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Calcium Sulfoaluminate Cements Obtained from Bauxite-Free Raw Mixes
No full textThe most important properties of calcium sulfoaluminate (CSA) cements are regulated by their key-component, C4A3, various calcium aluminates (C12A7, C3A, CA, C4AF, C2AS, CAS2), lime and/or
calcium sulfate (in relation to the type of application) can occur in CSA cements, depending on the synthesis
temperature as well as the nature and proportioning of raw materials.
As far as the manufacturing process is concerned, CSA-based binders show noticeable environmentally friendly
features. Compared to ordinary Portland cements, they are characterized by reduced limestone requirement, kiln
thermal input and CO2 generation as well as greater usability of industrial wastes and by-products often difficult to
reuse. Limestone, bauxite and gypsum are the main natural materials involved in the manufacture of CSA cements and
can be usefully replaced by industrial wastes such as blast-furnace slag, coal combustion ash from both traditional
combustors and fluidized bed reactors, waterworks slime, red mud, phosphogypsum and flue gas desulfurization
gypsum.
In particular, fluidized bed coal combustion waste, whose utilization is of critical importance for the success of this
technology, has proved to be an excellent source of CaO, SO3, SiO2 and Al2O3 for the synthesis of CSA cements.
Unfortunately, its Al2O3 content does not allow a full replacement of an expensive natural resource like bauxite and an
integration with Al2O3 rich by-products is therefore needed. In this regard, alumina powders and anodization mud are
worthy of consideration. The former are by-products derived from the secondary aluminium manufacture; the latter is a
residue generated during the production of anodized aluminium elements.
The synthesis process of CSA clinkers obtained from raw mixes (heated in a laboratory electric oven for 2 hours at
temperatures ranging from 1150°C to 1300°C) containing limestone, gypsum, fluidized bed combustion waste and/or
Al2O3 sources like alumina powders or anodization mud or both, was investigated in this paper, using XRD analysis as
main characterization technique. It has been found that a very good selectivity towards C4A3$, even better than that
achieved with the use of only natural materials, was displayed by waste-based raw mixes. DTA-TGA analyses showed
that CSA cements derived from synthesized clinkers behave, upon hydration, similarly to an industrial CSA cement
obtained from natural raw materials
Use of Industrial Byproducts as Alumina Sources for the Synthesis of Calcium Sulfoaluminate Cements
No full textCalcium sulfoaluminate (CSA) cements show some
desirable environmentally friendly features that include the possibility
of using several industrial byproducts as raw materials in their
manufacturing process. Alumina powder, from the secondary
aluminum manufacture, and anodization mud, from the production
process of anodized aluminum, have proved to be suitable as
partial or total substitutes for an expensive natural material like
bauxite. CSA clinker generating raw mixtures, containing limestone,
natural gypsum, bauxite, and/or one of the alumina-rich
byproducts, were heated 2 h in a laboratory electric oven at
temperatures ranging from 1150 to 1300 C. Conversion of
reactants into 4CaO 3 3Al2O3 3 SO3 (the key component of CSA
cements), evaluated using X-ray diffraction (XRD) analysis, increased
with an increase of both burning temperature and byproduct concentration. When examined through differential
thermogravimetric and XRD analyses, a synthetic CSA clinker (made from the raw mixture incorporating alumina powder as a
total replacement of bauxite) mixed with 20% gypsum showed a hydration behavior almost similar to that of an industrial CSA
cement containing the same amount of gypsum
Hydraulic behaviour of calcium sulfoaluminate cement alone and in mixture with Portland cement
No full textThe basic component of calcium sulfoaluminate (CSA) cement is C4A3
in the presence of calcium sulfate alone quickly generates, besides aluminium hydroxide, non-expansive ettringite
particles developing in the shape of large prismatic crystals responsible for an elevated mechanical strength. The most
relevant features of the hydration process are: 1) a high reaction rate and phase stability; 2) a considerable free water
consumption and a reduced capillary porosity; 3) a peculiar pore size distribution shifted towards low-porosity regions.
The phase (b) of the investigation mainly aimed at floor concrete applications, where both high compressive strength
and low drying-shrinkage are needed at early curing times. Blending Portland cement with CSA cement enables to
exploit not only the intrinsic contribution of the latter in terms of early strength and reduced shrinkage, but also the
shrinkage-compensating effect exerted by microcrystalline ettringite particles, responsible for an expansive behaviour
and formed by the C4A3$ reaction with water, calcium sulfate and calcium hydroxide generated by Portland cement
hydration. The hydration process of a suitable CSA-Portland cement blend is mainly characterized by: 1) the quick
formation of ettringite and its dominant role among the hydration products; 2) the reduced hydration rate of C3S and
C3A at early ages; 3) the absence of calcium hydroxide; 4) the more concentrated porosity distribution (within the
submicronic region) compared to that of Portland cement
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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