Letteratura scientifica selezionata sul tema "Concrete Ageing"
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Articoli di riviste sul tema "Concrete Ageing"
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Van Breugel, K., e T. A. Van Beek. "Ageing of old and modern concrete structures – Observations and research". Revista ALCONPAT 7, n. 1 (31 gennaio 2017): 57–72. http://dx.doi.org/10.21041/ra.v7i1.174.
Testo completoAbstract (sommario):
Ageing of old and modern concrete structures – Observations and researchABSTRACTAgeing is an inherent feature of nature. Yet it seems to be a rather new topic in both science and engineering. The main reason for increasing attention for ageing as a topic is the growing awareness that, particularly in industrialized countries, ageing of our assets is a financial burden for the society and affects the overall sustainability of our planet. In this contribution, the urgency and challenges of ageing of concrete structures are addressed. The complexity of ageing problems will be illustrated by looking in more detail to the evolution in concrete mix design and the consequences thereof for the long-term performance of concrete structures. Emphasis will be on ageing of concrete infrastructure and justification of research on ageing phenomena.Keywords: infrastructure; sustainability; ageing; mix design; autogenous shrinkage; codes. Envejecimiento de antiguas y modernas estructuras de concreto - Observaciones e investigacionesRESUMENEl envejecimiento es una característica inherente de la naturaleza. Sin embargo, parece ser un tema bastante nuevo en la ciencia y la ingeniería. La principal razón para aumentar la atención por el envejecimiento como tema es la creciente conciencia de que, en particular en los países industrializados, el envejecimiento de nuestros activos es una carga financiera para la sociedad y afecta la sostenibilidad global de nuestro planeta. En esta contribución se abordan la urgencia y los desafíos del envejecimiento de las estructuras de concreto. La complejidad de los problemas de envejecimiento se ilustra examinando con más detalle la evolución del diseño de la mezcla de concreto y sus consecuencias para el rendimiento a largo plazo de las estructuras de concreto. Se hace hincapié en el envejecimiento de las infraestructuras de concreto y en la justificación de la investigación sobre fenómenos de envejecimiento.Palabras clave: infraestructura; sostenibilidad; envejecimiento; mezcla de diseño; contracción autógena; códigos. Envelhecimento estruturas de betão antigos e modernos - Observações e pesquisaRESUMOO envelhecimento é uma característica inerente à natureza. No entanto, parece ser um bastante novo tópico em ciência e engenharia. A principal razão para uma maior atenção por tema envelhecimento é a consciência crescente de que, particularmente nos países industrializados, o envelhecimento dos nossos ativos é um encargo financeiro para a sociedade e afeta a sustentabilidade global do nosso planeta. Nesta contribuição a urgência e os desafios de estruturas de concreto envelhecimento são abordados. A complexidade dos problemas de envelhecimento está ilustrada em mais pormenor através da análise da evolução do desenho da mistura de betão e o seu impacto sobre o desempenho a longo prazo das estruturas de betão. A ênfase é colocada na infra-estrutura de envelhecimento do concreto e justificação da pesquisa sobre os fenómenos de envelhecimento.Palavras-chave: infra-estrutura; sustentabilidade; envelhecimento; misture projeto; retração autógena; códigos.
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Bamforth, P. B., e W. F. Price. "The Long-Term Properties of Concrete Used in Prestressed Concrete Pressure Vessels". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 208, n. 2 (maggio 1994): 123–34. http://dx.doi.org/10.1243/pime_proc_1994_208_021_02.
Testo completoAbstract (sommario):
Data are presented on the late-life properties of concretes used in prestressed concrete pressure vessels (PCPV) and containment structures. The effects of ageing under simulated PCPV conditions are discussed.
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MOCEIKIS, Rimvydas, Asta KIČAITĖ, Gintautas SKRIPKIŪNAS e Aleksandrs KORJAKINS. "AGEING MODELS AND ACCELERATED AGEING TESTS OF GLASS FIBER REINFORCED CONCRETE". Engineering Structures and Technologies 10, n. 1 (27 aprile 2018): 10–17. http://dx.doi.org/10.3846/est.2018.1467.
Testo completoAbstract (sommario):
Glass fiber reinforced concrete (GRC) is used for 40 years to create world’s most stunning and complex architectural elements due to its high mechanical properties, particularly flexural strength. Yet it is very important to note that any type of glass fibers in the concrete matrix are undergoing complex ageing processes, resulting to significant decrease of initial mechanical characteristics of this composite material under natural weathering conditions. Aspects of GRC durability are mainly dependent from the properties of fibers and interaction between them and concrete matrix. In this article, long term strength retention of this composite material is discussed, existing experimental data of weathering tests presented, and main corrosion mechanisms explained. Lack of knowledge about freeze- thaw resistance of glass fiber reinforced concrete is addressed. Finally, latest attempts of GRC durability improvement are reviewed, such as adding micro fillers, polymers to the concrete matrix and enhancing surface of fibers in Nano scale.
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Yu, Xin, Quantao Liu, Pei Wan, Jiangkai Song, Huan Wang, Feiyang Zhao, Yafei Wang e Jinyi Wu. "Effect of Ageing on Self-Healing Properties of Asphalt Concrete Containing Calcium Alginate/Attapulgite Composite Capsules". Materials 15, n. 4 (14 febbraio 2022): 1414. http://dx.doi.org/10.3390/ma15041414.
Testo completoAbstract (sommario):
Calcium alginate capsules within asphalt concrete can gradually release interior asphalt rejuvenator under cyclic loading to repair micro cracks and rejuvenate aged asphalt in-situ. However, asphalt pavement will become aged due to environmental and traffic factors during the service period. In view of this, this paper investigated the effect of ageing on the healing properties of asphalt concrete containing calcium alginate/attapulgite composite capsules under cyclic loading. The capsules were fabricated using the orifice-bath method and the morphological structure, mechanical strength, thermal stability, oil release ratios and healing levels of capsules in fresh, short-term ageing and long-term ageing asphalt concrete were explored. The results indicated that the different ageing treatments would not damage the multi-chamber structure nor decrease the mechanical strength of capsules but would induce the capsules release oil prematurely. The premature oil released from capsules in turn can offset the ageing effect owing to ageing treatment. The short-term ageing and long-term ageing plain asphalt mixtures gained strength recovery ratios of 39.3% and 34.2% after 64,000 cycles of compression loading, while the strength recovery ratios of short-term ageing and long-term ageing asphalt mixtures containing capsules were 63.5% and 54.8%, respectively.
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Xu, Shi, Xueyan Liu, Amir Tabaković e Erik Schlangen. "The influence of asphalt ageing on induction healing effect on porous asphalt concrete". RILEM Technical Letters 3 (18 febbraio 2019): 98–103. http://dx.doi.org/10.21809/rilemtechlett.2018.74.
Testo completoAbstract (sommario):
Induction healing is a proven technology which is able to improve the self-healing capacity of asphalt concrete. Healing is achieved via electromagnetic current produced by passing induction machine, where steel asphalt constituents heat up which in turn soften the bitumen in the asphalt layer, allowing it to flow and close cracks, repairing the damage. This paper reports on the study which investigated the influence of ageing on the healing capacity of Porous Asphalt (PA) concrete. Porous Asphalt concrete mix was prepared first, then subjected to an accelerated (laboratory) ageing process using a ventilated oven. In order to further evaluate the induction healing efficiency of asphalt concrete, Semi-circular bending (SCB) and healing cycles were performed on asphalt concrete specimens. The results show that with an increase of the ageing level of porous asphalt concrete, the induction healing efficiency decreases.
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Kucharczyková, Barbara, Petr Daněk, Dalibor Kocáb e Petr Misák. "Experimental Analysis on Shrinkage and Swelling in Ordinary Concrete". Advances in Materials Science and Engineering 2017 (2017): 1–11. http://dx.doi.org/10.1155/2017/3027301.
Testo completoAbstract (sommario):
The paper deals with the experimental determination of shrinkage development during concrete ageing. Three concrete mixtures were made. They differed in the amount of cement in the fresh mixture, 300, 350, and 400 kg/m3. In order to determine the influence of plasticiser on the progress of volume changes, another three concrete mixtures were prepared with plasticiser in the amount of 0.25% by cement mass. Measurements were performed with the goal of observing the influence of cement and plasticiser content on the overall development of volume changes in the concrete. Changes in length and mass losses of the concrete during ageing were measured simultaneously. The continuous measurement of concrete mass losses caused by drying of the specimen’s surface proved useful during the interpretation of results obtained from the concrete shrinkage measurement. During the first 24 hours of ageing, all the concrete mixtures exhibited swelling. Its magnitude and progress were influenced by cement, water, and plasticiser content. However, a loss of mass caused by water evaporation from the surface of the specimens was also recorded in this stage. The measured progress of shrinkage corresponded well to the progress of mass loss.
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Hall, Jon G. "AI Spots Crumbling Concrete". ITNOW 66, n. 1 (15 febbraio 2024): 28–29. http://dx.doi.org/10.1093/itnow/bwae014.
Testo completo
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BURMAN, A., D. MAITY, S. SREEDEEP e I. GOGOI. "LONG-TERM INFLUENCE OF CONCRETE DEGRADATION ON DAM–FOUNDATION INTERACTION". International Journal of Computational Methods 08, n. 03 (settembre 2011): 397–423. http://dx.doi.org/10.1142/s0219876211002472.
