1,721,026 research outputs found
Modelling the structure of the metastable phases in the reaction sequence kaolinite-mullite by X-ray scattering experiments
No full textThe crystal structure of two kaolinites with a different degree of planar disorder and their high temperature (HT) decomposition products have been investigated by means of symmetrical transmission powder X-ray diffractometry and the subsequent calculation of the radial distribution function (RDF). An ordered and a disordered kaolinite (international standard Kga-1 and Kga-2) were selected along with their HT reaction products at 600 degrees C (metakaolinite) and at 900 degrees C (mullite precursor). The calcinations and quenches have been carried out ex-situ prior to the data collection. The procedure for collection and reduction of the data and their interpretation is outlined. The structural characterization of the HT phase transformations is obtained by qualitative analysis of the RDF curves and is related to the extent of planar disorder in the original material. A model for the structure of metakaolinite is proposed on the basis of the present experiments, and of a review of literature data. According to this model, the structure of metakaolinite displays an almost uncollapsed structure with a short-range order in which Al is mainly in four-fold coordination. An ab initio modelling of the RDF curves provides a quantitative evaluation of the proposed structural model. Differences in the HT products from different kaolinites are directly correlated with the density of stacking faults in the starting kaolinites. Moreover the structure of the precursor of mullite is described and discussed with respect to the literature data. The nature and role of gamma-alumina is discussed as well. Finally the DTA exothermic peak of kaolinite is interpreted in the light of the proposed general model
Thermal expansion of C3S and Mg-doped alite
No full textThe lattice thermal expansion coefficients were measured using in situ high temperature x-ray powder diffraction on triclinic tricalcium silicate (C3S) in the temperature range 25-970 °C and on monoclinic alite of composition Ca2.879Mg0.112Al0.0439Si0.971O5 in the temperature range 30-1150 °C. Full profile refinements were performed using the Rietveld method. The structural model of Mumme [1] was adopted for the alite crystal structure, implying a space group Cm and cell constants a=12.18, b=7.04, c=9.25 Å, β=116.11 ° at 25 °C. All three lattice parameters show similar temperature behaviour and relative thermal expansion coefficients. There is a clear change in slope at about 900 °C, which is assumed to be related to the phase change between two monoclinic forms of alite. Refinements of C3S were conducted using the structural model of Golovastikov et al. [2] implying a space group P 1 and cell constants a=11.67, b=14.28, c=13.72 Å, α=105.3, β=94.2, γ=90.0 ° at 25 °C. The C3S lattice parameter b shows a different trend in temperature with respect to a and c. The same behaviour is reproduced by the relative thermal expansion coefficient a. Three clear changes in slope are found and regarded as phase transition points between triclinic modifications of C3S. Integrated intensity analysis for selected peaks, together with TG/DTA in the temperature range 25-1150 °C, were also used in order to preliminarly characterize the phase transitions
Compositional characterization of Etruscan earthen architecture and ceramic production
Full text linkThis study presents the results of new research into Etruscan technology for earthen architecture as well as ceramic production in the upper Tiber Valley in central Italy, using as a case study the Etruscan settlement of Col di Marzo (Perugia). It determines the compositional differences of the raw material employed as building material and for ceramic production by X-ray powder diffraction (XRD), thermogravimetric analysis and differential thermal analysis (TG-DTG), Fourier-transform infrared analysis (FTIR) and geotechnical analyses. The research also advances the knowledge of ceramic manufacturing technology, with a focus on impasto production, at Col di Marzo between the fifth and mid-third centuries bce and the surrounding territory on the left bank of the River Tiber. The compositional analysis of building material compared with the ceramics provides answers to questions related to their sourcing and deepens the understanding of the exploitation of natural resources
On the Formulation of Reactive Binders Containing Soluble Borate Compounds
No full textBoron efficiently absorbs neutrons due to its large cross section. Thus, boron containing materials are an effective shield to neutrons and are commonly used as containment barriers in nuclear reactors. The most economical way to include boron into shielding structures is to prepare B-rich mortars or concretes, to be used as structural elements or as plastering. However, colemanite [Ca(B3O4(OH)3)(H2O)], the most abundant B-containing mineral, is sufficiently soluble to release enough borate ions in solution to indefinitely stop Portland cement hydration. Here we present the formulation of hydraulically active binders containing 50% of colemanite. They are based on blends of calcium aluminate cements and blastfurnace slag. The main hydration product in the absence of colemanite is strätlingite along with other AFm phases. MgO causes an increasing hydrotalcite precipitation, and fly ashes further increase strätlingite content. The presence of colemanite causes the precipitation of B-ettringite, where B(OH)4 ̄ ions substitute for sulphate ions. These binders set in one day and harden in 4 days. The addition of hydrated lime in the formulations brings about the additional precipitation of B-containing AFm phases, where the trigonal HBO32- ion constitutes the interlayer between positive [Ca2Al(OH)6]+ sheets. These binders set in few hours and harden in one day
Correction to: Influence of cellulose nanofibrils on the rheology, microstructure and strength of alkali activated ground granulated blast-furnace slag: a comparison with ordinary Portland cement (Materials and Structures, (2021), 54, 1, (23), 10.1617/s11527-020-01614-5)
No full textLaura Riva and Carlo Punta have been added to the author group. The change of authorship is due to an error in the recognition of the role and importance of the work of synthesis and characterization of the materials object of the present study, which was not entirely recognized by the inclusion in the acknowledgements. A full recognition of the work performed is obtained by inclusion of the originally omitted authors in the authors’ list. Moreover, a recognition of these authors’ funding body was missing and has been included in the acknowledgement
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
Nuvole di punti e Fotogrammetria da drone per la modellazione 3D dell’abbazia di Sant’Eustachio a Nervesa della Battaglia (TV)
No full textL'abbazia benedettina di Sant'Eustachio a Nervesa della Battaglia (TV), posta nel bosco del Mon-tello a ridosso del fiume Piave, risale alla prima metà dell'XI sec. e raggiunse il massimo splendore nel XVI sec. (qui mons. Giovanni Della Casa compose nel 1552 il celebre “Galateo”).
