring materials with the biobased additives (up to 20 wt%) were investigated using X-Ray Fluorescence spectrometry (XRF), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TDA-TG), Mercury Porosimetry, Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM-EDS) and Filtration tests. The effect of adding the pore-forming agent on the physical and mechanical properties (apparent density, apparent porosity, average pore diameter and compressive Strength) was assessed and the results were interrelated to the microstructural changes. The mineralogical analyzes showed that original minerals together with thermal decomposition products were involved in the neoformation process. SEM observations displayed the appearance of several pores with various shapes, sizes and features corresponding to the neoformed phases (gehlenite and albite) and localized heterogeneous aspects. The experimental filtration tests have clearly shown the elimination of turbidity and suspended matter with the reduction of the chemical/biological oxygen demand and the dye concentration. Thereby, it was confirmed that ceramic membranes intended for filtration with homogenous morphological aspect, good physical properties and high mechanical strength could be manufactured and used in industrial wastewater treatments.     

木塑复合材料蠕变性能的研究进展

简要介绍了材料的蠕变特性以及木塑复合材料蠕变性能较差的原因,并从影响木塑复合材料蠕变性能的温度、应力及加载方式、湿度等因素以及抗蠕变性研究两方面对木塑复合材料蠕变性能的研究进展进行了综述,展望了今后木塑复合材料蠕变性能研究的重点及方向.     

超高分子量聚乙烯纤维蠕变性能改性研究

通过紫外线照射对超高分子量聚乙烯(UHMWPE)纤维进行交联改性。运用密度梯度法、声速取向测试及广角X射线衍射(WAXD)等手段测试分析了蠕变过程中纤维结晶度的变化和相变情况,并通过计算机编程对蠕变数学模型进行拟合,该方法可以快速、精确地拟合出材料的相关性能参数。拟合结果表明紫外照射处理的UHMWPE纤维普弹模量E_1略有降低,而高弹模量E_2、推迟时间τ和本体粘度η_3有一定的提高。说明紫外照射交联能改善纤维蠕变性能。     

Mineralogical characterization of iron-rich clayey soils from the middle plateau in the southern region of Brazil

We report mineralogical studies of clayey soils collected in various sites of the middle plateau in Rio Grande do Sul in the southern region of Brazil. The analysis of the XRD patterns indicated quartz, rutile, goethite, hematite and kaolinite in the samples. Mössbauer spectroscopy has been used to study the Fe-bearing species. The Mössbauer spectra of all the samples at room temperature consist of a large paramagnetic doublet, in some cases superimposed on a small sextet, whereas at 77 K a prominent sextet appears, which is associated with goethite and/or a hematite substituted structure. The results indicate that the studied soils have iron oxides with high contents of aluminum.     

特征值法在软岩巷道围岩变形形态分类中的应用

通过对变形曲线的分析，提出了研究围岩变形规律的特征值法，根据大量实测曲线中几类特征值离散性小的特点，介绍了该法在围岩变形形态分类中的应用。     

烟气管道的高温蠕变应力分析

石油化工厂的部分高温烟气管道长期在650~700℃左右运行,研究表明,碳钢部件工作温度高于350℃、合金钢部件工作温度超过420℃、不锈钢部件工作超过480℃时,进入蠕变温度。通过对某石化厂原有高温烟气出口管道运行工况分析,运用CAESARII应力分析软件优化管道布置,并通过计算管道蠕变条件下服役年限进行安全评定。     

深部开采岩体变形分析的双曲函数法

在软岩地层深部厚矿体开采条件下,给出了用于预测分析地下开采岩体移动变形的双曲正切函数模型,采用该模型对国内某地下矿山深部开采岩体移动变形进行了具体的计算分析,并与概率积分法理论分析结果和实测数据进行了对比,结果令人满意.分析结果表明,本文所提出的理论方法适用于预测分析深部矿体开采引起的岩体移动变形问题.     

尼龙1212熔体蠕变与回复行为的研究

通过对石油发酵尼龙1212(PFPA1212)熔体进行蠕变及回复试验,研究了温度对蠕变应变、蠕变柔量、蠕变粘度的影响,并对PA1212熔体的蠕变及回复行为特征机理进行了探讨。结果发现：PFPA1212熔体蠕变行为对温度有很强的依赖性,随温度的升高,蠕变柔量不断增加;蠕变粘度在较低温度下随时间增加较快,而在较高温度区随时间增加较缓。     

PPS/SiO_2复合材料蠕变行为的研究

研究了PPS/SiO2复合材料的蠕变行为,讨论了SiO2含量对复合材料普弹形变、高弹形变和黏流形变的影响。通过数值拟合的方法,得到了PPS/SiO2复合材料的松弛时间,通过松弛时间分析了共混体系中SiO2含量对PPS分子链段运动和大分子间滑移的综合影响。