Testo completoAbstract (sommario):
The dam–foundation interaction behavior under the application of seismic load has been investigated in the present paper using finite element technique in the time domain. Since the dam face is in constant contact with water, concrete degradation due to hygromechanical loading is inevitable and should be considered in the analysis procedure. This ageing process of concrete leads to loss of stiffness and strength of the material. Therefore, to assess the behavior of the dam at a later stage of its life, it is important to determine the proper strength of the concrete at a certain age. An approach to include the time-dependent degradation of concrete owing to environmental factors and mechanical loading in terms of isotropic degradation index is presented. An iterative scheme has been developed to model the dam–foundation interaction effects of the coupled system. The strains and the displacements are observed to increase if the ageing procedure of the gravity dam is taken into account. The long-term behavior of the aged concrete gravity and foundation interaction has been observed by using a developed ageing model for concrete.
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Radziszewski, Piotr. "MODIFIED ASPHALT MIXTURES RESISTANCE TO PERMANENT DEFORMATIONS". JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 13, n. 4 (31 dicembre 2007): 307–15. http://dx.doi.org/10.3846/13923730.2007.9636451.
Testo completoAbstract (sommario):
Permanent deformations, primarily in the form of ruts, are one of the basic asphalt pavement damages impairing its service properties. Application of appropriate asphalt mixtures and binder modification are effective methods for improving asphalt courses resistance. While being manufactured, stored, fitted into a road pavement and during long term service, bitumen binders and asphalt mixtures are subject to continuous unfavourable ageing processes during which pavement courses characteristics change considerably, resistance to permanent deformations being among them. This article presents rut and dynamic creep test results of concrete, SMA (stone mastic asphalt), MNU (thin courses of non‐continuous grain mixtures), Superpave mixture and porous asphalt mixture of two air void content percentages: 15 %, 20 %. Asphalt concrete mixtures, MNU's and porous asphalt mixtures contained elastomer, plastomer and fine rubber modified binders. Samples for laboratory rut tests were made by slab compaction because this method, as the author's previous research had shown, was the closest to ‘in‐situ’ conditions. Resistance to permanent deformations of the examined specimens was evaluated before aging, after technological aging (short term ageing) and after service ageing (long‐term ageing). The test results show that resistance to permanent deformations depends on the kind of asphalt mixture and binder applied. Concrete asphalts with fine rubber modified bitumens and concrete asphalts with 7 % polymer modified binders as well as SMA's and Superpave mixtures with unmodified binders appeared to be most resistant to permanent deformations after a long‐term laboratory ageing. It was proved that the overall evaluation of resistance to permanent deformations could be obtained by rut and creep testing of asphalt mixtures exposed to short‐ and long‐term ageing. Simultaneous determining 4 parameters: maximum rut depth after short‐term ageing, rutting coefficient after operational ageing, stiffness creeping modulus after long‐term ageing and cumulated deformation after short‐term ageing, facilitates full characteristics of modified asphalt mixes designed to be built in the wearing course of a road pavement.
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Sistonen, Esko, Fahim Al-Neshawy e Miguel Ferreira. "Ageing Management Platform For NPP Concrete Structures". IABSE Symposium Report 103, n. 1 (11 febbraio 2015): 280–87. http://dx.doi.org/10.2749/222137815815622942.
Testo completoTesi sul tema "Concrete Ageing"
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Mogilnickij, Edgar. "Betoninio ir gelžbetoninio elementų betono įtempių relaksacijos dėl tiesinio valkšnumo skaitinė analizė". Master's thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20120723_105605-79936.
Testo completoAbstract (sommario):
Baigiamajame magistro darbe pasiūlytas gelžbetoninio elemento skaitinis modelis itempių – deformacijų būvio analizei tirti veikiant ilgalaikei apkrovai. Betono relaksacijos uždaviniui spresti taikyta Volterra integraline lygtis. Sprendimas grindžiamas apibendrintosios vidurkio teoremos taikymu betono įtempių istorijai rasti. Skaičiavimams taikyta specialiai tuo tikslu parašyta kompiuterinė programa, realizuota pasitelkiant procedūrinio programavimo paradigma bei programavimo klaba C# (MS Visual Studio aplinka).
Gauti rezultatai atspindėti kiekybiškai tiriant, betono senėjimo koeficiento kitimą, įtempių kitimą, deformacijų kitimą laiko atžvilgiu. Gautų sprendinių korektiškumas patikrintas su Ghali et.al 2002 knygoje pateiktais sprendiniais betono senėjimo koeficientui. Darbe pasiūlytos apytikslės formulės leidžiančios nustatyti gelžbetoninio elemento senėjimo koeficientą pagal betono senėjimo koeficientą, gautą sprendžiant betono relaksacijos uždavinį. Tai leidžia daug tiksliau nustatyti betono įtempių kaitą nei EC-2 priimama senėjimo koeficiento reikšmė - 0.8. Paklaidų sumažinimimas, įvertinant betono įtempių kaitos istoriją, lemia tikslesnį įlinkių prognozavimą bei armatūrinio plieno taupymą išanksto įtempto gelžbetoninio konstrukcijose.
Darbą sudaro skyriai: įvadas, betono elgsena esant trumpalaikei ir ilgalaikei apkrovai, teorinė uždavinio formuluotė, pasiūlytas skaitinis modelis, analitinis modelis, skaitinio modelio realizacija, senėjimo koeficiento skaičiavimas ir... [toliau žr. visą tekstą]In the thesis, the numerical model for reinforced concrete time dependent stress – strain analysis has been proposed. Volterra‘s integral equation serves the basis to resolve the pure relaxation task of plain concrete element as well as predicting the stress development history in analysis of reinforced concrete uniaxialy loaded column. The calculations were conducted by an original computer code written using C# programming language (MS Visual Studio surrounding) according to the procedural programming technique. The results has been reflected studying the change in the time-dependent stresses of concrete as well as evaluating the coefficient of ageing and strains development with time. The correctness of the results obtained was verified with the results given in Ghali et.al 2002 book in terms of the concrete ageing coefficient resulted from the pure relaxation task. In the thesis, the approximate expressions for description of the reinforced concrete ageing coefficient using the plain concrete coefficient of ageing, obtained from relaxation task, were also proposed. This allows us to determine the concrete stresses in more accurate way than EC-2 approximate approach based on value of 0.8 for the ageing coefficient. These approximations enables the reduction of errors, more proper evaluation in the concrete stress history and deflections as well as can economize the reinforcement quantity in the prestressed concrete structures. The Thesis involves the following chapters:... [to full text]
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Honorio, de Faria Tulio. "Modelling Concrete Behaviour At Early-Age : Multiscale Analysis And Simulation Of A Massive Disposal Structure". Thesis, Cachan, Ecole normale supérieure, 2015. http://www.theses.fr/2015DENS0045/document.
Testo completoAbstract (sommario):
La prédiction précise du comportement à long et court terme des structures en béton dans le domaine nucléaire est essentielle pour assurer des performances optimales (intégrité, capacité de confinement) pendant leur durée de vie. Dans le cas particulier des structures massives en béton, la chaleur produite au jeune âge par les processus d'hydratation ne peut pas s’évacuer rapidement, si bien que des températures élevées peuvent être atteintes et les gradients de température qui en résultent peuvent conduire à la fissuration, en fonction des conditions aux limites et contraintes internes auxquelles ces structures sont soumises. Les objectifs de cette étude sont (1) d'effectuer des simulations numériques afin de décrire et prédire le comportement thermo-chimio-mécanique au jeune âge d'une structure massive en béton dédiée au stockage de déchets en surface, et (2) de développer et appliquer des outils de changement d'échelle pour estimer rigoureusement, à partir de la composition du matériau, les propriétés physiques du béton nécessaires à une analyse au jeune âge. Une étude chimio-thermique visant à déterminer l'influence de la convection, du rayonnement solaire, du re-rayonnement et de la chaleur d'hydratation sur la réponse thermique de la structure est tout d’abord menée. Des recommandations pratiques concernant les températures de bétonnage sont fournies afin de limiter la température maximale atteinte au sein de la structure. Ensuite, au moyen d'une analyse mécanique, des stratégies de modélisation simplifiées et plus complexes (prenant en compte l’endommagement couplé au fluage) sont mises en œuvre pour évaluer des scénarios intégrant différentes conditions aux limites issues de l'analyse chimio-thermique précédente. Dans un second temps, une étude prenant en compte le caractère multi-échelle du béton est réalisée. Un modèle simplifié de cinétique d'hydratation du ciment est proposé. Les évolutions des fractions volumiques des différentes phases au niveau de la pâte de ciment peuvent être alors estimées. Par la suite des outils d’homogénéisation analytiques et numériques développés dans un cadre vieillissant sont présentés et appliqués pour estimer les propriétés mécaniques et thermiques des matériaux cimentaires. Les données d’entrée utilisées dans l'analyse structurelle sont finalement comparées avec les estimations obtenues dans l'analyse multiéchelle. Pour conclure, la stratégie proposée dans cette thèse vise à prédire le comportement des structures massives en béton à partir de la composition du béton au moyen d'une approche séquentielle: le comportement du béton est estimé via les outils de changement d’échelle, fournissant ainsi les données d'entrée pour l'analyse phénoménologique à l’échelle de la structureThe accurate prediction of the long and short-term behaviour of concrete structures in the nuclear domain is essential to ensure optimal performances (integrity, containment roperties) during their service life. In the particular case of massive concrete structures, at early age the heat produced by hydration reactions cannot be evacuated fast enough so that high temperatures may be reached and the resulting gradients of temperature might lead to cracking according to the external and internal restraints to which the structures are subjected. The goals of this study are (1) to perform numerical simulations in order to describe and predict the thermo-chemo-mechanical behaviour at early-age of a massive concrete structure devoted to nuclear waste disposal on surface, and (2) to develop and apply upscaling tools to estimate rigorously the key properties of concrete needed in an early-age analysis from the composition of the material. Firstly, a chemo-thermal analysis aims at determining the influence of convection, solar radiation, reradiation and hydration heat on the thermal response of the structure. Practical recommendations regarding concreting temperatures are provided in order to limit the maximum temperature reached within the structure. Then, by means of a mechanical analysis, simplified and more complex (i.e. accounting for coupled creep and damage) modelling strategies are used to assess scenarios involving different boundary conditions defined from the previous chemo-thermal analysis. Secondly, a study accounting for the multiscale character of concrete is performed. A simplified model of cement hydration kinetics is proposed. The evolution of the different phases at the cement paste level can be estimated. Then, analytical and numerical tools to upscale the ageing properties are presented and applied to estimate the mechanical and thermal properties of cementbased materials. Finally, the input data used in the structural analysis are compared with the estimations obtained in the multiscale analysis. To conclude, the entire strategy proposed in this thesis aims at predicting the behaviour of massive concrete structures from the composition of the concrete by means of a sequenced approach: concrete behaviour is estimated using the upscaling tools, providing then the input data to the phenomenological analysis at the structure level
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Edwards, Ylva. "Influence of waxes on bitumen and asphalt concrete mixture performance". Doctoral thesis, KTH, Väg- och banteknik, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-553.
