Centrifuge model tests on clay based engineered barriers subjected to differential settlements

The objective of this paper is to investigate the influence of thickness of the clay barrier and overburden pressure on the integrity of the clay barrier, which is provided in the cover system of low low-level radioactive waste disposal sites. A series of centrifuge tests were performed on model clay barrier subjected to continuous differential settlement at 40 g. The model clay barrier material has been selected in such a way that it envelopes the material characteristics of the clay barriers. The model clay barriers were moist-compacted on the wet side of its optimum moisture content. The performance of the clay barrier as an effective hydraulic barrier was monitored throughout the deformation process and attempts have been made to arrive at strain distribution along the top surface of clay barrier with the help of marker based digital image analysis. A 1.2 m thick clay barrier with a nominal overburden pressure of the order of 12.5 kPa was found to experience multiple cracking extending up to its full depth; whereas with overburden pressure of the order of 25 kPa, it was observed to have suppression of cracks. A catastrophic nature of water breakthrough was registered for a 0.6 m thick clay barrier with an overburden equal to that of a closure system of a low-level radioactive waste disposal site, once settlement ratio attains 0.6. This indicates that provision of thickness of clay barrier equal to 0.6 m may not be adequate.     

Usage of marble wastes in traditional artistic stoneware clay body

Recycling of industrial wastes aids environmentally friendly production and has the advantage of lowering costs. Marble production generates large amounts of waste. Recycling of such wastes by incorporating them into ceramic industry is a practical solution for pollution problem. The aim of this work is to assess the possibility of the recycling of marble wastes in the production of stoneware clay bodies as a raw material for ceramic artwork production. Five different clay body mixes containing marble waste up to 27% were prepared and evaluated for firing color, water emission, morphology, microstructure, thermal expansion coefficient and thermal behavior. The results of the tests show that the utilization of marble waste in stoneware body is feasible for ceramic artwork production.     

Evaluation of different clay minerals as additives for soil water repellency alleviation

The objective of this study was to evaluate the effectiveness of kaolinite, illite, Na- and Ca-montmorillonite in alleviating water repellency for a simple model soil material of known composition before and after wetting and drying phases. Sand was rendered water repellent by adding 10 and 30 g kg^− 1 stearic acid followed by adding different amounts (1, 2 and 3 mass %) of respective clays. Treated and untreated control sand were wetted and exposed to prolonged drying phase at 50 °C to simulate the effects of wetting followed by drying under a hot spell. The persistence of water repellency was measured with the water drop penetration time (WDPT) test. During the wetting/drying cycle, the control samples (stearic acid treated sand) and clay treated sands behaved in a fashion typically observed in water repellent soils: they were wettable above and water repellent below a critical water content, with repellency persistence (WDPT) increasing with decreasing water content. Kaolinite and Na-montmorillonite were found to be the only clay minerals able to lower the persistence of repellency of the stearic acid sand. The difference between Ca- and Na-montmorillonite ability to alleviate water repellency is explained by the differences in inter-particle forces in the clay–exchangeable cation–water system. During the prolonged drying phase at 50 °C, the persistence of water repellency increased with the duration of heating at 50 °C, with the increase being greatest during the first 48 h in the majority of the samples. While kaolinite and Na-montmorillonite addition resulted in a reduction in the persistence of water repellency of the stearic acid sand, Ca-montmorillonite and illite addition increased the persistence of water repellency of the stearic acid sand. The net effect of clay mineral addition is dependent on the amount of Ca²⁺ ions occurring at the surface of clay minerals. Pools of available (exchangeable) calcium decrease in the order as follows: Ca-montmorillonite >> illite >> Na-montmorillonite ≈ kaolinite.     

