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This study is aimed at evaluating the performance of low-alkali activated clay-fly ash liners as an environmentally friendly approach to attrap heavy metals cations and prevent the leachate containing such hazardous materials from spreading through the soil medium. For this purpose, a series of unsaturated experimental column leaching tests is carried out on clay-fly ash samples containing 20% fly ash activated by 1, 2 and 4 M NaOH solutions, leading to different Na/fly ash ratios. The leachate, synthesized by various equal concentrations of copper sulfate CuSO 4 and zinc nitrate Zn(NO 3) 2 , i.e. 50 mg/L , 100 mg/L and 150 mg/L, is monitored while passing through various treated clayey soils to assess their time-dependent attenuation capacity and permeability at three different leaching times so as to select the sample with the best overall performance. The leaching test is then continued for the corresponding sample until 57 days in order to determine the unsaturated breakthrough curve and effective diffusion coefficient of the pollutants. The results of experiments show the mutual contribution of hydroxide precipitation and physical adsorption to the attenuation process, where the lower alkali concentration favors the former; thus the clay-fly ash liner activated by 1 M NaOH solution exhibits the best attenuation performance, achieving appreciably high removal rates of >99.71% for Zn(II) and 94.47% for Cu(II), after 192 h of leaching. Furthermore, having a lower breakthrough time and effective diffusion coefficient, 1 M alkali-activated clay-fly ash is observed to considerably work better than the untreated clay in the long-run attenuation. Microstructural analyses also reveal the presence of new crystalline phases and rise in amorphous content, referring to new chemical bonds produced due to the immobilization of heavy metals. [Display omitted] • Performance of low-alkali activated clay-fly ash liners to attrap heavy metals is evaluated. • Unsaturated experimental column leaching tests is performed on clay-fly ash liners. • Attenuation capacity, permeability, breakthrough curve and diffusion coefficient are evaluated. • Mutual contributions of hydroxide precipitation and physical adsorption are assessed. [ABSTRACT FROM AUTHOR]

Due to cyclic loading, clays composed of different mineral compositions exhibit non-linear viscoelastic characteristics. This study quantified the effect of the mineral composition on the non-linear viscoelastic properties of clays. Large-amplitude oscillatory shear rheological tests and cryo-electron microscopy tests were conducted on clays containing quartz, feldspar, montmorillonite, and kaolinite (Q, F, Mt., and Kaol). The results indicated that as the clay content in the soil sample increased, so did the value of relative intensity(I 3 / 1), the Lissajous curves shifted from elliptical to rectangular, and the absolute values of the overall non-linear viscoelasticity parameters (N E and N V) were also larger. In addition, its non-linear viscoelasticity was more prominent, supported by the cryo-electron microscopy test outcomes. Montmorillonite played a more significant role than kaolinite in increasing the nonlinear viscoelasticity of the soil samples. The study findings have significant academic and practical value, facilitating an in-depth understanding of the viscoelastic behavior of clays, rheological studies of other types of clay soils, and geotechnical engineering applications. • Studying clay non-linear viscoelastic behavior (NLVEB) using rheology. • Quantifying NLVEB of clay using overall characterization parameters (N E and N V). • Clay mineral composition and content have a great influence on the NLVEB in clays. • Montmorillonite is extremely important for the NLVEB in clays. [ABSTRACT FROM AUTHOR]

Silicon (Si) is an abundant element in terrestrial ecosystems and makes essential contributions to agricultural crops, environments, and industries; however, current knowledge of Si speciation in soil systems is based primarily on crystalline mineral types with limited information about the effect of Si-adsorbed species on the most chemically reactive clay fraction. Herein, we investigated Si speciation in the clay-sized fraction of tropical soils. Silicon K-edge X-ray absorption near edge structure (XANES) spectra of clay samples, together with a wide range of reference compounds varying in clay and Fe/Al oxide mineralogy, showed the predominance of Si in a beidellite structure and of Si adsorbed to montmorillonite and to kaolinite. Unique features, including a pre-white-line feature, white-line position and intensity, and post-edge numbers and positions of Si reference spectra, could differentiate most Si reference standard spectra. Silicon adsorbed to goethite, Si-ferrihydrite-natural organic matter complexes, and Si in the structure of biotite, illite-smectite, chlorite, quartz, and Si nanoparticle, variously occurred in different samples. The CaCl 2 extraction data revealed that extracted Si was below the limits of Si deficiency in one-half of the total soil samples and accounted for only 0.02% of total soil Si. Soil extractable Si had a positive correlation with pH, organic matter, and clay. Our results present a novel application of Si K-edge XANES as a tool for identifying Si speciation in natural clays that are the most chemically reactive phase of Si retention and release in terrestrial and aquatic systems. [Display omitted] • Reference spectra of silicon sorbed to clay mineral and Fe/Al oxides are presented. • Si-ferrihydrite-natural organic matter complexes have been synthesized and proposed. • White-line and post-edge features of Si reference spectra can identify most Si standards. • Structural Si in beidellite and Si sorbed to montmorillonite/kaolinite dominated Si species. • Si nanoparticles could form in clay-sized fractions of soil systems. [ABSTRACT FROM AUTHOR]

Biocementation is a low carbon footprint soil improvement technique alternative to the use of hydraulic binders such as cement, mainly applied in sandy soils due to the need for vital room for bacteria and easy access for nutrient transport to feed them. This treatment is not suitable for natural clayey soils, however pore clogging caused by the presence of clay in low percentages may not be a problem, and clay minerals can be beneficial to increase the area for bacteria to attach and therefore to precipitate larger quantities of biocement. In addition, clay minerals can also have a positive influence on bacteria activity itself, and this is the novelty of this investigation. The influence of kaolin and bentonite clays on biocementation using Sporosarcina pasteurii was measured by (i) the amount of calcium carbonate precipitated in sandy soil prepared with known percentages of the two clays (1%, 5%, 10% and 20% in dry sand mass), relating it with unconfined compression strength, and (ii) evaluating bacteria growth and urease activity in liquid media with 1% and 5% of each clay. The best enhancement of biocementation was found for kaolin percentage between 5% and 10% and for 5% of bentonite, considering as reference the case where no clay was added. These relatively small percentages were linked to physical aspects related with the room occupied by the clay minerals causing dispersion of the precipitate in the clay matrix, although the presence of clay in the fluids of soil voids could contribute positively for bacteria growth and long-term survival. These results confirm that biocementation treatment may be effective on soils with relatively small clay percentages and opens the possibility that clay can be used in controlled fixed amounts to improve the efficiency of this treatment in clean sands. • The positive influence of clay on bacteria growth was confirmed by optical density measurements. • Urease activity measurements along time showed that clay minerals contribute to bacteria survival. • Kaolin can be more beneficial to biocementation than the bentonite. • The clay presence only becomes a negative influence above 5% for bentonite and 10% of kaolin. • Highest strength increment and calcium carbonate content were found for 5% of bentonite and 5% to 10% of kaolin. [ABSTRACT FROM AUTHOR]

Abstract Swelling pressure is an important parameter for understanding the expansive nature of the bentonites and natural clayey soils. During the wetting process, the intergranular stresses evolve due to the capillarity and adsorption of clay minerals, and swelling pressure is developed if soil deformation is constrained by the boundary conditions. Strong physicochemical interactions between clay particles and water molecules prevail in the development of intergranular stresses in expansive soils. In this paper, an empirical approach considering Donnan's osmotic effect was proposed to calculate the change in swelling pressure of expansive soils infiltrated by salt solutions with different concentrations. In the model, the intergranular stress addresses the physicochemical interactions between the minerals of clay and saturating fluids with ion concentration gradients induced by fixed negative surface charges. The differential volumetric strain assuming nonlinear elasticity identifies two mechanisms for the variation of the swelling pressure with the concentration of salt solution. The Donnan osmotic pressure decreases as the concentration increases, and the bulk modulus decreases as the concentration increases. The experimental results show that the variation of the Donnan osmotic pressure dominants the evolution of the swelling pressure with the salt solution concentration for a given soil. The comparison between the simulations and the available experimental data in the literature illustrates well the prediction of the swelling pressure of expansive soils by using the proposed model. Highlights • The intergranular stress is introduced to describe expansive soils. • Address the physicochemical interactions between the clay and fluids. • The variation of small-strain shear modulus with the NaCl is considered. • The Donnan osmotic pressure dominates the swelling pressure change. • A model for the swelling pressure of clay saturated with NaCl is proposed. [ABSTRACT FROM AUTHOR]