Testo completoAbstract (sommario):
This doctoral thesis consists of a literature review, presented in two papers, and another six papers describing experimental studies of the influence of different kinds of wax and polyphosporic acid on bitumen and asphalt concrete mixture properties. The literature review should give an extensive description of the field of knowledge concerning wax in bitumen. Effects of wax in crude oil, bitumen and asphalt concrete as well as test methods for studying these effects are described. Theories behind possible mechanisms are also discussed, and commercial wax as additive to bitumen for different purposes included. The experimental parts comprise laboratory studies involving totally five 160/220 penetration base bitumens from different sources, two isolated bitumen waxes, five commercial waxes and one polyphosphoric acid. Asphalt concrete slabs, containing base or modified bitumen were prepared and tested. Binder properties were evaluated using different types of laboratory equipment, such as dynamic shear rheometer (DSR), bending beam rheometer (BBR), differential scanning calorimeter (DSC), force ductilometer, as well as equipment for determining conventional parameters like penetration, softening point, viscosity, and Fraass breaking point. Fourier Transform Infrared (FTIR) spectroscopy and Thin Layer Chromatography (TLC-FID) were used for chemical characterization. The binders were aged by means of the rolling thin film oven test (RTFOT) and pressure ageing vessel (PAV) in combination. Asphalt concrete properties were evaluated at low temperatures using the tensile strain restrained specimen test (TSRST) and creep test at -25°C. Dynamic creep testing was performed at 40°C, as well as complex modulus tests between 0 and 20°C. Binder test results indicated that the magnitude and type of effect on bitumen rheology depend on the bitumen itself, type of crystallizing fraction in the bitumen and/or type and amount of additive used. Bitumen composition was found to be of decisive importance. Adding polyethylene wax or polyphosphoric acid, especially to a non-waxy 160/220 penetration grade bitumen, showed no or positive effects on the rheological behaviour at low temperatures (decrease in stiffness) as well as medium and high temperatures (increase in complex modulus and decrease in phase angle). However, the corresponding positive effects could not be shown in dynamic creep testing (at 40°C) of asphalt concrete mixtures containing these modified binders. Adding FT-paraffin decreased the physical hardening index for all bitumens. Also polyethylene wax and montan wax showed this effect for some bitumens. Slack wax showed a large increasing effect on physical hardening, and polyphosphoric acid none or a minor negative effect. No correlation between physical hardening index (PHI) and wax content by DSC was found in this study, involving both natural bitumen wax and commercial wax. Addition of the commercial waxes used showed no or marginally positive influence on bitumen ageing properties for the bitumens and test conditions used. Comparing asphalt mixture test results to the corresponding binder test results, the effects on asphalt mixtures from adding commercial wax or polyphosphoric acid were less evident. Significant binder physical hardening by BBR could not be confirmed by TSRST.QC 20101006
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Horák, Marek. "Analýza stárnutí vybraných materiálů stokových sítí". Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-233817.
Testo completoAbstract (sommario):
The doctoral thesis deals with analysis of the ageing of concrete and reinforced concrete pipes in sewage systems. The ageing of the sewage system is caused by several reasons, for example material abrasion, chemical and biological corrosion and subsequent static overload sewer construction. One of the common causes of degradation of sewage systems made from materials bonded with cement sealant is biogenic sulphate corrosion. Due to the corrosion the degradation of the pipe walls accelerates, particularly in upper part of the pipe and reduces planned lifetime of the sewage system. There is proposed new ageing analysis monitoring method for observation and evaluation of the loss of thickness of concrete and reinforced concrete pipes, which is caused by biogenic sulphate corrosion. Residual lifetime is calculated from the expected corrosion rate, it`s the loss of wall thickness on the monitored section of the sewer system. There is designed the monitoring system of the loss of wall thickness on the sewage system for practical application of the measurement procedure, which is administrated in cooperation with the BVK, a. s. The thesis uses existing knowledge regarding this subject. We use this information for better understanding of the process of the loss of wall thickness in sewage systems in real time and the posibility to correct and in-time implementation of appropriate operational measures. This should cause the limitation of the degradation process of piping material while extended service life and safe operation in sewage systems within the required time period. Based on the methodology is proposed to determine the residual life of the sewage system and maintenance and rehabilitation can be done more effectively. There is needed to be noted that only long-term monitoring period can bring a better overview of the technical condition of sewage systems in time and thus better and more effective maintenance and rehabilitation, which is related to the effective u
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Staškus, Ignas. "Įtempių ir deformacijų būvis kintamai apkrovai laiko atžvilgiu". Master's thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140619_161144-46488.
Testo completoAbstract (sommario):
Monolitinio pastato įrąžoms skaičiuoti, projektuotojas kurdamas pastato skaičiuotinį modelį, jį traktuoja kaip ,,akimirksniu“ pastatytą. Pastato statybos metu nuolatinė apkrova nuo perdangų savojo svorio, auga palaipsniui, betonuojant aukštą po aukšto, kol galiausiai, užbetonuojamas paskutinis aukštas. Darbe pasiūlytas ir skaitiškai realizuotas modelis, įvertinantis betono ir armatūros įtempių bei deformacijų kitimo istoriją dėl laike palaipsniui augančios apkrovos nuo perdangų savojo svorio. Darbe taikomas superpozicijos principas betono valkšnumo deformacijoms, atsižvelgiant į Volterra lygtį. Pasiūlyta matematinė formuluotė pagrįsta matriciniu skaičiavimu ir apibendrintąja funkcijos vidurkio teorema taikant betono valkšnumui. Skaitiniu būdu gauti rezultatai patikrinti analitiškai. Modelis pritaikytas daugiaaukščio pastato papildomų šlyties jėgų perdangose, atsirandančių dėl gretimų kolonų skirtingų poslinkių vystymosi per laiką radimui. Gauti rezultatai patikrinti su apytikslio skaičiavimo rezultatais, taikant normų EC-2 reikalavimus betono valkšnumo deformacijoms. Perdangų praspaudimą kolona, kai pastarosios yra greta pastato standumo branduolių, kurių deformatyvumas yra ženkliai mažesnis, reiktų tikrinti atsižvelgiant į papildomas šlyties jėgas, atsirandančias dėl betono susitraukimo ir valkšnumo įtakos. Darbo apimtis – 99 p. teksto, 54 iliustr., 12 lent. ir 9 literatūros šaltiniai. Atskirai pridedami priedai.The designer calculates a building as an instantly built. However, during construction the permanent load is increasing gradually because the floors are built step by step. This paper introduces a numerically implemented mathematical model for the column analysis accounting for the stress and strain change in reinforcement and concrete with time due to the increasing in time permanent loads induced by the self-weight of each slab during construction. The mathematical formulation is based on the superposition principle for the creep strain described by Volterra's integro-differential equation and involves a matrix solution of linear equations derived via application of the generalized mean theorem for integration. The results obtained are also verified analytically. Finally, the proposed model is applied to calculate extra shear forces caused by the deflections appearing to the adjacent columns of different cross-sections. The results obtained are also compared with the approximate calculation treating the building as an instantly built. The results indicate that additional shear forces due to different displacements of the adjacent columns are quite mild. However, the additional shear forces can be sufficiently high, if the column is located near the high stiffness walls in a non-sway building. In this case, the extra shear forces should be determined via time-dependent analysis accounting on the creep and shrinkage strains relying on the gradually increasing load during... [to full text]
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Tchetgnia, Ngassam Inès Leana. "Durabilité des réparations des ouvrages d'art en béton". Phd thesis, Université Paris-Est, 2013. http://tel.archives-ouvertes.fr/tel-00981689.