Behaviour of silicon released during alteration of nuclear waste glass in compacted clay

Long term integrated in situ experiments are performed in the HADES underground research facility (Mol, Belgium) in order to study the coupled reactivity between the different components of an underground repository for vitrified high level radioactive waste (HLW): glass, compacted clay, and stainless steel containers, at 90 °C and under gamma irradiation. Studies pertaining to the behaviour of silicon, a major element released during glass alteration, are presented here. Data collected from the integrated experiment, from simplified tests, and from modelling are put together, giving complementary information. The integrated experiment is used to investigate overall reactivity, whereas diffusion experiments coupled with modelling focused on the precipitation of silica in clay media. In the integrated in situ experiment, a bentonite clay (FoCa7) mixed with 5 wt.% of powdered glass frit was put in contact with U/Th-doped SON68 reference glass specimens for 1.2 years. One of the samples was thoroughly analysed by ESEM, SEM-EDS, TEM, XRD, and FTIR. The observations showed that after combined heating and γ irradiation, the glass/clay interface is still fully reactive. At this interface, the most important process occurring is silica precipitation either as spherical flaky nodules, or in the form of coatings on the clay surface, as chalcedony and amorphous silica. In parallel, numerical modelling was used to investigate the interactions between silica and clay material in a simplified experiment using diffusion cells. A fit between calculation results and silica migration measurements in diffusion cells was performed, including sensitivity tests with regard to the diffusion coefficients and the precipitation rate of amorphous silica. A satisfactory agreement is reached with the experimental results, using a set of reasonable fitting parameters for the FoCa7 clay material. Surface area values for silica precipitation are found to be very high, i.e. 2% of the total surface area of the clayey material indicating that silica precipitation occurs on surfaces other than those of pure silica minerals.     

The role of a coal gasification fly ash as clay additive in building ceramic

The clean coal integrated gasification in combined cycle (IGCC) technology of electrical power generation is different than conventional process in combustible treatment which generates inorganic wastes in the form of glassy slag and fly ash with singular properties. We have studied the fly ash coming from ELCOGAS IGCC power plant as additive to clays for building ceramic fabrication.

The addition of this new kind of fly ash to a clay of medium plasticity to elaborate pressed specimens, that were baked at 900 °C, improves the sintering of the paste and consequently an improvement of absorption, saturation and mechanical properties of the fired bodies, with no negative effects on shrinkage, colour alteration or efflorescence. In contrast, this fly ash does not mend the excessive firing shrinkage when added to a clay of a high plasticity index.     

Evaluation of locally available amorphous waste materials as a source for alternative alkali activators

The production of alkali-activated materials with excellent mechanical performance requires the use of water glass, which has a significant carbon footprint. Such materials can have a lower carbon footprint if we replace water glass with alternative activators sourced from waste. In this study, we assessed the suitability of locally available amorphous waste materials (stone wool, glass wool, bottle glass and cathode-ray tube glass) as a source for the preparation of alternative alkali activators. We quantified the amount of silicon and aluminium dissolved in the activator solutions via inductively coupled plasma-optical emission spectrometry. The alternative activators were then used to produce alkali-activated fly ash and slag. The compressive strength values of alkali-activated fly ash specimens upon the addition of NaOH, water glass and the most promising alternative activator were 38.98 MPa, 31.34 MPa and 40.37 MPa, respectively. The compressive strength of slag specimens activated with alternative activators with the highest concentration of dissolved silicon (21 g/L) was, however, 70% higher than the compressive strength of slag specimens activated with only 10 M sodium hydroxide. The compressive strength of slag specimens with the addition of the most promising alternative activator was significantly lower (3.5 MPa) than the compressive strength of those that had been activated by commercial water glass (34.3 MPa).     

