Research Quality, Publications and Impact in Civil Engineering into the 21st Century. Publish or Perish, Commercial versus Open Access, Internet versus Libraries?

A research project is only completed when it has been published and shared with the community. Referees and peer experts play an important role to control the research quality. While some new electronic tools provide further means to disseminate some research information, the quality and impact of the works remain linked with some thorough expert-review process and the publication in international scientific journals and books; unethical publishing standards are not acceptable. The writer argues herein that the new electronic aids do not replace scholarship nor critical thinking, although they impact on the working environment of civil engineers

On the behavior of fine mud suspensions

Flows of natural mud-water mixtures are of great interest for industrial and civil engineering. But there is still no general agreement about the methods for determining the main rheological characteristics of these systems. We propose here an accurate rheological study of some natural mud-water mixtures. We first discuss the possible effects of changing various parameters such as temperature, pH, electrolyte concentration, solid concentration, clay type. The behaviour of these muds appears to be very sensitive to most of these parameters and to be hardly predictable from a knowledge of their components. Then we show that a Herschel-Bulkley model fits steady flow experimental data very well for a very large range of shear rates. We also suggest physical explanations of this model in agreement with our observations of behaviour changes when some parameters change. The yield stress value of this model provides a good estimation of real yield stress which is a key parameter for mixture behaviour. These considerations are very useful to characterize, predict and compare various mud flows. / On présente ici une étude du comportement en cisaillement simple de mélanges boueux fins naturels. De nombreuses difficultés expérimentales sont rencontrées lors de tests de rhéométrie avec ces fluides. On montre que ces mélanges sont fondamentalement des fluides à seuil et que leur thixotropie est peu apparente. La courbe d'écoulement peut être représentée par un modèle du type Herschel-Bulkley dans une large gamme de gradients de vitesse

Techniques de rhéométrie en cisaillement simple dans le cas dispersions et suspensions concentrées

Concentrated dispersions and suspensions exhibit complex properties (yield stress, thixotropy, coarse particles in suspension). Experiments aiming at determining the constitutive equation parameters of these fluids (considered as homogeneous) appear to be difficult. In this paper we examine the advantages and disadvantages of different rheometer geometries for testing materials of this type : large dimensions of the rheometer compared to particle diameter, shear homogeneity, possibility to test fluids containing coarse particles, means of checking the deformation field by direct observation... In parallel we review the possible experimental problems (slip at the wall, fracture, evaporation, sieving, settling, centrifugation, ejection), and precautions to avoid them. We then propose specific experimental procedures to determine the main characteristics of these fluids, i.e. yield stress and time-dependent properties (thixotropy). / Les dispersions et suspensions concentrées sont des fluides aux caractéristiques complexes (seuil de contrainte, thixotropie, présence de particules grossières). Lorsqu'on se donne pour but de mesurer les paramètres de la loi de comportement de ces fluides supposés homogènes et continus, les expériences de rhéométrie s'avèrent en général délicates. Dans cet article on examine les avantages et inconvénients de différentes géométries de mesure pour étudier ce type de matériau : dimensions du rhéomètre tenant compte du fait que l'intervalle minimum entre les outils doit être grand devant la taille de particules, homogénéité du cisaillement, aptitude à tester des fluides contenant des particules grossières, possibilité de contrôler le champ des déformations par visualisation directe, etc... En parallèle on passe en revue les problèmes expérimentaux qui peuvent survenir au cours des expériences (glissement, fracturation, creusement, évaporation, ségrégation, sédimentation, centrifugation, éjection) et les précautions qui peuvent permettre de les éviter. On suggère ensuite des protocoles expérimentaux adaptés à la détermination des principales caractéristiques de ces fluides, c'est à dire le seuil de contrainte et les propriétés temporelles (thixotropie) de ces fluides

A large-scale field coaxial cylinder rheometer for the study of the rheology of natural coarse suspensions