Testo completoAbstract (sommario):
Près de la moitié des réparations réalisées sur les ouvrages en béton se concluent par un échec prématuré. Cela se traduit principalement par le décollement de la couche réparatrice, dû à un manque d'adhérence de cette couche sur le support dégradé, et par la corrosion des armatures métalliques de la structure. C'est ainsi que l'Europe consacre la moitié du budget alloué à la construction à la réhabilitation des ouvrages. Deux types de produits de réparation sont principalement proposés sur le marché, les mortiers hydrauliques et les mortiers modifiés par des polymères. Les propriétés intrinsèques de ces produits sont connues mais peu d'études portent sur l'évolution de ces propriétés à long terme, notamment lorsque les matériaux sont appliqués sur un support en béton dégradé. L'objectif de cette thèse est de mieux comprendre l'influence de la présence de polymère dans les mortiers sur la durabilité des réparations des ouvrages d'art en béton. Pour mener à bien cette étude, des mortiers modifiés de formulation connue et contrôlée ont été préparés en laboratoire à partir de l'analyse de la composition de plusieurs produits de réparation commerciaux. Les propriétés intrinsèques à l'état frais et durci de ces deux types de matériaux ont été analysées, en s'intéressant notamment à l'influence de la nature et de la teneur en polymères et à l'influence de la cure appliquée sur ces matériaux. L'augmentation de la quantité de polymère entraîne l'accroissement des propriétés mécaniques des mortiers. Cet effet est surtout visible en flexion car les polymères viennent renforcer l'interface granulat-liant. La cure des mortiers à 40°C permet d'améliorer leurs performances mécaniques et de diminuer leur porosité car dans ces conditions, la formation de films de polymère entremêlés aux hydrates de ciment est favorisée. Un essai a également été développé pour mesurer l'adhérence des mortiers sur un support représentant le béton à réparer. L'influence de la présence de polymère et de l'état de surface du support sur l'adhérence a été analysée, ainsi que l'évolution de l'adhérence pendant la conservation des éprouvettes dans des environnements différents. Ces essais ont permis de montrer que l'addition de polymère permettait d'augmenter l'adhérence des mortiers contenant des polymères par rapport aux mortiers non-modifiés. Après trois mois de durcissement, l'adhérence maximale est obtenue à partir de 10% de polymère. L'augmentation de la rugosité et la saturation en eau du support n'ont pas entraîné d'augmentation de l'adhérence par rapport aux surfaces sèches et planes. Comme pour les propriétés intrinsèques des mortiers modifiés, une cure à 40°C permet d'améliorer l'adhérence alors qu'une immersion dans l'eau est défavorable. Enfin, le risque de corrosion des armatures enrobées de mortiers modifiés a été étudié en caractérisant les propriétés électrochimiques des aciers ainsi que les propriétés de transfert d'espèces agressives dans les mortiers. L'addition de polymères dans les mortiers renforce la protection des armatures métalliques grâce à leurs propriétés d'isolant électrique. Dans la plupart des cas, ils limitent également la diffusion du CO2 et des ions chlorure dans le matériau
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Bichet, Lionel. "Mécanismes de transports dans la fissuration des matériaux hétérogènes : application à la durée de vie d’exploitation des centrales nucléaires". Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS001/document.
Testo completoAbstract (sommario):
Les propriétés du béton constituant les enceintes de confinement des centrales électronucléaires évoluent sous les effets de mécanismes de vieillissement résultant notamment de transferts couplés de chaleur et de masse au sein du matériau. Ces phénomènes peuvent être modélisés par des équations de transports moyennées : lois de Fick pour le transport d’espèces en solution et lois de Fourier pour la description de la diffusion thermique. Dans cette étude, les développements concernent la diffusion de la thermique dans un milieu hétérogène fissuré représentant un matériau cimentaire dégradé chimiquement. Le problème thermo-mécanique est traité à l'aide d'une approche multi-corps reliés par des lois d’interactions enrichies (zones cohésives). La diffusion thermique est écrite dans le formalisme cohésif-volumique en prenant en compte le couplage entre un état d'endommagement local de la zone cohésive et une conductivité homogénéisée. Afin d'optimiser les coûts de calculs, une étude est menée sur la dimension d'un volume élémentaire représentatif (VER). Pour cela, la méthode d'eigenerosion est étendue à la fissuration de milieux hétérogènes puis appliquée aux milieux cimentaires. La propagation de fissures sous chargement thermique est ensuite analysée dans des VERs de béton dégradés représentatifs des enceintes de confinement des centrales nucléaires après plusieurs années. Le vieillissement est modélisé par un taux de pré-dégradation initial entre le mortier et les granulats. Le développement de multi-fissures est relié au taux de pré-dégradation et la formation "d'écrans" à la diffusion de la thermique est mise en avantDuring their confinement in a nuclear power plant, the mechanical properties of the constitutive materials of concrete change as a result of ageing. This is due to the transportation of chemical species at the microscopic level of the media. Firstly, this can be modelled with average equations. The Fick laws represent the evolution of chemical diffusion and the Fourier laws, the transportation of heat at a mesoscopic level. In this research, we will consider thermal evolution on a fractured media.This thermomechanical problem is solved with a staggered method. The mechanical contribution used an approach based on multi-bodies system linked with cohesive zone models. The thermal problem is based on the approximation of the heat transfer equation at the cohesive interface. This approach has been implemented and validated. The description of the heat trough the interface is composed with the definition of an homogenised conductivity and the local damage parameter. In order to optimize the computational cost with a good agreement of the crack propagation, a criterion is proposed for sizing a representative elementary volume (REV). The eigenerosion method is used, validated and extended to heterogeneous media. Two studies are carried out on the morphological properties on a cementious media. As a result of those studies, a minimal size for a REV is defined.Crack spread under thermal loads are investigated on a media representing the concrete of the containment of a nuclear power station. The ageing effect are taken into account as an initial damage between the mortar and the aggregates. These parameters are expressed in terms of rate of initial damage. A study is proposed for different values of this rate. As assumed, the development of multi-cracks is linked with the rate of initial damage and the creation of thermal border is proposed
8
Bouhjiti, David El Mahdi. "Analyse probabiliste de la fissuration et du confinement des grands ouvrages en béton armé et précontraint". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI058/document.
Testo completoAbstract (sommario):
Cette thèse porte sur le vieillissement des grands ouvrages en béton armé et précontraint dotés d’une fonction de confinement comme les bâtiments réacteurs des centrales nucléaires. Elle vise en particulier l'analyse probabiliste de l’évolution de leurs états de fissuration et de perméabilité dans le temps sous chargements Thermo-Hydro-Mécaniques (THM) simultanés et variables. L’étanchéité de telles structures est due à la faible perméabilité du béton mais reste conditionnée surtout par la maîtrise de la fissuration. Or, l'évolution de la perméabilité, l'apparition des fissures et leur propagation dépendent fortement de plusieurs aléas (les conditions de mise en œuvre, la variabilité spatio-temporelle des propriétés du béton et des chargements THM subis par la structure, etc.). Ainsi, la prise en compte de ces aléas dans les modèles numériques de vieillissement est une nécessité afin de permettre une meilleure évaluation de la performance de la structure dans son état présent et, surtout, permettre une prévision plus précise et plus fiable de son état futur. Pour y parvenir, cette thèse propose une stratégie globale de modélisation stochastique Thermo-Hydro-Mécanique avec post-traitement de la Fuite (THM-F), à l’échelle de Volumes Structurels Représentatifs, adaptée à la complexité du problème traité, au nombre important de paramètres THM-F intervenant dans les calculs et à son coût numérique. En particulier, les points suivants sont traités :(a) Modélisation du vieillissement tenant compte des effets de jeune âge : La modélisation des phénomènes de vieillissement est basée sur un modèle THM-F chaîné. En particulier, la modélisation proposée de la fissuration repose sur le couplage des lois d’échelle énergétique et des champs aléatoires autocorrélés selon une formulation locale, régularisée et vieillissante de l’endommagement. Cela permet une meilleure évaluation du risque de fissuration tant d’un point de vue qualitatif que quantitatif. Par conséquent, la prévision de l’étanchéité est aussi améliorée.(b) Identification des paramètres THM-F les plus influents : En appliquant une méthode d’analyse de sensibilité de type OFAT (One-Factor-At-a-Time) au modèle THM-F retenu, l’effet de la variabilité des différents paramètres en entrée sur la réponse numérique est quantifié. Cela permet de hiérarchiser les effets et de classifier les paramètres selon leur importance vis-à-vis du vieillissement (particulièrement en termes de fissuration et d’étanchéité).(c) Analyse de la propagation d’incertitudes THM-F : Des méthodes basées sur les surfaces de réponse (plans d’expérience adaptatifs, chaos polynomiaux) sont proposées pour construire des méta-modèles THM-F et analyser la propagation d’incertitudes moyennant un coût et une précision raisonnables. Étant donné la nature explicite des méta-modèles, la méthode de Monte Carlo est directement appliquée pour accéder à des fonctions de répartition, des indicateurs de sensibilité globaux et des analyses de fiabilité.L’applicabilité du modèle stochastique THM-F proposé aux grands ouvrages de confinement en béton armé et précontraint est évaluée en se basant sur la maquette VeRCoRs (enceinte de confinement à l’échelle 1 :3) selon des critères de représentativité physique du comportement et des mesures d’incertitudes simulés et de coût numériqueConcrete is a heterogeneous, multiphasic and ageing material. Consequently, its properties show intrinsically spatiotemporal variations. For large reinforced and prestressed concrete structures such as Nuclear Containment Buildings (NCB), these variations directly affect the kinetic of their ageing process in terms of cracking, drying, creep and tightness. They also lead, within the structure's volume, to a non-negligible spatial heterogeneity of the concrete's behavior to the applied Thermo-Hydro-Mechanical (THM) loads during the operational lifespan. Consequently, the introduction of such variations in numerical models is a mandatory step to enhance the assessment of these structures’ present behavior and the accuracy of predictive analyses of their future one. With that aim in view, the thesis suggests a global coupling strategy of THM-L models (Thermo-Hydro-Mechanical with Leakage estimation) and non-intrusive stochastic approaches adapted for the strongly non-linear and time consuming simulations of ageing phenomena and the large number of inputs they require. Applied to the VeRCoRs mock-up (1:3 scaled containment building) at the scale of Representative Structural Volumes (RSV), this thesis addresses the following issues:(a) RSV-based modeling of concrete ageing from the early age phase: The modeling of concrete’s ageing is based on a staggered Thermo-Hydro-Mechanical with Leakage evaluation (THM-L) strategy. In particular, concrete cracking is modeled according to a Stochastic Size Effect Law (SSEL) and a regularized, local, ageing and damage-based constitutive model. The spatial heterogeneity of the concrete's properties (mainly the Young's modulus) is described using Random Fields (RF). This leads to a better description of concrete cracking both qualitatively and quantitatively. Accordingly, the modeling of the structural tightness is also improved.(b) Most influential THM-L parameters: Using a 1st order sensitivity analysis strategy (One-Factor-At-a-Time OFAT perturbation method), the relative effect of the THM-F parameters on the computed behavior is quantified. The obtained results show a hierarchized list of the most influential parameters and their associated physical phenomena. A selection is then achieved to keep relevant parameters only for uncertainty propagation step and higher-order sensitivity analyses throughout the THM-L coupling path.(c) Uncertainties propagation through THM-L calculation steps: Surface Response Methods (SRM) are used to define the associated RSV-based THM-L meta-models. For the stochastic modeling of concrete’s cracking an original Adaptive-SRM-based algorithm is suggested. Whereas for continuous THM-L quantities, a Polynomial Chaos based strategy is retained. Finally, as the meta-models are explicit within a defined and bounded domain, crude Monte Carlo Method is applied, at low cost, aiming at the CDFs and the reliability analysis of the considered variables of interest.Eventually, the suggested SFEM shall lead operators to a better quantification of uncertainties related to the behavior of their strategic civil engineering structures. This remains a crucial step towards the enhancement of durability assessment and repair/maintenance operations planning
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Pedro, Rudimar. "Produção de blocos de concreto celular usando espumígeno de ácidos graxos de coco e resíduos de pedras roladas de ágata". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/163466.