Abstract The framework of the intrinsic compression behaviour of normally consolidated soft clay proposed by Burland (1990) is widely adopted in engineering practices. However, further investigations should be conducted on its validity in the coastal and offshore environments to verify the effect of pore water salinity. In the present work, oedometer tests were performed on remoulded artificial soft clays (mixtures of kaolin and bentonite with 0%, 5%, 10%, and 20% of bentonite by mass). The artificial clays were salinized with sodium chloride solutions at concentrations 0 mol/L (distilled water), 0.17 mol/L, 0.51 mol/L, 0.86 mol/L, and 1.70 mol/L at water contents equal to 1.0–1.5 times of the liquid limits. The results showed that the 'intrinsic' properties of clays, including the compression index C c ⁎(100–1000 kPa), void ratio e 100 *, and compression line based on the void index I v , changed with the pore water salinity. Following the empirical correlation proposed by previous researchers, the decrease in C c ⁎ caused by pore water salinity could be generally characterised by the liquid limit and void ratio at the liquid limit (e L). The dispersed correlation between the predicted e 100 ⁎ and the experimental results in this study were caused by the significant changes in e 0 / e L controlled by pore water salinity. The relationships between void index I v and vertical stress σ v ' deviated from the intrinsic compression line (ICL) under the saline environment. For the artificial clay rich in smectite, the slopes of I v –log σ v ' before yielding increased with pore water salinity at the initial water content. Pore water salinity affected the intrinsic compression behaviour of soft clays primarily composed of kaolinite to a lesser extent. Highlights • The pore water salinity changes e 100 ⁎. • Normalised compression curve deviates from Burland's intrinsic compression line at small stress. • Burland's framework needs to be updated considering salinity effect and small stress. • The particle flocculation alters the intrinsic compression behaviour of remoulded soft clays. [ABSTRACT FROM AUTHOR]

Abstract Bentonite (Bent) clay is a component of soil with useful properties for enzyme adsorption. In this work, the previously characterized antioxidant superoxide dismutase (SOD) enzyme named wGLP by wheat germin-like protein was immobilized in raw (Bent) and modified bentonites (Bent-DDA). The physicochemical characterizations of both supports were carried out. Successful adsorption of wGLP onto Bent and Bent-DDA occurred on the surface and within the interlayer spacing as was revealed by X-Ray Diffraction (XRD) and Thermogravimetric Analysis (TGA). The release of wGLP at different times and pHs was tested. While wGLP remained almost totally immobilized into Bent-DDA up to 96 h, it was released from Bent to reach nearly 60% after 72 h at pH 7.5 and preserving its SOD activity. Since tomato cell viability under the presence of Bent-wGLP was maintained, Bent-wGLP complexes are potential carriers of antioxidants in tomato cell suspension cultures. Highlights • -Immobilization of the wGLP antioxidant enzyme into Bent and organo-Bent (Bent-DDA). • -Effect of pH on in vitro release of wGLP from Bent and organo-Bent (Bent-DDA). • -Valorization of the antioxidant properties and cytoprotective action of Bent-wGLP in tomato cells. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate and relate the geotechnical parameters with the mineralogical properties of the Miocene and Plio-Quaternary (Pliocene to Quaternary) lacustrine and fluvial sediments, particularly clayey soils in the Orta County, Çankırı. The study area is located about 110 km northeast of Ankara which is the capital city of the Republic of Turkey and Orta is a small county of Çankırı. The study area is a structural depression in the northern part of the Orta plain which is filled by fault-controlled continental sedimentation. In order to correlate the geotechnical and mineralogical characteristics and to establish a relation between these properties, comprehensive geotechnical laboratory studies have been performed. For correlation purposes, disturbed and undisturbed soil samples were collected from twenty-two locations of the study area. On these samples, mineralogical (i.e., methylene blue absorption, specific surface area determination, X-ray powder diffraction (XRD) and scanning electron microscope (SEM-EDAX)) analysis and geotechnical (i.e., sieve analysis, hydrometer, Atterberg (consistency) limits, oedometer and swelling) tests were implemented. By the aid of the statistical analysis, cross-correlation of the soil properties was established by the regression analyses performed. In particular, the plasticity index was correlated with cation exchange capacity, specific surface area, clay content, percent of fines, smectite and smectite/kaolinite ratio (SKR). There was a direct relationship between PI and smectite percentage as well as between PI and SKR. Additionally, the liquid limit was correlated with the clay content and the effect of the specific surface area on the swelling characteristics was studied. The effects of the mineralogical properties of the Orta clays together with the geological history on geotechnical parameters were investigated by considering the relationships mentioned. The results of the study revealed that the mineralogical characteristics had a significant effect on the geotechnical behavior of clayey soils of the Orta County which was demonstrated by regression analyses. Finally it was identified that the geotechnical properties of clayey soils can be approximated and more reliably determined if the mineralogical character and composition of clay is accurately investigated and well developed. [ABSTRACT FROM AUTHOR]

Lightweight alkali-activated ground granulated blast furnace slag (LAS) is an energy-efficient and environment-friendly cementitious material that can be used as a binder for the fill soil stabilization in subgrade construction. Although physical, hydraulic and mechanical properties of LAS stabilized clayey soils have been previously characterized, their long-term durability under deteriorating environments has not yet been well assessed. This paper reports an experimental study on the sulfate attack resistance of a LAS stabilized clayey soil, which is composed of GGBS, sodium silicate, calcium carbide residue (CCR), air foam, and clayey soil. Stabilized soil specimens are submerged in a sodium sulfate solution for varying periods (3, 7, 14, 28, 60, 90 and 120 days). The mass change percentage, unconfined compressive strength and thermogravimetric characteristics are evaluated at the end of each varying soaking periods. The same virgin soil stabilized by the lightweight Portland cement (LPC) is also tested as a benchmark. The results suggest that the LAS stabilized soil has superior sulfate attack resistance in terms of greater water absorption and higher strength, which is attributed to the presence of larger amount of cementitious hydration products in the LAS stabilized soil, as confirmed via thermogravimetric measurement. [ABSTRACT FROM AUTHOR]

The main objective of this study was to provide a methodological insight in the archaeometric field of ceramic provenance and technology, through the identification of the scale of representative differences in terms of clay composition. For this purpose, a total of 78 clay specimens-representative of the three types of Daunian clayey raw materials (Sub-Apennine clays, alluvial deposits and terraced alluvial deposits)- was collected and geochemically investigated, with the aim of determining up to which geographical scale, the exclusive application of geochemical analyses can provide reliable results for the reconstruction of clayey raw materials supply. For the Daunian territory, the scale has been identified with that of a ‘riverine province’, i.e. between the local and the regional extension of the north Apulian fluvial courses. In practice, the Sub-Apennine clays can be chemically distinguished into a northern group, including the Salsola, Vulgano, Celone and Lorenzo streams and a southern group, including the Carapelle stream and the Ofanto river. Moreover, the comparison between the geochemical composition of the clay samples and that of local ceramic productions (previously investigated) has shown that the Sub-Apennine clays were either used as received (Clay 1 group) or refined through decantation (Clay 2 group), before being shaped into fine wares or building materials; conversely, both the alluvial and the terraced alluvial deposits were used “as received” for the production of coarse wares. Furthermore, for the first time, the geospatial network analysis was further applied to the investigation of ancient raw materials exploitation. This analysis was performed in order to reach a reasonable reconstruction of both routes and travel times linking supply areas with production and distribution sites. Surprisingly, the results have shown that, at small distances, the transportation of clayey raw materials is not only reliable but rather highly likely, especially in those sites where Sub-Apennine clays are not readily available. [ABSTRACT FROM AUTHOR]

This study shows that the controlled dispersion and distribution of nanoclay in clay/polyethylene (PE) nanocomposites result in peelable sealants with an ultra-wide peelable heat-seal temperature window (ΔT p ). Different nanoclays, unmodified montmorillonite (Mt) and organo-modified Mt. (OMt), were examined for their capacity to generate peelable clay/PE nanocomposites in a melt-blending film extrusion process. Clay/PE nanocomposite films containing 6 mass% organoclay (OC) exhibited a cohesive peel behavior with a ΔT p of about 12°C while PE film containing 6 mass% unmodified clay resulted in microcomposite with a lock seal performance. With the same mass% of OC, a much lower peel strength with a significantly broad ΔT p of 45°C was achieved mainly due to the fine dispersion of OMt when PE-grafted-maleic anhydride (PE-g-MA) was used as a compatibilizer. WAXD and TEM results confirmed that a substantial enhancement in the dispersion and distribution of intercalated nanoclays was achieved with PE-g-MA compatibilizer. Finally, an ultra-wide ΔT p of over 100°C was obtained for compatibilized OC/PE nanocomposite sealant containing only 3 wt% OC with partially exfoliated microstructure indicating that the exfoliation of nanoclay is in favor of peelability. The peel fracture mechanics of the clay/PE nanocomposite sealants were examined through T-peel test and SEM imaging. The results showed that the dispersion and distribution of nanoclay along with the interfacial adhesion between nanoclay and matrix are the key factors controlling the peel performance of the sealants. [ABSTRACT FROM AUTHOR]