When one wants to study the behaviour of coarse suspensions directly, one needs a special large-scale rheometer with a wide gap. As a first step towards the understanding of coarse suspension behaviour a wide-gap coaxial cylinder rheometer (1.2 m diameter, 0.2 m gap, sample volume: 0.5 m3) was built. This apparatus, which should be cheap and strong, was designed to be towed and used in the field to test fluids including particles whose diameter does not exceed 1 cm. The validity of hypotheses and the various theoretical problems of the rheometrical calculations in the case of a wide-gap rheometer when used to test a coarse suspension are then examined. The main advantage of this geometry appears to be that edge effects should not be too important. Its main disadvantage, especially for coarse suspensions with a complex behaviour (yield stress, thixotropy, presence of coarse particles), is the heterogeneity of shear rate from one tool to the other. Experiments with various natural materials (water-clay mixtures and water-debris flow sample mixtures) at different concentrations were done. Some experimental problems (settling, slip, fracture, etc.) were encountered but they could be mastered reasonably well. These results show that when the clay fraction is high enough, a Herschel-Bulkley model can well represent the flow curve of these mixtures in the range of shear rates [0.5; 50 s-1]. When the clay fraction is low and the solid particle fraction is high enough, suspensions behave in a very peculiar way: the flow curve has a minimum. / Afin d'étudier le comportement en cisaillement simple de mélanges boueux naturels grossiers, contenant notamment des particules d'un centimètre de diamètre, un rhéomètre de très grande taille a été construit. Cet appareil est basé sur la géométrie des cylindres coaxiaux. On passe en revue les difficultés expérimentales liées à son utilisation et on présente divers résultats expérimentaux obtenus sur la fraction fine d'échantillons de laves torrentielles

Rheometry of mudflows

The goal of this article is to study in detail the problems related to the rheometry of debris flows. By looking at the previous studies in the field of hyperconcentrated fluids, it has been observed that, even though theoretical models have been proposed and some interesting characteristics have been found, no complete rheometric study has been conducted to date. As natural debris flows are made of rough particles, the first step is to study the fine interstitial fluid of these flows. Various experimental problems may then be encountered with this type of material, such as slide toward the walls, fracture or rupture within the material, which can lead to an erroneous analysis of the results. Provided that some precautions are taken, or by correcting the computations, it is possible, however, to avoid these problems and to get correct results. The second step is to build a large size rheometer in order to directly test the complete debris flows. / L'objectif de cet article est une étude précise des problèmes rencontrés pour la rhéométrie des laves torrentielles. En examinant les travaux précédents dans le domaine des fluides hyperconcentrés, on a constaté que, bien que des modèles théoriques aient été proposés et des caractéristiques intéressantes observées, aucune étude rhéométrique complète n'a pour l'instant été réalisée. Comme les laves torrentielles naturelles comprennent des particules grossières, la première étape est l'étude du fluide interstitiel fin de ces laves. Avec ce type de matériau, on constate alors divers problèmes expérimentaux tels que le glissement aux parois, la fracturation ou la rupture au sein du matériau, qui peuvent conduire à une interprétation erronée des résultats. Moyennant certaines précautions ou en faisant des corrections dans les calculs, il est possible cependant d'éviter ces problèmes et d'obtenir des résultats corrects. La seconde étape consiste à contruire un rhéomètre de grande taille pour tester directement les laves torrentielles complètes

Elongational properties and crystallization of poly (isobutylene) melts probed by synchrotron radiation

In this paper, we describe a phase transition in poly(isobutylene) of various molecular weight under elongational stress. Rheometry and wide angle X-ray diffraction have been performed simultaneously to correlate mechanical and structural properties of the material. The low molecular weight samples did not crystallize under the flow in the range of the strain rates applied. On the other hand, as the molecular weight increases the crystallization is always preceded by a strain of the samples under stretching

Elongational properties and crystallization of poly (isobutylene) melts probed by synchrotron radiation

In this paper, we describe a phase transition in poly(isobutylene) of various molecular weight under elongational stress. Rheometry and wide angle X-ray diffraction have been performed simultaneously to correlate mechanical and structural properties of the material. The low molecular weight samples did not crystallize under the flow in the range of the strain rates applied. On the other hand, as the molecular weight increases the crystallization is always preceded by a strain of the samples under stretching

Seismic precursors linked to highly compressible fluids at oceanic transform faults

ACLInternational audienc

Etude theorique et experimentale des materiaux composites bitumineux par thermographie infrarouge

SIGLECNRS-CDST / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc