1,721,051 research outputs found
Multiscale Analysis on the Behaviour of a Lime Treated Bentonite
Get PDFAbstractAn insight into the microstructural evolution of clay-lime-water systems and its influence on the hydro-mechanical behaviour of treated bentonite has been presented. The time-dependent mineralogical and microstructural changes induced by lime addition on a natural bentonite have been investigated in order to provide a better understanding of the kinetic of the ongoing reactions. The effects of lime addition on the clay particle arrangements have been inferred from dynamic light scattering measurements, whereas the mineralogical changes have been monitored at increasing curing time by X-Ray diffraction and thermogravimetric analysis. The bentonite showed a high initial reactivity characterized by a rapid and total consumption of lime, which promoted the formation of new hydrated phases since the very short term (0 days of curing). Oedometer tests on not treated and lime stabilised saturated samples have been performed at increasing curing times. The results showed the combined effect of clay particles arrangement and bonding on the mechanical behaviour of treated samples
Alkaline activation of non-calcined kaolins
No full textDans un contexte de valorisation des ressources naturelles et de mode de construction réduisant l’impact environnemental, l’utilisation de matériaux alcali-activé pourrait être une solution alternative. L'activation alcaline (AA) du kaolin calciné (métakaolin) est bien connue pour produire un liant aux propriétés très intéressantes. Cependant, la calcination du kaolin est coûteuse et énergivore et pourrait ne pas s’avérer nécessaire lorsqu’on cherche à améliorer les propriétés mécaniques de sols par exemple de quelques mégapascals. Ainsi, dans cette thèse, nous avons étudié l’AA de kaolin non calciné par une solution de silicate de sodium enrichie ou non en soude afin d’évaluer le potentiel réactif de ce que pourrait être un sol modèle riche en kaolins. La description réactionnelle s’est principalement basée sur l’utilisation de la DRX et la RMN du solide ( 29 Si et 27 Al). La Kaolinite montre une réactivité qui augmente en présence de soude qui se traduit par la formation de différents gels riches en Si et par la formation de zéolites dont les caractéristiques diffèrent en fonction des concentrations étudiées (Hydroxysodalite, Phillipsite, Zéolite X). Enfin, une modification des conditions de cure a été étudiée. La cure au contact de l’air inhibe la formation de zéolites et favorise la formation d’un gel plus riche en Al. Pour finir les propriétés mécaniques des matériaux sont étudiées. Les résistances mécaniques développées sont faibles et l’incorporation de kaolin activé à un métakaolin réduit fortement la résistance à la compression des matériaux. La formation de zéolites (Chabazite-Na et Phillipsite) est proposée pour expliquer cette baisse des résistances.In a context to valorize natural resources and construction method which reduce environmental impact, the use of alkali-activated materials could be an alternative solution. Alkaline activation (AA) of non-calcined kaolin (metakaolin) is well known to produce a binder with very interesting properties. However, kaolin calcination process is expensive and energy consuming and is not necessary when trying to improve the mechanical properties of soils, for example, by a few megapascals. Thus, we studied the alkaline activation of non-calcined kaolin with a sodium silicate solution enriched or not in soda in order to evaluate the reactive potential of what a model soil rich in kaolins could be. The reaction description was based mainly on XRD and solid-state NMR ( 29 Si and 27 Al). Kaolinite shows an increased reactivity in the presence of soda, which results in the formation of different Si-rich gels and in the formation of zeolites whose characteristics differ according to the concentrations studied (Hydroxysodalite, Phillipsite, Zeolite X). Finally, a modification of the curing conditions was studied. The cure in contact with air inhibits the formation of zeolites and promotes the formation of a gel richer in aluminum. To finish the mechanical properties of materials were studied. The developed mechanical resistances are lowand the incorporation of activated kaolin with a metakaolin greatly reduces the compressive strength of the materials. Zeolites formation (Chabazite-Na and Phillipsite) is proposed to explain this decrease in resistance
Influence of Pore Water Chemistry on Hydraulic Conductivity of Kaolinite Suspensions
Get PDFAbstractThe role of pore water chemistry on particle aggregation and soil formation during sedimentation process has been investigated for a kaolinite clay suspensions. The modification of surfaces charge properties of clay minerals induced by different pore water chemistry rules the particles arrangement. As a consequence, at volume scale the sedimentation behaviour and in turn the physical, mechanical and hydraulic behaviour of the formed soil skeleton are changed. Sedimentation tests on several suspensions showed the influence of different aggregation on settling and self-weight consolidation stages. Hydraulic conductivity of kaolin suspensions has been estimated from the settling velocity recorded in sedimentation tests. Test results showed the relevant dependency of the hydraulic conductivity of the clay suspensions on the particle arrangement induced by the pore water chemistry
Utilisation d'argiles et de marnes calcinées dans le développement de ciments composés
No full textL’utilisation de Supplementary Cementitious Materials (SCMs) en substitution du clinker est
une technologie aujourd’hui bien connue qui permet de réduire le coût environnemental du
ciment. Parmi les SCMs largement utilisés aujourd’hui on retrouve les cendres volantes, les
laitiers de hauts fourneaux ou encore la poudre de verre. Dans les dernières années, un intérêt
grandissant s’est développé pour l’utilisation d’argiles calcinées comme ajouts cimentaires,
notamment du fait de leur forte réactivité et de leur grande disponibilité. Ce projet de thèse
s’intéresse à l’utilisation d’argiles et de marnes calcinées comme ajouts cimentaires. L’objectif
principal est d’identifier de nouveaux échantillons susceptibles de présenter un intérêt pour
une utilisation comme SCMs. Pour ce faire, une approche multi-échelle macro/micro est
utilisée afin d’étudier de manière précise la calcination, la réactivité pouzzolanique et le
comportement en système cimentaire de ces nouveaux échantillons. Il a été possible de
démontrer que les marnes (malgré leur composition minéralogique complexe) sont des
matériaux qui peuvent être utilisés comme ajout cimentaire après calcination, et ce, même
s’ils contiennent une faible proportion d’argiles. Par la suite, il a été démontré que la
palygorskite est une argile à haut potentiel pour une utilisation comme ajout cimentaire après
calcination, et peut être considérée comme une alternative viable au métakaolin. L’étude
poussée de l’utilisation de palygorskites calcinées comme ajouts cimentaires a également
permis d’apporter de nouvelles connaissances fondamentales sur la compréhension des
mécanismes impliqués lors de la calcination de ce type de matériaux.The use of Supplementary Cementitious Materials (SCMs) as a substitute for clinker is a wellknown technology that can reduce the environmental cost of cement. Among the SCMs widely
used today are fly ash, blast furnace slag and glass powder. In recent years, there has been a
growing interest in the use of calcined clays as SCMs, particularly due to their high reactivity
and availability. This thesis project focuses on the use of calcined clays and marls as
supplementary cementitious materials. The main objective is to identify new samples that
could be of interest for use as SCMs. To this end, a multi-scale macro/micro approach is used
to study the calcination, pozzolanic reactivity and performance in cementitious systems of
these new materials. It was possible to demonstrate that marlstones (despite their complex
mineralogical composition) have the potential to be used as supplementary cementitious
materials after calcination, even with a low proportion of clays. Subsequently, it was shown
that palygorskite is a high potential clay for use as a supplementary cementitious material after calcination, and can be considered as a viable alternative to metakaolin. The extensive
study of the use of calcined palygorskites as SCMs has also provided new fundamental insights
into the understanding of the mechanisms involved in the calcination of this type of material
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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