Jean-Marie Fleureau

Demineralized dentin 3D porosity and pore size distribution using mercury porosimetry.

OBJECTIVES The objectives of this study were to assess demineralized dentin porosity and quantify the different porous features distribution within the material using mercury intrusion porosimetry (MIP) technique. We compared hexamethyldisilazane (HMDS) drying and lyophilization (LYO) (freeze-drying) in sample preparation. METHODS Fifty-six dentin discs were assigned into three groups. The control (CTR) group discs were superficially acid-etched (15s 37% H(3)PO(4)) to remove the smear layer and then freeze-dried whereas LYO and HMDS groups samples were first totally demineralized using EDTA 0.5M and then freeze-dried and HMDS-dried respectively. MIP was used to determine open porosity and pore size distribution of each pair of samples. Field emission scanning electron microscopy (FESEM) was used to illustrate the results. RESULTS The results showed two types of pores corresponding either to tubules and micro-branches or to inter-fibrillar spaces created by demineralization. Global porosity varied from 59% (HMDS-dried samples) to 70% (freeze-dried samples). Lyophilization drying technique seems to lead to less shrinkage than HMDS drying. FESEM revealed that collagen fibers of demineralized lyophilized samples are less melted together than in the HMDS-dried samples. SIGNIFICANCE Demineralized dentin porosity is a key parameter in dentin bonding that will influence the hybrid layer quality. Its characterization could be helpful to improve the monomers infiltration.

Effect of pH on the rheological behavior of pure and interstratified smectite clays

The effects of pH and ionic strength on the rheological behavior of aqueous suspensions of both crude and purified Wyoming bentonite and natural interstratified illite-smectite from Tunisia were investigated. Flow tests were performed on the four clay suspensions at a 10% clay concentration at different pH values. They showed that the rheological properties were highly sensitive to pH and the nature of the clay. The evolution of the yield stress as a function of pH is characterized by the presence of maxima and minima attributed to changes in the mode of association of the particles. The effect of pH on the behavior of clay suspended in NaCl solutions was also studied. The results show that the presence of NaCl has very little effect on the pH and yield stress values of the four materials.

Small and large strain behaviour of an unsaturated compacted silt

ABSTRACT The results of small and large strain triaxial tests and matrix suction measurements, performed on a compacted low plasticity silt under different conditions of water content, density and confining stress, are presented. Simple models are proposed to interpret the results, one based on an empirical approach and the other one derived from micromechanics. Based on the calculation of the capillary forces between individual particles and using a single parameter, the micromechanical model yields a satisfactory interpretation of the changes in the elastic modulus and maximum strength of the soil with water content.

Micro–macro-experimental study of two clayey materials on drying paths

The objective of this research is to provide a better understanding of the relation between the macroscopic and microscopic behaviours of two clayey materials, a kaolinite and a mixture of kaolinite and montmorillonite. At the macroscopic scale, the approach consists of measuring the water content, void ratio and degree of saturation versus suction (s) during drying, which allows to specify the relationship between shrinkage and desaturation and highlights the characteristic phases of behaviour. At the microscopic scale, study of the orientation of the clay particles is carried out by scanning electron microscope (SEM) picture analysis under different suctions. On drying paths, the observations show an isotropy of the microfabric. The evolution of the porosity derived from mercury intrusion porosimetry tests is confirmed by SEM photograph observations.RésuméL’objet de cette recherche est d’offrir une meilleure compréhension du lien entre le comportement à l’échelle macroscopique et microscopique de deux matériaux argileux, une kaolinite et un mélange de kaolinite et de montmorillonite. A l’échelle macroscopique, l’approche consiste à mesurer la teneur en eau, l’indice des vides et le degré de saturation en fonction de la succion sur chemin de drainage. Ceci permet de préciser les relations entre le retrait et la désaturation et de mettre en évidence les phases caractéristiques du comportement. A l’échelle microscopique, l’étude de l’orientation des particules d’argile est réalisée par analyse d’images prises au microscope électronique à balayage (MEB). Sur chemin de séchage, les observations montrent une isotropie microstructurale du sol. L’évolution de la porosité est examinée à partir de mesures par porosimétrie au mercure, confirmées par des images seuillées de photos MEB.

