The role of suction and degree of saturation on the hydro-mechanical response of a dual porosity silt–bentonite mixture

To better understand the hydro-mechanical behavior of dual porosity expansive clays, three groups of tests were carried out. First, isotropic free drying and free wetting tests were performed to determine both branches of the soil water retention curve of a silt–bentonite mixture and its parameters. Next, constant suction oedometer tests at different matric suctions were employed using osmotic method. Finally, wetting–drying cycles were imposed on the samples in oedometric condition. At the end of wetting–drying tests, different suction values were enforced on the specimens and consolidation tests were performed, while the suction values were regulated through the samples using the osmotic method.Cross-examination of results indicates good consistency between the observed behaviors from different tests: Results of constant suction oedometer tests confirm the hardening phenomenon at low suctions indicated by the free drying test. Besides, all tests show that the amount of the suction hardening is negligible at suctions between the air entry of macropores and that of the micropores.However, the results contradict the physical models of hydro-mechanical behavior of expansive clays which do not take into account the suction induced hardening in the range of suctions less than the air entry value. Moreover, while most of the models assume that the shrinkage limit and air entry suction are coincident; results of the free drying test show the coincidence of the shrinkage limit and the air entry value of micropores.     

Assessment of the unsaturated water transport properties of an old concrete: Determination of the pore-interaction factor

In this study all the data needed to describe water transport (drying) within an existing concrete structure were characterized using a simple drying experiment. The properties (desorption isotherm, porosity and the unsaturated water transport properties namely, diffusivity and permeability) were evaluated by post-processing the weight loss data. Once obtained, the permeability evolution was used to check the validity of the Mualem–van Genuchten equations. It appeared that the default pore-interaction factor value proposed by Mualem (p = + 0.5) is just a rough estimate: the values obtained in this study were all negative. Comparing these values to the literature, the pore-interaction factor seems to be correlated to the van Genuchten's exponent m.     

Influence of temperature on the hydro-mechanical behaviour of a compacted bentonite

This paper reports the results on the influence of temperature (between 20 and 80 °C) on some hydro-mechanical properties of a compacted bentonite. The water retention capacity at higher temperature, both in confined and unconfined conditions, is lower, especially when suction is low. At high temperatures, the swelling capacity of clay decreases, although the influence of temperature is less evident when the applied stress is high. Furthermore, a decrease in swelling pressure as a function of temperature was observed. On the other hand, the measured increase in permeability with temperature is lower than expected on the basis of thermal change in water kinematic viscosity. The transfer induced by temperature between intra-aggregate adsorbed water and inter-aggregate free water may explain most of the features observed, taking into account that the physical characteristics (density, viscosity) of water in each one of these two states are different.     

Formulation of muds for pelotherapy: effects of “maturation” by different mineral waters

Spa centres in northern Italy use clayey admixtures for the formulation of muds to be used in pelotherapy. The basic ingredient (“virgin” clay) is a dressed bentonitic geomaterial with mineralogical composition: smectite 60–70%, illite 5–10%, kaolinite 10–15%, quartz 5–10%, calcite 5–10% and feldspars 2–3%.The peloid muds are obtained by “maturation” of the virgin clay with mineral waters gushing out in situ which have different geochemistry: sulphureous, Ca-sulphate, Ca–Mg-sulphate and Br–I-salty (after the Italian regulation DPR 105/92). The maturation treatment is varying with respect to the mixing procedure and lasting time.Peculiar parameters have been tested to verify the effects of various maturation treatments, i.e., changes with respect to virgin clay.Formation of organic matter is due to the presence of microorganisms and algae in the maturation habitat. The <2 μm fraction is generally decreased due to clay particles agglomeration. Mineralogical changes are mainly concerning the degradation of clay minerals, as smectite and illite, and subordinately to the dissolution of calcite. Cation exchange capacity (CEC), soluble salts, water retention, swelling index, activity, consistency parameters (WL, WP and PI), thermal behaviour and cooling kinetics are influenced by the geochemistry of mineral waters used for the maturation treatments but with some opposite trends for Br–I-salty water, and for sulphureous and Ca-sulphate waters, respectively.Noteworthy was the influence of high-pH value of the virgin clay on the pH of peloid muds (in fact, the pH of the used mineral waters is ranging around the natural value). Furthermore, the temperature reached by the peloid muds after 20 min of application (calculated after an innovative mathematical model) is influenced by water retention. An increase in plasticity index and a slower cooling are considered to improve the quality of the obtained peloid muds for pelotherapy.The observed different cation exchange behaviour and soluble salt content could be discriminant for either dermatological masks or thermal body cataplasms.A need of regulation (standard procedures) is suggested to certificate the clay geomaterials suitable for pelotherapy and also for drugs formulation.     