In order to explore the feasibility of improving zinc and chromium ability of zirconium-aluminium pillared clays (PILC), mixed zirconium-aluminium PILC with different Zr/Al ratio (Zr/Al = 100/0, 90/10, 50/50, 10/90 and 0/100) were prepared and investigated for their ability to remove zinc and chromium from water. Single and mixed PILC were characterized with X-ray diffraction, N 2 adsorption–desorption, FT-IR spectroscopy method, etc. Results indicate that, in the case of single PILC, zirconium PILC exhibited an adsorption capacity higher than aluminium PILC. In the case of mixed PILC, adsorption capacity increased as the ratio of Zr/Al increased. The influence of the pH values and the temperature on adsorption capacity was also investigated. [ABSTRACT FROM AUTHOR]

Marl was treated with Mg-rich lime to evaluate the effectiveness of lime stabilization for this expansive, clay- and carbonate-rich material. XRD and TEM analyses revealed very limited dissolution of expandable clay minerals and neoformation of Mg-enriched smectites. C-(A)-S-H phases formed and initially cemented clay particles. However, they experienced decalcification and decomposition over time, leading to disaggregation of clay particles and deterioration of some of the marl's geotechnical properties. Results question the effectiveness of lime stabilization for marls, especially using Mg-rich lime. Modifications to commonly used treatment protocols in order to overcome these shortcomings are discussed. [ABSTRACT FROM AUTHOR]

Studies of the volume change behaviour of saturated and unsaturated fine-grained soils upon exposure to various types of fluid are of significant interest while dealing with contaminated soils. In this study, the one-dimensional volume change behaviour of two clays (Spergau kaolin and Calcigel bentonite) with dominant minerals as kaolinite and montmorillonite was studied by inundating several initially unsaturated and saturated clay specimens with water and a non-polar organic liquid (heptane). For both cases, applied vertical pressures of 25 and 100 kPa were considered under oedometric conditions. The magnitude of compression and swelling deformations of the clays were found to be strongly dependent upon the mineralogy of clays, dielectric properties of the pore-fluid, initial compaction conditions, and applied stress during the wetting process. The test results indicated distinct interactions between unsaturated clays and water. Specimens of Spergau kaolin exhibited compression with water, whereas specimens of Calcigel bentonite exhibited swelling. Compression and swelling deformations of the clays with heptane as the inundating liquid remained within about ±1.0% for both clays indicating a very minor interaction between unsaturated clays and molecules of this non-polar organic liquid. The test results emphasized the significance of attractive and repulsive forces and their impact on the volume change behaviour of clays of different mineralogy. [ABSTRACT FROM AUTHOR]

The achievement of Optimum Compaction Moisture Content (OCMC) of clay soil plays an important role in compaction as well as the durability and strength of compacted soil. This is due to its effect on the structure and orientation of the clay soil particles. Most researchers on stabilised systems involving soils and/or industrial waste by-product additives for applications in roads and buildings are faced with the problem of how to approach the establishment of OCMC, when the complex mixtures involved. This paper reports on the laboratory investigation of theoretical methods of two different approaches to establish the OCMC in the stabilisation of clay soil involving multi-binary binder in cementitious binder system. Furthermore, this research also explores the use of an industrial by-product, Pulverized Fuel Ash (PFA) as partial target material and ground granulated blastfurnace slag (GGBS), with a view to reducing the reliance on the traditional cementitious binders, such as lime and/or Portland Cement (PC), in stabilising Lower Oxford Clay (LOC) soil combining with PFA at 50:50 ratio. LOC + PFA was stabilised both in conventional manner using Lime and PC as control and using sustainable binders incorporating GGBS. The results show that there was no one particular approach to the establishment of the optimal compaction moisture content for best strength development and durability. The best approach being dependent on the period of curing, stabiliser content and whether GGBS was blended with Lime or with PC. Of the various stabilisers studied, the highest strength magnitudes were however recorded with LOC-PFA stabilised using the blended binders incorporating GGBS. For all 7, 28 and 56 days of curing periods, the PC-based stabilisers were observed to be less sensitive to the different approaches to compaction moisture content, relative to the lime-based systems. [ABSTRACT FROM AUTHOR]

The threshold yield stress plays a key role in controlling the rheological consolidation behaviour of soft clay. A semi-analytical theory combining numerical and analytical methods is introduced that excludes the effects of clay self-weight. The governing equations assume the clay is an elasto-viscoplastic material. Approximate solutions as well as computational programme to surface loading for two drainage boundary conditions are obtained, while the clay profile is separated into material which is overconsolidated and normally consolidated. The effects of threshold yield stress and time-dependent loading on the rheological behaviour of soft clays are explored using the solutions developed. [ABSTRACT FROM AUTHOR]

Desiccation cracking process negatively impacts both mechanical and hydraulic properties of clayey soils. Traditional methods applied for the characterization of soil cracking behaviors are mainly based on visual inspections or destructive approaches. The electrical resistivity method provides a non-destructive, sensitive and continuous evaluation of the spatiotemporal variations of many soil physical properties. In this study, an integrated experimental setup is configured to simultaneously capture the evolution of temperature, relative humidity, water content, crack morphology, and apparent electrical resistivity in clay during continuous drying. Apparent electrical resistivity measurements at 1.0 cm electrode spacing are carried out to detect the initiation, propagation and coalescence of desiccation cracks. Image processing quantitatively describes the geometrical characteristics of shrinkage surface crack patterns. Experimental results indicate the strong correlation between the measured apparent electrical resistivity and cracking behavior of soil. As water content decreases during drying, the apparent electrical resistivity of initially saturated clayey soil decreases first before the onset of desiccation cracking, and then transits into the increasing trend. The evolution of apparent electrical resistivity in clayey soil is dominated by two competing effects, with one originated from the volumetric shrinkage-induced closer packing of soil fabric and higher concentration of ions in pore fluids, and another from the evaporation-induced water loss associated with hydration film contraction and desiccation crack insulation. The electrical resistivity method is an effective technique to characterize the development of desiccation cracks, and particularly reliable to map their positions. This study is expected to improve the fundamental understanding of desiccation cracking mechanisms in soils and provide insights on soil characterizations for enhanced stability and performance of earthwork structures. [ABSTRACT FROM AUTHOR]

Dispersive soils are clayey, high in sodium content, and washed easily when subjected to water with low salt concentrations. The works of stabilizing dispersive soils using chemical additives from throughout the world are well documented. In the current study, a highly dispersive clay was treated with various proportions of lignosulfonate, an environmentally friendly stabilizer. A 58% reduction in dispersivity of the soil was achieved by addition of 1.5% lignosulfonate by dry mass. Meanwhile, the electroosmosis technique is known as an effective and modern soil improvement method. In the subsequent stage of the study, the effects of electroosmosis treatment on the dispersive clay were investigated by using different potentials. The dispersivity of soils taken from around the anodes was found decreased by 52% after 7 days of electroosmosis application under 48 V potential. The above two methods were capable of reducing dispersivity however, when used alone, insufficient in bringing the treated soils into the non-dispersive category. Consequently, the simultaneous treatment by lignosulfonate addition and electroosmosis application was successful in reducing the dispersivity of the initially highly dispersive clay by 65% and qualifying it for the non-dispersive designation. [ABSTRACT FROM AUTHOR]

Clay soils, especially soft clay soils covered considerable parts of the earth. Cement and lime are used as traditional additives for clay soils stabilization but unable to increase the strength properties of clay soils significantly. So, it seems necessary to use new additives to increase the strength parameters of soft clay soils. Therefore, cement and epoxy resin are used for stabilization of soft clay soils in this study. The main objects of this study are the determination of the effect of epoxy resin on the mechanical parameters and microstructure properties of clay soils, the phenomenon of clay concrete and effect of clay minerals on its properties and also, using knowledge of the elastic modulus, toughness and elastic and plastic strain of the stabilized soft clay as a practical criterion for determination of the optimum additive percentage in soft clays stabilization in addition to UCS. In this study, two samples of clay soils with different clay minerals were investigated. Clay soil samples that tested experimentally were bentonite and kaolinite. A series of microstructure and macrostructure experiments were conducted on the samples. The results show that using epoxy resin increases strength parameters about 100 to 1000 times while UCS reaches to more than 50 MPa in some samples based on the clay mineral types in the soils. Unlike the cement concrete, as the strength increases the failure strain and material toughness will increase simultaneously as well. In addition, the important and prominent result of stabilization by epoxy resin is the best efficiency in the weakest and the most sensitive soils. [ABSTRACT FROM AUTHOR]

