Article

The influence of smectite content on microstructure and geotechnical properties of calcium and sodium bentonites

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Abstract

Ca-bentonite with 68% and 92% of smectite, and Na-bentonite with 68% and 92% of smectite were studied by XRD, chemical analysis and scanning electron microscopy (SEM) to evaluate differences in microstructure formation and geotechnical properties. Plasticity and liquid limit, water adsorption by Enslin test, free swell test and standard swell test were performed, as well as the determination of ignition loss and permeability test.The differences in bentonite quality and quantity of smectite critically influence permeability, which is confirmed by the decrease in permeability in the direction Ca (68%)→Ca (92%)→Na (68%)→Na (92%). Ca-bentonite with 92% smectite content showed similar permeability as the 68% Na-bentonite, but it retained lower water sorption characteristics. Na-bentonite is used as a sealing component in geosynthetic clay liners (GCL) and may undergo an ion exchange by calcium ions, converting it to Ca-bentonite because the calcium content of most soils is sufficient to induce such a process. All significant Na-bentonite properties are being changed when converted back to Ca form. Our study has made an attempt to uncover differences in various bentonite-type behaviors and suggests one way to improve sealing properties of Ca-bentonite with lower smectite content upgrading it by flotation to smectite-rich Ca equivalent instead of natrification.

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... During the electro-osmotic stabilization process, complex chemical reactions occurred near the anode and cathode, including electrolysis of pore water, electrode corrosion, ion exchange and transport, and cementation (Acar and Alshawabkeh, 1993;Chien et al., 2009). Therefore, the microfabric and chemical compositions changed and induced the change of soil properties (Zimmie and Almaleh, 1976;Du et al., 1999;Santamarina et al., 2001;Dananaj et al., 2005;Mitchell and Soga, 2005;Al-Hamdan and Reddy, 2008;Yong et al., 2009;Karakaya et al., 2011;Zhang et al., 2012;Du et al., 2014). Dananaj et al. (2005) studied the influence of sodium and calcium contents on the coefficient of permeability and swelling parameters of bentonite. ...
... Therefore, the microfabric and chemical compositions changed and induced the change of soil properties (Zimmie and Almaleh, 1976;Du et al., 1999;Santamarina et al., 2001;Dananaj et al., 2005;Mitchell and Soga, 2005;Al-Hamdan and Reddy, 2008;Yong et al., 2009;Karakaya et al., 2011;Zhang et al., 2012;Du et al., 2014). Dananaj et al. (2005) studied the influence of sodium and calcium contents on the coefficient of permeability and swelling parameters of bentonite. Du et al. (2014) reported the microfabric characteristics of cement-stabilized zinccontaminated kaolin, which showed that the change of soil microfabric and zinc concentration had significant influence on soil properties including Atterberg limits and stress-strain characteristics. ...
... The theory about electrical double layer illustrated that the species and concentration of ions adsorbed in the double layer had significant influence on the thickness of the double layer and the potential distribution in it (Van Olphen, 1977; Shang et al., 1993). The previous studies also confirmed the influence of microfabric and chemical compositions on the soil properties (Dananaj et al., 2005;Mitchell and Soga, 2005;Al-Hamdan and Reddy, 2008;Du et al., 2014). The polar water molecules can easily enter the space between the lattices and cause the clay minerals to expand since the repulsion force between the soil lattices is relatively high in the presence of sodium ions (Mitchell and Soga, 2005). ...
... During the electro-osmotic stabilization process, complex chemical reactions occurred near the anode and cathode, including electrolysis of pore water, electrode corrosion, ion exchange and transport, and cementation (Acar and Alshawabkeh, 1993;Chien et al., 2009). Therefore, the microfabric and chemical compositions changed and induced the change of soil properties (Zimmie and Almaleh, 1976;Du et al., 1999;Santamarina et al., 2001;Dananaj et al., 2005;Mitchell and Soga, 2005;Al-Hamdan and Reddy, 2008;Yong et al., 2009;Karakaya et al., 2011;Zhang et al., 2012;Du et al., 2014). Dananaj et al. (2005) studied the influence of sodium and calcium contents on the coefficient of permeability and swelling parameters of bentonite. ...
... Therefore, the microfabric and chemical compositions changed and induced the change of soil properties (Zimmie and Almaleh, 1976;Du et al., 1999;Santamarina et al., 2001;Dananaj et al., 2005;Mitchell and Soga, 2005;Al-Hamdan and Reddy, 2008;Yong et al., 2009;Karakaya et al., 2011;Zhang et al., 2012;Du et al., 2014). Dananaj et al. (2005) studied the influence of sodium and calcium contents on the coefficient of permeability and swelling parameters of bentonite. Du et al. (2014) reported the microfabric characteristics of cement-stabilized zinccontaminated kaolin, which showed that the change of soil microfabric and zinc concentration had significant influence on soil properties including Atterberg limits and stress-strain characteristics. ...
... The theory about electrical double layer illustrated that the species and concentration of ions adsorbed in the double layer had significant influence on the thickness of the double layer and the potential distribution in it (Van Olphen, 1977; Shang et al., 1993). The previous studies also confirmed the influence of microfabric and chemical compositions on the soil properties (Dananaj et al., 2005;Mitchell and Soga, 2005;Al-Hamdan and Reddy, 2008;Du et al., 2014). The polar water molecules can easily enter the space between the lattices and cause the clay minerals to expand since the repulsion force between the soil lattices is relatively high in the presence of sodium ions (Mitchell and Soga, 2005). ...
Article
Electro-osmotic stabilization has long been studied as a soft soil improvement technique, while the influence of an applied electrical field on the soil microfabric and minerals is always ignored. In this study, three laboratory experiments were conducted on sodium bentonite using copper, iron and graphite electrodes to investigate the microfabric and chemical composition change before and after electro-osmotic stabilization. The soil samples near the anode were identified using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The microfabric of the sodium bentonite changed from flocculated fabric to aggregated fabric after electro-osmotic stabilization. Regular calcium sulfate tubes were generated near the copper and iron anodes. EDX tests showed that the content of sodium near the anode decreased, while the copper, iron and calcium presented substantial increase, indicating that the sodium ions were substituted by copper, iron, and calcium ions in copper, iron and graphite experiments respectively. The change of microfabric and the ion exchange reactions between sodium, copper, iron and calcium ions are the main reasons for the significant decrease of the plasticity index and free swelling ratio.
... An important area of progress is the coupling between chemical, structural and hydraulic mechanisms. A significant body of research has documented the structural changes undergone by bentonite following ion exchange, whereby sodium initially present in the clay is replaced by divalent cations (in particular Ca 2+ ) present in solutions in contact with the clay (see for example Pusch, 1999;Guyonnet et al., 2005;Dananaj et al., 2005). These structural changes may lead to permeability increases. ...
... Meanwhile, the d 060 peak at 1.50 Å, which is typical of dioctahedral smectites, 14,23 reached a maximum in the 0.4-AAB pattern. The intensity of the d 004 and d 005 peaks of montmorillonite, which were seen as combined features with those of tridymite (T) at 3.80 and 2.99 Å, 24,25 paralleled the weakening of the d 001 peak. The simultaneous decrease of the diffraction apexes of the d 060 and other peaks indicates that no long-range crystallinity was retained at acid/clay ratios above 0.4. ...
Article
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... However, the S-I assemblage shows smectite with moderate to low crystallinity (with V/P of 0.5 on average). Considering smectite composition suggested by some authors (Grim and Güven 1978;Dananaj et al. 2005), X-ray spectra show that 001 reflections of smectite vary between 12.3 to 12.8 Å on air-dried samples (Fig. 10), suggesting Na or Mg interlayer occupancy rather than Ca. An exception is at locality 4, where the lower section shows calcium smectite (001 reflections , 14.4 to 15.1 Å ). ...
... However, the S-I assemblage shows smectite with moderate to low crystallinity (with V/P of 0.5 on average). Considering smectite composition suggested by some authors (Grim and Güven 1978;Dananaj et al. 2005), X-ray spectra show that 001 reflections of smectite vary between 12.3 to 12.8 Å on air-dried samples (Fig. 10), suggesting Na or Mg interlayer occupancy rather than Ca. An exception is at locality 4, where the lower section shows calcium smectite (001 reflections , 14.4 to 15.1 Å ). ...
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The Mata Amarilla Formation marks the onset of the foreland stage of the Austral basin, which is composed of mostly nonmarine and littoral siliciclastic sediments, thus providing an opportunity to study the detrital record of the Late Cretaceous southern foreland Andes. Our dataset provides, for the first time, a comprehensive picture of the Late Cretaceous evolution of the Austral foreland basin, constituting a possible analogue to other foreland basins at the foot of the Andes. Sandstones from the Mata Amarilla Formation testify to variable contributions from Jurassic bimodal volcanic rocks of the Deseado Massif and the Patagonian fold-and-thrust belt, in the context of an eastward-advancing orogen. Sandstone petrography shows an overall feldspathic litharenite composition, whereas sandstones coming from the northeast (Deseado Massif) have higher Lv and lower Qp proportions than samples coming from the west (Patagonian fold-and-thrust belt). In the central part of the study area, sandstones are characterized by higher proportions of Qt associated with a greater distance and time of transport relating to its position in the Austral foreland basin. In spite of the increased maturity of sandstone in the central area, X-ray analyses permit recognition of the compositional signature of Mata Amarilla Formation, in which four clay-mineral assemblages were identified: S (rich in smectite), S-K (rich in smectite and kaolinite), Pg (rich in palygorskite), and IS (rich in illite smectite mixed layers). S-assemblage evidences well-crystallized smectite, characteristic of volcaniclastic origin. Most smectite was formed during early diagenesis through alteration of labile tuffaceous material derived from the Southern Andes. The stratigraphic variations in clay-mineral assemblages reveal a strong environmental control on their distribution. The transformation of smectite into illite and kaolinite is considered as product of pedogenesis, whereas the presence of palygorskite indicates a coastal environment with paleosol development under poorly drained conditions.
