Catálogo de publicaciones - libros

Electrical conductivity of agarose gels in 0.15 M KCl was measured. From the experimental data, a functional relation of solute diffusivity to tissue permeability and solute size was derived. This relationship agreed with the experimental results on macromolecule diffusivity in agarose gel published in the literature.

Unsteady liquid flow and chemical reaction characterize hydrodynamic dispersion in soils and other porous materials and flow equations are complicated by the need to account for advection of the solute with the water, and competitive adsorption of solute components. Advection of the water and adsorbed species with the solid phase in swelling systems is an additional complication. Computers facilitate solution of these equations but it is often physically more revealing when we discriminate between flow of the solute with and relative to, the water and the flow of solution with and relative to, the solid phase. Space-like coordinates that satisfy material balance of the water, or of the solid, achieve this separation. Advection terms are implicit in the space-like coordinate and the flow equations are focused on solute movement relative to the water and water relative to soil solid. This paper illustrates some of these issues.

This paper is concerned with the experimental identification of some chemoporoelastic parameters of a reactive shale from data obtained in pore pressure transmission - chemical potential tests. The parameter identification is done by matching the observed pressure response with a theoretical solution of the experiment. This solution is obtained within the framework of Biot theory of poroelasticity, extended to include physico-chemical interactions. Results of an experiment on a Pierre II shale performed in a pressure cell are reported and analyzed.

The fluxes of water and solutes across membranes are expressed as functions of differences of the hydraulic and osmotic pressures at both sides. Such difference equations are deduced from more fundamental differential equations. The distributions of concentration and pressure in a series array of membranes are derived. The order in which the individual membranes are placed exerts a strong influence upon the effects of the applied differences of hydraulic and osmotic pressures. The effect of the interchange of two membranes in a series array of an arbitrary number of membranes can be summarized in four simple rules. The special case of reversal of the flow is also discussed.

In this paper we deal with an enlarged theory of binary mixtures: a second gradient solid constituent and a perfect fluid are considered. On the basis of this assumptions we obtain, for a linear elastic hollow cylinder, a set of density profiles of the solid matrix, parameterized by a suitable energetic coupling coefficient and characterized by the presence of boundary layers arising at the external surfaces of the body. A structural stability analysis of the partial differential equations, governing the motion of the mixture, is also developed, in a case which may be of interest in applications to underground structural engineering.

Salt weathering is one of the major causes of deterioration of buildings and monuments. We have determined the underlying moisture and ion transport within a representative building material by measuring the time evolution of NaCl saturated samples during one-sided drying with Magnetic Resonance Imaging. The obtained NaCl concentration profiles reflect the competition between advection to the surface and redistribution by diffusion. By representing the measured moisture and NaCl profiles in a so-called efflorescence pathway diagram (EPD) also information about the crystallization process is obtained. The pathways followed in the EPDs indicate that for historical objects in general crystallization at the surface cannot be avoided, when evaporation cannot be prevented.

Given the sensitivity of soils to disturbance, the use of low perturbation (i.e., non-destructive) electromagnetic waves provides a viable option for studying soil properties. The measured parameters during the excitation of a material by an electromagnetic wave are electrical conductivity, dielectric permittivity, and magnetic permeability. Electrical conductivity is a measure of charge mobility in response to an electrical field. Dielectric permittivity represents the polarizability of a material. Magnetic permeability indicates the degree of magnetic dipole alignment within a material under the excitation of the magnetic field. Factors that affect electromagnetic wave parameters include water content/degree of saturation, porosity, spatial distribution of the phases (e.g., anisotropy), particle properties (e.g., specific surface), pore fluid characteristics, and temperature. This paper presents a review of electromagnetic parameters, provides experimental data showing the impact of the various factors on the electromagnetic response, and gives a physical explanation of why these factors affect electromagnetic properties. Finally, various applications of electromagnetic wave-based techniques are presented, including monitoring the diffusion of salt through a soft kaolinite sediment and the hydration process in cemented paste backfill.

Frequency-dependent electrokinetics offers a different approach to obtaining information about porous media. In this work, we examine the possibility of using frequency-dependent streaming potential (FDSP) and frequency-dependent electro-osmosis (FDE) to obtain information concerning porous media. The theoretical basis for this work is done using the simple geometry of a capillary because it allows for an easier interpretation of the underlying physics. Pride [1994] formulated a more generalized porous media case which has been shown to give equivalent results to the capillary case for streaming potentials [Reppert et al., 2001].

In a thermodynamic framework which exploits the entropy inequality to obtain constitutive equations, it is common practice to assume charge neutrality and enforce this restriction using Lagrange multipliers. In this paper we show that the Lagrange multiplier used to enforce charge neutrality does not correspond to any known physical parameter, raising the question of whether charge neutrality can really be enforced.

Volume reduction of wet non-rigid porous media is at first “normal”, i.e. the void ratio reduction is equal to the moisture ratio reduction. Upon air entry, with or without cracking, and further drying, several stages of shrinkage can usually be observed, such as “structural”, “proportional”, and “zero” shrinkage. The complete shrinkage phenomenon, from the saturated to the oven-dry state, can be accurately modelled using the Groenevelt-Bolt constitutive shrinkage equation [2]. The first derivative of this equation (slope) provides the tool to predict how the water potential will change upon loading the porous body. The second derivative (curvature) provides the tool to separate the different stages of shrinkage. The location of these separation points reveals important structural properties of the porous body. Experimental data for swelling soils will be used to demonstrate several principles and practical implications.