Highly active porous materials composed of calcite and periclase nanoparticles was prepared by the carbonation of thermally treated clayey dolomite, having great potential for heavy metal pollution control in water and soil. The effect of coexisting steam and hydration pretreatment on the carbonation of calcined clayey dolomite (CCD) was studied by fixed bed reactor and mass spectrum on-line monitoring. The phase, surface chemistry, thermal activity, pore type and morphology of CCD after carbonation were characterized by XRD, FTIR, TG, N 2 adsorption–desorption isotherm and TEM. The results showed that the initial and complete carbonation temperatures of CCD under anhydrous conditions were 400 °C and 600 °C, respectively. The presence of 10% steam decreased the initial and complete temperatures by 100 °C, respectively. The complete carbonation temperature was reduced to 400 °C when the CCD was hydrated and dried before carbonation. However, the hydrated CCD which not dried can be directly carbonated at room temperature, and the carbonation rate (newborn calcite mass fraction) firstly decreased, then increased with the increase of temperature in the range of 50–500 °C. According to the TG results, the decomposition temperatures of the newborn calcite produced by 650 °C carbonation of CCD decreased by 50 °C compared with that of common calcite. The research on cadmium removal showed that the removal efficiency of 50 mg/L Cd (II) by 650 °C carbonation of CCD rapidly reached 99.8% within 1 h, while the equilibrium pH decreased by 2 units compared with CCD without carbonation. The carbonation of CCD formed nano calcite of lower decomposition temperature and also hampered the hydroxylation to decrease the effluent pH. The experimental results displayed carbonation can control the physicochemical property of the CCD, and the carbonated product is potential to be used for the removal of Cd (II) from aqueous solution. [ABSTRACT FROM AUTHOR]

Liquid limit (LL) is defined as a limiting water content separating the viscous liquid state and plastic state of soil consistency. LL of clays, being a basic physico-chemical property, plays a role in environmental geotechnical engineering practice. Since it is well-known that kaolinite and smectite behave quite differently from each other from the geotechnical point of view, ninety-one data regarding smectite (Na and Ca) and kaolinite mixed with organic pore fluids having different dielectric constant (ε) values have been carefully analyzed. Data confirm that for a decreasing ε value of the pore fluid a decrease in LL is observed for the smectitic clays, with different magnitude depending on the main ion, whereas for kaolinitic clays this decreasing ε causes an increase in attractive forces causing flocculation and increase in LL values. A probabilistic approach has been performed to assess the robustness of the regression functions. For smectitic and kaolinitic clays the mathematical dependency of LL with ε is validated by the probabilistic analysis. [ABSTRACT FROM AUTHOR]

Clay amendments are used widely in the horticultural industry in peat-based substrates, as they have the capability to improve the potassium (K) buffering capacity. The K adsorption and desorption behavior of different clays was characterized here to develop criteria for identification of clays suitable for substrate amendment and to evaluate their significance for plant K uptake. K adsorption of saprolitic, bentonitic and relocated clays from the Westerwald area, Germany, was characterized with adsorption isotherms for calculating the maximum adsorption capacity for K. The K desorption was quantified in a percolation experiment using 0.01 M CaCl 2 as extractant. The influence of a varying K adsorption capacity of the clays on the K availability to plants was investigated in a growth experiment. The availability of K in substrates was determined by 0.01 M CaCl 2 (CAT), Ca-acetate-lactate and NH 4 acetate. Different cultivation practices were simulated by varying the start of K topdressing: “immediate,” “delayed” and “no” K topdressing. A higher K adsorption capacity of the clays amended resulted in a lower K concentration in the pore solution of clay-amended peat-based substrates, while the CAT extractable K concentration was the same. It also resulted in an enhanced plant growth and higher K concentrations in the shoot without K topdressing. The uptake of K by plants exceeded the amount of exchangeable K in some peat-clay blends where no K was fertilized. The amount of K released from the clays in the plant experiments was in the same magnitude as the maximal desorbable K determined in the percolation experiment and was highly dependent on the mineralogical composition in the order: smectitic > illitic, kaolinitic clay. The K released from the clays contributed significantly to the supply of K to plants. [ABSTRACT FROM AUTHOR]

Clays are employed in a wide variety of industries such as ceramic industry, manufacture of paper, rubber, etc. In this sense, it is well known that at industrial processes in which clayey materials are used, such as ceramic industry, in order to carry out some specific stages, the wetting of clays is commonly required. Moreover, it is also long established that wetting is an appropriated measure to reduce particulate matter emissions during clays storage and handling. The present study was undertaken to assess the influence of moisture on clay dustiness because, though the complex behaviour of the clay–water system has been known since antiquity, the mechanisms involved in clay hydration and their influence on dustiness are still not well understood. To encompass a wide range of specific surface areas, three clays and a kaolin were studied. Chemical and mineralogical analysis of these four raw materials was performed and their particle size distribution, flowability, true density, plastic limit, and specific surface area were determined. Raw materials dustiness was determined using the continuous drop method. As against what might intuitively be expected, the results showed that the relationship between moisture and dustiness was quite complex and strongly related to the hydration mechanisms. In this regard, to better understand the phenomena involved in the clay hydration process, a specific methodology was developed to estimate the critical points of the clay hydration process (regarding dustiness). This methodology can be readily applied to other clays or even to materials of different nature to predict the optimum moisture and, therefore, it could be employed to propose specific measures which could entail an improvement of outdoor and indoor air quality. [ABSTRACT FROM AUTHOR]

Nanoclays, which are active component of soils, play a very important role for enzyme adsorption. To study the effect of nanoclays on enzyme adsorption, these were isolated from three genetically different Indian soils, i.e. black soil (Vertisols), red soil (Alfisols) and recent alluvial soil (Inceptisols). Then X-ray coherent particle sizes of different nanoclays (with and without amorphous aluminosilicates) before and after acid phosphatase adsorption were studied. Result showed that basal spacing of smectite present in nanoclays increased due to intercalation of enzyme molecules, whereas ‘d’ spacing in kaolinite did not change due to enzyme immobilization. Average particle size, calculated by Scherrer equation, increased due to enzyme immobilization for all nanoclays. In case of kaolinite, enzyme molecules acted as linkers and bind more than one particle together, which resulted in increased apparent particle size. Crystallite size of kaolinite was also more than that of mica or smectite. Increased average particle size after enzyme immobilization was confirmed from transmission electron microscopy (TEM) images. [ABSTRACT FROM AUTHOR]

Considerable quantities of pyrophosphate and orthophosphate are introduced to soils as fertilizers and fire retardants. While the fate of orthophosphates added to soils has been extensively studied, less attention has been paid to the behaviour of pyrophosphates in soils. In this work sorption edge and surface charge measurements of orthophosphate and pyrophosphate by boehmite and kaolinite, were conducted at 10, 25 and 50 °C between pH 3.5–11.5. Pyrophosphate and orthophosphate sorption edges differ significantly, showing greater quantities of phosphorous as pyrophosphate sorbed by the minerals in lower pH. Boehmite consistently had higher pyrophosphate uptake across the three temperatures compared to kaolinite. For kaolinite, temperature changes had a more pronounced influence on pyrophosphate sorption. Temperature increases also shifted boehmite point zero charge to lower pH. Analysis of pyrophosphate isotherm data suggests outer-sphere electrostatic attraction is the principal interaction between absorbent and absorbate material at pH 8. The difference observed in sorption results indicate that the type and structure of various phosphates will affect sorption to different mineral types and stresses the importance of studying pyrophosphate sorption processes under a range of environmental conditions. [Display omitted] • The minerals removed more phosphorus when applied as pyrophosphate compared to orthophosphate. • Orthophosphate and pyrophosphate both showed higher affinity to boehmite than to kaolinite. • Temperature effects were more pronounced in pyrophosphate sorption to kaolinite compared to boehmite. • The results show the importance of studying the sorption of different phosphate species by soil clays and minerals. [ABSTRACT FROM AUTHOR]