... XRD is applied to distinguish Ca-Bent from Na-Bent. Literatures [7,9,10] reveal that the montmorillonite has the strongest intensities and bright peaks on (001) crystal face. Moreover, d(001) of Ca-Bent is about 1.55 nm, and 2θ(001) is 5.66 • ; relatively, d(001) of Na-Bent is 1.25 nm, and 2θ(001) is 7.1 • . ...
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Hunyuan Ca-based bentonite is one of large-type bentonite deposits in China, the reserve of which is more than 0.15 billion tons. However, they are not completely utilized in the pellet production. Process mineralogy investigation shows that the bentonite is a kind of typical Ca-bentonite (Ca-Bent). The sodium modification of the sample is studied by suspension method in this study. Results present the alkali coefficient K of modified Na-bentonite that is increased from 0.34 to 1.33, and the 2HWA, dilation, and colloid index are, respectively, increased to 601%, 32.4 mL/g and 87.6 mL/(3 g) under optimal conditions of Na2CO3 dosage 3.0%, pulp density 20%, sodium temperature 55°C, and sodium time 0.5 h. The XRD patterns show that d(001) of the sample bentonite is reduced from 1.5539 nm down to 1.2467 nm, and 2θ(001) of the sample bentonite is increased from 5.6875° to 7.0907°, indicating that the sample Ca-Bent is effectively modified into Na-Bent.
... Such treatment leaches out ferric, ferrous, aluminum and magnesium ions. It results in the improvement the crystal structure and increase in the specific surface area and porosity to be used in refining of oil (Grim, 1962;Taylor and Jenkins, 1986;Francisco and Persio, 2001;Rifai et al., 2001;Jozefaciuk andBowanko, 2002 andDananaja, et al., 2005). Bentonites and Fullur's earth have many industrial applications including oil drilling, foundry sand bonding material, iron ore and animal and poultry feed pelletization, oil refining, civil engineering, and in paints, cosmetics and pharmaceuticals (Harben, 1995;Murray, 1999). ...
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The Pliocene bentonitic clays located in Wadi El-Natrun area and its surroundings at the Western Desert of Egypt, were activated and evaluated for some commercial uses based on their mineral, chemical and physical properties. Mineralogical data shows that montmorillonite is the dominant clay mineral, followed by kaolinite and less proportions of illite. Quartz, halite, calcite and gypsum are the main non-clay minerals. Montmorillonite is mainly calcium-based with some sodium in the exchange positions. The bentonitic clays were alkali activated in wet basis with Na2CO3 with different dosages varying between 0.5 and 6. 5gm Na2CO3 /100 gm bentonitic clay. Changes in their mineral, chemical, physical and rheological characteristics were assessed. Calcium- montmorillonite was completely converted to sodium-montmorillonite upon treatment with Na2CO3 dosages with range of 2.64-6.36 gm Na2CO3 /100 gm clay. The rheological properties of some of the treated samples met the international requirements of the drilling mud. On the other hand, acid-activation of some of the studied bentonitic clay samples was undertaken through treatment with 1, 2, 4 and 6 N H2SO4 at different bleaching periods. This resulted in an increase in their surface area (A), pore volume (V) and bleaching ability to meet requirements for use in oil refining.
... Th e addition of Na salts to Ca-bentonites has been shown to increase strength (Odom, 1984). Alternatively, when Na-bentonites, which are often used in geosynthetic landfi ll liners, were saturated with Ca, an increase in permeability was observed (Stern and Shackelford, 1998; Dananaj et al., 2005). Additions of gypsum also decreased strength in the WFSs studied (Table 5 ), so that all high strength WFSs were below the 1.4 MPa threshold that could potentially stunt root growth. ...
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To avoid increasing costs of landfill disposal, it has become increasingly important for U.S. foundries to identify beneficial reuses for the 8 to 12 million tons of waste foundry sand (WFS) generated annually. A major drawback to the reuse of some WFSs as a soil amendment is their high soil strength, under dry conditions, where root growth may be limited. Fifteen WFSs were analyzed for strength to rupture using lab-formed clods, exchangeable cations (Na, Mg, Ca), metal oxide concentration (Fe, Mn, Al, Si), cation exchange capacity (CEC), and % clay. Several WFS samples from gray iron foundries demonstrated high strength to rupture values (> 1.5 MPa), and could potentially restrict root growth in amended soils. The percentage of Na-bentonite exhibited a positive correlation (R(2) = 0.84) with strength to rupture values. When WFSs containing more Na-bentonite were saturated with 1 mol L(-1) Ca ions, strength values decreased by approximately 70%. Waste foundry sands containing less Na-bentonite were saturated with 1 mol L(-1) Na ions and exhibited a threefold increase in strength. Additions of gypsum (up to 9.6 g kg(-1) sand) to high strength waste foundry sands also caused decreases in strength. These results indicate that high strength WFSs have properties similar to hardsetting soils which are caused by high Na(+) clay content and can be ameliorated by the addition of Ca(2+).
... The knowledge of these characteristics can help for a best exploitation and eventually may open-up new areas of application [3]. The properties of clay based ceramics depend on the characteristics, mineralogical composition of the parent clay and the processing conditions [4,5]. ...
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... In previous research, detailed information regarding the mineralogical composition of the bentonite, and in particular accessory minerals that accompany the smectite (e.g. Dananaj et al., 2005) is often lacking. Yet this appears to be one of the primary factors influencing GCL long-term hydraulic performance. ...
Article
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When a geosynthetic clay liner (GCL) containing sodium bentonite is brought into contact with fluids containing other cations, the latter may exchange with the sodium present between clay layers. This modification of clay surface chemistry may change the clay microstructure and hence its hydraulic conductivity. The influence of clay surface chemistry on microstructure and permeability, after prolonged contact between two GCLs (a natural sodium bentonite GCL and a sodium-activated calcium bentonite GCL) and different fluids in oedometer cells, was investigated using exchangeable-cation analysis, small-angle x-ray scattering, and transmission electron microscopy. Results suggest that calcium carbonate in the bentonite, formed during activation of the calcium bentonite, may redissolve during contact with a dilute permeant, releasing calcium ions that exchange with sodium in the clay. This exchange leads to obliteration of a so-called "gel" phase (beneficial in terms of low permeability) and to the development of a more permeable "hydrated-solid" phase. Sodium replacement by calcium during GCL contact with a 0.1 M CaCl2 solution was found to be virtually complete, with or without GCL prehydration with dilute water. No gel phase was observed in these samples. When in contact with real leachate, however, a gel phase appeared, especially when GCL samples were prehydrated. A correlation was observed between the level of hydraulic conductivity and the relative proportions of gel phase and clay interlayer occupation by sodium.
... As revealed by small angle X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) observations, the fluid composition has clearly modified the texture of the material. The permeabilities measured by Dananaj et al. (2005) in a sodium bentonite are weaker than in a calcium bentonite. Scanning electron microscope (SEM) observations of both materials highlighted the more homogeneous aspect of sodium bentonite, while calcium bentonite exhibited more void spaces in its structure. ...
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In underground repository concepts for radioactive waste, bentonite is studied as a reference swelling material to be used as an engineered barrier. Under the changing geochemical conditions prevailing within the barrier (saturation with the fluid coming from the host formation, diffusion of various chemical plumes caused by the degradation of some constituents of the barrier-system, etc.), the surface chemistry of the clay particles could evolve. This work aims to characterize the effects of these changes on (i) the microstructure of compacted bentonite samples and (ii) the diffusion properties of HTO and Na in these samples. For this purpose, bentonite sets were equilibrated with different solutions: NaCl, CaCl2, CsCl solutions as well as an artificial clayey porewater solution. The microstructure of the different samples was characterized by HRTEM and XRD, in a water saturated state. In parallel, effective diffusion coefficients of both HTO and 22Na were measured for the different samples. The density of the bentonite in the diffusion tests and in the HRTEM observations was set at 1.6 Mg m−3. From the microstructural observations and the results of diffusion tests, it is deduced that one key parameter is the occurrence of a gel phase in the material, which is found to depend strongly on the bentonite set: the gel phase dominates in Na-bentonite, while it is lacking in Cs-bentonite. The HTO diffusion coefficients are found to be lower in the samples with high gel phase content. Sodium diffusion does not follow the same trend: when compared with HTO, Na diffuses faster when the gel phase content is high. The latter result could indicate that the “accelerated diffusion mechanism” of cations, already mentioned in the literature, is enhanced in clayey materials that contain a gel phase.