电涡流制动器在卧螺离心机差转速定值控制中的应用

介绍了电涡流制动器的结构和特性,以及由电涡流制动器、数字转速表、ＰＩＤ调节器和程控稳压稳流电源构成的卧螺离心机差转速定值控制装置。     

Evaluation of the bond properties between concrete and reinforcement as a function of the degree of reinforcement corrosion

In order to investigate the effect of reinforcement corrosion on the bond properties between concrete and reinforcement, the pullout tests were conducted using reinforcements embedded in concrete specimens, which were corroded by an accelerated electric corrosion method. A finite element method (FEM) analysis was also carried out on the basis of the results of the pullout tests. The maximum bond strength (τ_max) and the bond rigidity (D_s) of specimens decreased in proportion to the increase of corrosion percentage (Δ_w), respectively. Also, the curves of bond stress-free end slip could be analyzed by the FEM, if the τ_max and D_s were determined as a function of corrosion percentage. The equations for calculating the maximum bond strength and the bond rigidity necessary for an FEM analysis of RC members with corroded reinforcements were obtained by the experiments and the FEM analysis of the pullout tests.     

Performance of lipid‐based moisture barriers in food products with intermediate water activity

Nine lipid‐based barrier films (three chocolates, acetomonopalmitine, white beeswax, and four commercial blends: two acetoglycerides/beeswax blends, two hydrogenated and fractionated vegetable oils) were characterised using classical water‐related and physical properties of edible barriers, such as water vapour permeability, moisture adsorption isotherm, moisture effective diffusivity, surface hydrophobicity, firmness and solid fat content (20 °C). Classifications based on these properties were established and compared to the barrier efficiency under real conditions of use, i.e. in a model food product (cereal‐based component – intermediary a_w gel). Moisture migrations were performed using self‐supported barriers (300 µm) and fitted with a predictive model based on Fick's Second Law. White beeswax and acetoglycerides enabled the best extensions of the dry‐component shelf life from 2 h to between 100 and 330 h. Moisture effective diffusivity and calculated water vapour permeability combined to a mechanical property evaluation of the barrier were more discriminating to assess the barrier efficiency in the model food than the moisture sorption and experimental water vapour permeability. The importance of combining both water‐related and physical characteristics of the barrier and the advantages of an integrated approach through the simulation of the material behaviour under its real conditions of use with the model are highlighted.     

Optimized design of multilayer barrier films incorporating a reactive layer. II. Solute dynamics in two‐layer films

Extending the model of transient permeation through the reactive barrier film presented in part I of this series to two‐layer reactive–passive barrier structures, we devote part II to the analysis of the evolution of interfacial solute concentrations between the layers. The concepts developed earlier are applied to the transient ingress analysis of two‐layer films where one of the layers contains a noncatalytic solute scavenger. In particular, we show that for reactive–passive films, the averaging approximation of the transient interfacial solute concentration provides good agreement with numerical results for the transient effective flux. The applicability range of this averaging and the error introduced by it are quantified. For the passive–reactive films, the same averaging fails to predict the effective flux dynamics. A new method of ingress analysis is presented for such structures to correct the situation. The method is based on the effective flux dynamics in the homogeneous reactive membrane and the dynamic reactive to the passive–reactive flux scaling between the initial and final solute concentration profiles corresponding to the scavenger activation and scavenger exhaustion times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1952–1965, 2006     

Evaluation of municipal compost/limestone/iron mixtures as filling material for permeable reactive barriers for in‐situ acid mine drainage treatment

The aim of the present study was to assess the potential of municipal compost as a carbon source for sulfate‐reducing bacteria for acid mine drainage bioremediation for use in permeable reactive barriers at high flow rates (>0.1 m d^?1). Two different mixtures of municipal compost, limestone and zero‐valent iron were assessed in two column experiments. The effluent solution was systematically analysed throughout the experiments. At the end of the experiments precipitates from both columns were withdrawn for scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and X‐ray diffractometry examination and solid digestion and sequential extraction were carried out. Results showed that the effluent was free of metals and acidity. It seems that metal removal was not due to biogenic sulfide generation but to pH increase, ie metal (oxy)hydroxides precipitation. These precipitates can sorb other metals onto the surface. Sorption to organic matter could also contribute to metal removal. When zero‐valent iron was present, cementation of copper also occurred. It can be concluded that municipal compost was a poor carbon source to support continuous bacterial activity under high flow rates. Copyright © 2003 Society of Chemical Industry     