Seguì una lenta decadenza con vari saccheggi e spogliazione dei beni, aggravata nel 1866 con la soppressione degli Ordini e delle Corporazioni religiose; il colpo di grazia avvenne durante la Prima Guerra Mondiale, con la distruzione di circa il 70% dell'abbazia, trovatasi in mezzo alla “Battaglia del Piave”. Il complesso abbaziale era composto dalla chiesa (36,77 x 20,01 m) a croce latina con tre navate, dal chiostro a pianta trapezia (15,26 x 12,35 m) e dalla parte conventuale (di lunghezza 45,58 m), originariamente su tre piani, che circondava il chiostro e si congiungeva alla chiesa.
Il lavoro qui presentato è stato svolto per una tesi di laurea magistrale in Architettura presso l’Università degli Studi di Udine ed ha riguardato la modellazione 3D dello stato di fatto, la ricostruzione 3D della situazione ante 1918 ed un’ipotesi di restauro e valorizzazione.
È stato eseguito un rilevamento topografico con una stazione Leica TRCA 1103, anche per ottenere il piano quotato dell’intera collina, un rilevamento fotogrammetrico sia da terra, con CCD Panasonic DMC-TZ25 e Canon EOS M, che aereo mediante drone, ancora con la Canon EOS M, ed anche un rilevamento laser scanning con il sistema Faro Focus3D S120. Per elaborare ed integrare questi cinque dataset sono stati utilizzati diversi software, ad esempio mediante MeshLab e Pointools. Le elaborazioni di maggior interesse sono quelle sulle immagini con software di Structure from motion, quali 123DCatch e VisualSfM per i primi tentativi con approccio “cloud computing” e poi Agisoft Photoscan per ottenere il modello finale. Dopo l’estrazione&matching delle features, è stato eseguito l’orientamento delle immagini, sfruttando opportunamente le coordinate acquisite topograficamente e per scansione laser. Le successive fasi automatiche sono la generazione della sparse cloud, quella della dense cloud, la costruzione delle mesh del DSM ed il texture mapping di quest’ultimo.
Sono state ricavate una serie di ortofoto su vari piani (quattro prospetti e tre sezioni raster in scala 1:100) che poi sono state vettorializzate ed opportunamente migliorate in ambiente CAD (le corrispondenti sette rappresentazioni vector) quali dettagliate mappe del degrado; sono state create anche tre piante-sezioni a diversa quota in scala 1:100.
A partire dal modello 3D delle rovine, è stato quindi creato un modello solido 3D virtuale dell’intero complesso antecedente alla Prima Guerra Mondiale, facendo riferimento ad informazioni documentarie e ad immagini d’epoca, alcune di fonte militare.
Infine è stato creato un ulteriore modello 3D virtuale, quello del progetto dell’ipotetico restauro e basato proprio sul modello 3D ante 1918, i cui volumi saranno ricreati mediante una struttura tubolare che ripropone gli spigoli dell’estradosso e dell'intradosso. L'idea di fondo è quella di proteggere e garantire solidità strutturale ai pochi muri rimasti e, allo stesso tempo, di valorizzare il sito. I tubi di acciaio dell'intradosso saranno disposti a gruppi di quattro nella posizione originaria della pilastratura della navata centrale, mentre gli archi tra le campate saranno realizzati con un telaio metallico mascherato da due fasce in legno. L’originario soffitto a cassettoni sarà ricostruito con un telaio in acciaio rivestito di legno e cassettoni in vetro. L'estradosso sarà costituito ancora da una struttura tubolare e, per la copertura, da un sistema di teli abbassabili in caso di maltempo.
In definitiva, questo esempio illustra come le tecniche geomatiche hanno permesso di costruire il modello 3D dello stato di fatto, ma anche come esso è stato restaurato virtualmente per modellare lo stato originario e come quest’ultimo abbia guidato il progetto di restauro dei volumi crollati
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