... The knowledge of rheological properties of suspensions is of paramount importance and its correct measurement provide useful information for development of flow models for engineering applications, formulation of commercial production, design and process evaluation, quality control, and storage stability Van Olphen 1977; Speers et al. 1988. Therefore, bentonite suspensions have been an object of interest for a rather long time and the rheological, colloidal, physicochemical, microstructural, geotechnical, or electrical properties have been investigated by several authors Gao et al. 1999; Luckham and Rossi 1999; Arroyo et al. 2000; Durán et al. 2000; Ramos-Tejada et al. 2001a; 2001b; Coussot et al. 2002a; Besq et al. 2003; Tombácz and Szekeres 2004; Dananaj et al. 2005; Dellisanti and Valdré 2005. A literature survey indicates that although bentonite thixotropy is often not taken into account because of the complex nature of materials, and the lack of quantitative understanding and availability of simple, systematic, and relevant methods of measurements, its study has been and still is the focus of rheology research and the subject of a great deal of experimental and theoretical work Moore 1959; Cheng and Evans 1965; Cheng 1973; 1987; 2003; Mewis 1979; Pignon et al. 1996; 1998; Barnes 1997; Coussot et al. 2002a; Mujumdar et al. 2002; Roussel et al. 2004, to name just a few. ...
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The thixotropic behavior of bentonite suspensions was studied using different experimental procedures. It was found that the bentonite dispersions exhibit a time-dependent non-Newtonian behavior. In addition to the major factors affecting the rheological properties in the dispersion were the shearing value and duration, the rest time preceding the measurements and the structural state of the dispersion. The Herschel–Bulkley model was found to correlate well with the behavior of bentonite suspensions. The time evolution of the shear stress at constant shear rates was correlated by the Bird–Leider equation. In order to take into account structural evolution of the suspensions, the rheological law was modified by the introduction of the phenomenological model of Tiu and Boger derived from Moore’s kinetics evolution. It was observed that at short rest times and low shearing conditions, this model describes satisfactorily the time-dependent behavior of the bentonite suspensions. The behavior laws and kinetics evolution were established through the determination of structure destructuration and reorganization rates values. The structure parameters were found to be dependent on the clay concentration, providing evidence that the scale characteristic times of the buildup and breakdown processes are also concentration dependent.
... The range of water content for a plastic soil-like behaviour of palygorskite is lower than for bentonite, as confirmed by the value of plasticity index inTable 2. This characteristic is closely related to the specific surface area and mineralogy of clay. The water adsorption and free swell of the BP samples correspond to the values measured for Cabentonite equivalents (Dananaj et al. 2005). The specific surface area of palygorskite, at 19 830 m 2 /kg, is higher than that of Na-bentonite. ...
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Sodium bentonite (Na-bentonite) is used as a sealing component in geosynthetic clay liners (GCL). Na-bentonite is very sensitive to chlorides and flocculation occurs when exposed to saline environments. The purpose of this work is to investigate properties of Na-bentonite and bentonite-palygorskite filler material for GCL in saline solutions in range between 0.5 % and 10 % (0.09 and 1.8 M) of NaCl concentration. The investigation has been carried out to evaluate/study chemical and geotechnical properties of Na-bentonite and bentonite-palygorskite mixture. The observations suggest that the resistance of Na-bentonite to chlorides has been increased by adding 40 % palygorskite. The bentonite-palygorskite mixture is characterised by high liquid and plasticity limits and also by high water adsorption and free swell in water, crude oil and petrol. Hydraulic conductivity was determined for water and for 10 % NaCl (1.80 M) solution. The results show that Na-bentonite palygorskite mixture serves as the effective absorber of both water and saline solutions up to the concentration of 10 % (1.80 M) of NaCl without increasing hydraulic conductivity.
... Results show that sodium bentonite is less permeable to tap water than calcium bentonite. Thus, the nature and quality of bentonite influences its hydraulic performance (Dananaj et al., 2005;Mesri and Olsen, 1971). Calcium bentonite has a smaller swelling capacity and a higher hydraulic conductivity, chemically resistant compared to sodium bentonite. ...
Article
The present paper discusses the hydro mechanical behavior of activated Ca–bentonite mixed with two soluble polyelectrolyte powder polymers. To understand better the clay polymer interaction, swelling, water adsorption and hydraulic performance are studied. Synthetized leachate (LS) is used to reproduce the hydrochemical phenomena in the system. Hydraulic performance tests were performed with an oedopermeameter and modified API filter press. Both methods gave the similar bentonite material behaviors and classification order, showing that polymers are reducing the permeability, in contact with the LS. Water adsorption and free swell index tests results have confirmed that (1) adsorption, swelling and permeability parameters are linked for clay polymer mixtures and (2) the polymers could improve the overall clay properties. Each polymer has a different effect: the anionic polymer induces a low permeability to the mixture; the cationic polymer makes the bentonite more swellable, with high ability to retain water and to become more resistant to the LS. Laboratory tests results demonstrate that the behavior of bentonite polymer mixtures for landfill liner applications depends essentially on the nature of the surface charge of the polymer.
... In previous research, detailed information regarding the mineralogical composition of the bentonite, and in particular accessory minerals that accompany the smectite (e.g. Andrejkovicova et al., 2008;Dananaj et al., 2005;Kolstad et al., 2004a) is often lacking. Yet this appears to be one of the primary factors influencing GCL hydraulic performance. ...
Article
The results of a project aimed at identifying performance-based indicators that can be used by landfill operators to check the suitability of GCLs for bottom barrier applications are presented. The general methodology consisted of performing detailed characterization of the prevalent GCLs used in France for landfill barrier applications, before and after prolonged contact with several fluids during oedo-permeameter tests. Results of mineralogical analysis illustrate the variety of composition of the tested bentonites, which in addition to smectite clay contain a large number of accessory minerals. For one of the GCLs tested, the proportion of smectite was lower than 30 wt%, which highlights the limitations of the generic designation “bentonite” when referring to GCLs destined to landfill applications. Results also underline the correlation between cation exchange capacity (CEC) and smectite content, the correlation between free swell volume and proportion of exchangeable sodium and the influence of the bentonite's calcium carbonate fraction on hydraulic conductivity. Transmission electron microscopy (TEM) photographs illustrate the effect of cation exchange on clay microstructure, with the formation of clay particles which lead to increased hydraulic conductivity. The exchange is also documented by exchangeable cation analyses. Results of isotopic analyses indicate that information provided by suppliers with respect to the “natural” versus “activated” nature of the bentonite, may sometimes be arbitrary and related to factors that are very difficult to check in practice, even by the suppliers themselves. This further underlines the need for performance-based indicators, rather than generic designations, to provide objective information regarding GCL suitability for landfill applications. Several performance-based indicators are selected in order to provide practical tools for checking the suitability of sodium-bentonite GCLs in bottom barrier applications and limit values are proposed.
... Dhakal (2001) found that the slake durability and other geotechnical behaviors of argillaceous rocks are strongly influenced by mineralogy. Dananaj et al. (2005) studied the influence of chemical composition of the smectite-rich bentonite on its geotechnical and petrophysical properties. They stated that the differences in bentonite quality and smectite quantity influence the permeability. ...
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The Eocene and Miocene shallow marine clays compose several foundation beds in the new cities, east of Cairo, Egypt. Mineralogical and chemical compositions of these clays were examined using XRD, SEM, ICP-OES techniques. Geotechnical and physical characteristics were investigated according to the standards of ASTM (1994). The XRD and SEM analyses confirm that the major non-clay minerals are quartz, halite, feldspars, calcite and goethite whereas the clay minerals are Na montmorillonite and kaolinite. The chemical data suggest that the sources of Si in the analyzed samples are essentially sand and silt fractions, whereas Al is derived from the clay fraction. Fe, Mg and Na occur either as main constituents of smectite or as replacements for Al in the clay mineral structures. The substitution of Al by the divalent cations results in formation of a negative charge on the clay crystal lattice. This negative charge is mostly balanced by adsorption of monovalent cation such as Na+ and K+ from the groundwater and/or during the diagensis process. Mn exists mainly as MnO cement and partially at the expense of Fe and Mg. The cement materials include also Fe, Ca and Na salts. Cu, Zn and other heavy metals are mainly adsorbed on the surface of clay platelets. The clays of the study area range in swelling from low to very high; these might cause serious engineering problems on wetting at the foundation levels. Fe, Ca, Mn, Mg, Na, K, Cu, and Zn enhance the swelling potentiality when present as substitution for Al or adsorption on the clay minerals and reduce it when exist as components of the cement materials. Results facilitate the interpretation that the swelling potentiality is largely affected by the type of clay mineral, its percentage, chemical composition, structures and presence of both cement materials and fine sand cushions. تكون الصخور الطينية الضحلة التابعة لعصرى الإيوسين والميوسين العديد من طبقات الأساس فى المدن الجديدة شرق القاهرة بمصر. تم فحص التركيب المعدني والكيميائي لهذه الصخور الطينية باستخدام أجهزة حيود الأشعة السينية والميكروسكوب الإلكتروني الماسح وجهاز البلازما المصاحب للإنبعاث الطيفى. تم فحص الخواص الجيوتقنية والفيزيائية باستخدام طرق الجمعية الأمريكية للقياس والمواد (1994). أكدت تحاليل كل من حيود الأشعة السينية، والميكروسكوب الإلكتروني الماسح، أن المكونات غير الطينية تتمثل فى الكوارتز، والهاليت، والفلسبار، والكالسيت، والجوتيت، وأن المعادن الطينية تتمثل فى المونتموريللونيت الصودى، والكاولينيت. بينت التحاليل الكيميائية أن مصدر السيليكون الأساسي فى العينات المدروسة هو من الرمل والغرين، بالإضافة إلى معادن الطين بينما الألومنيوم فمن الطين، أساسا. يوجد الحديد، والماغنسيوم، والصوديوم إما كمكونات أساسية للسميكتيت، أو كإحلالات للألومنيوم فى بنية معادن الطين. يتسبب إحلال الكاتيونات الثنائية محل الألومنيوم فى تكوين شحنة سالبة على البنية الفراغية للطين. غالبا ماتتعادل هذه الشحنة السالبة بادمصاص كاتيونات أحادية مثل الصوديوم والبوتاسيوم من المياه الجوفية، و/أو أثناء تغيرات مابعد الترسيب. يوجد المنجنيز أساساً كأكسيد منجنيز لاحم وجزئياً على حساب كل من الحديد والماغنسيوم. تحتوى أيضا المواد اللاحمة على أملاح كل من الحديد والكالسيوم والصوديوم. يحدث ادمصاص لكل من النحاس والزنك وباقى العناصر الثقيلة على صفائح الطين. للصخور الطينية من منطقة الدراسة انتفاش يتراوح من منخفض إلى عالي جدا، وقد يسبب ذلك مشاكل هندسية خطيرة عند تعرض الأساسات للمياه. يزيد كل من الحديد، والكالسيوم، والمنجنيز، والماغنسيوم، والصوديوم، والبوتاسيوم، والنحاس والزنك درجة الانتفاش إذا ماوجدوا كإحلالات محل الألومنيوم، أو كادمصاص على معادن الطين، ويقللون منها عند وجودهم كمكونات للمواد اللاحمة. دعمت النتائج تفسير التأثر الكبير لدرجة الانتفاش بنوع معدن الطين، ونسبته، والتركيب الكيميائى، وبنية الصخور، ووجود كل من المواد اللاحمة، والرمال الناعمة.
