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Studio del comportamento di nuovi calcestruzzi sostenibili ed innovativi ottenuti dal riciclo di rifiuti plastici (PET) ed aggregati di demolizione
Full text linkLa risposta a lungo termine alla sfida di sostenibilità dei materiali da costruzione comporta una sostanziale riduzione del dispendioso consumo di risorse naturali e materiali. In questo scenario, il riciclo di materiali di scarto si inserisce coerentemente nella strategia di sviluppo di sistemi innovativi per la produzione e la distribuzione di energie sostenibili. In particolare, con riferimento a un settore commercialmente promettente quale quello degli aggregati derivati da rifiuti, scarti e simili, per la produzione di impasti cementizi, gli studi condotti vedono delineate due filosofie di approccio: il processo esogeno che prevede il riciclo di rifiuti urbani, nello specifico plastiche post-consumo, ed il processo endogeno che prevede la frantumazione diretta di rifiuti derivanti da attività di costruzione e demolizione. La presente dissertazione mira ad offrire contributi innovativi per ampliare le frontiere della conoscenza nel campo dei materiali da costruzione che coinvolgono l’utilizzo di prodotti di scarto, mediante lo sviluppo di ampi studi sperimentali, simulazioni numeriche della risposta meccanica e la proposta di nuove possibili applicazioni strutturali ed architettoniche. Il principio metodologico che ha guidato lo sviluppo dell’intera attività di ricerca è quello di ridurre al minimo l’impatto ambientale derivante dall’attività edilizia e dai processi industriali, limitando il continuo consumo di materie prime e garantendo diversi livelli prestazionali attesi del prodotto. Nel dettaglio, la studio si concentra sull'aggiunta/sostituzione di fibre e/o aggregati riciclati, quali plastiche di scarto costituite da polietilene tereftalato (PET) nella forma di fibra da rinforzo, e rifiuti di costruzione e demolizione (CDW) nella forma di aggregato riciclato all’interno della tradizionale miscela. Un’approfondita analisi dello stato dell’arte, accompagnata da riferimenti bibliografici relativi a studi condotti su calcestruzzi innovativi con carattere eco-sostenibile, ha permesso di studiare la risposta strutturale di elementi in calcestruzzo fibro-rinforzato (FRC) con PET e di indagare l’influenza della presenza di materiali di scarto, nella composizione della miscela cementizia.
Le fibre da rinforzo in PET riciclato, comunemente utilizzate per conferire maggiore duttilità al calcestruzzo, sono state impiegate in aggiunta a miscele di cemento (massetti premiscelati). I risultati dell’ampia campagna sperimentale condotta hanno permesso di valutare l’influenza sulle proprietà meccaniche e termo-acustiche del materiale e valutarne la fattibilità in applicazioni non strutturali.
Nell’ambito dell’applicazione delle fibre riciclate come rinforzo del calcestruzzo, seppure l’evidenza sperimentale abbia mostrato la efficacia del materiale fibro-rinforzato (FRC) con PET nel migliorare le prestazioni meccaniche a trazione, ad oggi, non sono disponibili modelli di previsione del comportamento post-fessurativo. La validità di tale rinforzo per le miscele cementizie è stata simulata proponendo un modello di previsione del legame costitutivo a trazione di calcestruzzi contenenti diverse percentuali di PET.
Parallelamente, il materiale di scarto costituito da CDW è stato implementato all’interno di calcestruzzi target in sostituzione dell’aggregato naturale. Aggregati di scarto di differente natura, composizione e trattamento sono stati utilizzati per valutare le caratteristiche meccaniche del calcestruzzo con aggregati riciclati (RAC) e le proprietà fisiche legate alla durabilità del materiale. Differenti rapporti di sostituzione (dal 20% al 100%), superiori a quelli previsti dalle principali norme internazionali sul calcestruzzo strutturale, sono stati applicati in tre calcestruzzi con differente classe di resistenza. Il focus della ricerca vede la sua completa risoluzione nell’ultima parte della dissertazione con l’implementazione di entrambe le tipologie di tecniche analizzate, quella endogena e quella esogena. Infatti, l’aggiunta di fibre riciclate ottenute dal riutilizzo di sacchi in Polipropilene (PP) e la sostituzione di aggregati naturali con detriti riciclati all’interno della miscela di calcestruzzo, hanno permesso di valutare l’influenza di tale tecnica sulle proprietà meccaniche del materiale. I risultati dei test condotti rivelano che con una corretta progettazione può rivelarsi sicuro e fattibile applicare rifiuti riciclati nel calcestruzzo al fine di ottenere un materiale definito strutturalmente performante nell'ingegneria civile.
