1,721,044 research outputs found
Effects of Sodium Silicate Proportion on Strength Development of Calcined Clay Geopolymer Mortar
No full textGeopolymers are derived from the synthesis of reactive alumino silicate source with alkali metal source to produce a binder that has lower carbon footprint compared to the traditional Portland cement. The long-term supply of precursors for geopolymers in the UK will be difficult to secure based on the dominant used materials – PFA, GGBS and white Metakaolin. Iron rich lateritic clay may offer a good alternative due to its low embodied energy and abundance. In this study, seven mixes were designed and tested. The first five mixes were based on varying the molar oxide ratios of the mortar mixes by activating the flash calcined lithomarge clay with different proportions of 54.5% Na2SiO3 solution. The last two mixes were grouts based on different water togeopolymer solid ratios. The important characteristics of the fresh and hardened mortars that were investigated based on the relevant standards are: strength development, setting times, UPV and rheological properties. The mix that achieved the peak strength of 30 MPa at 28 days cured under sealedcondition has molar oxide ratios - SiO2/Al2O3, Na2O/Al2O3, Na2O/SiO2 and H2O/Na2O of 4.12, 1, 0.24 and 14.1 respectively. The results also showed that a more controllable and consistent rheology was achieved by increasing the water to geopolymer solid ratio of the grout
Effects of Sodium Silicate Proportion on Strength Development of Calcined Clay Geopolymer Mortar
No full textGeopolymers are derived from the synthesis of reactive alumino silicate source with alkali metal source to produce a binder that has lower carbon footprint compared to the traditional Portland cement. The long-term supply of precursors for geopolymers in the UK will be difficult to secure based on the dominant used materials – PFA, GGBS and white Metakaolin. Iron rich lateritic clay may offer a good alternative due to its low embodied energy and abundance. In this study, seven mixes were designed and tested. The first five mixes were based on varying the molar oxide ratios of the mortar mixes by activating the flash calcined lithomarge clay with different proportions of 54.5% Na2SiO3 solution. The last two mixes were grouts based on different water togeopolymer solid ratios. The important characteristics of the fresh and hardened mortars that were investigated based on the relevant standards are: strength development, setting times, UPV and rheological properties. The mix that achieved the peak strength of 30 MPa at 28 days cured under sealedcondition has molar oxide ratios - SiO2/Al2O3, Na2O/Al2O3, Na2O/SiO2 and H2O/Na2O of 4.12, 1, 0.24 and 14.1 respectively. The results also showed that a more controllable and consistent rheology was achieved by increasing the water to geopolymer solid ratio of the grout
Influence of power ultrasound on the portland cement pore solution compositions
No full textThe composition of the cement pore solution reflects the kinetics of hydration process and determine essential insight into the rate at which cement phases hydrated. This characterization can therefore provide information about the stable and unstable solid phases which may precipitate and dissolve, respectively. Power ultrasound (PUS) is currently under consideration to improve the hydration of cementitious materials and to promote the effectiveness of replacing supplementary cementitious materials; SCMs, in terms of mechanical, microstructural and transport properties. This could enhance the properties of cementitious composites, reduce the quantity of waste materials, as well as decreasing the CO2 footprint of cementitious materials. Thisstudy investigates the effect of direct PUS on the Portland cement pore solution compositions at early hydration using inductively coupled plasma-optical emission spectroscopy (ICP-OES) technique. The sonication influence is also inspected by microstructure study of the cement paste using scanning electron microscopy (SEM). The results shows PUS increases high and low concentration ions in the cement pore solution due to the physical and chemical effect of acoustic cavitation, speeding up the hydration process and enhancing the Portland cement performance. The SEM micrographs indicates the more volume of compacted solid phases of hydration products.<br/
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
Fibrous cementitious material development for additive building manufacturing.
Get PDFAdditive Manufacturing (AM) in the construction industry is still in a relative state of infancy. Research has focused on heavy, ground based methods, with the building envelope determined by the dimensions of the deposition system. By comparison, the approach of using robots is not geometrically restricted but requires a degree of miniaturisation to the deposition process. Many studies utilise the AM principal of fused deposition modelling (FDM), which creates an object by extruding a suitably viscous material through a nozzle and depositing one layer at a time. Crucial to the development of cementitious materials for additive building manufacturing (ABM) without formwork, is the material possessing both workability and buildability, and appropriately balancing the contrasting requirements of these properties. Cementitious materialsare typically brittle, requiring reinforcement to provide tensile and flexural capabilities. Reinforcing steel bars are not naturally compatible with ABM and chopped fibres are considered as a viable alternative. This paper investigates the development of a fibrous cementitious mortar suitable for use with a miniaturised deposition system based upon the FDM principal. Three types of fibres – polypropylene, alkali-resistant glass and polyvinyl alcohol (PVA) - were investigated to assess suitability for a miniaturised ABM deposition method and contributions to the mechanical strength of a mortar. PVA fibres provided the best buildability and increased flexural strength, with the appropriate quantity contained in mixes being informed by the degree of detrimental impact upon workability
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
Fibrous cementitious material development for additive building manufacturing.
Get PDFAdditive Manufacturing (AM) in the construction industry is still in a relative state of infancy. Research has focused on heavy, ground based methods, with the building envelope determined by the dimensions of the deposition system. By comparison, the approach of using robots is not geometrically restricted but requires a degree of miniaturisation to the deposition process. Many studies utilise the AM principal of fused deposition modelling (FDM), which creates an object by extruding a suitably viscous material through a nozzle and depositing one layer at a time. Crucial to the development of cementitious materials for additive building manufacturing (ABM) without formwork, is the material possessing both workability and buildability, and appropriately balancing the contrasting requirements of these properties. Cementitious materialsare typically brittle, requiring reinforcement to provide tensile and flexural capabilities. Reinforcing steel bars are not naturally compatible with ABM and chopped fibres are considered as a viable alternative. This paper investigates the development of a fibrous cementitious mortar suitable for use with a miniaturised deposition system based upon the FDM principal. Three types of fibres – polypropylene, alkali-resistant glass and polyvinyl alcohol (PVA) - were investigated to assess suitability for a miniaturised ABM deposition method and contributions to the mechanical strength of a mortar. PVA fibres provided the best buildability and increased flexural strength, with the appropriate quantity contained in mixes being informed by the degree of detrimental impact upon workability
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