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Mechanical and thermal characterisation of geopolymers based on silicate-activated metakaolin/slag blends
No full text[EN] This article assesses the effect of mix design parameters on the compressive strength and thermal performance of alkali silicate-activated blends of metakaolin (MK) and granulated blast furnace slag (GBFS). A strong interrelationship between the effects of activator composition and the GBFS/(GBFS + MK) ratio is identified through statistical analysis of compressive strength data. Pastes formulated with higher SiO 2/Al 2O 3 molar ratios show improvements in mechanical strength with increasing GBFS addition, associated with the formation of a structure comprising coexisting aluminosilicate 'geopolymer' gel and Ca-rich Al-substituted silicate hydrate (C-(A)-S-H) reaction products. The inclusion of GBFS in MK-based geopolymers seems also to improve their performance when exposed to high temperatures, as higher residual compressive strengths are reported for these mixtures compared to solely MK-based systems. Only slight differences in shrinkage behaviour are observed at temperatures of up to 600 °C with the inclusion of GBFS; however, slag-blended pastes exhibit enhanced stability at temperatures exceeding 800 °C, as no variation in the compressive strength and no additional shrinkage are identified. These results suggest that nanostructural modifications are induced in the gel by the inclusion of GBFS into MK-based geopolymers, improving the overall performance of these materials. © 2011 Springer Science+Business Media, LLC.This study was sponsored by Universidad del Valle (Colombia), Instituto Colombiano para el Desarrollo de la Ciencia y Tecnologia "Francisco Jose de Caldas" (COLCIENCIAS) and the Center of Excellence of Novel Materials (CENM). The participation of JLP was funded by the Australian Research Council (ARC), including partial funding through the Particulate Fluids Processing Centre, a Special Research Centre of the ARC.Bernal, SA.; Rodríguez Martínez, ED.; Mejía De Gutiérrez, R.; Gordillo, M.; Provis, JL. (2011). Mechanical and thermal characterisation of geopolymers based on silicate-activated metakaolin/slag blends. Journal of Materials Science. 46(16):5477-5486. doi:10.1007/s10853-011-5490-zS547754864616Shi C, Krivenko PV, Roy DM (2006) Alkali-activated cements and concretes. Taylor & Francis, Abingdon, UKDavidovits J (1991) J Thermal Analysis 37:1633Palomo A, Glasser FP (1992) Brit Ceram Trans J 91:107Provis JL, van Deventer JSJ (eds) (2009) Geopolymers: Structures, Processing, Properties and Industrial Applications, Woodhead. 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Solid Reactant-Based Geopolymers from Rice Hull Ash and Sodium Aluminate
Full text linkHigh carbon rice hull ash and solid sodium aluminate were used as silica, alkali and alumina sources to synthesise one-part “just add water” geopolymer binders. Three binders with different Si/Al ratios and different water contents were studied. Due to the high carbon content of the samples, using a high amount of water is required to satisfy the workability of the binders. Similar to traditional geopolymer systems, high water content increases the crystallinity, decreases the reaction rate and negatively affects the microstructure of samples. In high carbon rice hull ash system, silica concentration is not a suitable indication of the silica availability for reaction, and the amount of unburned carbon in ash particles affects silica release rate. Increasing the silica content of raw materials leads to higher amount of Si/Al ratio in the final geopolymer binder and improves the mechanical and microstructural properties of samples. All samples studied here successfully made geopolymer binders. The highest strength achieved was 22 MPa after 3 weeks
Characterisation of One-Part Geopolymer Binders Made from Fly Ash
Full text linkThe kinetics of one-part “just add water” geopolymerisation reaction is studied in the system of fly ash as an aluminosilicate precursor and solid sodium silicate as alkali activator. The rates of the release of Si and Al nutrients from source materials can significantly affect their availability for reaction and their extent of participation in geopolymer gel structure. The crystalline phases that usually appear in fly ash geopolymers are missing in the one-part mix binders studied here, and by increasing the Si/Al ratio the amount of Si contribution in the final geopolymer gel is decreased. The sample with lower water content sees the participation of more Si in both stages of gel formation. Adjusting the composition of raw materials can improve the mechanical properties of the final one-part mix binder. Reasonable mechanical strength with the maximum strength of 65 MPa is achieved
Dissolution behaviour of source materials for synthesis of geopolymer binders: A kinetic approach
No full textControlling the initial release rate of alumina and silica from source materials is known to have a significant effect on the nanostructure of geopolymer gel and its final mechanical properties. However, most of the studies regarding the solubility of source materials take an equilibrium approach, and there is a gap in understanding of the release rates at far-from-equilibrium conditions. In the present study, the initial dissolution rate of some geopolymer precursors is characterised. The liquid to solid ratios are designed to be sufficiently high to minimise precipitation of hydration products, and the effects of solution alkalinity and milling on dissolution rates are investigated. While fly ash and blast furnace slag particles seem to release Si and Al at approximately similar rates, metakaolin shows a distinctively higher release of Si from the very early time of dissolution. Increasing solution alkalinity increases the dissolution of source materials up to some point, and the greatest effect is observed on fly ash particles. The most interesting result of milling is observed on fly ash particles where the release rate of silica has become higher than alumina, while contrasting behaviour is observed in the non-milled fly ash system. The opposite behaviour is observed in the slag system where milling rapidly increases the release rate of Al while the release rate of Si is increased slowly
The Durability of Fly ash based Geopolymers as Construction Material.
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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
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