... Dhakal (2001) found that the slake durability and other geotechnical behaviors of argillaceous rocks are strongly influenced by mineralogy. Dananaj et al. (2005) studied the influence of chemical composition of the smectite-rich bentonite on its geotechnical and petrophysical properties. They stated that the differences in bentonite quality and smectite quantity influence the permeability. ...
Article
The Eocene and Miocene shallow marine clays compose several foundation beds in the new cities, east of Cairo, Egypt. Mineralogical and chemical compositions of these clays were examined using XRD, SEM, ICP-OES techniques. Geotechnical and physical characteristics were investigated according to the standards of ASTM (1994). The XRD and SEM analyses confirm that the major non-clay minerals are quartz, halite, feldspars, calcite and goethite whereas the clay minerals are Na montmorillonite and kaolinite. The chemical data suggest that the sources of Si in the analyzed samples are essentially sand and silt fractions, whereas Al is derived from the clay fraction. Fe, Mg and Na occur either as main constituents of smectite or as replacements for Al in the clay mineral structures. The substitution of Al by the divalent cations results in formation of a negative charge on the clay crystal lattice. This negative charge is mostly balanced by adsorption of monovalent cation such as Na + and K + from the groundwater and/or during the diagensis process. Mn exists mainly as MnO cement and partially at the expense of Fe and Mg. The cement materials include also Fe, Ca and Na salts. Cu, Zn and other heavy metals are mainly adsorbed on the surface of clay platelets. The clays of the study area range in swelling from low to very high; these might cause serious engineering problems on wetting at the foundation levels. Fe, Ca, Mn, Mg, Na, K, Cu, and Zn enhance the swelling potentiality when present as substitution for Al or adsorption on the clay minerals and reduce it when exist as components of the cement materials. Results facilitate the interpretation that the swelling potentiality is largely affected by the type of clay mineral, its percentage, chemical composition, structures and presence of both cement materials and fine sand cushions. Abd-Allah et. al.
... Dhakal (2001) found that the slake durability and other geotechnical behaviors of argillaceous rocks are strongly influenced by mineralogy. Dananaj et al. (2005) studied the influence of chemical composition of the smectite-rich bentonite on its geotechnical and petrophysical properties. They stated that the differences in bentonite quality and smectite quantity influence the permeability. ...
Article
Full-text available
The Eocene and Miocene shallow marine clays compose several foundation beds in the new cities, east of Cairo, Egypt. Mineralogical and chemical compositions of these clays were examined using XRD, SEM, ICP-OES techniques. Geotechnical and physical characteristics were investigated according to the standards of ASTM (1994). The XRD and SEM analyses confirm that the major non-clay minerals are quartz, halite, feldspars, calcite and goethite whereas the clay minerals are Na montmorillonite and kaolinite. The chemical data suggest that the sources of Si in the analyzed samples are essentially sand and silt fractions, whereas Al is derived from the clay fraction. Fe, Mg and Na occur either as main constituents of smectite or as replacements for Al in the clay mineral structures. The substitution of Al by the divalent cations results in formation of a negative charge on the clay crystal lattice. This negative charge is mostly balanced by adsorption of monovalent cation such as Na + and K + from the groundwater and/or during the diagensis process. Mn exists mainly as MnO cement and partially at the expense of Fe and Mg. The cement materials include also Fe, Ca and Na salts. Cu, Zn and other heavy metals are mainly adsorbed on the surface of clay platelets. The clays of the study area range in swelling from low to very high; these might cause serious engineering problems on wetting at the foundation levels. Fe, Ca, Mn, Mg, Na, K, Cu, and Zn enhance the swelling potentiality when present as substitution for Al or adsorption on the clay minerals and reduce it when exist as components of the cement materials. Results facilitate the interpretation that the swelling potentiality is largely affected by the type of clay mineral, its percentage, chemical composition, structures and presence of both cement materials and fine sand cushions.
... Such treatment leaches out ferric, ferrous, aluminum and magnesium ions. It results in the improvement the crystal structure and increase in the specific surface area and porosity to be used in refining of oil (Grim, 1962;Taylor and Jenkins, 1986;Francisco and Persio, 2001;Rifai et al., 2001;Jozefaciuk andBowanko, 2002 andDananaja, et al., 2005). Bentonites and Fullur's earth have many industrial applications including oil drilling, foundry sand bonding material, iron ore and animal and poultry feed pelletization, oil refining, civil engineering, and in paints, cosmetics and pharmaceuticals (Harben, 1995;Murray, 1999). ...
Conference Paper
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The Pliocene bentonitic clays located in Wadi El-Natrun area and its surroundings at the Western Desert of Egypt, were activated and evaluated for some commercial uses based on their mineral, chemical and physical properties. Mineralogical data shows that montmorillonite is the dominant clay mineral, followed by kaolinite and less proportions of illite. Quartz, halite, calcite and gypsum are the main non-clay minerals. Montmorillonite is mainly calcium-based with some sodium in the exchange positions. The bentonitic clays were activated in wet basis with Na2CO3 with different dosages varying between 0.5 and 6. 5gm Na2CO3 /100 gm bentonitic clay. Changes in their mineral, chemical, physical and rheological characteristics were assessed. Calcium- montmorillonite was completely converted to sodium-montmorillonite upon treatment with Na2CO3 dosages with range of 2.64-6.36 gm Na2CO3 /100 gm clay. The rheological properties of some of the treated samples met the international requirements of the drilling mud. On the other hand, acid-activation of some of the studied bentonitic clay samples was undertaken through treatment with 1, 2, 4 and 6 N H2SO4 at different bleaching periods. This resulted in an increase in their surface area (A), pore volume (V) and bleaching ability to meet requirements for use in oil refining.
... A schematic is presented in Figure 2.11 that illustrates the association of two adjacent montmorillonite particles and the exchangeable cations and water associated with the interlayer space between the particles. Yong and Warkentin (1975) The charge deficiency of bentonite is balanced by hydrated cations and several layers of water molecules attached to the montmorillonite particle (1 x 10 -9 to 6 x 10 -5 cm/sec) Jo et al. (2001) 0.005 M CaCl 2 to 0.1 M CaCl 2 Hydration Solution ↓ Swell index (27 mL/2g to 9 mL/2g) Jo et al. (2001) 0.005 M CaCl 2 to 0.5 M CaCl 2 Hydration Solution ↓ Swell index, ↓ Liquid Limit (reduction from 350-550% to 100%) Lee et al. (2005) Na-bentonite versus Ca-bentonite Ca-bentonite exhibits larger voids Dananaj et al. (2005) Na-bentonite versus Cabentonite Ca-bentonite exhibits larger bentonite particle sizes Egloffstein (2001) The effects of cation exchange on bentonite may be explained by the diffuse double-layer theory (Yesiller and Shackelford 2010). The concentration of exchangeable cations is highest at the montmorillonite surface, and decreases with distance from the surface due to a concentration gradient imposed by the influx of water to the interlayer region during hydration (Mitchell and Soga 2005). ...