Role of a clay sediment deposit on the passivity of carbon steel in 0.1 mol dm NaHCO3 solutions

The role of clays in the corrosion processes of carbon steel was investigated. Four different minerals, silica, kaolinite, chlorite and montmorillonite, were considered. They were deposited by sedimentation on carbon steel electrodes. The electrochemical behaviour of steel electrodes covered with mineral deposits was studied in 0.1 mol L⁻¹ NaHCO₃ solutions by cyclic voltammetry (4 cycles between −0.8 V/SCE and −0.1 V/SCE) and compared to that of a bare electrode. Potentiostatic experiments were performed at −0.62 V/SCE, close to the corrosion potential, and the interfacial processes were investigated by electrochemical impedance spectroscopy. Analysis of the corrosion products accumulated at the inner side of the deposited mineral layer was performed by μ-Raman spectroscopy. As it could be expected, the deposits hindered the transport of dissolved oxygen and Fe(II) species, inducing changes in the interfacial solution and modification of the composition of the rust layer. Moreover, specific interactions between minerals and dissolved Fe species also influenced the corrosion processes.     

Improved efficiency of a divalent herbicide in the presence of clay, by addition of monovalent organocations

A severe decrease in efficacy of contact herbicides such as diquat (DQ) is caused by dust accumulated on the weeds. Such inactivation was explained by the adsorption of herbicides on dust particles. As a result of this inactivation, the rates of pesticides needed for efficient pest control are usually larger than the recommended rates, which increases the expenses, and pose a real danger to the environment and to the ecological balance of watersheds. We proposed the hypothesis that the addition of a monovalent organic cation to the herbicide formulation might improve the efficacy by lowering the amount of herbicide that is inactivated by the sorption to clay minerals. This hypothesis was tested on lettuce and pepper plants dusted with clay, using the commercial formulation of diquat (“Reglone”) and adding the monovalent organic cations acriflavin (AF) and mepiquat (MQ). We observed that a clay mineral with a high cation exchange capacity (CEC), such as montmorillonite, reduced the herbicidal activity of DQ more than a lower CEC clay as sepiolite. However, addition of 5–20 mM concentrations of AF or MQ may overcome the influences of a clay dust on the activity of a cationic herbicide. Such addition allowed the obtainment of good herbicidal results with less than 1/3 of the normal used amount of herbicide. The results of our research point out to a mechanism that may lower the needed doses of contact herbicides, due to a competitive adsorption on the clay–dust particles between the pesticide and monovalent organic cations that leaves more herbicide available to act on the weed.     

Clay minerals and iron oxides-oxyhydroxides as fingerprints of firing effects in a limestone monument

Different Portuguese limestones-Encarnadão, Amarelo de Negrais, Lioz and Gresoso-have been widely used as building materials and ornamental stones in the architecture of Lisbon (Portugal) area.The aim of the study of those materials was focused on fire-induced stone damage, mainly on identifying the thermal transformations of clay minerals and iron oxides-oxyhydroxides. Taking into account an applied component to the cultural heritage, a special attention was given to one of the most ancient Portuguese monuments — Lisbon Cathedral, specifically its cloister that was severely damaged by a fire that occurred right after the 1755 earthquake.A set of samples collected from outcrops were studied and subjected to artificial heating. The results were compared with those obtained from samples collected in the monument. XRD, SEM-EDS and ⁵⁷Fe Mössbauer spectroscopy were used. The < 2 µm fraction varies significantly between unheated (outcrop samples) and artificially heated samples, particularly in relation to iron oxides-oxyhydroxides. Kaolinite is the dominant clay mineral, followed by illite and smectite. Goethite is the iron oxyhydroxide characteristic of all studied lithotypes both in unheated samples and samples artificially heated to 250 °C. Encarnadão is the exception presenting hematite in those conditions. As firing temperature increases (300 °C–600 °C) disordered hematite appears at the expense of goethite, and smectite is no longer detected. Mössbauer spectra further reveal that Fe²⁺ in silicate minerals is fully oxidized at 600 °C but remains in the carbonate structure up to this temperature. The SEM-EDS analyses show that 2:1 clay minerals have Si and Al as main cations and minor amounts of K and Fe. It also shows that all the clay minerals and Fe-rich particles are always associated to the limestone porosity.. The present results show that the clay minerals, namely illite–smectite mixed-layer and smectite, can be used as indicators of stone provenance used in Lisbon Cathedral Cloister as well as fingerprints of the temperature achieved during the fire of Lisbon Cathedral that most likely was not higher than 350 °C.     

