1,721,037 research outputs found
Preparation of magnesium phosphate cement by recycling the product of thermal transformation of asbestos containing wastes
No full textAsbestos containing wastes have been employed for the first time in the formulation of magnesium phosphate cements. Two samples were mixed with magnesium carbonate and calcined at 1100 and 1300 °C. Under these conditions, complete destruction of asbestos minerals is known to occur. The product, containing MgO, after reaction with water-soluble potassium di-hydrogen phosphate, led to the formation of hydrated phases at room temperature. Crystalline and amorphous reaction products were detected, with the latter being likely the metastable precursor of the former. Measured strengths were found to be in line with data from the literature, suggesting that this material may be used as cement. The process here described represents a viable recycling opportunity for this class of hazardous wastes. Simultaneous destruction of asbestos minerals and formation of reactive MgO during thermal treatment, bring benefits in terms of energy requirements and preservation of natural resources in cement manufacturing
Recycling the product of thermal transformation of cement-asbestos for the preparation of calcium sulfoaluminate clinker
No full textAccording to recent resolutions of the European Parliament (2012/2065(INI)), the need for environmentally friendly alternative solutions to landfill disposal of hazardous wastes, such as asbestos-containing materials, prompts their recycling as secondary raw materials (end of waste concept). In this respect, for the first time, we report the recycling of the high temperature product of cement-asbestos, in the formulation of calcium sulfoaluminate cement clinkers (novel cementitious binders designed to reduce CO2 emissions), as a continuation of a previous work on their systematic characterization. Up to 29 wt% of the secondary raw material was successfully introduced into the raw mix. Different clinker samples were obtained at 1250 °C and 1300 °C, reproducing the phase composition of industrial analogues. As an alternative source of Ca and Si, this secondary raw material allows for a reduction of the CO2 emissions in cement production, mitigating the ecological impact of cement manufacturing, and reducing the need for natural resources
The visualization of microcracks in aged cement mortar using tomography
No full textThe investigation of microcracks formation and their evolution in cement mortars during hardening of Portland
cement-based materials is still a challenging task. Microcracks play a fundamental role in transport processes and
localization of deformation. Their growth impairs durability of composite materials such as mortars and concretes. Even if
cementitious materials are extensively utilized for construction works, only limited amount of knowledge is available on
the structural development at the micro-metric scale. Nowadays, very fine Portland clinker phases are utilized due to their
faster reaction rates required to speed up construction works. However, rapid hardening of cements is associated with
potential risks of accelerated formation of microcracks, that, after some time needed for their interconnection, may be
responsible for the serious deterioration, especially in outdoor environment. X-ray computed microtomography was applied
to visualize microcracks formation in aged Portland cement mortar and image analysis helped to distinguish between air
bubbles entrapped during mortar preparation and newly-formed microcraks in fully three dimensional non-destructive
fashion. Besides the interest for modern concrete, since a high number of concrete immovable objects are now part of our
Cultural Heritage, it is expected that the obtained results will also contribute to the conservation of such objects
Plasters and mortars from the theatre in Nea Paphos (Cyprus): A multidisciplinary study
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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
Evolution of microstructure and performance in magnesium potassium phosphate ceramics: Role of sintering temperature of MgO powder
No full textThe reactivity of the MgO powder employed in the formulation of Mg–K phosphate ceramics can be modulated through the calcination temperature of MgCO3 source material, which has a direct impact on production costs. Upon annealing, MgO undergoes sintering, and in order to optimize the design of products for applications, it is of primary importance to disclose the link between the sintering temperature, reaction mechanisms, microstructure and performance in this class of ceramics. Small angle neutron scattering was used to measure the specific surface area of pores in samples aged 30 days produced with 5 different MgO powders, and to follow the evolution of pore size distribution during the setting reaction, in a time-resolved experiment. Quantification of amorphous and crystalline fraction up to 28 days was accomplished in synchronous with flexural strength tests. Results indicate that mechanical properties improve thanks to the progressive buildup of a pervasive network of tabular crystals filling the entire volume. Increasing the sintering temperature above 1500 °C yields a more compact ceramic, with less, but larger, pores, containing more crystalline fraction and less amorphous. This is consistent with the recently proposed mechanisms describing the ceramic setting reaction. The analysis of the fractured surface suggests that strength might be effectively improved modifying the density and orientation of crystals in the ceramic volume, a way for engineering new tailor-made ceramics
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
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