1,721,192 research outputs found
Gender Balance in Construction Material Research: The Analysis of Alkali-Activated Materials by a Bibliometric Study Using Scopus Database
Full text linkResearch in alkali-activated materials (AAMs) is an innovative and dynamic material science topic. This is due to the relevant performances in terms of physico-mechanical properties comparable to traditional construction materials (e.g., ordinary Portland cement). The sustainability of AAMs is often highlighted since they can be developed by using many natural or industrial by-products–based precursors. This leads to challenges with the optimization of AAM production due to their different performances, availability, and costs. However, they are flexible and locally adapted materials. The research interest in AAMs has rapidly increased in the early 2000s. In recent years, about 1,000 international articles have been published each year. This study aims at assessing the gender balance of this specific research topic to investigate the relevance of women’s participation. Author lists of the published articles were analyzed throughout the Scopus database, applying “alkali-activated material” and “geopolymers” as keywords in the titles, abstracts, and keywords search. The last 10 years (2009–2019) were taken into account. The gender of the most prolific authors was analyzed, and a focus of European authors on this topic was considered, as more than 25% of the research in AAMs have been carried out in Europe. The analysis of 5,900 publications in the last decade shows that there is currently a shift toward men in the gender balance in this specific research, and female authors only covered 22% of the most productive authors worldwide. Considering European authors, a more equal gender distribution is reached, when the first author is considered, with a concentration of women in the range of 36–56%, recorded over 1,396 articles
New sustainable alkali-activated composite materials reinforced with natural fiber: preliminary experimental investigations
No full textA new class of materials known as alkali-activated materials (AAM) has rapidly grown in interest in the last two decades in order to reduce the CO2 emissions for cement and ceramic materials productions. This new class of materials is based on alkali-activation of precursors able to consolidate at room or slightly higher temperatures. One of the main advantages of AAM is the possibility to use waste-based powders as for example coal fly ashes, thus promoting a circular economy approach.
Although being characterized by a lower environmental impact, AAM suffer from some drawbacks, mainly the extreme brittleness and the low dimensional stability. The most frequently used solution to these problems is the addition of fibers, such as polypropylene, steel or basalt ones. The use of natural fibers with the scope to obtain a similar improvement could provide a huge environmental benefit.
In this work, the effect of natural fibers (i.e., bamboo, Arundo, hemp and kenaf) on the properties of mortars formulated with fly ashes activated by alkaline solutions has been investigated. The length of the fibers was varied in order to obtain the best properties of the composite materials. A certain amount of water has been added in all the alkali-activated mixes to obtain a good workability. A reference mortar without fibers and the same liquid/binder and binder/sand ratio has been prepared for comparison. No heat curing has been used in all the mortars.
The consistency at the fresh state, as well as the microstructure, physical and mechanical properties at the hardened state of the obtained materials have been studied. Higher flexural strength and increased toughness have been obtained. These preliminary results foster the use of natural fibers to improve the performance of low carbon footprint building materials such as alkali-activated composites in the civil engineering applications. Further studies are necessary to better explain these preliminary results
L'individualismo solidale
No full textFin dai primi numeri, uno degli elementi che ha caratterizzato “La società degli individui” è stata la costante attenzione verso le molteplici forme che l’individualismo ha assunto nella storia del pensiero filosofico, etico, politico, sociale e religioso, privilegiando i rappresentanti di quella tradizione cui, pur con differenze marcate, potrebbe convenire la dicitura di «individualismo solidale». Questa tradizione cerca di coniugare i valori individualistici della modernità con istanze di appartenenza e di solidarietà, formulando di volta in volta proposte teoriche in cui le diverse espressioni dell’intersoggettività sono identificate e definite all’interno di un processo comune di costituzione delle individualità singole e collettive. Nel quadro di indagine della rivista, la solidarietà, in particolare, è analizzata nella sua compatibilità con l’individualismo ‘moderno’, ma tale prospettiva non esclude un esame delle forme di solidarietà che si pongano, invece, in alternativa a determinate manifestazioni di tale ‘individualismo moderno’. La solidarietà, in effetti, è una parola spesso usata in modo insufficientemente determinato, e che, senza pretesa di esaustività, può richiamare diverse sfere di significato, come quelle che seguono: la fraternité dei rivoluzionari francesi, il legame associativo dei lavoratori, la coesione sociale dei primi sociologi, l’appartenenza comune al genere umano, il mondo dei diritti da allargare agli esclusi, le attività di volontariato e di cooperazione, la fratellanza religiosa. È proprio tale ampiezza di riferimenti a spingerci a interrogare il concetto di solidarietà, a partire dalla possibilità di definirlo in relazione ai differenti contesti in cui è utilizzato, esplicitando il ruolo che riveste in relazione al singolo e alla società.
