1,721,046 research outputs found
Effect of Improper Curing on Concrete Performance
No full textIn a drive to reduce the carbon footprint of construction, the cement industry increasingly uses supplementary cementitious materials, such as pulverised fuel ash (PFA). However, such binder hydrates more slowly and may require longer curing times. This project has looked at the impact of improper curing as a function of concrete mix design; (CEM I 52.5N) vs. CEM I plus 30%PFA replacement, workability (10 to 30 and 60 to 180 mm slump) and target mean strength (20, 50 and 80MPa). Samples were cured in fog room at 200 C or under ambient conditions 200 C and 42% RH. The degree of saturation (DOS) of concrete affects the measured strength. Performing strength testing at constant degree of saturation is of interest to know the effect of improper curing. Therefore, in this study subsequent to curing, the specimens will be dried in oven at 400 C to constant weight, unconfined compressive strength will be determined at various degrees of saturation while changes in weight will be measured also. The result of compressive strength against time will be plotted and there the effects due to DOS will be obtained with the effect due to degree of hydration. The impact of each of the mix design variables mentioned above on improper curing and the DOS will be studied
Microwave Curing Techniques for Manufacturing Alkali-activated Fly Ash
No full textAlkali-activated fly ash (AAFA) has been identified as a low-carbon alternative to Portland cement (PC). However, conventional thermal oven curing, typically at 85ºC, is commonly required to firstly initiate and then accelerate the chemical reaction, which may result in more energy consumption, offsetting the environmental benefits which could be obtained from AAFA.
In this study, the potential of using microwave as an alternative low-energy thermal curing method for manufacturing AAFA has been explored. A microwave curing regime based on a control strategy using temperature feedback data was developed and evaluated in the manufacture of AAFA. The temperature profile within the AAFA sample produced under microwave curing was obtained by using an embedded optical fibre temperature sensor, which was thus used to adjust the microwave power in real-time in order to achieve a desired internal temperature. The AAFA samples manufactured by microwave curing were characterized using compressive strength, XRD, NMR, MIP and SEM, which were also compared with the samples from thermal oven curing. The results indicated that the AAFA manufactured with microwave curing not only showed an equivalent performance, similar reaction products and microstructure, but also showed dramatic reduction in energy consumption
Use of Oil-Based Mud Cutting Waste in Cement Clinker Manufacturing
Full text linkOil-based Mud (OBM) cutting waste is generated during the process of oil well drilling. The drilled rocks are removed from deep within the drilled well and pumped to the surface. The portion removed , known at "cutting", is a mixture of rocks, mud, water and oil. Most drilling companies store this waste in open yards with no specific treatment solution. The environmental regulations in Oman specify that storage should involve isolation, to prevent penetration of the contamination to the surface and underground water. This has made OBM waste an environmental problem, with an associated cost for oil companies. OBM chemical analysis shows an interesting compositionthat may be used in cement manufacture. It has high calcium, silicon and aluminium contents, which are the major oxides in cement manufacture. Also the oil contents are useful for reducing the fuel used during the calcining and clinkerization process. In this research, the OBM waste has been analysed and used as a constituent of the raw meal for cement clinker production. The impact of OBM addition on the resultant clinker has also been investigated
Slag Hydration in composite cements
No full textDespite reported synergies between alumina rich supplementary cementitious materials (SCMs) and limestone, previous studies have focused on up to 5% limestone content. Slag hydration in the presence of 10% limestone is reported in this paper. Hydration was followed through chemical shrinkage, calorimetry, thermal analysis, electron microscopy and X-ray powder diffraction. The results show that limestone incorporation improves slag hydration
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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