Clay dispersion

We have used the newly developed concept of CROSS (cation ratio of soil structural stability) instead of SAR (sodium adsorption ratio) in our study on dispersive soils. CROSS incorporates the differential dispersive powers of Na and K and the differences in the flocculating effects of Ca and Mg. The CROSS of the dispersed soil solutions, from the differently treated soils of three soil types varying in clay content, mineralogy, and organic matter, was highly correlated with the amount of clay dispersed. The relation between CROSS and exchangeable cation ratio depended on soil type, and particularly organic matter and the content and mineralogy of clay. Threshold electrolyte concentration of the flocculated suspensions was significantly correlated with CROSS of the dispersed suspensions. The cationic flocculating charge of the flocculated suspensions, which incorporates the individual flocculating powers of the cations, was significantly correlated with CROSS. However, these types of...

French Guiana heavily relies on high-cost imported materials to sustain its strong population growth and construction demand. Local alternatives such as earth concrete are needed to reduce the use of conventional concrete. It is currently unknown if tropical soils are suitable for non-cement stabilized earth construction and especially what are the characteristics of these soils. In this study, 14 soils were characterized (particle size, EDS-SEM, FTIR, color) and evaluated as building materials on earth mortar prismatic specimens. For each soil, physical and mechanical mortar properties were evaluated based on two formulations of equivalent plastic consistency, with or without dispersant (0.5% of dry mass). The results show that hardened mortar properties were driven by water content at fresh state, particle size, and Fe and Al-oxide content. Water content directly correlated with fine-grains content and negatively impacted all mortar properties. The use of dispersant reduced water content and considerably improved compressive strengths, reaching up to 4 MPa. Compressive strength positively correlated with Fe and Al content and could be predicted by soil color. Overall, the characterized soils demonstrated good mechanical aptitude when mixed with a low level of dispersant, indicating a high potential for construction, particularly for metal oxide-rich soils.

In order to pour an earthen material in a liquid state, as a concrete, technologies used by concrete and ceramic industries can be transferred to the field of earthen construction. Two different methods should be employed simultaneously. The first relates to theories of grain packing that have led to models of Apollonian packing and spaced packing, commonly used for the development of cement concrete (ultra high performance concrete and self-leveling concrete). It concerns the optimization of the granular skeleton of natural materials. The second relates to the dispersion of the colloidal fraction of earthen materials. In natural soils, clays are organized as porous aggregates composed of several tens of particles. These aggregates trap water that is not used to liquefy the mixture. The dispersion of these aggregates, releasing this interstitial water, liquefies the earthen material without adding water. This dispersion is obtained by adding a small proportion (on the order of a few tenths of a percent by mass relative to the dry material) of deflocculating agents such as those commonly used for the development of industrial ceramics. The combined action of these two methods leads to a solid material that does not crack while drying, and can easily be implemented at a viscosity comparable to that of vibrated concrete with the same tools than those employed by the concrete industry (cement mixer, shuttering, vibrating needle). This new technique is particularly suited for the implementation of slabs and other horizontal surfaces, and also for vertical walls.

Dispersion of organically modified clay in the blend of PLA and PBAT and its effect on the morphology, thermal and mechanical properties of the blend were studied. Mechanical strength of the blend was enhanced and the morphology the blend was affected due to the clay's presence.

Irrigation waters with high sodicity and low salinity levels may deteriorate soil physical properties, consequently affecting the water movement in the soil. The objectives of this study were: (i) to evaluate the effect of supplemental irrigation with waters that have a residual sodium carbonate (RSC) [Richards, L.A. (Ed.), 1954. Diagnó stico y rehabilitació n de suelos salinos y só dicos. Manual de Agricultura, vol. 60. Limusa, Mé xico] greater than 1.25 mmol c L À1 on the hydraulic conductivity (K) of Hapludolls and Argiudolls located in Santa Fe State (Argentina) and (ii) to identify the possible causes of K alteration. Irrigated and non-irrigated plots were selected to evaluate soil bulk density, water dispersed clay content, and K in two depth intervals: 0-7 and 15-25 cm. K was measured with tension infiltrometers at three tension values: 0, 0.15, and 0.3 kPa. Increases in ESP in both depths from 1 to 10 caused a 10% to 79% decrease in K in the irrigated relative to non-irrigated treatments. Changes in K were associated with increased clay dispersion suggesting that this factor results in failure of the structure, resulting in increased blockage of soil pores. Between 51% and 62% of the total clay was dispersed in water in irrigated treatments, and 36-44% in nonirrigated treatments. Results emphasize the importance of preventing soil dispersion. This process induces degradation of big pores, especially those with equivalent radii greater than 1000 mm, which is essential for quick water flow. The conductivity of these pores was decreased from 48% to 79% in irrigated relative to non-irrigated treatment. A field method is proposed to determine when reclamation practices should begin.

In aqueous dispersion, Na-montmorillonite swells due to absorption of water and exfoliate into smaller entities, known as tactoids, with electric double layers on their surfaces. The exfoliation rate of such tactoids in aqueous Laponite dispersion was seen to be greatly reduced at the jamming transition and was reported by this group in a recent article [Langmuir, 2013, 29, 12663-12669]. The work reported here uses ultrasound attenuation spec-troscopy experiments on Na-montmorillonite dispersions and shows that the complete exfoliation of tactoids is not achieved even below the jamming concentration. This behavior indicates that screened Coulomb repulsions between and within tactoids, as well as the osmotic pressure of hydrated Na + ions, play very important roles in the exfoliation kinetics of tactoids. In this work, the phenomenon of tactoid exfoliation is studied systematically by changing clay mineral concentration, ionic conditions and the ages of the dispersions. A signature of an irreversible process of tactoid reformation under certain ionic conditions is also observed. Finally, electroacoustic measurements and rheometry are used to assess the influence of tactoid exfoliation on the stability and viscoelas-ticity of the arrested phases formed under different ionic conditions.

Na-montmorillonite is a natural clay mineral and is available in abundance in nature. The aque-ous dispersions of charged and anisotropic platelets of this mineral exhibit non-ergodic kinetically arrested states ranging from soft glassy phases dominated by interparticle repulsions to colloidal gels stabilized by salt induced attractive interactions. When the salt concentration in the dispersing medium is varied systematically, viscoelasticity and yield stress of the dispersion show non-monotonic behavior at a critical salt concentration, thus signifying a morphological change in the dispersion microstructures. We directly visualize the microscopic structures of these kinetically arrested phases using cryogenic scanning electron microscopy. We observe the existence of honeycomb-like network morphologies for a wide range of salt concentrations. The transition of the gel morphology, dominated by overlapping coin (OC) and house of cards (HoC) associations of clay particles at low salt concentrations to a new network structure dominated by face-face coagulation of platelets, is observed across the critical salt concentration. We further assess the stability of these gels under gravity using electroacoustics. This study, performed for concentrated clay dispersions for a wide concentration range of externally added salt, is useful in our understanding of many geophysical phenomena that involve the salt induced aggregation of natural clay minerals. * Electronic address: samim@rri.res.in † Electronic address: ranjini@rri.res.in 1 arXiv:1507.02844v1 [cond-mat.soft] 10 Jul 2015