In Vitro and in Vivo Evaluation of Lactoferrin-Conjugated Liposomes as a Novel Carrier to Improve the Brain Delivery

In this study, lactoferrin-conjugated PEGylated liposomes (PL), a potential drug carrier for brain delivery, was loaded with radioisotope complex, ^99mTc labeled N,N-bis(2-mercaptoethyl)-N′,N′-diethylethylenediamine (^99mTc-BMEDA) for in vitro and in vivo evaluations. The hydrophilicity of liposomes was enhanced by PEGylation which was not an ideal brain delivery system for crossing the blood brain barrier (BBB). With the modification of a brain-targeting ligand, lactoferrin (Lf), the PEGylated liposome (PL) might become a potential brain delivery vehicle. In order to test the hypothesis in vitro and in vivo, ^99mTc-BMEDA was loaded into the liposomes as a reporter with or without Lf-conjugation. The mouse brain endothelia cell line, bEnd.3 cells, was cultured to investigate the potential uptake of liposomes in vitro. The in vivo uptake by the mouse brain of the liposomes was detected by tissue biodistribution study. The results indicated that Lf-conjugated PEGylated liposome showed more than three times better uptake efficiency in vitro and two-fold higher of brain uptake in vivo than PEGlyated liposome. With the success of loading the potential Single Photon Emission Tomography (SPECT) imaging probe, ^99mTc-BMEDA, Lf-PL might serve as a promising brain delivery system for loading diagnostics or therapeutics of various brain disorders.     

Evaluation of the engineered polysaccharide alpha-1,3 glucan in a thermoplastic polyurethane model system

Enzymatic polymerization is under development as novel scalable process technology to convert sucrose to engineered polysaccharides. Similar to established monomer-based polymerization processes, this approach allows for the synthesis of glucose-based polymers with controlled polymer linkage, structure, and material morphology. Using enzymatic polymerization, alpha-1,3-polyglucose (glucan) can now be produced from sugar on scales required for industrial applications. This alpha-1,3 glucan material, with accessible primary and secondary hydroxyl groups within the overall defined particle morphology, is especially of interest as a partially reactive component in polyurethane chemistry. This study explores the impact of alpha-1,3-glucan as additive in a thermoplastic polyurethane model system and the improvement in mechanical properties of these composites. Glucan was effectively first mixed with a polyether polyol diol, forming a stable dispersion with narrow particle size distribution, followed by reaction with diisocyanate and chain extender to form the polyurethane matrix. The analysis of the generated polyurethane matrix indicates that the hydroxyl groups of the dispersed glucan particles directly react with isocyanate. Tetrahydrofuran solubility of the formed polyurethane compound decreased with the addition of glucan, providing evidence of covalent bonding of glucan leading to cross-linking of the polyurethane matrix. Thermal analysis of this model system suggests that the glucan additive induces hard segment crystallization, resulting in increased hardness and tensile modulus compared with the reference. Based on the observed property enhancements, engineered polysaccharides provide a sustainable performance additive for polyurethane materials.     