The role of clay minerals on the strength development of cement stabilized clays at different cement contents, water contents and curing times was studied in this research. Kaolin and sodium bentonite were used to represent non-swelling and high swelling soils respectively. The soils studied were mixtures of kaolin and bentonite at replacement ratios of 0, 25, 50, 75, and 100% of the dry weight of bentonite to have various swelling potentials. The water content of the soil samples was adjusted to the optimum water content (OWC) and to the liquidity index (LI) of 0.25–1.50, so as to simulate different initial soil phases. The macro- and micro-observation indicated that the clay mineral, water content and cement content were the predominant influence factors controlling the strength development of cement stabilized clays, at a particular curing time. For a particular clay mineral, the total soil water to cement content, s-w/c was found to be the prime parameter reflecting the effect from both water content and cement content on the strength development in cement stabilized clay. The generalized strength model can be represented in the form: q u = A/B(s-w/c) where q u is unconfined compression strength, and A and B are constant. The values of parameters A and B were found to be primarily controlled by the clay mineral, which was found to be described by plasticity index. The generalized strength model was validated using separated test data. This model will facilitate the engineering decision of selecting the water content and cement content to attain the target strengths of clayey soils at required curing time with minimum number of trials. • Study microstructure of unstabilized and cement stabilized clayey soils via SEM. • Study roles of clay mineral, cement content, and water content on strength development. • Develop the generalized strength model of cement stabilized clays with 25% < PI <257%. • Verify the generalized strength model with test data at very high R2 > 0.97. [ABSTRACT FROM AUTHOR]

In a series of our previously published papers, we reported a broad range of experiments and theoretical studies devoted to the interaction of carbon dioxide with the anatase titania surface. In the current study, we demonstrate oxygen mobility between gaseous carbon dioxide and solid natural clay minerals. This surprising feature implies that such behaviour is typical not only for titania but also for oxides with different chemical composition and structure. The oxygen mobility was demonstrated by the interaction of isotopically labelled carbon dioxide – C 18 O 2 – with the mineral surfaces. In most cases, we observed rapid oxygen exchange between the gas and the mineral. It was therefore discovered that carbon dioxide is more active than was previously thought because it exchanges its oxygen atoms with inorganic surfaces. Moreover, this feature seems to be very significant in natural clays of various compositions. This finding points not only towards high activity of CO 2 but also towards high surface reactivity of clays, which are quite common surface minerals on Earth and other planets. [ABSTRACT FROM AUTHOR]

Clays including bentonite hold a great potential in improving the efficacy of organic contaminants degradation by bacteria. However, the mechanisms of interactions involving both biotic (microorganisms) and abiotic (clays) components during bioremediation are largely unknown. Here, we report the interaction of a biosurfactant producing bacterium, Pseudoxanthomonas kaohsiungensis, with bentonite clay. Using instrumental analyses including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma mass spectroscopy (ICP-MS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) techniques we investigate the microstructural changes of smectite following introduction of the bacterium. The interaction resulted in a spherical clay-bacterial micro-agglomerate formation which deciphered an enhanced growth of the bacterium in a minimal medium supplemented with traces of olive oil. The bacterium brought about a significant dissolution of silicon (Si) preferentially from the tetrahedral silica edges of smectites. The deposition of bacterial biosurfactants and exopolysaccharides (EPS) slightly expanded the smectite interlayers and modified the clay's interaction with water molecules. This study has direct implication in the clay-mediated bioremediation of hydrophobic organic contaminants in the environment. [ABSTRACT FROM AUTHOR]

The Bazhenov Shale Formation (BSF) of the west Siberian Basin is considered to be a promising unconventional hydrocarbon reservoir, acting as a source, store and seal of the oil and gas contained therein. It has a high content of organic matter, ranging from 2 to 20% (average 8–12%), and was deposited in a marine environment at an average water depth of 2220 to 2500 m where depositional conditions were of an intensely reducing nature. Deposition took place over a period of 8 to 10 million years mainly during Upper Jurassic times. This study reports the mineralogy of 83 core samples representative of the clayey-silty siliceous rocks of the Bazhenov Shale Formation (BSF) taken from six wells in the south-east of the west Siberian Basin. The mineralogy of most samples was found by X-ray diffraction (XRD) to be strikingly similar with most being dominated by quartz, and with albite, mica-like minerals (illite plus mixed-layer illite/smectite (I/S)) and pyrite commonly occurring in subsidiary amounts. Kaolinite and chlorite occur intermittently, usually in no great quantity. Throughout all six wells, plagioclase feldspar (albite) predominates over K-feldspar which is only of sporadic occurrence. The clay (< 2 μm) fraction of available core samples largely consists of illitic material comprising a combination of true illitic mica and mixed-layer I/S with R 3 stacking. Both optical microscopy and scanning electron microscopy (SEM) show the BSF to be composed of a mixture of detrital and authigenic minerals. Thus, quartz occurs as a detrital mineral and as the crystallized product of radiolarian tests subsequent to deposition. The micaceous (muscovitic) material seen in thin section is clearly of terrigenous origin but the fine-grained illitic material is considered to be at least partly diagenetic . With regard to feldspars, although thin sections show some to be detrital, it is considered that albite is also likely to be a diagenetic mineral, as it is in many sandstone reservoirs. In many of the core samples albite is the only feldspar detectable and it is improbable that provenance could yield feldspar detritus consisting only of pure albite over such an extended period of time. Other minerals in the BSF must also be regarded as diagenetic rather than detrital. This is certainly true of the carbonate minerals and pyrite, and the book-like aggregates and euhedral morphology of kaolinite observed by SEM and TEM are also indicative of a diagenetic origin. Finally, the illitic clay mineralogy of the BSF is considered in a general way in the context of their permeability, particularly as it relates to their anisotropic structure and pore water chemistry. It is also suggested that the siliceous nature of the Bazhenov shale makes it a suitable candidate for the creation of enhanced permeability through hydraulic fracturing technology, although matrix permeability may be adversely affected by reactions involving the external basal surfaces of the illitic clays exposed in slit-like pores. [ABSTRACT FROM AUTHOR]

Clayey marl from four localities in the Neogene basin of Jijel (NE Algeria) were studied by mineralogical and physico-chemical characterization in order to evaluate their potential suitability as raw materials in ceramic applications. X-ray diffraction (XRD) and Fourier Transform-Infrared (FT-IR) spectrometry are used to establish the mineralogical composition. Chemical and physical properties were carried out by XRF and particle size distribution, consistency limits, calcimetry of Bernard and density of solid particles, respectively. Quartz, clay and calcite were present as dominant mineral phases associated with feldspars, plagioclase and dolomite. The clay minerals prevail in all samples, with kaolinite and illite being the dominant phase and interstratified 10–14 Å and chlorite, comprising the rest of the clay components. The chemical compositions indicated that SiO 2 (42–54%), Al 2 O 3 (12–19%) and CaO (2–17%) are major elements while Fe 2 O 3 is less abundant (4–8%). The classification of the clays using appropriate ternary diagrams suggests their possible use in the production of red products like tiles and masonry bricks. [ABSTRACT FROM AUTHOR]

Equilibrium sediment volume (ESV) is used as an important parameter for understanding the expansive nature of the bentonites and natural clay soils, for assessing a given bentonite for engineering applications, and for the determination of the type of dominant clay mineral present in a given soil. The ESV is often estimated using different salt solutions to understand the compatibility of given clay soil for long-term engineering application such as landfills. A theoretical approach based on physicochemical behavior of clays was proposed in this paper for the estimation of equilibrium sediment volume of bentonites in the presence of salt solutions. A simple analytical expression relating equilibrium sediment volume with different influencing physicochemical parameters such as clay surface and pore-fluid parameters was presented using the diffuse double layer theory. A quantitative estimation of ESV by the proposed theory was validated on the measured data. A very good agreement between the theoretical and measured data was observed for the commercial bentonite. The theory was in good agreement with the measurements in the concentration range of 0.01 M ≤ n < 1 M for Kutch bentonite while the concentration range was 0.001 M ≤ n < 1 M for Barmer bentonite in NaCl solutions. The influence of different exchangeable cations and the presence of non-clay content on the prediction were analyzed with a great detail using theory and by comparing the ESV data of studied bentonites with the homoionic sodium clay. The parallel plate assumption made in the theory overestimated the ESV data in CaCl 2 solution. The proposed analytical model is very useful for understanding the influencing parameters on the bentonite behavior. [ABSTRACT FROM AUTHOR]