Article
A laboratory test program was conducted to determine the moisture-suction relationships of geosynthetic clay liners (GCLs). Moisture-suction relationships were determined by combining suction data from pressure plate tests, contact filter paper tests, and relative humidity tests, then fitting water retention curves (WRCs) to the data. WRCs were determined for wetting processes and drying processes in terms of gravimetric moisture content and volumetric moisture content. The effects of GCL type, hydration solution, wet-dry cycles, and temperature on the moisture-suction relationships were analyzed. The three GCLs of the test program consisted of configurations of woven and nonwoven geotextiles reinforced with needlepunched fibers. A geofilm was adhesively bonded to the nonwoven side of one of the GCL products. The hydration solution tests involved hydrating GCLs with deionized water, tap water, 0.1 M CaCl2, or soil water from a landfill cover test plot for a 30-day conditioning period prior to testing. Cyclic wet-dry tests were conducted on the GCL specimens subjected to 20 wet-dry cycles from 50% to 0% gravimetric moisture content prior to testing. Temperature tests were conducted at 2°C, 20°C, and 40°C. GCL type affected moisture-suction relationships. The GCLs with an adhesively-bonded geofilm exhibited lower air-entry suction and higher residual suction than GCLs without a geofilm. The degree of needlepunched fiber pullout during hydration contributed to hysteresis between wetting WRCs and drying WRCs. Hysteresis was high for suction values below air-entry suction and was low for suction values greater than air-entry suction. Cation exchange reduced the water retention capacity for all three GCL types. The saturated gravimetric moisture contents were reduced from approximately 140% to 70% for wetting WRCs and 210% to 90% for drying WRCs for GCLs hydrated in deionized water compared to CaCl2 solution. Hysteresis of the nonwoven product decreased from 71%, to 62%, to 28% with respect to deionized water, tap water, and CaCl2 solution. Hysteresis of the woven product exposed to soil water was 24% and 0%, in terms of saturated gravimetric moisture content and saturated volumetric moisture content, respectively. The swell index, Atterberg Limits, mole fraction of bound sodium, and scanning electron microscopy images that were determined of bentonite from the conditioned GCLs indicated that changes in water retention capacity corresponded with cation exchange. Wet-dry cycles and temperature affected the moisture-suction behavior for GCLs. Wet-dry cycles reduced hysteresis and increased the swelling capacity of GCL specimens. Microscopy images indicated that wet-dry cycles caused weak orientation of the clay particles. Increasing temperature resulted in a small decrease in water retention capacity. Results of the test program provided a means for predicting unsaturated behavior for GCLs.
... The mineralogical and geochemical properties of soil including clay minerals affect the engineering properties of cohesive soils [1][2][3][4][5][6][7]. Although mineralogical and chemical properties of soils are very important, most geotechnical studies are not taken into consideration [8]. ...
Article
Both geotechnical and mineralogical characteristics of the sixty five disturbed Pliocene core samples taken from Eskişehir province were examined in detail. In order to evaluate the mineralogical properties of soil samples, X-ray, differential thermal analysis-thermal gravimetric (DTA-TG), infrared spectroscopic (IR) and scanning electron microscopy (SEM) analyzes were performed. In the soil samples, the predominant clay mineral is smectite and a small amount of chlorite and illite are also observed based on the ideal DTA-TG and IR peaks and SEM analysis. The percentage of smectite, chlorite and illite positive correlated with liquid limit (LL), plastic limit (PL), plasticity index (PI) and clay activity (A). As the chemical composition of major oxides and geotechnical properties was evaluated together, it was determined that LL, PL and PI values with SiO2 and Al2O3 content have a positive relationship and also the increase of Fe2O3, Na2O and K2O amounts result in increasing LL and clay’s activity in Eskişehir soils. As a result of the study, it was evaluated that CaO content can be used as an alternative to A value in the evaluation of swelling potential.
... The microstructure of soil will be changed under the action of gravity and external loads, and this also changes the mechanical properties of soil (Katti and Shanmugasundaram, 2001;Ouhadi and Yong, 2003;Yamamuro and Wood, 2004;Dananaj et al., 2005;Kikkawa et al., 2013;Zhao et al., 2017). The macroscopic mechanical behavior of soil is closely related to its microstructure. ...
Article
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Accurate quantification of soil micro-pore is important for understanding compression deformation and thaw settlement of fine-grained soils, including clay. This study presents mercury intrusion porosimetry (MIP) data on the four types of soil samples before and after freeze-thaw and compression under four different cold-end temperatures. Undisturbed clay specimens were subject to one-directional freeze-thaw in a closed system under different freezing temperatures. The frozen-thawed specimens were divided into three layers and averaged along the height direction for a consolidation test. The mercury intrusion test data were analyzed, and three typical micro-pore parameters including (1) total pore volume, (2) median pore size, and (3) average pore size were selected to quantitatively describe the variation of soil micro-pores before and after freeze-thaw and consolidation. Close correlations were observed between the variation of micro-pore parameters and variation of compression index, pore ratio, water content, and density. This study demonstrates that compared with traditional test methods, MIP can be advantageous in revealing the internal micro-pore change of soil due to freeze-thaw and compression both quantitatively and nondestructively.
... The increasing application of microstructural studies has led to improved techniques and more robust interpretations of the results. At present, most of the SEM studies are devoted to the determination of the size and orientation of pores and their evolution under various conditions of stress on consolidation, compaction or shearing paths (e.g., Osipov and Sokolov 1978a, b, c;Osipov et al. 1984;Sokolov 1990;Gens and Alonso 1992;Hicher et al. 2000;Katti and Shanmugasundaram 2001;Yong 2003;Dananaj et al. 2005;Schmitz et al. 2005;Gratchev et al. 2006;Fleureau 2010, 2011). ...
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Wójcik, E., Trzciński, J. and Łądkiewicz-Krochmal, K. 2019. Microstructural changes of expansive clays during dehydration caused by suction pressure-a case study of Miocene to Pliocene clays from Warsaw (Poland). Acta Geologica Polonica, 69 (3), 465-488. Warszawa. This paper presents the qualitative and quantitative characteristics of microstructures of Neogene clays from Warsaw, Poland. Scanning Electron Microscope (SEM) studies were used for the microstructural analysis of natural clays and clay pastes. Qualitative microstructural changes were observed: from a honeycomb micro-structure for the initial clay paste to a turbulent microstructure for the dried paste. It was also noticed that water loss caused by the increase of the suction pressure had a significant impact on the microstructural transformations. Significant changes in the quantitative values of the pore space parameters were also observed. Increase of suction pressure and water loss caused a decrease in porosity and changes in the values of morphometric parameters, such as pore distribution; for example, a significant increase of the number of pores of 0−10 μm size and changes in the geometric parameters of the pore space were noticed with the increase of suction pressure. The pore space with larger isometric pores was modified into a pore space with the dominance of small aniso-metric and fissure-like pores. The increased degree of anisotropy from a poorly-oriented to a highly-oriented microstructure was also observed. After rapid shrinkage the reduction in the number of pores, maximum pore diameter, and total pore perimeter was recorded. The process of rapid water loss induced the closure of very small pores. A similar effect was observed during the increase of the suction pressure, where the closure of pore space of the clay pastes was observed very clearly.
... Among the natural bentonites, BR had a higher proportion of Al 2 O 3 . Meanwhile, BG had the highest SiO 2 value [34]. With respect to iron oxide, ocher bentonite had the highest value. ...
Article
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The aim of the present work was to study Argentinean natural clays with different modifications and their use as desiccants. To this end, bentonite clays collected from different regions were characterized and modified by heat treatment and calcium addition, and the desiccant capacity, in the form of powder and pellets, was studied. In addition, the hydration degree reversibility of these materials was estimated. The mineralogical and structural characterization was performed by X-ray diffraction, Fourier-transform infrared spectroscopy, differential thermal analysis, and thermogravimetric analysis. The textural characterization was performed by adsorption-desorption of N2, chemical composition by X-ray fluorescence and cation exchange capacity. The water adsorption was determined at 25 °C between 11-98% relative humidity. The results indicated that the desiccant power has a close relationship with the degree of clay purity, drying of the sample and the method of calcium incorporation.
... Dananaj et al. [46] investigated the microstructural formation and geotechnical properties of Ca-bentonite and Na-bentonite by XRD, chemical analysis and scanning electron microscopy (SEM). Researchers suggested that the diferences in bentonite quality and smectite quantity inluence the permeability. ...
... The hydraulic conductivity of GCLs has widely been interpretted with the swell index of bentonite (Ashmawy et al. 2002, Di Emidio et al. 2015, Hosney and Rowe 2013, Jo et al. 2001, Katsumi et al. 2008, Kolstad et al. 2004, Lee et al. 2005, Shackelford et al. 2000. In addition, some attempts have been made to evaluate the hydraulic conductivity with liquid limit (Lee et al. 2005, Liu et al. 2015, Mishra et al. 2011, sedimentation volume (Lee et al. 2005), cation exchange capacity (Guyonnet et al. 2009), exchangeable sodium percentage (Mishra et al. 2011) and smectite content (Ashmawy et al. 2002, Dananaj et al. 2005, Guyonnet et al. 2009, Shackelford et al. 2000 of the bentonite. Most of these studies basically investigate and report the influence of permeant type (i.e., inorganic salt solutions had been used in these studies) and the concentration of the permeant on the hydraulic conductivity of GCLs (Jo et al. 2001, Katsumi et al. 2008, Kolstad et al. 2004). ...
