Comportement hydrique et évolution structurale et texturale des montmorillonites au tours d'un cycle de dessiccation-humectation: partie I. Cas des montmorillonites calciques

Abstract

RI~SUMt~: L'~volution structurale et texturale ainsi que le comportement hydrique de deux montmorillonites-Ca (Wyoming et grecque) ont ~t~ &udi~s par microscopic ~lectronique fi transmission (MET) et plus pr~cis~ment par analyse de la diffusion aux petits angles des rayons X (DPAX). L'~tude au MET a permis de montrer qu'/l faible contrainte, le mat~riau est form~ par un r~seau de particules d~formables d~limitant des pores de grandes dimensions (~2 #m). L'6tude en DPAX des m~mes syst~mes soumis fi une contrainte de type succion a montr~ que: 1. Lors de la premiere dessiceation il y a d'abord d~formation du r~seau sans regroupement des particules (p <~ 1 bar), puis regroupement des particules face-face pour former des particules de plus grande ~palsseur (p > 1 bar). On montre aussi que l'eau est essentiellement extraite de la porosit~ interparticulaire. 2. Lors de la r~hydratation, on met en ~vidence qu'apr~s dessiccation le syst6me perd une grande partie de son aptitude ~, reprendre de l'eau et que cette perte est d'autant plus importante que le niveau de dessiccation pr~alable a &~ ~lev6. Ceci est dO au falt qu'une partie de la porosit~ est r~duite fi des espaces ayant la propri~t~ de l'espace interfoliaire.ABSTRACT: The structural and textural changes and swelling behaviour of two Camontmor]llonites (Greek and Wyoming) were studied by TEM and small-angle XRD. When examined by TEM at low stress, the texture was a network of particles enclosing large-size pores (~ 2 #m). XRD examination of the clays under suction showed that: 1. When first dried, the network changed configuration without coalescence of the particles (p ~< 1 bar). Afterwards, the particles became bound face-to-face and formed thicker groupings (p > 1 bar). Water was also found to be derived essentially from inter-particle porosity. 2. During rehydration the desiccated system had lost, to a great extent, its ability to recover water, this loss being greater the higher the preliminary desiccation. This is due to the fact that porosity was confined in part to spaces which had the same property as the interlayer space.Au niveau de la structure des sols, il est clair que les argiles jouent un r61e sp6cifique qui n'est pas seulement dfi fi leur propri6t6, commune fi beaucoup de constituants des sols, de pouvoir capter et retenir l'eau. Le fait important est que cette prise, ou ce d6part d'eau, s'accompagne g6n6ralement d'une modification du volume apparent et qu'elle se traduit, fi diff6rentes 6chelles, par une r6organisation du mat6riau (

Structural Organization of Na- and K-Montmorillonite Suspensions in Response to Osmotic and Thermal Stresses

“…An examination of the experimental patterns (Figures 3a and 3b) shows that they fall into 2 groups: 1) the 0.1 M NaCI and 0.1 M KC1 patterns, showing a continuous decrease of the intensity; and 2) the 0.5 and 1 M NaC1 or KC1 spectra, showing some modulation of the intensity situated between 4 and 6 ~ These results indicate that: 1) the samples in the first group have a gel-like structure, and are composed of dispersed elementary layers (Pons 1980;Pons et al 1981;Ben Rhaiem et al 1987); 2) the samples corresponding to the second group have a structure of hydrated solids in which occur short-distance interactions between first neighbors (Pons et al 1981;Ben Rhaiem et al 1986;Ben Rhaiem et al 1987;Gaboriau 1991). The sample then consists of a set of particles, connected or not, created by the more or less disordered stacking of hydrated layers with a limited number of interlayer water layers (0, 1, 2, 3 or 4) and internal porosity.…”

“…The sequence of spacings that separate the M layers is defined as a series of r different translations (d:) that are influenced by the probabilities of occurence (Pi) (M6r-ing 1949;Mac Ewan 1958;Ports 1980;Reynolds 1980). The interlayer distance distribution function pi(di) characterizes the order within the particle (SaezAunon et al 1983;Ben Rhaiem et al 1986;Gaboriau 1991). In the case of a heterogeneous clay system with high water content, a particle consists of: 1) a swelling phase in which interlayer spaces can be different from one layer to another; 2) a nonhydrated phase in which, whatever the water content, there is only 1 distance between first neighbors.…”

“…Numerous works (Ben Rhaiem 1983;Tessier 1984;Ben Rhaiem et al 1986;Touret et al 1990;Gaboriau 1991) have shown that different types of water could be defined. We will call "total internal water" the water contained in the swelling phase of clay particles.…”

“…Under stress, the uptake or loss of water by the clay occurs with a concomitant structural reorganization of the material at different scales (Millot 1964;Concaret 1967;Henin 1971;Monnier et al 1973;Pedro 1976;Pons et al 1981Pons et al , 1982Robertson et al 1982;Tessier 1984; Ben Rhaiem 1983; Ben Rhaiem et al 1986;Touret et al 1990). In order to characterize the structural changes of these clays under different stresses, it was necessary to get a continuous picture of the organization levels from the structural ordering of the layer stacks up to the size of the first aggregates (Pons et at.…”

Stacking Order in a 14.30-Å Mg-Vermiculite

“…The behavior of soil materials has also been simulated in the laboratories in order to determine the mechanisms involved in these transformations. The behavior of soil vermiculites of different geographic origin can be compared if a reference state is defined (Ben Rha'iem et al, 1986). This reference state corresponds to the condition in which the sample occurs in the soil, i.e., with Mg as the interlayer cation and hydrated with two-water layers (d(001) = 14.3 ~).…”