The sorption characteristics of landfill silty clay soil (LSC), taken from AL Hammam landfill site, as a retardation barrier of Zn 2 + , Cd 2 + and Pb 2 + ions were investigated. LSC consists mainly of kaolinite, quartz and calcite minerals, is a part of thin blanket of Miocene rocks forming a vast persistent limestone plateau of the north part of the western desert of Egypt. The results showed that the percentage equilibrium uptake of the metal ions by LSC are 94.8, 92.7, and 86.0 for Zn 2 + , Pb 2 + , and Cd 2 + , respectively. The coefficient of diffusion's value was found in the range (3.32–6.8)0.10 − 17 m 2 /s and increases with the increase in temperature. The distribution coefficient for Pb 2 + , Cd 2 + , and Zn 2 + ranged from 404.9 to 568, 230.1 to 281.9, and 371.4 to 466.7 ml/g in the temperature range 298 to 333 ± 1 K, respectively. The value of retardation factor and the sorption affinity onto LSC took the order Zn 2 + > Pb 2 + > Cd 2 + . The experimental investigation on ionic concentrations in sorption batches suggested that sorption behaviors of Zn 2 + , Pb 2 + , and Cd 2 + ion metals onto LSC are mainly controlled by cation exchange. The wetting front of water movement in the LSC as an unsaturated soil reached to about 0.06, 0.19 and 0.25 cm after 6, 24 and 48 h of steady infiltration. The saturation hydraulic conductivity of the LSC (< 2.0 μm) fraction is 2.18 × 10 − 10 m/s therefore, it matches the condition of suitability of soils as mineral liners for a landfill facility. The Pêclet number values (< 32) indicate dominance of dispersion over advection. The < 2 μm fraction of LSC may be used to attenuate Zn 2 + , Cd 2 + and Pb 2 + ions presented in AL Hammam landfill leachate from reaching the shallow groundwater. [ABSTRACT FROM AUTHOR]

This study proposes some useful practical charts representing the relationships between oxide composition and the type of predominant clay mineral present in clay soils. In order to produce the charts, the data set are collected from published literature. Some useful classification schemes for predominant clay mineral type were obtained by using binary and ternary graphs of oxide composition data. The most successful relations indicating the type of clay mineral have been found on SiO 2 versus Al 2 O 3 + Fe 2 O 3 + FeO, SiO 2 versus MgO + CaO + Na 2 O + K 2 O binary plots, SiO 2 − Al 2 O 3 − Others and SiO 2 − Al 2 O 3 − K 2 O ternary plots. [ABSTRACT FROM AUTHOR]

The fall cone test is one of the most popular methods used to determine the soil liquid limit. In this study, a series of laboratory tests were conducted on kaolin soil, which is considered representative of low-swelling clays, in order to determine the penetration depths for different cone parameters (angle and weight) under a liquid limit state. The required soil undrained shear strength of kaolin at liquid limit was determined using a hand-held vane shear device. Based on the analysis of the test results, the relationship between the angle of the fall cone and the ratio of undrained shear strength and fall cone penetration depth over cone weight was obtained and represented by a power function. The established relationship was then used to determine the penetration depth at liquid limit for different cone parameter values. A difference in liquid limit of less than 15% was recorded between tests using standard and alternative cone parameter values, respectively. Furthermore, a better and more reliable result was obtained when cone angles were below 90°, with a standard deviation of less than 2.5% from the standard method. Based on critical analysis of the test data, an equation with which to determine the penetration depth under a liquid limit state, as well as a one-point test method with which to determine the liquid limit for different cone parameter values are proposed for low-swelling clays. [ABSTRACT FROM AUTHOR]

The Morrón de Mateo bentonite deposit (Cabo de Gata region, Spain) has been studied as a natural analogue of the thermal and geochemical effects on the clayey barrier in a deep geological repository of high level radioactive wastes. This deposit was intruded by a volcanic dome inducing an increase of temperature and supplying Fe–Mg-rich solutions, which were responsible for the alteration of the previously bentonitised pyroclastic materials (white tuff formation). The textural, mineralogical and crystallochemical features of the smectites located within the vicinity and away from the dome have been studied in order to elucidate the intrusion effects on these smectites. The results obtained show that distal smectites are Al-montmorillonites, similar to those from other bentonite deposits in the Cabo de Gata region; whereas proximal smectites are a mixture of Al-montmorillonites, Fe-rich montmorillonites and beidellites, and intermediate smectites between beidellite and Fe-rich-saponite. The textural relationships between these smectites indicate that smectites with intermediate composition come from the transformation of Al-montmorillonite, through gradual steps, consisting of increasingly Mg and Fe-rich smectites. This transformation process is confirmed when the structural formulae of proximal smectites are plotted on the Mg VI vs (Al + Fe 3 + ) VI diagram. Thus, a gradual transition from dioctahedral smectites to smectites with an intermediate chemical composition is observed, which tend toward trioctahedral smectites. These observations suggest that the transformation of dioctahedral smectites into an intermediate term between di- and trioctahedral Fe-rich smectites could be originated under natural conditions. This transformation can be considered as an analogue process to that expected in the bentonite barrier from a deep geological repository of radioactive wastes whether the two following conditions would occur: i) an increase of temperature due to the radioactive decay of the fission products, and ii) a supply of Fe as result of the canister corrosion under intermediate redox conditions. Furthermore, similar results were obtained in laboratory experiments focused on the Fe/Al-smectite interaction processes, related to the durability of the clayey engineered barrier. [ABSTRACT FROM AUTHOR]

Since the texture triangle developed by the U.S. Department of Agriculture (USDA) has traditionally been a basic tool in soil classification, a thorough examination of its suitability has been carried out in this research. A total of 256 soil samples from 21 different countries and 35 publications containing both textural (sand, silt and clay percentages) and Atterberg limits data have been analyzed. The soils were classified according to traditional particle size criteria using the USDA texture triangle. On the other hand, the Plasticity index / Liquid limit ratio, a parameter called clay factor (C F) in this research, was calculated and plotted against the percentage of sand to classify the soil according to the texture-plasticity system proposed by the authors in 2018. The evaluation through C F and comparison with the authors' proposal has shown the limitations of the USDA classification, which only determines soil texture in terms of particle size, but not how this texture affects actual soil properties, an aspect that could be very useful. It has been demonstrated that a significant percentage (20%) of soils classified with the USDA system actually exhibit plastic behavior that is completely unrelated to the assigned name (e.g., non-plastic soils classified as clay). However, the fact that about 80% of the classified soils with both systems present the same group designation (∼37%) or are adjacent groups (∼43%), shows that the authors' classification does not break sharply with the textural criteria accepted to date, which is positive if this new proposal is intended to be used as an alternative. Therefore, the proposed classification conciliates plastic and textural properties, allowing to classify the soil in a more accurate way, adjusting it to its real behavior. • The U.S. Department of Agriculture (USDA) texture triangle was tested on 256 soils. • Clay factor (C F = Plasticity index/Liquid limit) was the examining parameter. • 63% of the names assigned by USDA does not match the plastic behavior of the soil. • An innovative proposal combining C F and texture has been examined as an alternative. • The authors' classification is more accurate and realistic than that of the USDA. [ABSTRACT FROM AUTHOR]

The Sado Basin is located in the southwestern part of the Iberian Massif. In order to improve the lithostratigraphic and palaeoenvironmental knowledge of this Cenozoic basin, mineralogical and geochemical profiles were assessed on three lithostratigraphic units: Ervidel and Vale do Guizo (Eocene) formations and Esbarrondadoiro (Miocene) Formation. Samples representative of the most exposed outcrops of these units were collected and analyzed by XRD, XRF and SEM–EDAX. Mineralogical and chemical results were analyzed statistically using PERMANOVA, principal components analysis and factor analysis. SEM–EDAX was used to calculate the chemical formula of palygorskite. Clay mineral associations were used as stratigraphic markers as well as for palaeoenvironmental reconstructions and diagenetic analyses. [ABSTRACT FROM AUTHOR]

Previous studies have used the clay content of soils for estimating the specific surface areas and different correlations have been found, including plasticity-value correlations. Based on several assumptions, Dolinar (2012) proposed a simplified method for determining the external specific surface area of non-swelling fine-grained soils. An equation relates the external specific surface area (BET-nitrogen) with percentage of clay fraction (< 2 μm), determined by hydrometer method, and plasticity index (Atterberg). In this work, based on that simplified method, the authors have developed an improved method for determining the external specific surface area of fine-grained clay samples. Instead of percentage of clay fraction, it was proposed to use the clay mineral content estimated by XRD methods. From an analysis of previous Dolinars results, the calculated and measured values of external specific surface area were studied for a group of non-swelling and fine-grained soil samples (Dolinar's samples), five non-swelling clayey samples and data samples from the literature. Additionally, an estimation of the plasticity index (Atterberg) has been also considered in this improved method. Both these methods, simplified and improved, were tested and compared using all these samples. It demonstrated the practical application of both these methods for an estimation of external specific surface area and plasticity index. However, in the present research two models were considered to determine the specific surface areas (BET and Langmuir) and the influence of several sources of errors in these predictions was discussed. The predictions were found more accurate when specific surface area from Langmuir's model is considered. It is concluded that the present research will be useful for the prediction of external specific surface area and plasticity index of non-swelling clayey materials and to dispose of theoretical practical relationships between clay mineralogy and geotechnical properties of valuable interest. [ABSTRACT FROM AUTHOR]