Effet de la température sur le comportement des sols non saturés sur les chemins de drainage et d'humidification

The behaviour of soils subject to suction on drying and wetting paths depends on the type of material and its in- itial state. Exposure to heat modifies the state of pore water and therefore the hydromechanical behaviour of the soil. A new experimental device has been developed to study the thermohydric behaviour of unsaturated soils. Salt solution desic- cators and polyethylene glycol (PEG) osmotic solutions are dipped in thermostatic baths, whose temperature ranges from room temperature to 80 8C. Tests were carried out on a sandy clay prepared in the laboratory and on a natural undisturbed clay, extracted from an experimental site for deep underground storage of radioactive waste. Results show that temperature plays an important role in the shrinkage of soil, especially when subjected to high levels of suction. The results can be ap- plied to observe the response of confining clay barriers submitted to hydric and thermal changes.

Effect of lime on some physical parameters of a natural expansive clay from Algeria

Over the last three decades, highly plastic soils have been one of the major sources of problems in roads, railways and buildings in Algeria. In these cases, soil treatment is essential to improve the engineering properties of these materials. The aim of this article was to study the effect of added lime on the physical properties of soil. Experiments were performed on a local natural clayey soil in order to investigate the influence of lime on consistency limits, total specific surface, compaction characteristics, swelling potential and swelling pressure. In addition, mercury intrusion porosimetry tests were carried out to determine the pore size distribution of the untreated and treated samples. The results show that the liquid limit decreases, the plastic limit increases and the total specific surface area decreases with the percentage of added lime. Compaction characteristics are affected by the addition of lime, the optimum water content increasing and the maximum dry unit weight decreasing in the presence of a high amount of lime. This stabilisation method leads to significant reductions in the swelling of the studied soil, exceeding 60%. The treatment with a high percentage of lime significantly reduces the average pore diameter of the treated clay.

Estimation de la porosité dans un matériau argileux

Porosity measurements on a clay material, carried out through various microscopic techniques, show a significant difference with the total porosity macroscopically estimated. Analyses have allowed to assign this difference, whose importance is linked to the hydromechanical stresses sustained by the material, to microporous spaces lower than 2 nm and to closed pore volumes, not accessible by the used techniques. Besides, the role of the drying methods of samples, which do not allow the removal of a part of the water, is highlighted. Its elimination would lead to irreversible microtextural modifications, prejudicial to the understanding of the macroscopic behaviour of the material. To cite this article: X. Guillot et al., C. R. Geoscience 334 (2002) 105–109.

Conductivité hydraulique non saturée de l'argile de Mers El Kébir (Algérie)

ABSTRACT This paper presents hydraulic conductivity measurements carried out on unsaturated Mers El Kebir clay, from Algeria, using the vapour equilibrium technique. The principle is to measure the water exchanges between the sample and the environment under a relative humidity imposed by saturated salt solutions, to establish the relationships between hydraulic conductivity, water content (w), degree of saturation (Sr) and suction (uc). Samples are initially compacted to the standard Proctor optimum water content and maximum density and used as such and after saturation or drying. Drying-wetting paths were also performed in order to compare the direct hydraulic conductivity measurements to the values derived from Fredlund et al. (1994) and Mualem (1976)-van Genuchten (1980) models.

Durability of Bioclogging Treatment of Soils

A study of the clogging of two soils, a sand with grains ranging from 0.4 to 4 mm, and a gravel with grains ranging from 1 to 10 mm, was carried out by feeding the bacteria initially present in the soils. The focus of this research is to study the durability of bioclogging. The results showed that clogging occurred quickly after the injection of nutrients. The soils were subjected to gradient increases and a critical hydraulic gradient i(crit) (corresponding to the gradient for which unclogging occurred and an increase in the flow of water was observed) was determined. It is equal to 0.8 for the sand and to 0.06 for the gravel. The durability of bioclogged soils was also studied by performing 10 to 30 hydraulic gradient cycles between the initial value and i(crit)/2. For the sand, the permeability increase after the cycles was very low. In contrast, in the gravel, unclogging occurred very quickly, highlighting the influence of grain size and materials grading

Some Aspects of the Effect of the Temperature on the Behaviour of Unsaturated Sandy Clay

The paper describes experimental results on triaxial paths at high temperature concerning an unsaturated clay (w_L = 38%, I_P = 19 and C_c = 0.23). Unsaturated drained triaxial compression tests on normally consolidated samples were carried out at constant temperatures varying from 22 to 80˚ C. Desaturation of samples were carried out by the imposition of suctions using the osmotic method. This required the development of a new triaxial cell equipped with a collar heating and an osmotic pedestal which allows the circulation of an osmotic solution of Poly Ethylen Glycol (PEG) 6000, in contact with the sample via a dialysis membrane. The principal phenomena simultaneously related on the temperature and saturation were highlighted, in particular the hardening of material on isotropic path, a secant modulus which decreases with temperature and increases with suction, a light reduction in the maximum stress on deviator path at high temperature and the increase in this maximum stress when suction increases.