Water retention and gas relative permeability of two industrial concretes

This experimental study aims at identifying the water retention properties of two industrial concretes to be used for long term underground nuclear waste storage structures. Together with water retention, gas transfer properties are identified at varying water saturation level, i.e. relative gas permeability is assessed directly as a function of water saturation level S_w. The influence of the initial de-sorption path and of the subsequent re-saturation are analysed both in terms of water retention and gas transfer properties. Also, the influence of concrete microstructure upon water retention and relative gas permeability is assessed, using porosity measurements, analysis of the BET theory from water retention properties, and MIP. Finally, a single relative gas permeability curve is proposed for each concrete, based on Van Genuchten–Mualem's statistical model, to be used for continuous modelling approaches of concrete structures, both during drying and imbibition.     

MEASUREMENT OF THE RESIDUAL ADSORPTION CAPACITY OF CHARCOAL FILTERS UNDER CONDITIONS OF VARIABLE HUMIDITY

High surface area charcoals are used to remove noxious vapor from gas streams. Recently our laboratory has developed a simple and reliable method to determine a filter's residual adsorption capacity under dry and humid conditions. Work has been performed on ASC whetlerite saturated to various extents with an “irreversible” adsorbed adsorbate (dimethyl methylphosphonate). Data are presented which illustrate how the retention time of a 1 ml(NTP) pulse of methane can be used to quantify the fraction of unoccupied adsorption sites for a strong adsorbent when a filter is saturated with water or dry. In addition, data are presented which suggest that with some charcoals the retention time of methane can be used to determine a filter's residual absorption capacity regardless of its previous water loading history.     

On equations for the total suction and its matric and osmotic components

A clear fundamental understanding of suctions is crucial for the study of the behaviour of plastic cement mortar and concrete, including plastic shrinkage cracking. In this paper, the expression relating the change in free energy of the pore water with an isothermal change in pressure is first derived. Based upon definitions of suctions, it is then shown that total, matric, and osmotic suctions can all be expressed in the same thermodynamic form. The widely accepted, but not yet satisfactorily validated, assumption that the total suction comprises matric and osmotic components is then confirmed theoretically. The well-known Kelvin equation for matric suction, and Morse and van't Hoff equations for osmotic suction are subsequently derived from the corresponding thermodynamic equations. The applicability of latter two equations in evaluating the osmotic suctions of cement mortar and concrete is highlighted.     

Dependence of the properties of chamotte on the firing regime of the briquette

Conclusions The physicomechanical properties and phase composition of chamotte depends on the composition of the gas medium, the firing temperature, and the cooling regime. In the briquettes fired at 1500°C in an oxidizing medium with the cooling temperature lowered from 1500 to 1200°C, the apparent density increases and the porosity decreases. In the briquettes fired in a reducing medium with the cooling temperature lowered from 1500 to 1300°C, there is a reduction in the apparent density and an increase in the porosity but with a further reduction of the cooling temperature to 1200°C, these properties change in the opposite direction.The apparent density of chamotte and its concentration of mullite is increased with a reduction in the cooling rate. The apparent density of the chamotte from the Polozhsk kaolin under analogous cooling conditions increases more rapidly than that from the Novoselitsk kaolin chamotte.The temperature interval in which the cooling rate effectively increases the apparent density of the chamotte fired in an oxidizing medium is 1500–1300°C. In a reducing medium this interval is shifted 100°C toward lower temperatures.The experiments have shown that an increase in the cooling rate of the fired briquettes at temperatures below 1200°C has only a very slight effect on the apparent density and porosity of the Novoselitsk kaolin chamotte. When the chamotte has been obtained from Polozhsk kaolin, a reduction in the cooling rate at temperatures below 1200°C, and particularly in a reducing medium, has a quite perceptible effect on the increase in apparent density and reduction of porosity of the material.Translated from Ogneupory, No. 3, pp. 22–26, March, 1982.     

Characterization of wheat-rice-stone developed from porphyritic hornblende andesite

Porphyritic hornblende andesite showing wheat-grain stone is known as a “wheat-rice-stone” (WRS) or “mei-fun-shi” (MFS), and has many applications in industry. However, its compositions have not yet been fully investigated. Samples of the porphyritic hornblende andesite from the Tuluanshan Formation (Pleistocene) on the eastern coast range of Taiwan, the Mainland China, and commercial products from Japan were collected in order to characterize their physical and chemical properties, and mineralogical compositions. The major component in the WRS has been identified by X-ray diffraction (XRD) as a smectite. Cation-exchange capacity (CEC) and exchangeable cations of the WRS were related to its water-softening ability. Infrared and elemental analyses indicated that this smectite contained large amounts of water and has a low concentration of nitrogen. Scanning electron micrographs of the porphyritic hornblende andesite displayed a honeycombed polygonal pattern, which has replaced the original bubbled-wall shards. It is because of its water retention capacity rather than its mineral composition that the WRS was used as a fertilizer. The WRS is capable to sorb heavy metals.     