Article
In this study, the relationships between hydraulic conductivity of GCLs and physico-chemical properties of bentonites were assessed. In addition to four factory manufactured GCLs, six artificially prepared GCLs (AP-GCLs) were tested. AP-GCLs were prepared in the laboratory without bonding or stitching. A total of 20 hydraulic conductivity tests were conducted using flexible wall permeameters ten of which were permeated with distilled deionized water(DIW) and the rest were permeated with tap water (TW). The hydraulic conductivity of GCLs and AP-GCLs were between 5.2☓ 10⁻¹⁰ cm/s and 3.0☓ 10⁻⁹ cm/s. The hydraulic conductivities of all GCLs to DIW were very similar to that of GCLs to TW. Then, simple regression analyses were conducted between hydraulic conductivity and physicochemical properties of bentonite. The best correlation coefficient was achieved when hydraulic conductivity was related with clay content (R=0.85). Liquid limit and plasticity index were other independent variables that have good correlation coefficients with hydraulic conductivity (R~0.80). The correlation coefficient with swell index is less than other parameters, but still fairly good (R~0.70). In contrast, hydraulic conductivity had poor correlation coefficients with specific surface area (SSA), smectite content and cation exchange capacity (CEC) (i.e., R < 0.5). Furthermore, some post-test properties of bentonite such as final height and final water content were correlated with the hydraulic conductivity as well. The hydraulic conductivity of GCLs had fairly good correlation coefficients with either final height or final water content. However, those of AP-GCLs had poor correlations with these variables on account of fiber free characteristics.
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Bentonite, which is a mineral component of geosynthetic clay liners, has important physical and chemical properties that ensure very small hydraulic permeability. The main component of bentonite is a clay mineral called sodium montmorillonite whose very low permeability is due to its ability to swell. The deposits of bentonite are spread all over the world, however, only a very small number of those deposits satisfies all the quality and durability demands that must be met if the bentonite is to be used in the sealing barriers. Depending on the location of installation and their purpose, geosynthetic clay liners must meet certain requirements. Their compatibility with the prescribed criterion is confirmed through various laboratory procedures. Amongst them are tests examining the index indicators (free swell index, fluid loss index, and water absorption capacity). This paper presents results regarding the impact of laboratory air temperature and relative humidity of the testing area on the water absorption capacity. This is one of the criteria that bentonite must satisfy during the quality and durability control of the mineral component of geosynthetic clay liner.
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Soil-bentonite slurry-trench cutoff walls are used extensively as engineered barriers for groundwater contaminants containment. The compressibility and hydraulic conductivity of sand/Ca-bentonite and sand-clayey soil/Ca-bentonite backfills for slurry-trench cutoff wall are evaluated via a series of oedometer tests and falling-head hydraulic conductivity tests. The backfills are prepared by mixing base mixture with bentonite-water slurry containing 10% bentonite, and the water content is adjusted to achieve target slump for workability via slump test using miniature slump cone. The results indicate that a total Ca-bentonite content of 8.3% is required in soil/Ca-bentonite backfills to achieve typical regulatory limit (k<10-9 m/s). The compression index and hydraulic conductivity are insignificantly affected by the amount of clayey soil in backfill. In addition, the values of hydraulic conductivity measured using falling-head hydraulic conductivity test (kFH) are quite similar to these evaluated based on Terzaghi's one-dimensional consolidation theory (kT), and the ratio of kFH to kT is in the range of 1/3 to 3. Finally, the compressibility and hydraulic conductivity are assessed and predicted based on physical properties, including void ratio at effective vertical compression stress of 1 kPa (e1), void ratio of bentonite (eb), and liquid limit. ©, 2015, Shuili Xuebao/Journal of Hydraulic Engineering. All right reserved.
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Even in karst areas, considerably thick soils can be found in accumulation zones. Here, the degree of groundwater vulnerability depends not only on the thickness, but also on the hydraulic conductivity and retention properties of the soil cover. The hydraulic conductivity of fine-grained karst soils from Slovakia, Croatia and Austria was studied within several international research projects, by the application of four different test methods. Results are discussed from different points of view. Triaxial tests yielded a very broad interval between the maximum and minimum hydraulic conductivity (from 5.83x10-7 m.s-1 to 3.50x10-11 m.s-1), therefore the mean value cannot be used in any calculations. The consolidometer method gave lower values in general, between 9.40x10-10 m.s-1 to 3.59x10-8 m.s-1. However, this method overestimates the soil “impermeability”. Estimates based on grain size are unsuitable, as fine-grained soils did not fulfil the random conditions of known formula. Finally, the “in situ” hydraulic conductivity was measured using a Guelph permeameter. As expected, “in situ” tests showed 100 to 1000-times higher kf than the laboratory tests. This method best reflects the real conditions. Therefore, only this type of data should be considered in any environmental modelling. In a soil profile, hydraulic conductivity depends on the mineral composition, depth, secondary compaction, etc. The degree and duration of saturation with water is very important for young soils containing smectite. Their hydraulic conductivity might be very low when saturated for long time, but also very high, when open desiccation cracks occur. A very slight trend was found, but only in Slovak soils, showing a decrease in the hydraulic conductivity with increasing content of the clay fraction <0.002 mm. These results should contribute to a better estimate of the protective role of soils in groundwater vulnerability maps.
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Nuclide migration poses a problem to the potential geological disposal site performance assessment of radioactive waste. Effective diffusivity of clay is an important factor in radionuclide retention. In this study, a set of diffusion experiments were performed with radioactive water tracers (HTO and ³⁶Cl⁻) on the Téguline Clay using the in-diffusion method, and the effect of location was emphasised. The results show that the apparent diffusion coefficient (D a) did not vary linearly with the depth of the Téguline Clay. From the depth of 0–60 m, the effective diffusion coefficients of HTO and ³⁶Cl⁻ were 5.2–10.3 (×10⁻¹¹m²s⁻¹) and 1.3 –6.3 (×10⁻¹¹m²s⁻¹), respectively. Téguline Clay at different locations and the same depth showed similar results. The results showed that all the diffusion coefficients of ³⁶Cl⁻ in the Téguline Clay at different positions were lower than those of HTO. HTO exhibited lower anisotropy in the region, while HTO and ³⁶Cl⁻ showed anisotropies between 1 and 2.2. Numerical analysis predicted different initial concentrations and time affect the diffusion of contaminants in Téguline Clay. These findings can provide ideas for the prevention and control of contaminant in radioactive waste disposal.
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In this paper, a method for calibrating and compensating the errors of magnetometer is proposed, in which the error sources consist of constant bias, scale factors, nonorthogonality, hard iron effects and soft iron effects. Related estimation algorithms were proposed, calibration procedure was presented. Two dimensional and three dimensional cases are considered, the efficiency of the proposed algorithms and calibration method is validated by the simulation results, performance comparison of two kinds estimation methods are given based on the accuracy and time consuming.
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Compaction and hydraulic conductivity tests were conducted using deionized (DI) water to determine how exchangeable cations affect the hydraulic conductivity of compacted bentonite. Regardless of the compaction pressure, the maximum dry density decreased and the optimum water content increased with increasing equivalent fraction of Na+ ions (XNa). The hydraulic conductivity decreased with increasing XNa. The initial dry density of bentonite generally had no effect on the hydraulic conductivity, regardless of the type of exchangeable cations. The hydraulic conductivity of bentonite decreased with increasing a final dry density. The decrease in hydraulic conductivity was more significant at higher XNa. The difference in hydraulic conductivity of the specimens at a given final dry density decreased with increasing a final dry density. When permeated with DI water, compacted Ca-bentonite with a very high dry density might have a very low hydraulic conductivity (< 10− 9 cm/s) similar to compacted Na-bentonite, if no volume change is allowed (i.e. very high effective stress).
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Several technologies are currently available to stabilize the unbound layers of road pavements. The use of these solutions, often manufactured by means of chemical processes, is steadily increasing worldwide. As an alternative natural resource, the use of bentonite represents a valid option when it comes to road stabilization and its application in this context is still relatively unexplored. This study characterises the use of calcium based bentonite and sodium based bentonite to stabilize a typical road base layer. Considering two types of aggregates with different geological origin, the laboratory investigation is performed by means of repeated load triaxial tests, which assess the enhancement in stiffness and resistance to permanent deformation. The findings show that both the investigated types of bentonite are suitable for road stabilization. Even if negligible from a road engineering standpoint, the performance stemming from calcium bentonite was slightly better than the one pertaining to sodium bentonite when it came to the increase in resilient modulus.
Article
Some soils under construction cause numerous problems in terms of geotechnical engineering. Clay soils cause significant problems in the construction of roads, airports, pavements and highways. Some soils contain mixed additives, such as lime, cement, fly ash and bitumen. In this study, the microstructures of uncured and cured lime/cement-stabilised clay samples are investigated. Compacted soil samples were evaluated by mercury intrusion porosimetry, X-ray diffraction, scanning electron microscopy (SEM) analyses and specific surface area analysis. The results indicated that the addition of lime and cement was effective in the treatment of compaction properties. The pore sizes in the SEM images vary with an increase in the percentage of lime and cement and an increase in curing time.