Tale riflessione costituisce, idealmente, lo sfondo concettuale di questo nuovo numero de “La società degli individui”, dedicato al tema della solidarietà, ripensato in una prospettiva plurale e dialogica, capace di riunire contributi storici e teoretici che possano spaziare tra filosofia, sociologia, antropologia e politica
Formulating Geopolymer Mortars through Construction and Demolition Waste (CDW) Recycling: A Comprehensive Case Study
Full text linkThe overall amount of construction and demolition waste (CDW) is steadily increasing due to urbanization-related phenomena in metropolitan cities. Only a small fraction is recycled to produce new concrete, a practice that would avoid the exploitation of natural aggregates. Furthermore, the Portland cement production process causes the release of high values of CO2 emissions into the atmosphere, increasing the global warming potential. For these reasons, materials alternative to ordinary Portland cement (OPC) are becoming more and more widespread, such as alkali-activated materials, which, when used with recycled aggregates, could become environmentally friendly substitutes for traditional concrete. During this study, various mix designs were formulated for alkali-activated metakaolin mortars containing recycled concrete aggregates. Their properties in the fresh and hardened states were analyzed. The main problem encountered was the presence of the adhered mortar layer on the recycled concrete aggregate. This layer not only caused a detrimental effect deriving from the increase in open porosity but also activated competitive reactions which partially compromised the alkali activation of metakaolin. All these phenomena deteriorated the final compressive strength of the composites containing recycled aggregates, which after 28 days, was around 20 MPa for samples with 12.5% of replacement of natural aggregate and 15 MPa for those with 25% of replacement, corresponding to a reduction of 35% and 50% compared to the standard sample without replacement, respectively
Effects of Biochar Addition on the Properties of Alkali-Activated Materials
Full text linkThe addition of biochar to Portland cement composites has been proven to increase some of the material properties. The effect on alkali-activated materials has not been fully investigated. In this study, different recipes of metakaolin pastes at different biochar amounts are tested. Their physical and mechanical properties are analyzed to understand if any beneficial effects can be found even for alkali-activated binders. The results show that the addition of small amounts of biochar (<2 wt%) increases the compressive strength of metakaolin pastes (+15% after 28 days) and decreases the water absorption by capillarity, possibly leading to increased durability. Higher biochar content decreases the mechanical properties but provides higher dimensional stability and reduces the formation of efflorescence
Geopolymers reinforced with natural fibers: A comparison among different sources
Full text linkThe performance of different natural fibers (hemp, kenaf and bamboo) used to formulate composites with an alkali-activated matrix based on metakaolin is evaluated. Short fibers were randomly dispersed up to about 3% of the binder weight, and the fresh and cured properties of the derived composites were determined. Up to the investigated fraction, it is still possible to obtain adequate workability without the supply of additional water or additives. Upon modification with fibers, the mechanical behavior changes from completely brittle to pseudoplastic with increased toughness. The flexural strength increases by up to 80% at the highest bamboo amount and up to 20% for kenaf. Hemp fibers have a negligible effect on flexural strength but strongly improve the materials’ toughness. Moreover, the addition of fibers does not change the manner in which the material interacts with moisture. Indeed, the water uptake of the modified samples was comparable to that of the unmodified samples, and the composites showed a decreased rate of water diffusion as the amount of fiber increased
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