实验参数对固废基发泡混凝土试块性能的影响研究

以超细粉煤灰和钢渣超微粉为主要原料,配加少量水泥和铝粉发泡剂制备发泡混凝土试块.实验系统考察了不同水灰比、发泡剂掺量、发泡温度对发泡混凝土试块的绝干密度、抗压强度、吸水率和孔隙率的影响.结果表明,铝粉发泡剂掺量从1‰增加到7‰,所得试块的绝干密度和抗压强度分别降低36％和84％;而对应的吸水率和孔隙率增加幅度分别高达79％和30％.水灰比从0.65增加到0.95,所得试块的绝干密度和抗压强度分别降低26％和82％;而对应的吸水率和孔隙率均出现"先增后减"趋势,其中吸水率增加幅度为34％,降低幅度为24％;孔隙率增加幅度为18％,降低幅度为9％.发泡温度从25 ℃增加到90 ℃时,试块的绝干密度和抗压强度整体上呈"先降后升"趋势,绝干密度降幅约为30％,升幅约为60％;抗压强度降幅为50％,升幅高达140％.优化后的实验条件为:铝粉掺量1‰～3‰、水灰比65％～75％、发泡温度40 ℃左右.试块抗压强度与绝干密度随制备条件变化幅度不一致,这说明有可能通过制备工艺优化获得"高强度、低密度"的发泡混凝土产品.     

A study of the sintering of diatomaceous earth to produce porous ceramic monoliths with bimodal porosity and high strength

Diatomite powder, a naturally occurring porous raw material, was used to fabricate ceramic materials with bimodal porosity and high strength. The effect of the sintering temperature on the density and porosity of dry pressed diatomite green bodies was evaluated using mercury porosimetry and water immersion measurements. It was found that the intrinsic porosity of the diatomite particles with a pore size around 0.2 µm was lost at sintering temperatures above 1200 °C. Maintaining the sintering temperature at around 1000 °C resulted in highly porous materials that also displayed a high compressive strength. Microstructural studies by scanning electron microscopy and energy-dispersive X-ray analysis suggested that the pore collapse was facilitated by the presence of low melting impurities like Na₂O and K₂O.     

Effect of feed concentration and inlet air temperature on the properties of soymilk powder obtained by spray drying

In this study, soymilk powder was produced by spray drying. The inlet air temperature of spray dryer was varied from 200 to 280°C and the feed concentration was varied from 15 to 25% (w/v). Response surface methodology was used to examine the effects of these independent variables on the detailed characteristics in terms of physical, structural, functional properties of powder. Overall, results show that rising the inlet air temperature caused a decrease in tapped and loose bulk density, true density, filling rate, water holding capacity, and water content of powder; and an increase in compressibility, Hausner ratio, porosity, interstitial air volume, and wettability index. An increase in feed concentration led to an increase in true density, compressibility, Hausner ratio, porosity, interstitial air volume, and wettability index; and a decrease in tapped and loose bulk density, filling rate, water holding capacity, and water content; whereas oil holding capacity might be increased or decreased and it depended almost solely on the feed concentration.     

球形木素基正离子交换树脂的制备与性能

以木素磺酸钙为原料,在一种价廉无毒的分散介质中通过反相悬浮聚合制备了球形木素基正离子交换树脂。研究了分散介质和分散剂用量、聚合温度及搅拌速度等多种因素对聚合反应和成球效果的影响,并对交换树脂的形貌、粒径、含水量、密度、交换容量及吸附性能进行表征与测;定。结果表明,在实验室条件下,交换树脂对;Cr^3＋的饱和吸附量达到59．28mg／g（干树脂）。     

Pore structure of plain cement pastes hydrated at different temperatures

Concrete outside the laboratory cures at temperatures other than 20°C. This paper describes an investigation of the pore structure of plain cement pastes hydrated at 5°, 20°, and 50°C to reflect a range of temperatures encountered in practice. Parallel specimens of 0.50 water/cement ratio pastes were examined using mercury intrusion porosimetry and backscattered electron image analysis. Increases in curing temperature resulted in increased porosity, particularly for pores of radius 200–1000 as measured by mercury intrusion, or 2500–12,500 as measured in the backscattered electron images. The difference between the two results indicates the magnitude of the “ink bottle effect” inherent in the mercury intrusion technique. However, both methods suggest that elevated curing temperatures could have a deleterious effect on the durability of plain cement concretes.     

