1,721,030 research outputs found
Performance Prediction for Innovative Crushable Material used in Aircraft Arrestor Beds
No full textSurveys on innovative materials for aircraft arrestor beds are of great interest in airport safety research. In the event of a runway overrun, the arrestor bed has to provide for the complete stop of the aircraft. In doing so, the bed essentially collapses under the effect of the vertical load of the nose and main gears. Along the contact areas between the wheels and bed, the horizontal drag forces generated depend on the dissipative properties of the material used in the bed. The use of innovative materials in arrestor beds could lead to a significant improvement in the performance of same. In the paper, the authors propose a cellular mortar with expanded polystyrene spheres and the use of static and dynamic tests to determine its characterization. The aim is to optimize its composition in terms of mechanical properties, to evaluate its durability under the effects of environmental actions, and to estimate the stopping distances for selected aircrafts. The code arrestor provided by the Federal Aviation Administration (FAA) was used as a reference for distance calculation
In-situ Raman study of mineral phases formed as by-product in a rotary kiln for cement production
No full textPortland clinker production consists essentially in the burning of material with defined composition in a rotary kiln at temperatures around 1450°C. The main fuel used in this process is coal, even though in the last few years the use of alternative fuels has been increasing. Four main minerals are formed, namely, tricalcium and dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. Along with these main phases, variations in burning conditions of fuels or in the local composition of raw materials can lead to the formation of relatively high amounts of secondary by-products, which can negatively affect the quality of the final material. Characterization of these by-products allows not only optimization of the process of clinker production but also the design of special refractory materials for the wall of kilns and preheaters. Being found as particles included in (or alternating to) a hard solid clinker matrix, a detailed characterization of these extra phases could be achieved only via microscopic techniques. In this work, micro-Raman spectroscopy has been successfully tested as a highly selective method for characterization and localization of included minerals that formed as overlapped crusts deposited on the internal wall of a conventional rotary kiln for cement production, without any manipulation of the sample. Understanding the chronological order of deposition of these overlapped layers is extremely important, as it is the only way to go back up to the production process and to individuate the problem
Ettringite and calcium sulfoaluminate cement: investigation of water content by near-infrared spectroscopy
No full textCalcium sulfoaluminate (CSA) cement is a sulfate-based binder whose high-performance hydraulic behavior depends on the rapid formation of ettringite, when grinded clinker is hydrated in presence of gypsum. Ettringite is a calcium aluminum sulfate mineral characterized by high water content, estimated as 32 water molecules per formula unit. Three examples of utilization of near-infrared (NIR) spectroscopy are here shown. First of all, information on water distribution in pure ettringite was deduced and compared with infrared analyses. Then its thermal behavior has been followed up to 400 °C, allowing to improve the knowledge about water loss and thermal decomposition of this hydrated phase. Finally, the obtained results have been employed in order to follow hydration of CSA cement sample, demonstrating thus that NIR spectroscopy, being highly sensitive to water amount and dis- tribution, can be an extremely useful tool for hydration studies
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
CLSM con aggregati e leganti innovativi
No full textRapidità di posa, autocompattazione e bassa densità rendono le malte cementizie a resistenza controllata alternative ai materiali granulari tradizionali per fondazioni o riempimenti. Presentiamo i risultati di uno studio incentrato sullo sviluppo di “CLSM” ancora più performanti e ecosostenibili, impiegabili nelle trincee per sottoservizi. Tra le innovazioni: un legante solfo‐alluminato al posto del cemento e scarti della lavorazione della pietra naturale a parziale sostituzione delle sabbie
Landfill redevelopment
No full textLandfill redevelopment plays a significant role in efficient land use management acting as a catalyst in sustainable planning: the demand of more room for city growth makes abandoned landfills a sort of “recycled” resource that can upgrade spaces and activities in terms of city form, land value and environment features. Risk’s issues concern environmental, social, financial and political aspects of redevelopment. Moreover risk could be determined by a single topic but it rapidly involves the whole project (see risk definition below). Risk is not only a technical matter regarding engineering solution or environment vulnerability: it is more a general issue that decides the failure in terms of social and financial expectation and political credibility. It represents the main obstacle in order to promote redevelopment policies by public sector. So to enhance redevelopment, it’s important to improve the decision process by an innovative approach, concerning not only the engineering solution but also social and financial aspects of redevelopment that involve a quantity of subjects that play a role in the project course: public sectors, developers, site residents, associations, and expert’s lead decision process toward a flow that needs a continuous feedback among the different stages of knowledge, assessment and decision
LONG-TERM INVESTIGATION INTO THE USE OF NEW RAPID HARDENING CEMENT FOR CONTROLLED LOW-STRENGTH MATERIALS TO BE EMPLOYED IN PAVEMENT APPLICATIONS
No full textControlled low strength materials (CLSMs) are engineered, cement based materials of growing interest in all trench backfilling and bedding applications where low stiffness, strength and density are required. Despite the fact that 50 years have passed since its first application, the technology has been the source of continuous innovation. In particular, the current challenge concerns the excessive and undesirable long-term gain in strength of current CLSMs available on the market which leads to difficulties in the event of future removal and to unbalanced stress strain behavior with surrounding soils.
In this investigation, the authors present a long-term laboratory work aimed at the creation of new formulations to be used for pavement applications with the objective of avoiding or limiting any gain in stiffness and resistance over time. For this purpose, a rapid hardening cement has been used as a substitute for Portland cement. The particular formulation of cement adopted presents many advantages in terms of rapid set, high early strength development and insignificant gain in strength over long periods.
All the mixtures studied were subjected to static and dynamic triaxial tests taking the mechanical characteristics of a reference granular soil as the target for the mix design of new CLSM formulations. The results deriving from the use of different admixtures and mixing procedures in terms of mixing time, batching sequence and type of mixer were also investigated
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