Lipid based therapy for ulcerative colitis-modulation of intestinal mucus membrane phospholipids as a tool to influence inflammation

Ulcerative colitis (UC) is the result of an inappropriate colonic inflammatory response triggered by environmental and genetic factors. We have recently shown that mucus from UC patients has a decreased phosphatidylcholine (PC) content, while clinical trials revealed that therapeutic addition of PC to the colonic mucus alleviated the inflammatory activity. The mechanisms behind this are still unclear. We hypothesized that PC has at least two possible functions in the intestine: First, it establishes the surface hydrophobicity of the mucus and therefore protects the underlying tissue against intraluminal aggressors; recent experiments on surgical specimens revealed reduced surface tension and hydrophobicity in UC patients. Second, mucus phospholipids might also be integrated into the plasma membranes of enterocytes and thereby influence the signaling state of the mucosa. PC has been shown to inhibit TNF-α induced pro-inflammatory responses including: (1) assembly of plasma membrane actin; (2) activation of MAP kinases ERK and p38; and (3) activation of NF-κB and synthesis of pro-inflammatory gene products. Other phospholipids like phosphatidylethanolamine or sphingomyelin had no effect. PC also inhibited latex bead phagosome actin assembly, killing of M. tuberculosis in macrophages, and sphingosine-1-phosphate induced actin assembly in macrophages. Collectively, these results provide a molecular foundation that shows PC, firstly, as an anti-inflammatory, and secondly, as a surface hydrophobicity increasing compound with promising therapeutic potential in the treatment of inflammatory bowel disease.     

Effects of waste glass as a sand replacement on the strength and durability of fly ash/GGBS based alkali activated mortar

This study incorporates fine waste glass (GS) as a replacement for natural sand (NS) in fly ash (FA) and/or ground granulated blast furnace slag (GGBS) based alkali activated mortar (AAm). Tests were conducted on the AAm to determine the mechanical properties, water absorption, apparent porosity and the durability based on its resistance to Na₂SO₄ 5% and H₂SO₄ 2% concentrated solutions. Whereas the microstructure and chemical composition of AAm was analyzed by SEM-EDX to support results obtained from the experimental tests. The study revealed that the effects of GS depends on the ratio of binders used to synthesize the mortar. For high FA/GGBS mortar, an increase in strength and reduction of porosity was observed with increasing GS up to 50 wt%. For lower FA/GGBS mortar, increasing GS up to 100 wt%, increased strength and decreased porosity. The lower porosity attained with the incorporation of GS, improved the resistance of mortar to Na₂SO₄ solution thus increasing durability. The resistance of mortar to H₂SO₄ was also improved with lower porosity due to incorporation of GS. However, the durability of mortar was negatively impacted with the further reduction of porosity observed with increasing GS and GGBS above 50 wt% believed to be caused by the stress induced as a result of expansive reaction products created when the mortar reacted with acid.     

Evaluation of the influence of adding clay in polymeric hydrogels based on partially hydrolyzed polyacrylamide and aluminum citrate

Polymeric hydrogels have been evaluated for their ability to block high-permeability regions of heterogeneous reservoirs, distributing the injected fluids to low-permeability regions, aiming to improve oil recovery. However, the stability of these hydrogels can be reduced under conditions of high temperature and salinity typical of reservoirs. Thus, the objective of this study was to assess the properties of hydrogels based on partially hydrolyzed polyacrylamide, with different molar masses, crosslinked with aluminum citrate, in the presence or absence of bentonite clay. We call these systems composite hydrogels or conventional hydrogels, respectively, and prepared them in synthetic brine containing 29,940 mg/L of total dissolved solids. The selected hydrogels were submitted to rheology tests and scanning electron microscopy for assignment of gel strength codes. The results showed it was possible to obtain composite hydrogels with enhanced thermal properties in comparison with conventional hydrogels, mainly at a temperature of 85°C. The rheological tests, by determining the viscous modulus (G"), elastic modulus (G'), and the ratio between the two (G"/G'), along with the tan δ factor, indicated competition in the interaction between the clay and crosslinker, due to the latter's positive charges in relation to the negative charges present in the polymer chains. The scanning electron microscopy micrographs showed the presence of clay particles adhered in the polymer chain, improving the thermal resistance of the system.