Pilot plant studies on the removal of trihalomethanes by composite reverse osmosis membranes

The effect of single trihalomethane (THM) (CHCl₃) content in various types of water on the performance of two types of reverse osmosis composite membranes (the AFC99 membrane in tubular module B1, PCI, and the FT30 membrane in a spiral-wound element BW3040, FilmTec) have been investigated. The performance of these membranes in RO tests carried out using distilled water, tap water and brackish water (1000–5000 ppm NaCl) with the addition of THM have been evaluated in terms of permeate flux and the rejection of dissolved solids and THM. The FT30 membrane provided THM rejection better than 99.5% during the reverse osmosis treatment of tap water and brackish water. The AFC99 membrane exhibited only 80% retention of THM, obtained for the transmembrane pressures in the range of 10 to 30 bars. It was found that the presence of CHCl₃ slightly affects the transport and separation properties of the composite membranes used.     

Water and synthetic urine sorption capacity of cellulose‐based hydrogels under a compressive stress field

A new apparatus was developed and used to investigate the swelling behavior of crosslinked hydrophilic polymers under an applied load as a function of the absorbed weight in both water and water solutions. A model able to predict the material water uptake as a function of the isotropic compressive stress was also studied. Centrifugation tests were performed to measure the material retention capacity under load, in both water and synthetic urine. The polymers studied in the tests were from a particular class of superabsorbent hydrogels based on cellulose derivatives chemically crosslinked with divinyl sulfone. The hydrogels showed high sorption and retention capacity in both water and water solutions, both in the free state and under load, and significant variations were observed during the modulation of the dry sample porosity.© 2004 Wiley Periodicals, Inc.J Appl Polym Sci 91: 3791–3796, 2004     

Effect of process parameters on the energy requirement in ultrasonical treatment of waste sludge

Mechanical treatment methods are used as pre-treatment methods in order to enhance the efficiency of conventional sludge treatment processes and the sludge becomes more suitable for its complete treatment. The ultrasound is an alternative method among other methods, but because of its high energy requirement it should be optimized before utilization. This work gives the optimized parameters such as sonication time, sonication power (these parameters are the two factors which play part for energy calculations), type of sludge, cooling requirements and solid content in the sludge solution. Even if the previous researchers prefer to use the energy (specific energy usually), we have found out that both the sonication time and the sonication power have individual importance. For municipal sludge the main conclusion can be summarized as: “high power-short retention time” is more effective than “low power-long retention time”. As this phenomenon may alter from sludge to sludge, various combinations of power and retention time should be tried while keeping the volume small and the concentration below a certain level. The process should be performed at moderate temperatures and the efficiency increases if the sludge is as homogeneous as possible.     

Thermal conductivity of corundum,high-alumina,magnesia, zirconium,and chromate refractories in the 400–1800°c range

Conclusions The temperature relationship of the thermal conductivity of corundum, mullite-corundum, magnesia, zirconium, and chromate refractory parts in the range of average temperatures of 400–1800°C was determined. Data is presented on their porosity, density, and chemical composition.Translated from Ogneupory, No. 5, pp. 16–20, May, 1982.     

Diffusion coefficients and accessible porosity for HTO and Cl in compacted FEBEX bentonite

The transport properties of a Spanish bentonite (FEBEX bentonite) were studied. The behaviour of the conservative anionic species ³⁶Cl⁻ is compared with HTO (neutral and conservative tracer, tritiated water). Apparent and effective diffusion coefficients, as well as the accessible porosity, were determined in a wide range of clay dry densities. Effective diffusion coefficients for HTO and ³⁶Cl⁻ were measured in through-diffusion experiments. Apparent diffusion coefficients were measured for HTO with in-diffusion (ID) experiments.A very important parameter for describing the transport of radionuclides is the accessible porosity, which is often difficult to determine, especially at high clay densities, for the anions. Therefore, it is very important to use different methods to compare the results obtained in order to understand the limitations of each technique and finally provide reliable results. Furthermore, the use of different techniques and the independent determination of each transport parameter can be used to validate the results.Apparent and effective diffusion coefficients for both HTO and Cl⁻ showed an exponential decrease when the dry density increased, with the decrease being more pronounced in the case of Cl⁻. The accessible porosity for HTO is equal to the total porosity. The accessible porosity for chloride is only a small fraction of total porosity (2–3% at a dry density of 1.65 g/cm³, when the total porosity is about 40%).