Article
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The effect of varied firing temperature on the mechanical properties of fired masonry bricks samples produced from Ipetumodu clay was investigated. The clay sample was characterized using scanning electron microscopy (SEM) for the evaluation of the morphology of the sample using secondary electron imaging; and the phases/compositions of the samples using energy-dispersive X-ray (EDX) analysis, X-ray diffractometer (XRD), X-ray fluorescence (XRF) and atomic absorption spectroscopy (AAS). The brick samples of standard dimensions were prepared from the clay slurry. The prepared samples were sun dried for 72 hours and then fired at varied temperature (held for an hour) and then allowed to cool to room temperature in the furnace. The mechanical properties (compression strength, shear strength, modulus of rupture, density and hardness) of the samples were then investigated. It was observed that the mechanical properties of the fired brick samples varied with varying firing temperature due to phase changes/chemical reaction between the phases in the clay sample. It was concluded that the optimum mechanical property for brick samples within the temperature range considered is obtained at 950oC.
Article
Thermal analysis (TG, DTG), powder diffraction analysis (XRD) and infrared (IR) spectra were used to study of composition and release of benzimidazole from Ni(II)-exchanged montmorillonite under heating. Diffraction analysis indicated that benzimidazole molecules are intercalated into the interlayer space of montmorillonite. IR spectra and the analytical characteristics have shown that different type of interactions of benzimidazole is connected with different reaction conditions (acid or neutral solution). The release of benzimidazole from Ni(II)-montmorillonite under heating from studied samples proceeds in three distinct steps. The first step can be assigned to the release of water molecules while the last (third) one corresponds to the lattice dehydroxylation. The second step can be assigned to release of chemically bonded benzimidazole.
Thesis
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The aim of the present work is to establish a bibliographical synthesis on the microstructure, the colloidal and rheological characterization of bentonite suspensions with and without polymer/surfactant addition; to lead to a rheological characterization of clay-additive mixtures and to understand the interaction between the clay particles and polymer/surfactants. Different experimental measurements: rheology, particle sizing, and x-ray diffraction were used to study the rheological character of the water-bentonite-anionic additive mixtures (CMC, SDS, xanthane) as well as the nature of the particle-particle interactions and particle-additive. The modeling part led to the adoption of Tiu and Boger's model to predict the thixotropy of the bentonite suspensions without additive. Thus, a new model is proposed with physical parameters for a better correlation of the rheological behavior of the various studied mixtures.
Article
In order to study the seepage control performance of Geosynthetic Clay Liner (GCL) in lining channel in the cold and arid regions, the antifreeze characteristics of three different GCL (produced in Korea and China, 1#, 2#, 3#) were studied with indoor simulation method. The results showed that by hydrating with the Yellow River water and after 31 times of freeze-thaws, the free swelling volume of 1#?2#?3# GCL increased by 16.7%, 4.5% and 8.0% respectively; The filtration loss reduced by 31.1%, 28.9% and 27.0% respectively; The yield value increased by 200.0%, 23.3% and 90.6% respectively, and the EC values of the filtrate reduced by 27.3%, 27.0% and 31.0% respectively. The permeability coefficient increased by one order of magnitude, but was still small, which was 0.35-0.72% in canal bed. These indicated the GCL can be used in canal lining in the northwest arid and saline regions.
Thesis
Environmental engineering investigates hazardous waste contaminants, their pathways, transport, fates and disposition. It also explores ways of protecting groundwater, thereby , protecting humans and the environment from hazardous wastes. Petroleum products, for instance, account for sixty-nine percent of soil contamination in Quebec (Environment Quebec, 1994). Landfills are currently one of the most effective ways to dispose of wastes. Underground storage tanks (UGST) are also used to store hydrocarbon fluids that include different types of fuels. The bottom part of the landfills and UGST is critical. This liner material and its composition prevent heavy metals and leachate from seeping through to the groundwater. Failure of this layer presumably causes most landfill failures.
Article
Bentonites are used for various industrial applications. Their physicochemical properties depend on the mineralogical and chemical composition, the type of smectite, the grain size distribution, the cation exchange capacity (CEC), the dominant interlayer cation (Na+, Ca2+, Mg2+), and the layer charge density. All these parameters can be measured with acceptable precision. Nevertheless, the performance of a bentonite in a given application is often unpredictable. An additional relevant parameter is the “microfabric” describing the arrangement of minerals and/or the intergrowth of the minerals with glass. The microfabric is supposed to affect different bentonite properties such as swelling capacity and rheology. The present study focuses on the influence of different microfabrics on the abrasivity by bentonite dispersions.The abrasivity of bentonite dispersions mainly depended on two factors: 1) on the amount of hard and sharp accessory minerals and volcanic glass and 2) the grain size distribution, which was produced by different grinding techniques. The abrasivity increased with decreasing grain size, which was caused by breaking the hard components (minerals and glass) leading to an increased number of sharp edges.In addition, there was evidence for a subordinate influence of the type of exchangeable cations. This influence is explained by the different relative arrangements of smectite particles towards the surfaces of hard and sharp minerals. Na+ exchanged glass rich samples showed higher abrasion values than the Ca2+ exchanged samples.
Article
In this study, the relationships between geotechnical index properties and the pore-size distribution of compacted natural silt and artificial soil mixtures, namely, silt with two different clays and three different clay percentages (10%, 20%, and 40%), were examined and compared. Atterberg’s limit tests, standard compaction tests, mercury intrusion porosimetry, X-ray diffraction, scanning electron microscopy (SEM) analysis, and Brunauer-Emmett-Teller specific surface analysis were conducted. The results show that the liquid limit, the cumulative pore volume, and specific surface area of artificially mixed soils increase with an increase in the percentage of clay. The cumulative pore volume and specific surface area with geotechnical index properties were compared. High correlation coefficients were observed between the specific areas and both the liquid limit and the plasticity index, as well as between the cumulative pore volume and both the clay percentage and the
Chapter
HYDRAULIC PROPERTIES OF SOILS ABSTRACT The current chapter addresses the hydraulic properties of soils, which are primarily expressed through the concept of the hydraulic conductivity parameter that enters Darcy’s law. In that respect it is a companion to chapter 5 of this book, which provides the background of the material discussed here. Initially, different models to estimate the hydraulic conductivity are presented followed by laboratory methods of its estimation. Particular emphasis is given on the scale effect, the discrepancy that has been observed between laboratory and field estimates of hydraulic conductivity, which may range over several orders of magnitude. Field tests, through the pumping of wells in aquifers, are extensively presented. Steady state solutions are initially discussed, followed subsequently by methods to assess the hydraulic parameters when the test, as is in most cases, has not reached equilibrium flow conditions. Transient radial flow to a well in a confined aquifer is presented through the Theis and the Cooper-Jacob methods. In addition, the Hantush-Jacob method for leaky aquifers, and the Neuman method for pumping tests in unconfined aquifers are described. The chapter discusses also the physical and chemical factors that affect the hydraulic properties of clay-mixtures that are used as engineered barriers, such as the heterogeneity, soil structure and composition, fracturing, and adsorption capacity, among others. It concludes with the effect that inorganic and organic contaminants may have on the hydraulic properties of soil-engineered barriers. Keywords: hydraulic conductivity, Kozeny-Carman model, cluster model, Komine model, laboratory methods to estimate hydraulic conductivity, rigid wall permeameter, flexible wall permeameter, scale effects, Neuman’s universal scaling law, pumping tests to estimate hydraulic conductivity, steady state (equilibrium) well tests, unsteady (non-equilibrium) pumping tests, Theis method for confined aquifers, Cooper-Jacob method for confined aquifers, Hantush-Jacob method for leaky aquifers, Neuman method for unconfined aquifers, physical factors affecting hydraulic conductivity, chemical factors affecting hydraulic conductivity, effect of inorganic contaminants on hydraulic properties, effect of organic contaminants on hydraulic properties.
Article
Organophosphate (OP)-insecticide-absorbing hybrid film containing 10% (w/w) organobentonite and carboxymethyl chitosan (CMCh) was fabricated and tested. Bentonite clay was modified to organobentonite by two steps modification with (1) NaCl and (2) plant alkaloid monovalent cation berberine. CMCh was synthesized from commercial shrimp chitosan. Afterwards, organobentonite was immobilized into CMCh matrix via in situ polymerization of CMCh to cast a hybrid film with 0.5 mm thickness. Scanning electron microscopy images of organobentonite powder and the film revealed the porous material and layer-upon-layer structure, respectively, which is supposed to enhance the water permeability of the film. Fourier transform infrared spectrometry analysis revealed similarly chemical characteristics of the CMCh component in the film and synthesized CMCh polymer powder. The film was then investigated to remove four OP insecticides including profenofos, chlorpyrifos, methyl parathion and dimethoate of 5 ppm concentration in spiked water samples via batch filtration. High-pressure liquid chromatography analysis showed that the removal rates for profenofos, chlorpyrifos, methyl parathion and dimethoate after seven batches were 42, 39, 24 and 20%, respectively. Hence, absorptivity of this film for tested OP insecticides was demonstrated. Furthermore, the combination of organobentonite and natural chitosan is promising for novel absorptive film material generation with regard to environmental clean-up study.