The use of new materials for soil strengthening is crucial for geotechnical engineering, especially in the methods commonly used for ground improvement, such as deep mixing. The main objective of this study was to investigate the potential use of two-component water-soluble epoxy resins to improve the mechanical properties (compressive strength, splitting tensile strength, elastic modulus, shear strength parameters, and long-term mechanical behavior) of silty clay soils because the efficacy of these resins for soil strengthening has not yet been properly investigated. The experiments were conducted using soil mixes with different epoxy resin-to-water ratios, solid-to-water ratios and cement contents, cured at different ages. The results of this study indicate that most of the epoxy resin-treated soil samples, even with the adverse influence of water content on the development of strength, appeared to have noticeable strength improvement after a curing period of 90 days. The addition of cement significantly improved the strengths of all mixes at all curing ages. The values of the strength parameters increased with cement content. This increment in strength for epoxy resin/cement-treated specimens could be mainly attributed to the consumption of large quantities of water from cement compounds, which results in the promotion of polymerization of the epoxy resin with the hardener. [ABSTRACT FROM AUTHOR]

This paper presents a new method for testing the behaviour of soils placed under tensile load and demonstrates its suitability for testing a number of soil types under various conditions including saturation, compaction and stabilisation. Validation of the results obtained for the soils at relatively low saturation has been conducted using the established Brazilian (indirect) test for measuring the tensile strength of brittle materials. A fair comparison has been found and the results highlight the limited applicability of the Brazilian method to soils at very low water contents at which the tensile failure criterion has been assumed using this methodology. Optical characterisation of the performance of both testing methods has also been conducted using Digital Image Correlation. The consistent, accurate measurement of directly induced tensile strains using the proposed new method has been confirmed, verifying its capability to apply a direct tensile stress in the absence of shearing, a problem commonly associated with other tensile testing methods. The developed technique has then been used to investigate the water content–tensile strength relationship for compacted, unsaturated soils and offers significant advantages in the characterisation of clay soils subjected to variable climatic loading. [ABSTRACT FROM AUTHOR]

The development of clay mineral-based soil amendments has drawn significant concerns in modern agriculture. However, little attention was paid to multifunctional amendments enabling both soil remediation and nutrients sustained release. In this work, a novel montmorillonite (Mt)-based amendment (denoted as KMt-P) was developed by modifying Mt with alkali followed by decoration with phosphate, and was further applied to remediate Cd/REEs contaminated soil. The XRD pattern of KMt-P demonstrated the presence of various silicophosphate and aluminophosphate phases. 27Al and 29Si MAS NMR results indicated the destruction of crystal structure of Mt. FTIR and XPS analyses confirmed the formation of Si-O-P, P-O-P, and Al-O-P bonds in KMt-P, which, as we envisioned, should be conductive to the immobilization of Cd and sustained release of nutrients. The addition of KMt-P to soil (1 wt%) could effectively reduce the bioavailable Cd in soil by 91.3% within 30 days. Sustained release of multiple nutrients was also achieved: the concentration of soluble K, Si, and P increases by 15, 3, and 135 times, respectively, in comparison with the control treatment. The increased K and P contents arose from the added modifiers, and that of Si could be ascribed to the destruction of Mt crystal structure under alkali attack. Application of only 1% KMt-P could reduce the concentrations of 17 REEs in the soil by 92.01%–98.89%. In general, KMt-P has proven a promising multifunctional amendment enabling both Cd/REEs immobilization and sustained release of nutrients. [Display omitted] • A novel multifunctional clay mineral-based amendment (KMt-P) was synthesized. • KMt-P shows fast, and stable immobilization of Cd with high capacity. • KMt-P enables Cd immobilization and sustained release of nutrients simultaneously. [ABSTRACT FROM AUTHOR]

Microstructural (fabric, forces and composition) differences due to hydrocarbon contamination in a clayey soil (glacial till) were studied using scanning electron microscopy (microfabric analysis) and sedimentation bench test (PSD). Uncontaminated and contaminated glacial till from NE Poland (in the area of a fuel terminal) were used for the study. Because the contaminated samples exhibited lower electric charge, the electrostatic repulsive forces in the contaminated samples were much lower than in uncontaminated samples. All sedimentary-based particle size test results gave similar results and were inconclusive to find difference between contaminated and uncontaminated samples. Mastersizer PSD data show smaller aggregates in contaminated in comparison to the uncontaminated sample. The present test's finding may support earlier microstructure investigation results, where diesel-contaminated clay soil shows more open porosity, consisting consequently of looser aggregates, which were easier dispersed in water during Mastersizer measurements than the more coherent uncontaminated clay sample. This in effect increased the percentage of finer than 0.1 mm grain fraction within the broad diameter range in contaminated samples results, in comparison with the uncontaminated sample results. [ABSTRACT FROM AUTHOR]

Dispersive clays may pose considerable distress if not adequately taken care of. On the other hand, the treatment of problematic soils with waste materials has been recently proved to be a useful option from economic and environmental view point. Hence, in this research, the potential use and effectiveness of dispersive soil stabilization using two types of industrial by-product, including granulated blast furnace slag (GBFS) and basic oxygen furnace slag (BOFS) were investigated. The slags were separately added (ranging from 2.5 to 30%) to a laboratory dispersed sample and a set of experiments were performed to study the physicochemical, mechanical and microstructural changes of the stabilized soil. The results indicate that the soil dispersion can be eliminated upon adding 10% BOFS. This is attributed to the exchange of interlayer sodium ions on the clay surfaces by multivalent cations from the agent. Besides, an increase in the ion concentration of soil-additive mixtures induces a more depression of the diffuse double layer that decreases the soil dispersivity potential. With increasing the curing time, an improvement in the strength of composite samples is observed. The formation of cementitious compounds due to the pozzolanic reactions is responsible for such a treatment, as confirmed by the XRD analyses and SEM micrographs. It appears that the GBFS has a lower activity as compared to BOFS, therefore causes less influence on the soil engineering parameters and a higher percentage (20–25%) of GBFS is required to govern soil dispersion. Overall, utilization of the studied slags particularly of BOFS is very effective to overcome the problems associated with dispersive soils. [ABSTRACT FROM AUTHOR]

Previous studies have shown that clayey soil admixed with Ca-bentonite can be considered as an alternative backfill for slurry-trench cutoff walls. However, the effects of contaminant exposure on the engineering properties of the clayey soil/Ca-bentonite backfills, such as compressibility and hydraulic conductivity, have not been investigated. This study presents several series of oedometer tests conducted to evaluate the compressibility and hydraulic conductivity of clayey soil/Ca-bentonite backfills exposed to different levels of lead (Pb) contamination. Kaolin is used as the base clayey soil, and it is amended with Ca-bentonite at three content levels (5, 10 and 15% by dry weight) to prepare the backfill samples. Pb is a representative metal contaminant commonly found at contaminated sites. The backfills are prepared by thoroughly mixing the kaolin–bentonite mixture with Pb concentrations of 60, 120 and 600 mmol/L. The results reveal that the level of Pb concentration and bentonite content are the critical factors that affect the compressibility of the backfill. The ratio of the compression index of the Pb-contaminated backfill to that of the clean backfill decreases with an increase in the Pb concentration and bentonite content. The void ratio at an effective vertical compression stress of 1 kPa is a useful characteristic parameter to correlate with the compression index for all the backfills tested here. The Pb-contaminated backfills exhibit a maximum fifty-fold increase in hydraulic conductivity when compared to clean backfills. The hydraulic conductivity of the clean backfills and those contaminated at low concentration of Pb (60 mmol/L) is generally less than the typical regulatory limit of 10 − 9 m/s; whereas the hydraulic conductivity exceeds the regulatory limit when the Pb concentration is higher than 120 mmol/L. The ratio of hydraulic conductivity for Pb-contaminated backfills to that for clean backfill decreases with an increase in the effective vertical compression stress. This indicates that under relatively higher effective vertical compression stress conditions the detrimental effect of Pb on hydraulic conductivity can be insignificant. The hydraulic conductivity of the Pb-contaminated backfills decreases slightly when there is an increase in the bentonite content for a given Pb concentration, while the hydraulic conductivity ratio increases significantly with a rise in the bentonite content. A proposed empirical method is assessed to predict the hydraulic conductivity of Pb-contaminated clayey soil/Ca-bentonite backfills as well as clean ones subjected to vertical compressive stress lower than 1600 kPa. Using this method, the predicted hydraulic conductivity values fall in the range of 1/3 to 3 times those obtained from the oedometer tests. [ABSTRACT FROM AUTHOR]