Testo completoAbstract (sommario):
O estado do Rio Grande do Sul é o terceiro maior produtor de pedras preciosas do Brasil, atrás apenas de Minas Gerais e da Bahia, destacando-se a produção de ágatas na região de Salto do Jacuí. Na lavra e beneficiamento são produzidos grandes quantidades de resíduos que estão a espera de destino e utilização ambientalmente correta. De modo específico, este trabalho avaliou a possibilidade de utilização do resíduo de ágata rolada na fabricação de blocos de concreto celular espumígeno (BCCE), utilizados como blocos de vedação na construção civil. Adicionalmente, desenvolveu-se uma mistura de dois agentes espumígenos provenientes de ácidos graxos de coco, como agente incorporador de ar, pela adição de espuma pré-formada. A metodologia de produção foi baseada no modelo de produção dos blocos de uma pequena indústria na Região de Passo Fundo/RS, que produz e comercializa BCCE. Em um estudo prévio de bancada, foram estudadas a composição da espuma, a granulometria do resíduo, o teor de água e o tempo de mistura. Os materiais componentes do BCCE são resíduo de sílica de pedras roladas de ágatas (SiO2 - 92,5%), espuma preparada com ácidos graxos de coco, água de qualidade potável e cimento como agente aglomerante. Nos testes de bancada, foram confeccionados 36 corpos de prova, em forma cilíndrica, de tamanho 50 mm de diâmetro por 100 mm de altura, com diferentes volumes de ar incorporado, divididos em três grupos. As amostras foram deixadas durante 28 dias à temperatura ambiente, em processo de cura, e após foram analisados quanto à resistência à compressão, densidade e distribuição das bolhas de ar. Os resultados foram avaliados pela Análise de Variância e demonstraram que o Grupo II apresentou densidade de 430 Kg/m3, e resistência de 0,92 MPa. Este resultado está próximo do atendimento aos requisitos da norma para classe de resistência de < 400 Kg/cm3 (NBR 13438, 2013).The state of Rio Grande do Sul is the third largest producer of gemstones in Brazil, only losing to the states of Minas Gerais and Bahia, and agate production stands out in the region of Salto do Jacuí. Great amounts of waste, which are waiting for environmentally correct destination and use, are produced in mining and processing. Particularly, this study assessed the potential use of rolling waste of agates in civil construction, and the manufacturing of foam concrete blocks as a full substitute for sand. Additionally, a mixture was made of two foaming agents derived from coconut fatty acids as air-developer agent, and as hydraulic binder the Portland CP V ARI-RS cement. The production methodology was based on the production model of the blocks in a small industry, which produces and sells foam concrete blocks in the region of Passo Fundo, RS, Brazil. In a previous bench study the parameters foam composition, residue granulometry, water content, and mix time were adequate and later replicated industrially. The materials composing foam concrete blocks are rolled agate stones silica (SiO2 – 92.5%), foam from coconut fatty acids, fresh water, and cement as binder. In bench tests, 36 cylindrical specimens were produced, with 50 mm of diameter and 100 mm of height, with different volumes of incorporated air, divided into three groups. The samples were kept at room temperature for 28 days with healing process, and after that, the resistance to compression, density, and air bubbles distribution were analyzed. Results were assessed by Analysis of Variance, and showed that Group II presented density of 430 Kg/m3 and resistance of 0.92 MPa. This result is close to meeting the requirements of the norm for resistance class of < 400 Kg/cm3 (NBR 13438, 2013).
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Alachek, Ibrahim. "Comportement au cours du temps des éléments de structure multi-matériaux collés : application aux structures hybrides béton – GFRP". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1111/document.
Testo completoAbstract (sommario):
Ce travail porte sur l'étude des comportements en flexion à court et long termes des poutres hybrides collées constituées d'un profilé pultrudé GFRP et d'une dalle en béton, assemblés par un joint de colle époxy. L'utilisation du collage dans des structures réelles se heurte encore à la réticence des concepteurs en raison du manque de garanties sur la durabilité à long terme et de l'absence d'outils de modélisation donnant la durée de vie en service des assemblages collés. La présente étude constitue donc un jalon dans cette démarche de compréhension du comportement à long terme de ces structures collées. Elle s'appuie sur analyse multi-échelles qui permet d'aborder le problème à l'échelle locale de l'interface (essai pushout) et à l'échelle globale de l'élément de structure (essai de flexion sur des poutres). Des essais de vieillissement accéléré ont tout d'abord été conduits pour étudier les effets de l'humidité et de la température sur l'adhésif seul et sur l'assemblage structural et il en ressort que l'eau, et notamment une immersion prolongée, s'avère particulièrement néfaste à la résistance au cisaillement des éprouvettes et modifie leur mode de ruine. La réponse instantanée de l'assemblage pultrudé-béton a ensuite été plus amplement étudiée. Grâce à une étude paramétrique expérimentale, une géométrie et une méthode de fabrication des éprouvettes ont été définies pour assurer la reproductibilité des résultats et limiter leur dispersion. De plus, un modèle numérique 3D a été développé dans le code d'éléments finis Cast3m et montre une distribution de contraintes, notamment de cisaillement, non uniforme le long de la surface de collage avec une concentration aux extrémités du joint. Une analyse paramétrique numérique a permis d'identifier les dimensions des dallettes et du joint de colle comme des paramètres influents sur la résistance des éprouvettes. Enfin, le comportement en fluage d'une poutre hybride est étudié. Sous l'effet d'un vieillissement naturel, seul, le joint d'adhésif ne s'avère pas impacté. Des essais de fluage en flexion 3-points ont été effectués pour étudier les réponses à long terme du profilé seul et de la poutre hybride. Ils montrent une augmentation considérable du déplacement des poutres en raison du fluage et du retrait du béton et du fluage du profilé. Des modèles 3D en variables locales, dans le cadre de la viscoélasticité linéaire, sont développés dans Cast3m et permettent de fidèlement restituer l'évolution des déplacements et des états de déformation au cours du temps pour les différentes poutres testéeThis dissertation focuses on the short- and long-term responses of bonded hybrid beams consisting of a GFRP-pultruded profile bonded by an epoxy adhesive joint to a reinforced concrete-slab. The problems related to the durability and the long-term response of these structures still represent an open issue. The present study is meant to increase the knowledge and understanding of these hybrid structures in this context. Firstly, different accelerated ageing tests were carried out to evaluate the effects of some environmental agents such as water, moisture and freeze thaw cycles in the behaviour of GFRP/concrete bonded assemblies. Mechanical characterizations were carried out on control and exposed of both materials and push-out specimens to quantify the degradation and damage of the mechanical resistance of each material and of the adhesive bond properties. The water effect on the adhesion of the joints was found to be significant, especially at longer immersion times. The second part was directed at characterizing the push-out test. An experimental parametric study was performed to elaborate a methodology of fabrication of the push-out specimens that can reduce the dispersion of results and give an accurate prediction of the shear strength on a limited set of specimens. Also, a 3D finite-element model was developed using the finite-element code Cast3m. This model showed that the stress components, especially peel and shear stresses, are not constants across the bonding area and peaking near the free edges (stress concentrations). A numerical parametric study allowed to conclude that the most effective geometrical parameters influencing bond between GFRP and concrete were the bonded length and the dimensions of the concrete substrate. Last part deals with experimental and numerical investigations carried out to study the short- and long-term flexural behaviour of full-scale hybrid beams. All experiments showed considerable increase in beam deflection over time due to concrete creep and shrinkage and GFRP creep. Finally, 3D-finite-element models, realized with Cast3m, are developed based on the incremental formulation of the linear-viscoelasticity theory. The proposed models allow evaluation of the long-term deflection of the pultruded and hybrid beams. Using the proposed model, evolution with time of stresses, strains and displacements in different location of the hybrid beam are obtained
Libri sul tema "Concrete Ageing"
1
Dunster, A. Durability of ageing high alumina cement (HAC) concrete: A literature review and summary of BRE research findings. London: BRE, 2000.
