1,721,007 research outputs found
Mechanical performance of inorganic polymer-based mortars with glass fibre reinforced polymer bars
No full textGlass fibre reinforced polymer (GFRP) bars have found a place in specific structural applications as concrete reinforcement thanks to certain advantages regarding chemical attack behaviour, corrosion resistance, non-conductive characteristics, high strength/weight ratio and production simplicity. However, the negative effect that elevated temperatures have on the mechanical performance of these bars constrains their spread adoption. In contrast, inorganic polymers (IP) are characterized by a low thermal conductivity, good mechanical performance and stability at elevated temperatures. The aim of the study is the preliminary evaluation of the mechanical interaction between an IP mortar made by alkali activated fayalite slag (FS) and the embedded GFRP bars used for reinforcement, defining the bearing capacity of the dual system under flexural loading
Modifying the pore size to minimise shrinkage by curing and using reactive and non-reactive additives in Fe-rich inorganic polymer mortars
Full text linkInorganic polymers (IPs) are binding materials that can be formed by alkali activating reactive Fe-rich slags; with mechanical properties comparable to those of Ordinary Portland Cement (OPC) based systems. However, IPs durability properties, such as shrinkage, is so far poorly investigated. Therefore, the current research focuses on determining the autogenous and drying shrinkage behaviour of Fe-rich IP mortars and its associated driving forces. IP were produced with an activating solution of a 1.7 SiO2/K2O molar ratio and 65 wt% H2O. IP mortars at ambient curing conditions exhibit an autogenous expansion and a high drying shrinkage, which must be reduced to avoid cracks and to meet durability criteria. In order to reduce the expansion and the drying shrinkage, 2-Methyl-2.4-Pentanediol (2M) and ground granulated blast furnace slag (GGBFS), were introduced to the mixture and sealed curing was performed at ambient or at an elevated temperature. The 2M additive reduces the drying shrinkage with 80% and modified the pore size distribution in such a way that a higher porosity was achieved, while the mechanical properties remained similar. Heat curing of IP mortars with 2M has no significant effect on the drying shrinkage. The introduction of GGBFS in IPs, cured at ambient conditions, had lower autogenous shrinkage but negatively affect the drying shrinkage due to the formation of a finer pore structure. Heat curing, on the other hand, reduces the drying shrinkage significantly and improves the mechanical properties considerably. Current research provides an insight in different pathways to reduce drying shrinkage while maintaining adequate mechanical properties
Reaction kinetics and structural analysis of alkali activated Fe–Si–Ca rich materials
No full textThis paper describes the outcomes of a study conducted to investigate the influence of solid-to-liquid (S/L), K2O/SiO2 molar ratio and type of activation solution on reaction kinetic, structural development and final mechanical properties of Fe–Si–Ca rich inorganic polymers (IP). IPs were synthesized with alkali hydroxide and alkali hydroxide/silicate type activators to investigate the kinetic and structural impact of soluble silicates on the activating solution. Multiple characterization techniques, including isothermal conduction calorimetry (ICC), X-ray diffraction (XRD) and infrared spectroscopy (FTIR), were used to give insights on the impact of each of the considered synthesis parameters. Solid-to-liquid and K2O/SiO2 ratios were found to be the compositional parameters governing the reaction kinetics, whereas the introduction of silicate species in the activating solution contributed to further densification and strength development. By combining the effect of the studied parameters, IP binders incorporating a high content of a Fe–Si–Ca rich residues (≥92.7 wt% of solid content) were synthesized at room temperature to achieve a compressive strength exceeding 119 MPa. This work contributes with new insights into the reincorporation and upscaling of a vast group as yet unexplored Fe–Si–Ca-rich waste streams into the materials cycle, such as non-ferrous slags and vitrified residues generated during the incineration of municipal solid waste or during the gasification refused-derived fuel. The study demonstrates the feasibility of producing high strength IPs with only minor usage of virgin raw materials and the possibility of using the developed products as an alternative to conventional cementitious binders. Promoting synergetic interactions between proxy industries is crucial to the sustainability of our current production processes and will play a critical role in achieving current environmental targets
Porous glass-ceramics made from microwave vitrified municipal solid waste incinerator bottom ash
No full textGlobal warming and depletion of resources have fueled research towards innovative building materials of low environmental impact and high performance engineering properties. Porous glass-ceramics were synthesized using municipal solid waste incinerator (MSWI) bottom ash (BA) as a starting material. BA was initially milled and then vitrified, as a purification step, by direct microwave heating, characterized by a high glass yield. Highly porous glass-ceramics were produced by intensive mechanical stirring of vitrified bottom ash (VBA) aqueous suspensions under weak alkali activation (1 M NaOH and 2.5 M NaOH) and sinter-crystallization at 800 °C or 900 °C. The obtained glass ceramics, with up to 70 vol% porosity, exhibited compressive strength well above 1 MPa, being comparable to lightweight construction materials, such as aerated concrete. High relative permittivity was measured for the 10 wt% soda-lime glass doped porous VBA material sintered at 800 °C, paving the way for its use as a potential semiconductor catalyst
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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