This paper investigates the microstructure and mineralogical compositions of soft clay soil stabilized with bassanite that is produced from gypsum waste materials. Bassanite was mixed in different ratios with cement and lime, as a solidification agent, to prevent the solubility of bassanite. Different amounts of these admixtures were mixed with the tested soil. Scan electron microscopic (SEM) and X-ray diffraction (XRD) were used to identify the microstructure and mineralogical compositions of stabilized soil specimens, respectively while unconfined compression test was used to examine the compressive strength. Test results showed that the addition of recycled bassanite improves the strength of the tested soil. The improvement in the soil strength, based on compressive strength, is in agreement with the SEM and XRD results. The XRD results revealed the presence of various cementation compounds in the soil matrix when recycled bassanite was added. Both the content and ratio of the admixture had a significant effect on the formation of the cementation compounds and the improvement of compressive strength. The formation of ettringite increased with the increase of admixture content in soil mixture for both admixtures used. The ratio of admixture had a clear effect on the reduction of the formation of ettringite in the case of bassanite–cement admixture while it had no significant effect in the case of bassanite–lime admixture. Curing time had a significant effect on the formation of ettringite and the improvement of compressive strength. These results support the suitability of using recycled bassanite produced from gypsum wastes as a low cost and efficient stabilizer material in ground improvement projects. [ABSTRACT FROM AUTHOR]

Five clayey materials from two quarries located in the Amezmiz region (Morocco) were sampled and investigated for their physical, chemical, mineralogical and thermal characteristics to evaluate their potential suitability as raw materials in various ceramic applications. Physical properties were identified by particle size distribution, consistency limits and total organic content. Chemical, mineralogical, and thermal properties were investigated by XRF, XRD, and TG/DTA techniques, respectively. A common raw material in pottery manufacturing of Morocco was used as reference sample (REF). Results show that the main oxides in the samples were SiO 2 , Al 2 O 3 , and Fe 2 O 3 , whereas the other oxides were present only in small quantities. Quartz, illite and vermiculite were present as dominant mineral phases and the minor phases of kaolinite, calcite and smectite also appeared in the samples. The results showed that two of the studied clayey materials have adequate characteristics for the production of structural ceramics. However, for the two other clays it is necessary to add more plastic clays to enhance the workability. [ABSTRACT FROM AUTHOR]

Compacted clay liners (CCL) can be used to isolate hazardous wastes like the soil and military scrap contaminated with depleted uranium that emanated from the Iraqi wars in 1991 and 2003. Near-surface repositories for such dangerous waste can preferably be located in the Iraqi deserts, which make up 60% of the territory of Iraq. CCLs are usually constructed using a mixture of clayey soil and coarse material compacted in air-dry form or suitably wetted. In the present study, two smectitic soils from Iraq, termed green and red clays, were investigated for potential use in CCLs. The shear strength, swelling pressure, hydraulic conductivity and creep properties were determined and used for preliminary design of top and bottom-liners. The engineering properties were determined for various dry densities and water contents ranging from air-dry to fully saturated conditions. The results showed that mixtures of sand and 30%–50% green clay and mixtures of sand and 40%–60% red clay are suitable for constructing top-liners with a hydraulic conductivity between 1 × 10 − 10 and 1 × 10 − 9 m/s. For bottom-liners, mixtures of sand and 70% green clay and mixtures of sand and 80% red clay can be considered. They were found to have a hydraulic conductivity of 1 × 10 − 11 m/s for a density at saturation of 2.1 g/cm 3 (dry density, 1.7 g/cm 3 ). As to the slope stability of top-liners, the shear strength for different clay percentages was found to guarantee slope stability for 18° inclination under both air-dry and water saturated conditions. [ABSTRACT FROM AUTHOR]

Soil–bentonite vertical cutoff walls, consisting of a sandy soil mixed with Na-bentonite as backfill, are used extensively as engineered barriers for contaminant containment. However, suitable sandy soil and Na-bentonite may not be available at some sites. Consequently, locally available clayey soil and Ca-bentonite may be considered as an alternative backfill. The use of clayey soil/Ca-bentonite backfill may be advantageous to achieve relatively low hydraulic conductivity, which has equivalent performance as that of conventional sandy soil/Na-bentonite backfills. However, studies on the compressibility and hydraulic conductivity of these clayey soil–bentonite backfills are very limited. This paper presents a comprehensive laboratory investigation on the compressibility and hydraulic conductivity of clayey soil/Ca-bentonite backfill through a series of oedometer tests. Kaolin is used as the control clayey soil and it is amended with different contents of Ca-bentonite, 0 (kaolin alone), 5, 10, and 15% (by dry weight basis), to prepare the clayey soil/Ca-bentonite backfills. The initial water contents for the backfills are selected to be 0.75, 1.0, 1.25, and 1.50 times their corresponding liquid limits. The results reveal that the backfills exhibit a noticeable inverse ‘S’ shaped e -log( σ ′) compression curves attributed to the existence of the remolded yield stress ( σ ′ yr ). The compressibility, in terms of σ ′ yr and the compression index ( C c ), is significantly affected by the initial water content and bentonite content. The void ratio at an effective vertical compression stress of 1 kPa (denoted as e 1 ) is a useful characteristic parameter to uniquely correlate with C c for the clayey soil/Ca-bentonite backfills in this study as well as for sandy soil/Na-bentonite and sandy soil–clay backfills that are reported in previous published studies. Unique relationships are also found between the σ ′ yr , initial void ratio ( e 0 ), e 1 , and the void ratio at liquid limit ( e L ). The hydraulic conductivity of the clayey soil/Ca-bentonite backfills is significantly reduced by the bentonite content; generally to less than 10 − 9 m/s. An empirical method based on the framework of Kozeny–Carman equation is proposed to predict the hydraulic conductivity of the clayey soil/Ca-bentonite backfills, and the predicted hydraulic conductivity values using these methods are found to fall in the range of 1/3 to 3 times those obtained from the oedometer tests. The proposed method is shown to estimate the hydraulic conductivity for both the clayey soil/Ca-bentonite backfills in this study and the sandy soil–bentonite backfills from published study with reasonable accuracy. Additional research is warranted to prepare the backfills to simulate typical field practice (e.g., use of tap water) and at workable initial water contents (based on the slump testing). [ABSTRACT FROM AUTHOR]

Predicting the compaction parameters, in terms of maximum dry unit weight and optimum water content, from index properties of fine-grained soils has been of interest for the last few decades. Although various index properties, such as liquid limit, plastic limit and clay contents, have been used for the prediction, it was revealed that plastic limits of fine-grained soils correlate well with the compaction parameters. As an alternative method, this paper proposes sediment volume test to estimate the compaction parameters. In order to show its relevance, compaction and sediment volume tests were performed on nine fine-grained soils. The final sediment volumes (FSVs) of soils were determined from sediment volume tests. Then, the correlations between compaction parameters and FSVs were investigated. It is found from this experimental investigation that there is a good relationship between the compaction characteristics namely maximum dry unit weight (γ dmax ) and optimum water content (w opt ) and the FSV, indicating that this method can be used as an alternate way of predicting the same. [ABSTRACT FROM AUTHOR]

Because expansive and dispersive soils damage engineering structures, extensive studies on using additives to ameliorate the effects of these soils have been conducted. In this study, the effect of magnesium chloride (MgCl 2 ) solution on the engineering properties of clay soils was evaluated. Previous studies on this subject have shown that MgCl 2 is more commonly used as an anti-icing agent on roads than as a soil stabilizer. MgCl 2 is also used to control dust and humidity on roads and to reduce the scattering of coarse particles from road surfaces. However, as the use of MgCl 2 becomes more common, its potential to improve the geotechnical properties of problematic soils will receive increasing attention. To this end, the variation in the engineering properties of expansive and dispersive clay soil samples as functions of the added MgCl 2 content was investigated. First, the physical and chemical properties of the soil sample were determined. Next, the swell percentage, swell pressure, crumb, pinhole and unconsolidated undrained (UU) triaxial compression tests were performed at different curing times on samples with and without the additive by compressing the sample to achieve particular compaction characteristics. Scanning electron microscopy (SEM) analyses were performed to observe the microstructures in the sample without the additive and with the amount of additive that most strongly improved the expansive and dispersive qualities of the clay. The results show that dispersive and expansive clay soils can be effectively improved using an additive MgCl 2 solution. [ABSTRACT FROM AUTHOR]