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Development of Non-Proprietary Ultra-High-Performance Concrete and Railway Tie Application
No full textThis study reports on properties of non-proprietary ultra-high-performance concretes (UHPCs) for railway ties. The research work is divided into three major phases. The first phase reports on optimization of cementitious materials and aggregates and selection of the most suitable water-to-cementitious materials ratio. In the second phase, the transport and durability properties of the optimized UHPCs are determined. In the third phase of the study, assessment on the structural behavior of the full-scale UHPC railway ties is reported. The major variables of this study are binder types (Type V cement, class F fly ash, silica fume, Ground granulated blast-furnace slag, natural pozzolan), binder combinations (binary, ternary, quaternary), aggregate-to-cementitious materials ratio (0.80, 1.00, and 1.20), steel fiber types (hooked and straight), and steel fiber content (0%, 2%, and 3%). The experimental program assesses the fresh properties (flow), demolded unit weight, mechanical properties (compressive, tensile, and flexural strengths, and modulus of elasticity), transport properties (water absorption, volume of permeable void, water penetration, rapid chloride penetration, and surface resistivity), durability (freezing and thawing resistance, deicing salt resistance, and abrasion resistance), and dimensional stability (drying shrinkage). The structural performance of non-proprietary UHPC ties is examined under static center negative moment test, static rail-seat moment test, and center negative cyclic loading conditions.
The outcome of this study revealed that the selected optimized UHPCs displayed excellent bulk properties and dimensional stability. Amongst the utilized cementitious material combinations, UHPCs made with the combined silica fume and class F fly ash, as a partial replacement of cement, performed the best, while the companion mixtures incorporating only class F fly ash exhibited the contrary. An apparent strain-hardening and -softening was observed in the load-deflection response of steel fiber-reinforced UHPCs. Due to better steel to concrete surface adhesion, straight steel fibers had a more positive influence on the mechanical properties and dimensional stability of the studied UHPCs than those of the hooked fibers. Overall, this experimental study supports that, with proper gradations and proportioning, traditional fine aggregates can be used as an effective substitute for the expensive filler materials used to produce the proprietary UHPCs without compromising their mechanical properties and dimensional stability.
The findings of this study also indicated that the type and combination of cementitious materials had a greater influence on surface resistivity and chloride ion penetration resistance than on the strength of the studied UHPCs. The inclusion of silica fume reduced water absorption and permeable voids, while ternary UHPCs with silica fume and fly ash showed a significant reduction in charge passed compared to the reference UHPC. The study also highlighted the unsuitability of the RCPT test for assessing chloride transport through steel fiber-reinforced UHPCs since fibers can short the circuit to result in invalid indication of conductance. The surface resistivity results showed excellent correlation with RCPT findings.
The investigated UHPCs also exhibited exceptional resistance against freezing and thawing deterioration. The post-F-T exposed UHPCs gained strength due to the availability of unhydrated pozzolanic materials, coupled with a favorable curing environment. Amongst the utilized pozzolanic material combinations, the UHPCs made with silica fume and class F fly ash, as a partial replacement for the cement, performed best against freezing and thawing, whereas the companion mixtures containing only class F fly ash, to replace a portion of the cement, showed the highest mass loss. The addition of straight steel fibers had a more positive influence on the freezing and thawing resistance than hooked fibers.
The studied UHPCs also exhibited excellent resistance to de-icing salts, with ternary blend UHPCs and steel fibers further enhancing the material\u27s resistance by arresting crack development. The studied UHPCs also displayed excellent resistance against wear, well above that of the typical concrete currently used in prestressed concrete sleepers/ties. Amongst the utilized cementitious material combinations, the UHPCs made with silica fume as a partial replacement of cement performed best against abrasion, whereas mixtures containing fly ash showed the highest depth of wear. The relative gain in abrasion of the studied UHPCs was independent of cementitious materials compositions, and steel fiber content and type.
The UHPC Ties constructed using grade 468 MPa steel reinforcing bars exhibited higher ductility and energy absorption. Although the UHPC ties made with grade 738 MPa reinforcing bars sustained higher ultimate loads, they exhibited lower bending displacement at the peak load. Attributed to the shorter span and larger sectional size, the static support negative moment test showed higher ultimate load capacity compared to the static center moment test. The UHPC ties subjected to cyclic loading performed similarly to their static loading counterparts, with the ties made with grade 468 MPa steel reinforcing bars demonstrating higher ultimate load capacity, better energy absorption, and greater ductility. The studied UHPC ties exhibited flexural type failure with vertical cracks, and the observed crack frequencies were slightly higher under cyclic loading. Good bond behavior between reinforcing rebars and concrete was observed for all the studied UHPC ties. Unlike the UHPC ties constructed using grade 738 MPa reinforcing bars, the load-strain response of the UHPC ties made with grade 468 reinforcing bars indicated clear yielding under both static and cyclic loading conditions
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
Abrasion Resistance of Ultra-High-Performance Concrete for Railway Sleepers
No full textThis study aimed to determine the abrasion resistance of ultra-high-performance concretes (UHPCs) for railway sleepers. Test samples were made with different cementitious material combinations and varying steel fiber contents and shapes, using conventional fine aggregate. A total of 25 UHPCs and two high-strength concretes (HSCs) were selected to evaluate their depth of wear and bulk properties. The results of the coefficient of variation (CV), relative gain in abrasion, and abrasion index of the studied UHPCs were also obtained and discussed. Furthermore, a comparison was made on the resistance to wear of the selected UHPCs with those of the HSCs typically used for prestressed concrete sleepers. The outcomes of this study revealed that UHPCs displayed excellent resistance against abrasion, well above that of HSCs. Amongst the utilized cementitious material combinations, UHPCs made with silica fume as a partial replacement of cement performed best against abrasion, whereas mixtures containing fly ash showed the highest depth of wear. The addition of steel fibers had a more positive influence on the abrasion resistance than it did on compressive strength of the studied UHPCs
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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