Article
Fine-grained soils containing clay minerals have very high (specific) surface area and good sorption properties, which are important for environmental applications such as rehabilitation of contaminated areas or construction of geological and technical barriers of the repository for the inert and hazardous waste. The specific surface area, which is rarely used in geotechnics, helps to describe the soil and this characteristic is in good correlation with some geotechnical characteristics. In the article, the relationship between specific surface area and some geotechnical properties is analysed, in particular for use in determining the characteristics of the coefficient of permeability.
Thesis
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The storage of highly radioactive waste from nuclear power plants is currently planned to be solved in the Czech Republic by the construction of a deep repository with a multibarrier concept. The key component of one of the barriers is bentonite, whose sealing properties will help to ensure optimal conditions for the disposal of radioactive waste. The focus of the thesis is on a review of the knowledge on the mechanical properties of bentonite and their change after exposure to high temperatures. The review is complemented by the current knowledge of the czech bentonite BCV from the Černý Vrch locality, which is also the material for the laboratory measurements carried out in this thesis. The key part of the work consists of laboratory tests, necessary for experimental verification of the discussed bentonite properties. Internally developed multipurpose cells (MPC cells) were used for the majority of the laboratory tests, as the standard equipment of soil mechanics laboratories has relatively little application for bentonite barrier research. The aim of the experimental part was to investigate how the swelling capacity and hydraulic conductivity of the material change due to previous thermal loading. The main objective of the work is to obtain an overview of the behaviour of the Czech Ca-Mg bentonite BCV after temperature treatment at 150 °C and 200 °C (BCV 150 and BCV 200) and comparison of the results with the original, temperature-unloaded BCV material. The results of the laboratory tests showed that the temperature loading have a significant effect on the time taken for a stabilization of the swelling pressure, which increased significantly. After settling, the swelling pressures were comparable. The results for the temperature-treated samples showed lower retention capacity when rehydrated from air humidity and a slight, not very significant increase in hydraulic conductivity.
Article
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Paper is a shortcut of a doctoral thesis dealing with the retention of heavy metals in mineral linings of waste disposal sites. The problem of the evaluation of the retardation capability of clays has two aspects: neither standard methods, nor a classification were found in literature. An overview on reported research methods is given here, followed by the description of own suggested procedures applied in the presented study, with a special accent to the laboratory sorption tests. These methods were applied to a set of fine-grained soils of different mineral composition, from pure kaolin through polymineral clays to a high-quality natural bentonite. Besides laboratory tests, also research of the "in situ" retardation was possible at some old landfills. Results of the laboratory sorption tests allowed to construct a draft classification plot, as well as to create a draft classification system of fine-grained soils (clays). Both products enable a qualitative estimate of the retardation capability of a certain soil without sorption tests. In the classification plot, the carbonate content and CEC were regarded, while similar mineral composition is the criterion used in the classification system. In both cases, the classification is open for further completion due to further tests on other kinds of soils. Finally, advantages and disadvantages of particular groups of research methods were summarised.
Article
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Hydro-chemio-mechanical coupling effects in an expansive clay have been studied along soaking paths with oedometer cells equipped with two solute injection systems. Two sets of boundary conditions for soaking were applied: solute and gas-solute mixture. The clay used for the experiments was a Ca French expansive clay known as Fo-Ca. The role of solute chemistry on clay permeability, swelling strain, porosity and on the retention curve was investigated. Copper cations were chosen for taking into account strong adsorption capacity, as the migration of toxic cations normally occurs in acid solutions, exchanges being produced with alcaline content. Permeability as well as swelling strain changes along soaking paths have been investigated with copper concentration with respect with the two sets of boundary conditions. Moreover, the ability of the Fo-Ca for ions sorption was studied by means of leachate analyses. Porosity and retention curves were also given after testing with respect to copper concentrations. Significant changes resulting from the copper solute injection have been obtained for all these material parameters.
Article
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A number of major problems associated with the containment approach to landfill management are highlighted. The fundamental flaw in the strategy is that dry entombment of waste inhibits its degradation, so prolonging the activity of the waste and delaying, possibly for several decades, its stabilisation to an inert state. This, coupled with uncertainties as to the long-term durability of synthetic lining systems, increases the potential, for liner failure at some stage in the future whilst the waste is still active, leading to groundwater pollution by landfill leachate. Clay liners also pose problems as the smectite components of bentonite liners are subject to chemical interaction with landfill leachate, leading to a reduction in their swelling capacity and increase in hydraulic conductivity. Thus, their ability to perform a containment role diminishes with time. More critically, if diffusion rather than advection is the dominant contaminant migration mechanism, then no liner will be completely impermeable to pollutants and the containment strategy becomes untenable.
Article
The geotechnical and chemical approach to the evaluation of blended mineral fillers in a geosynthetic mat for sealing purposes is introduced. Properties measured include water sorption characteristics, heavy metal sorption, neutralization ability, occlusion of saturated vapors of water and nitrogen dioxide and permeability. Bentonite is the main component in the blend; zeolite and diatomite are added minerals. All materials are mined in Slovakia. Bentonite–zeolite mineral filler is used in the geosynthetic mat TATRABENT manufactured since 1996.The significance of the relation between liquid limit (wL) and swell characteristics like water adsorption by Enslin (ES) free swell and one-dimensional swelling has been studied to assess the quality of mineral fillers. Similarly, the relation between liquid limit and coefficient of permeability of mineral fillers is concerned herein. The review of recommended properties for blended mineral filler of Tatrabent is given as well (300%≤wL
Article
A buffer consisting of blocks of compacted Na bentonite powder absorbs water by which the grains expand and exfoliate, yielding clay gels that occupy the voids between them. The expandability of the grains and thereby the bulk density and hydraulic conductivity depend on the density of the gel fillings and hence on the grain density. Since the porewater electrolytes affect the pore size distribution of the gels they have an impact on the hydraulic conductivity as well. The density distribution in matured MX-80 clay determines both the hydraulic conductivity and the ion diffusion transport as well as the swelling pressure. It can be evaluated from micrographs covering a sufficiently large fraction of a cross-section of the clay.
Article
The Atterberg Limits have been repeatedly shown to be useful indicators of clay behaviour. This paper proposes that they should also be used to assess the effect of temperature on clays. To improve on previous attempts, this paper describes a new simple and rapid method by which such assessments can be made. The method enables consistent results to be obtained over a larger range of temperatures (i.e. 10–80°C) than previously possible. This method is, therefore, potentially useful when assessing the behaviour of clay soils which are likely to be exposed to elevated temperature, such as landfill liners. Results are presented for kaolinite, smectite and mixtures of these clays of various percentages. These demonstrate that smectites are considerably more sensitive to temperature changes than kaolinites. For smectitic clay the liquid limit increases with temperature, whereas a very slight decrease occurs with kaolinite. The variation in liquid limit appears to be closely related to the specific surface area of the clay, and the resulting nature of inter-particle contacts.
Article
A mixture theory framework is adapted to analyze the effects of changes in clay chemistry during dehydration and rehydration on clay mechanical properties. Macroscopic and microscopic evidence points to a possibility of modeling the mineralogical processes of illitization of smectites and re-smectitization of illite as kinetic reactions in closed systems. A version of thermo-chemo-plasticity for rehydrating illite is presented in which a hidden variable of hardening depends on temperature and the reaction progress variable in addition to plastic strain.
Article
The microstructure controls most physical properties of clays. This is obvious when comparing natural smectitic clay and clay prepared by drying, grinding and compression of air-dry powder. The hydraulic conductivity of the artificially prepared clay is higher than that of the undisturbed, natural clay. If the latter clay is percolated with distilled water and Ca-rich water, the difference in conductivity is obvious, while percolation of the natural clay with these solutions does not yield a very dramatic change. This is because the microstructure of the natural clay is very homogeneous, while the artificially prepared clay preserves the high density of the powder grains while the gels in the voids between the grains are soft.
Article
The response of water repellency to added clays dominated by kaolin or smectite was investigated for 23 highly water repellent sandy soils from the West Midland Sandplains, Western Australia. The effects of soil properties, and wetting and drying cycles on this response were also examined. Two standard clays—Georgia kaolinite and Wyoming bentonite—were compared with two soil clays—Jarrahdale laterite pallid zone kaolin and Folly Flats soil smectite—in laboratory experiments. The clays were saturated with either sodium or calcium, and were applied at rates of 0%, 0.2%, 0.4%, 0.8% and 1.6% by weight. Water repellency was measured by recording water-drop penetration time (WDPT). Clay morphology and the distribution of clay on the surfaces of sand grains were examined using optical and electron microscopy.
Ložiska nerud (Deposits of nonmetallic raw materials
  • I Kraus
  • M Kužvart
Kraus I., Kužvart, M., 1987. Ložiska nerud (Deposits of nonmetallic raw materials), Praha: SNTL Naklad. Naklad. Techn. Literatury, Alfa, Bratislava. 232 pp.
Microstructures of clayey soils in relation to shear strength
  • Klukanova
Klukanova, A., 1995. Microstructures of clayey soils in relation to shear strength. Proceedings of the 6th International Symposium Landslides, Christchurch, New Zealand. A.A. Balkema, Rotterdam, Netherlands, pp. 1587 -1591.
  • K H Head
Head, K.H., 1992. Manual of Soil Laboratory Testing. Vol. 1: Soil Classification and Compaction Tests, 2nd ed. Pentech Press, London, UK.
New perspectives for geosynthetic clay liners using calcium bentonite
  • Allexiew