Tutti i risultati ottenuti sono stati riassunti ed argomentati nella sezione dedicata alle conclusioni. La ricerca presentata rappresenta un contributo che vuole esaltare e far emergere le potenzialità delle tecniche investigate e fornire le basi per un approfondimento teorico ed analitico che permetta di sviluppare e distribuire modelli per una progettazione diretta alla valorizzazione dell’eco-sostenibilità.The long-term response to the sustainability challenge of building materials entails a substantial reduction of the wasteful natural and material resources consumption. In this scenario, the recycling of waste materials is coherently inserted in the strategy of developing innovative systems for the production and distribution of sustainable energy. To reference at a commercially promising sector such as that of aggregates derived from waste and scraps for the produce cement mixtures, the studies carried out have outlined two philosophies of approach: the exogenous process that involves the recycling of urban waste, specifically post-consumer plastics, and the endogenous process which involves the direct crushing of waste deriving from construction and demolition activities. The present dissertation aims to offer an innovative contribution to extend the frontiers of knowledge in the field of construction materials involving the use of waste products, through the development of large experimental studies, numerical simulations of the mechanical response and the proposal of new possible structural and architectural applications. The methodological principle that has guided the development of the entire research activity is to minimize the environmental impact deriving from construction activity and industrial processes, limiting the continuous consumption of raw materials and ensuring different expected performance levels of the product. In detail, the study focuses on the addition/replacement of recycled fibers and/or aggregates, such as consisting of polyethylene terephthalate (PET) waste plastics in the form of reinforcing fibers, and construction and demolition waste (CDW) in the form of recycled aggregate within the traditional mixture. A careful state of the art analysis with bibliographical references relating to studies conducted on innovative and eco-sustainable concretes, it allowed to study the structural response of PET-fiber-reinforced concrete (FRC) elements and to investigate the influence of the waste materials presence in the composition of the cement mixture. The recycled PET fibers reinforcement, commonly used to improve the concrete ductility, have been used in addition to cement mixtures (premixed screeds). The results of the extensive experimental campaign conducted show the influence of the material on the mechanical and thermo-acoustic properties and it allowed to evaluate its feasibility in non-structural applications.
In the context of the recycled fibers application as concrete reinforcement, although experimental evidence has shown the effectiveness of the PET-fiber-reinforced material (FRC) to improve the tensile performance, currently, prediction models of post-cracking behavior are not available. The validity of this concrete reinforcement was simulated by proposing a prediction model of the constitutive tensile stress-strain response of the material containing different percentages of PET. At the same time, the waste material consisting of CDW was implemented within the target concrete to replace the natural aggregate. Waste aggregates of different nature, composition and treatment were used to evaluate the mechanical characteristics and the physical properties related to the durability of the concrete with recycled aggregates (RAC). Different substitution ratios (from 20% to 100%), higher than those required by the main international standards on structural concrete, were applied in three concretes with different strength classes. The focus of the research sees its complete resolution in the last part of the dissertation with the implementation of both types of analyzed techniques, i.e., the endogenous and the exogenous one. In fact, the addition of recycled fibers obtained from the reuse of polypropylene (PP) bags and the replacement of natural aggregates with recycled inside the concrete mix, allowed to evaluate the influence of this technique on the mechanical properties. The results of the tests carried out reveal that with a correct design it can be safe and feasible to apply recycled waste in concrete in order to obtain a material defined as structurally performing in civil engineering. All the results obtained have been summarized and discussed in the section dedicated to the conclusions. The presented research represents a contribution that aims to enhance and bring out the potential of the techniques investigated and provide the basis for a theoretical and analytical study that allows the development and distribution of models for a design aimed at enhancing eco-sustainability
Experimental Characterization of Traditional Mortars and Polyurethane Foams in Masonry Wall
Full text linkMasonry is a composite material largely used in construction. It exhibits several advantages, including significant compressive strength, thermal inertia, and aesthetic beauty. A disadvantage of masonry is mainly related to the inadequate shear strength due to the poor capacity and ductility of the adopted mortar. This aspect is crucial in seismic areas. In this paper, the behavior of polyurethane foams, used as adhesives for the construction of thin joints brick masonry walls, has been investigated. First, the characterization of components was carried out, followed by laboratory uniaxial tests on masonry walls and shear tests on triplets. Moreover, a comparison of the behavior of the foam-brick walls with respect to the traditional mortars masonry was carried out, as the type of joints varies and the arrangement of the holes of the bricks varies with respect to the direction of the applied load. Results provide indications on which adhesive has to be adopted for masonry buildings in reference to the site of construction (i.e., seismic hazard)
Mechanical Characteristics and Water Absorption Properties of Blast-Furnace Slag Concretes with Fly Ashes or Microsilica Additions
Full text linkThe paper shows the results of an experimental tests campaign carried out on concretes with recycled aggregates added in substitution of sand. Sand, in fact, has been totally replaced once by blast-furnace slag and fly ashes, once by blast-furnace slag and microsilica. The aim is both to utilize industrial by-products and to reduce the use of artificial aggregates, which impose the opening of pits with high environmental damage. The results show that in the concretes so made the water absorption capacity has reduced and durability has improved. The test campaign and the results described in the present article are certainly useful and can be especially utilized for research on a larger scale in this field
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
Effect of the Chemical and Mechanical Recycling of PET on the Thermal and Mechanical Response of Mortars and Premixed Screeds
Full text linkIn this paper, recycled polyethylene terephthalate (PET) was used to produce eco-innovative engineering materials with optimized performance, minimizing the environmental impact deriving from plastic consumption activity and limiting the continuous consumption of raw materials. The recycled PET obtained from waste bottles, commonly used to improve the ductility of concrete, has been used with a different weight percentage as plastic aggregate in the replacement of sand in cement mortars and as fibers added to premixed screeds. In detail, the effect of PET treatment (chemical or mechanical) on the thermal performance was evaluated. Non-destructive physical tests were conducted to determine the thermal conductivity of the investigated building materials. The performed tests showed that chemically depolymerized PET aggregate and recycled PET fibers derived from plastic wastes can reduce the heat conduction capacity of the cementitious materials with limited reduction in compressive strength. The results of the experimental campaign have made it possible to evaluate the influence of the recycled material on the physical and mechanical properties and its feasibility in non-structural applications
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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