Cerca il testo completo
2
IAEA. Ageing Management of Concrete Structures in Nuclear Power Plants. International Atomic Energy Agency, 2016.
Cerca il testo completo
3
Andersen, Jorgen Vitting. From Minority Games to $-Games. A cura di Shu-Heng Chen, Mak Kaboudan e Ye-Rong Du. Oxford University Press, 2018. http://dx.doi.org/10.1093/oxfordhb/9780199844371.013.17.
Testo completoAbstract (sommario):
This chapter argues for the use of game theory or agent-based modeling to go beyond the standard methods used in traditional approaches to finance. The theory of rational expectations is at the core of most theories of finance in use since the 1970s, but it is also very unrealistic. This chapter first introduces some very general thoughts about elements needed in a new framework for finance. Then a few concrete examples of heterogeneous agent-based models will be introduced, and several of their main results will be discussed. Finally, applications and methods to real-market data will be introduced, notably the idea of “decoupling” to explain the short-lived synchronization of investors.
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Bacon, Andrew. Vagueness and Decision. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198712060.003.0009.
Testo completoAbstract (sommario):
If linguistic vagueness is more fundamental than propositional vagueness, it is natural to think that vague propositions won’t play a substantive role in decision theory. On a linguistic picture, what it is rational for an agent to do is completely determined by their attitudes towards precise propositions. This is vacuously true if all propositions are precise, but it also seems like a natural idea if, like the expressivist discussed in Chapter 8, a distinction is drawn between metaphysically ‘first-rate’ precise propositions and metaphysically ‘second-rate’ vague propositions. This chapter considers how to formulate decision theory in a setting where there are vague propositions, and discusses ways in which vague beliefs, desires, and actions can have concrete impacts on practical deliberation and action.
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Blackham, Alysia. Reforming Age Discrimination Law. Oxford University PressOxford, 2022. http://dx.doi.org/10.1093/oso/9780198859284.001.0001.
Testo completoAbstract (sommario):
Abstract Age is a critical issue for labour market policy. Both younger and older workers experience significant challenges at work. Despite the introduction of age discrimination laws, ageism remains prevalent. This book offers a roadmap for the future development of age discrimination law in common law countries, to better address workplace ageism. Drawing on theoretical, doctrinal, and empirical legal scholarship, and comparative perspectives from the United Kingdom, Australia, and Canada, the book provides a grounded critique of existing age discrimination laws and their enforcement, and puts forward concrete suggestions for legal reform and change. It examines the challenges and limitations of existing legal frameworks and the individual enforcement model for addressing age discrimination in employment, mapping the stages of claiming, negotiation, or alternative dispute resolution, and hearing and judgment, using mixed method case studies of the enforcement of age discrimination law in the United Kingdom and Australia. The book puts forward a fourfold model of reform to strengthen age discrimination law, to improve the individual enforcement model, strengthen positive equality duties, bolster the roles of statutory equality agencies, and enhance collective enforcement. The book critically considers how these options might address the limits of existing laws, and the practical measures necessary to ensure their success.
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DeJonge, Michael P. Church and State. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198824176.003.0005.
Testo completoAbstract (sommario):
Chapter 3’s discussion of kingdoms and orders in the context of political life leads naturally into the topic of this chapter: the church, the state, and their relationship. The present chapter locates the state (or, better, political authority in general) in relationship to Chapter 3’s categories by presenting it as one of the orders by which God’s structures the world. It is an important actor in the temporal kingdom, where God has ordained it to preserve the world through law. The church in its essence is an agent of the spiritual kingdom, bearing God’s redemptive word to the world. The themes of preservation and redemption, the kingdoms, and the orders find many of their concrete expressions in themes of the church, the state, and their relationship.
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Humphreys, Paul. Computational Economics. A cura di Don Ross e Harold Kincaid. Oxford University Press, 2009. http://dx.doi.org/10.1093/oxfordhb/9780195189254.003.0013.
Testo completoAbstract (sommario):
Computational economics is a relatively new research technique in economics, but it is inexorably taking its place alongside the more traditional methods of general theory, abstract modeling, data analysis, and the more recent experimental economics. Perhaps because of its relative newness, the term computational economics currently has no determinate meaning. In contemporary use, it refers to a heterogeneous cluster of techniques implemented on concrete digital computers ranging from the numerical solution of the Black-Scholes partial differential equation for pricing options through automated trading strategies to agent-based computer simulations of the evolution of cooperation. Because of this heterogeneity, it is not possible to provide a comprehensive coverage of the topic in this article. Another reason for this restricted scope is that many of the methods used in computational economics have considerable technical interest but no particular philosophical relevance.
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Tsur, Reuven. Elusive Qualities in Poetry, Receptivity, and Neural Correlates. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780190457747.003.0013.
Testo completoAbstract (sommario):
Arnheim’s terms “actively organizing mind” and “passively receiving mind” can usefully be applied in practical criticism to suggest the significance of poetic structures as described by more concrete terms. But it is not quite clear what exactly they refer to. This chapter explores how the latter term can be illuminating in close readings of poems by Verlaine. Neuropsychological findings proposed in the last section fill those terms with more solid meaning. When you experience sensory stimuli, certain areas in the secondary somatosensory cortex light up. When you perceive yourself as the voluntary agent causing the sensations, this activity is suppressed. This may account for the observation that the actively organizing mind is less sensitive to elusive sensations in poetry than a passive attitude. This chapter explores the linguistic means—syntactic, semantic, and phonetic—by which Verlaine’s texts manipulate the fictional speaker and/or the flesh-and-blood reader into a passive stance.
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Leftow, Brian. The Argument from Possibility. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780190842215.003.0025.
Testo completoAbstract (sommario):
This chapter sketches an argument from the metaphysics of possibility to the existence of something that looks very like God. The argument concerns what is called broadly logical, metaphysical, or absolute possibility. The argument begins by contending that the best theory of this places the truth-makers of absolute possibility claims in the powers of actual existing concrete things: this, it contends, provides the most parsimonious metaphysics of possibility. It shows this inter alia by quick comparison with Meinongian, Platonist and David Lewis’ views. The argument leads to something resembling God: an omnipotent, necessarily existing rational agent. The chapter outlines three factors that lead one to ascribe a mind to this necessary being. It would be less strange to us if it had a mind. This provides the overall most adequate “powers” theory of possibility. And it alone seems to let this being provide the possibility that other beings act with libertarian freedom.
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Hasty, Christopher. Meter as Rhythm. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190886912.001.0001.
Testo completoAbstract (sommario):
Rhythm is often regarded as one of the most problematic and least understood aspects of music. Restricted to those attributes that are susceptible to calibration and measurement, rhythm is usually identified with meter, durational pattern, or durational proportion. But how shall one account for those attributes of rhythm that point to the particularity and spontaneity of aesthetic experience as it is happening? Drawing on insights from the modern “process” philosophy of Henri Bergson, William James, and A. N. Whitehead, this book releases meter from its mechanistic connotations and recognizes it as a concrete, visceral agent of musical expression. It reinterprets oppositions of law and freedom, structure and process, determinacy and indeterminacy to form a theory that engages diverse repertories and aesthetic issues. Ultimately, this revised 20th anniversary edition of Christopher Hasty’s Meter as Rhythm facilitates the work’s current contexts of application, from new subfields in ethnomusicology and music cognition to non-music fields like literary studies, physics, and biology
Capitoli di libri sul tema "Concrete Ageing"
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Pijaudier-Cabot, Gilles, Khalil Haidar, Ahmed Loukili e Mirvat Omar. "Ageing and durability of concrete structures". In Degradations and Instabilities in Geomaterials, 255–86. Vienna: Springer Vienna, 2004. http://dx.doi.org/10.1007/978-3-7091-2768-1_9.
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Gallittre, Etienne, James Mok e Jean Luc Valfort. "Ageing Management of Concrete Structures of NPPs". In RILEM State-of-the-Art Reports, 49–61. Dordrecht: Springer Netherlands, 2016. http://dx.doi.org/10.1007/978-94-024-0904-8_4.
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Miyazato, Shinichi, Takashi Yamamoto e Ryousuke Takahashi. "Study on Triage for Deteriorated Concrete Structures by JSCE-342". In The Ageing of Materials and Structures, 69–79. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-70194-3_6.
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Seni, Claude, e Leonid Ianko. "An International Database of Nuclear Concrete Structures Ageing". In Industrial Information and Design Issues, 285–90. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-642-80286-7_32.
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Benzarti, Karim, Marc Quiertant, Sylvain Chataigner e Christophe Aubagnac. "Durability of FRP Strengthened Concrete Specimens under Accelerated Ageing". In Organic Materials for Sustainable Construction, 529–52. Hoboken, NJ USA: John Wiley & Sons, Inc., 2013. http://dx.doi.org/10.1002/9781118616734.ch24.
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Quiertant, Marc, Karim Benzarti, Julien Schneider, Fabrice Landrin, Mathieu Landrin e Frédéric Boinski. "Durability of FRP to Concrete Bonded Interface Under Accelerated Ageing". In RILEM Bookseries, 605–11. Dordrecht: Springer Netherlands, 2016. http://dx.doi.org/10.1007/978-94-024-0867-6_85.
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Valliappan, Somasundaram, e Calvin Chee. "Ageing Degradation of Concrete Dams Based on Damage Mechanics Concepts". In Computational Structural Engineering, 21–35. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-90-481-2822-8_3.
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Pareek, Sanjay, Yusuke Suzuki, Ken-ichi Kimura, Yusuke Fujikura e Yoshikazu Araki. "Radiation Shielding Properties and Freeze-Thaw Durability of High-Density Concrete for Storage of Radioactive Contaminated Soil in Fukushima". In The Ageing of Materials and Structures, 97–109. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-70194-3_8.
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Kouevidjin, B., J. F. Barthélémy, C. Somé, H. Ben Dhia e A. Feeser. "Effect of Thermal Ageing on the Mechanical Properties and Cracking Behaviour of Asphalt Concrete". In RILEM Bookseries, 631–37. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-46455-4_80.
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Benzarti, K., M. Quiertant, C. Marty, S. Chataigner e C. Aubagnac. "Effects of Accelerated Ageing on the Adhesive Bond Between Concrete Specimens and External CFRP Reinforcements". In Advances in FRP Composites in Civil Engineering, 385–89. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-17487-2_84.
Testo completoAtti di convegni sul tema "Concrete Ageing"
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de Haan – de Wilde, F. H. E., e C. G. M. de Bont. "International Civil Ageing Management and Assessment Methodology of Concrete". In ASME 2019 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/pvp2019-93029.
Testo completoAbstract (sommario):
Abstract For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years in the coming years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures. Knowledge about the strength of concrete structures and modelling thereof can be improved for a more complete knowledge base on ageing and degradation mechanism in nuclear facilities. Therefore, effort is required to improve the knowledge of concrete, material models and finite element modelling techniques as well as the assessment method. Recent developments have shown that ageing of civil structures receive more attention internationally (E.g. concrete degradation in bunker building Doel). Traditionally a large part of the research and development is focused on mechanical issues like piping and vessels. In order to increase the knowledge in the field of civil structures, the focus is on investigation of ageing of concrete and determining analysis methods. This paper focuses on the development of a practical assessment method for ageing of civil structures. As a first step information from international publications and other sources on civil structures ageing issues and management thereof, will be gathered. Well known international standards taking care of ageing phenomena based on problem areas and good practices are IGALL and GALL. IGALL and GALL contain information tables based on international experience. This is the starting point of the research in finding an assessment methodology for civil ageing management. It will be shown that IGALL and GALL contain very similar elements. Sorting on the AMPs results in a practical set of datasheets with summarizing information per AMP, including the underlying international experience. The datasheets are of limited size, presenting an helpful overview of the relevant structures or components, materials, environment and mechanisms. A method for civil ageing management is proposed which will be applied and developed in more detail in future research. Further research is necessary to develop a specific assessment methodology for concrete.
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Ov, David, Rolf Breitenbücher, Martin Radenberg e Dominik Twer. "Innovative test method for the reliable evaluation of joint sealants in concrete pavements". In 12th International Conference on Concrete Pavements. International Society for Concrete Pavements, 2021. http://dx.doi.org/10.33593/x3x4t4o9.
Testo completoAbstract (sommario):
Joint sealants as indispensable filling systems in jointed plain concrete pavements (JPCP) are permanently exposed to various stresses during their service life, which often leads to a replacement of the sealing after approx. 7 to 10 years. Aside from seasonal unsteady climatic changes, the cyclical stresses caused by traffic and the ageing of joint sealants are especially significant. Considering the rising number of damages that occur within the overall "joint" system, an increased demand for a durable solution is requested as it is a relevant element for the life cycle costs of concrete pavements. In this context, a testing and ageing method was developed which comprises of the entire "joint" system, including the saw-cut concrete joint flanks, the primer as well as the joint sealant. This procedure depicts the decisive scenarios of in-situ stresses and allows the characterization of joint sealants. For this purpose, specimens were subjected to horizontal and vertical loads (static/cyclic) as well as to various ageing effects (temperature conditioning, UV-conditioning and freeze-thaw-cycles). After conditioning, a significant influence of the artificial ageing on the residual strength was observed in the tensile/shear tests. By comparing the artificially aged samples tested in the laboratory with extracted and in-situ aged samples, a reliable correlation was determined. Considering these system tests an initial approach was established which enables the evaluation of joint sealants in both unaged and artificially aged conditions on the basis of scientific parameters and limits.
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Hasa, Ledia, e F. H. E. de Haan - de Wilde. "An Update of the Assessment Methodology for Civil Ageing Management: Damage Development in Concrete Structures of a Reactor due to Ageing Mechanisms". In ASME 2022 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/pvp2022-84008.
Testo completoAbstract (sommario):
Abstract For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures. Recent developments have shown that ageing of civil structures receive more attention internationally. In order to increase the knowledge in the field of civil structures, this paper focusses on investigation of ageing of civil structures and determining an ageing management strategy. Knowledge of the ageing mechanisms of civil structures and especially concrete, will lead to improvement of ageing management and assessment methods of concrete. The presented work is part of ongoing research. In the past several steps have been made. Gathering of international information on civil structures ageing issues and management thereof (see PVP2019-93029 [3]), testing of a proposed assessment methodology by application to a nuclear reactor and comparison with another PWR with a steel containment (see PVP2020-21838 [4]) and creating a list of plant specific AMPs dealing with the relevant mechanisms at the various locations in a practical manner (see PVP2021-61499 [5]). The result was a general list with possible relevant locations and what type of measures could be taken. The current steps in the research focus on material behavior of structural concrete and practical assessment in finite element modelling techniques. In a this step, the concrete material and behavior will be investigated and explained. The characteristic properties of the concrete will be summarized and the degradation mechanisms will be identified. The assessment criteria for concrete finite element modelling are defined. The overall goal of the project is to obtain more knowledge on ageing management of civil structures and especially concrete. In the current research steps the aim is to create a predictive tool with the FE modelling technique for the damage quantification in concrete due to its ageing mechanism. The results of this ongoing work are presented in this report. The characteristic properties, degradation mechanisms including modelling options are identified together with an investigation on the assessment criteria for concrete finite element modelling. The behavior of structural concrete will be explained. The conclusion represents input parameters, modelling options and assessment criteria for finite element modelling of concrete. In the future steps a practical assessment in finite modelling techniques will be introduced in order to take into consideration the degradation of the concrete. The material properties will be analyzed and adapted in an FE Model.
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Kang, Ki-Sig, e John H. Moore. "IAEA Activities on Concrete Ageing in Containment and Other Structures in Nuclear Power Plants". In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97570.
Testo completoAbstract (sommario):
Significant industry developments over the past decade have placed concrete ageing at the forefront of life extension decisions related to nuclear power plants. Recent issues encountered include alkali–silica reactivity in concrete, delamination events, larger than anticipated loss of pre-stressing force, spent fuel pool leakage, corrosion of steel reinforcement in water intakes, and others. Concrete structures at nuclear power plants are being asked to perform for longer periods than originally design life. Utilities around the world are investigating plant service life extensions (with 60 years or more total being a quoted target), and for some projects delayed construction schedules, and/or decommissioning strategies that involve the use of containment as a “safe store” for periods of up to 100 years, mean that containment buildings and other concrete structures often have to perform their functions for a time period significantly greater than their initial design life. Newer plants are designed with design lives of 60 years or more. Concrete is a durable material and its performance as part of the containment function in NPPs has been good. However, experience shows that ageing degradation of concrete structures, often caused or accelerated by factors such as faulty design, use of unsuitable or poor quality materials, improper construction, exposure to aggressive environments, excessive structural loads, and accident conditions, can impair its safety functions and increase risks to public health and safety. Effective ageing management of concrete containment buildings and other concrete structures is therefore required to ensure their fitness-for-service throughout the plant service life and during decommissioning. The paper presented will present current International Atomic Energy Agency activities in the area of concrete structures and ageing management, and point to where guidelines and best practises related to concrete structure ageing management, relevant operating experience, and applicable codes and standards may be located.
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Honorio, Tulio, Benoit Bary e Julien Sanahuja. "Effective ageing linear viscoelastic properties of composites with phase precipitation: comparisons between numerical and analytical homogenization approaches". In 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures. IA-FraMCoS, 2016. http://dx.doi.org/10.21012/fc9.228.
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Podroužek, Jan, Alfred Strauss e Drahomír Novák. "SPATIAL DEGRADATION IN RELIABILITY ASSESSMENT OF AGEING CONCRETE STRUCTURES". In 1st International Conference on Uncertainty Quantification in Computational Sciences and Engineering. Athens: Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens (NTUA) Greece, 2015. http://dx.doi.org/10.7712/120215.4318.690.
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Niu, Zhiguo, Ziyang Tang e Ri You. "Seismic safety assessment of concrete dam with ageing degradation". In International Conference on Computational Intelligence and Industrial Engineering. Southampton, UK: WIT Press, 2014. http://dx.doi.org/10.2495/ciie140171.
Testo completo
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de Haan - de Wilde, F. H. E., e C. G. M. de Bont. "An Assessment Methodology for Civil Ageing Management and Concrete for LTO/CSO Based on International Standards and Engineering Judgement". In ASME 2020 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/pvp2020-21838.
Testo completoAbstract (sommario):
Abstract For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years in the coming years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures. Recent developments have shown that ageing of civil structures receive more attention internationally (for example concrete degradation in bunker building Doel and buried piping attention in topical peer review EU). In order to increase the knowledge in the field of civil structures, this work focusses on investigation of ageing of civil structures and determining an ageing management strategy. Knowledge of the ageing mechanisms of civil structures and especially concrete, will lead to improvement of ageing management and assessment methods of concrete. As a first step international information was gathered on civil structures ageing issues and management thereof (see PVP2019-93029). In addition a very high level assessment methodology was proposed. The goal of the project is to obtain more knowledge on ageing management of civil structures and especially concrete. It will lead to an assessment method for civil ageing management and ageing management programs dealing with the relevant mechanisms at the various locations in a practical manner. The results of this ongoing work are presented in this report. The initial proposed assessment methodology has been tested by application to the HFR research reactor. The resulting list of relevant AMPs has been verified with the outcome for another PWR with a steel containment. With this experience the assessment methodology is improved. In addition each civil SSC in the scope of the Continued Safe Operation program is linked to the relevant AMP(s). The improved, but not finalized assessment method of ageing management for civil structures can be seen in figure 2. The proposed assessment method for ageing of civil structures has been tested, compared and improved. The results indicated that the method can be used to obtain a list of plant specific AMPs. The comparison of the list of relevant AMPs for a steel containment PWR, showed similar results. What is added to the assessment method is the link to the TLAAs for civil structures. The detailing to a level of practical work instructions for the maintenance of the plant has to be made in the near future. In the near future the step will be made from a high level of IGALL AMP to a practical AMP that will deal with the relevant mechanisms at the various locations. Therefore further steps are in studying of relevant degradation mechanisms, relevant AMPs (like AMP305 [9],AMP306 [10]) and applicable literature (e.g.[21]) in combination with the practical knowledge from operation of a reactor. The international developments on ageing management of concrete will be included. It is foreseen that the future report will contain information on concrete degradation mechanisms relevant for nuclear reactors. If findings requires calculations the assessment method will be verified with the finite element modelling techniques.
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de Haan - de Wilde, F. H. E., e M. J. Janssen. "An Update of the Assessment Methodology for Civil Ageing Management for LTO/CSO Based on International Standards and Engineering Judgement". In ASME 2021 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/pvp2021-61499.
Testo completoAbstract (sommario):
Abstract For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years in the coming years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures. Recent developments have shown that ageing of civil structures receive more attention internationally. In order to increase the knowledge in the field of civil structures, this paper focusses on investigation of ageing of civil structures and determining an ageing management strategy. Knowledge of the ageing mechanisms of civil structures and especially concrete, will lead to improvement of ageing management and assessment methods of concrete. As a first step international information was gathered on civil structures ageing issues and management thereof (see PVP2019-93029). In addition a highlevel assessment methodology was proposed. In the next step the initially proposed assessment methodology has been tested by application to a nuclear reactor. The resulting list of relevant AMPs has been verified with the outcome for another PWR with a steel containment. With this experience the assessment methodology is tested, compared and improved (see PVP2020-21838). The results indicated that the method can be used to obtain a list of plant specific AMPs. What was added to the assessment method is the link to the TLAAs for civil structures. In this follow up step the transition is made from a high level of IGALL AMPs to a practical AMPs that will deal with the right mechanism at the right location. The detailing to a level of practical work instructions for the maintenance of the plant has to be made in order to make real life implementation possible. In this step studying of relevant degradation mechanisms, relevant AMPs (like IAEA AMP305 and AMP306 ) and applicable literature in combination with the practical knowledge from operation of a reactor, has taken place. The international developments on ageing management of concrete will be included. The goal of the project is to obtain more knowledge on ageing management of civil structures and especially concrete. It will lead to an assessment method for civil ageing management and ageing management programs dealing with the relevant mechanisms at the various locations in a practical manner. The results of this ongoing work are presented in this report. For the research reactor all SSCs in scope of the Continued Safe Operation could be linked to the relevant AMP(s) and a resulting set of plant specific AMPs for civil ageing management was obtained. Including the international developments, literature and guidelines, a more general applicable list was created (Table 5 through Table 13). The conclusion is that Figure 2 represents a practical method for obtaining a set of plant specific civil AMPs ready for implementation. For representation in this paper the final outcome is given in as a generic list of actions for a generic reactor (Table 5 through Table 13). In these tables the relevant SSCs, ageing mechanisms and actions are listed. The tables represent an generic list of actions for civil ageing management that might others help develop their ageing management program. Future steps are shifting the focus from the general but practical assessment methodology to finite element modelling techniques for concrete. The assessment criteria for concrete (e.g. in ASME III, ASME XIII or Eurocode) will be investigated and investigation on the modelling of the concrete for ageing are planned.
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Honorio, T. "Numerical and analytical estimation of the ageing linear viscoelastic behavior of a two-phase composite with expansive inclusions". In 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures. IA-FraMCoS, 2019. http://dx.doi.org/10.21012/fc10.235550.
Testo completoRapporti di organizzazioni sul tema "Concrete Ageing"
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Baral, Aniruddha, Jeffrey Roesler, M. Ley, Shinhyu Kang, Loren Emerson, Zane Lloyd, Braden Boyd e Marllon Cook. High-volume Fly Ash Concrete for Pavements Findings: Volume 1. Illinois Center for Transportation, settembre 2021. http://dx.doi.org/10.36501/0197-9191/21-030.
Testo completoAbstract (sommario):
High-volume fly ash concrete (HVFAC) has improved durability and sustainability properties at a lower cost than conventional concrete, but its early-age properties like strength gain, setting time, and air entrainment can present challenges for application to concrete pavements. This research report helps with the implementation of HVFAC for pavement applications by providing guidelines for HVFAC mix design, testing protocols, and new tools for better quality control of HVFAC properties. Calorimeter tests were performed to evaluate the effects of fly ash sources, cement–fly ash interactions, chemical admixtures, and limestone replacement on the setting times and hydration reaction of HVFAC. To better target the initial air-entraining agent dosage for HVFAC, a calibration curve between air-entraining dosage for achieving 6% air content and fly ash foam index test has been developed. Further, a digital foam index test was developed to make this test more consistent across different labs and operators. For a more rapid prediction of hardened HVFAC properties, such as compressive strength, resistivity, and diffusion coefficient, an oxide-based particle model was developed. An HVFAC field test section was also constructed to demonstrate the implementation of a noncontact ultrasonic device for determining the final set time and ideal time to initiate saw cutting. Additionally, a maturity method was successfully implemented that estimates the in-place compressive strength of HVFAC through wireless thermal sensors. An HVFAC mix design procedure using the tools developed in this project such as the calorimeter test, foam index test, and particle-based model was proposed to assist engineers in implementing HVFAC pavements.
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Niesten, Hannelore. Taxation Policies, Processes, and Performances of Mobile Money Providers in Côte d’Ivoire. Institute of Development Studies, maggio 2024. http://dx.doi.org/10.19088/ictd.2024.030.
Testo completoAbstract (sommario):
This policy brief examines the effects of cumulative, specific 7.2 per cent taxes on mobile money (MM) service providers in Côte d’Ivoire. It assesses the unique tax framework, which deviates from the consumer-centric trend observed in many African countries, where end-users typically bear the burden. Initially targeting telecom companies, the tax expanded to encompass MM providers created by licensed telecom operators (Orange Money, MTN Money, and Moov Money) and, later, all companies providing MM operations. Concerns over potential investment declines persist, yet concrete evidence is absent. The data available suggests a decrease in MM turnover, partially due to lowered MM service prices, though telecom regulator reports note a lack of communication in MM revenue reporting. If specific taxes were reduced or abolished, the funds originally allocated could be reinvested, particularly to bolster agent commissions in rural zones, given the heightened competition between diverse payment service players in Côte d’Ivoire. The study emphasises the importance of a level playing field with other money transfer services provided by banks, local businesses, and fintech.
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Ucak-Astarlioglu, Mine, Jedadiah Burroughs, Charles Weiss, Kyle Klaus, Stephen Murrell, Samuel Craig, Jameson Shannon, Robert Moser, Kevin Wyss e James Tour. Graphene in cementitious materials. Engineer Research and Development Center (U.S.), dicembre 2023. http://dx.doi.org/10.21079/11681/48033.
Testo completoAbstract (sommario):
This project aims to determine the influence of laboratory-generated graphene (LGG) and commercial-grade graphene (CGG) on the chemical structure and compressive strength of graphene-cement mixtures. Determining the graphene-cement structure/processing/property relationships provides the most useful information for attaining the highest compressive strength. Graphene dose and particle size, speed of mixing, and dispersant agent were found to have important roles in graphene dispersion by affecting the adhesion forces between calcium silicate hydrate (CSH) gels and graphene surfaces that result in the enhanced strength of cement-graphene mixtures. X-ray diffraction (XRD), Raman, and scanning electron microscope (SEM) analyses were used to determine chemical microstructure, and compression testing for mechanical properties characterization, respectively. Based on observed results both LGG and CGG graphene cement mixtures showed an increase in the compressive strength over 7-, 14-, and 28-day age curing periods. Preliminary dispersion studies were performed to determine the most effective surfactant for graphene dispersion. Future studies will continue to research graphene—cement mortar and graphene—concrete composites using the most feasible graphene materials. These studies will prove invaluable for military programs, warfighter support, climate change, and civil works.