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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

Stanovení účinnosti zařízení Polymer Separation System Purifier N 1024 / Evaluation of Polymer Separation System Purifier N 1024 device efficiency

Duliková, Michaela January 2014 (has links)
In this Diploma Thesis the recycling of the PET bottles in the company PETKA CZ, a.s. is under focus. Thesis describes the Italian technology AMUT designed for physical recycling of the PET bottles. The primary goal is the quality of the final recycled product, PET flakes, particularly in the context of undesirable admixtures such as PVC, other polymers and impurities. Due to the deteriorating quality of the PET flakes the equipment Polymer Separation System Purifier N 1024 has been tested, which had significantly reduced admixtures in PET flakes. As it turned out, the current procedures for solving problems with the PET flakes quality are no longer sufficient.
62

Vliv částečné náhrady portlandského cementu diatomitovou zeminou na vybrané parametry cementových malt / Effect of partial replacement of Portland cement by diatomaceous earth on selected parameters of cement mortar

Rousková, Jana January 2016 (has links)
The subject of this thesis is selected parameters cement mortars with partial replacement of Portland cement diatomaceous earth. This work provides information on the basic properties of diatomaceous earth and its deposits with a focus on deposit in Borovany. From the properties is very important pozzolanic activity due to the high content of amorphous silica of this soil. The main use of diatomaceous earth is in the area filtration and is used widely as a nutritional supplement. In the building industry, diatomite can be applied as an admixture to mortar and concrete, where it can, with its abilities, improve some physical mechanical properties. In the experimental part was diatomaceous earth, in its raw and calcined form, tested as admixture for cement pastes and mortars. The main criterion for evaluating these composites was bulk density, flexural and compressive strength. It was also investigated mineralogical composition, microstructure, freeze–thaw resistance and sulfate resistance.
63

Sledování vlivu složení betonu na odolnost proti abrazi / Monitoring the influence of concrete composition on abrasion resistance

Černá, Hana January 2019 (has links)
This diploma thesis focuses on the resistance of concrete to abrasion with regard to the raw materials used for their production. In the theoretical part of the thesis are described admixtures, different types of aggregate and aggregate composition which influence the resistance of concrete to abrasion. In the experimental part, 15 different C30 / 37, S4 concrete formulations were proposed. Different types of aggregates - fecal gravel (Žabčice), biotic granodiorite (Olbramovice) and amphibolite (Želešice) have always been used in the recipes. Fine ground limestone, micro-silica, high-temperature fly ash and finely ground slag were ingredients that were added to the proposed recipes. Consistency was determined by the method of cone seating and the density of fresh concrete. In the hardened state, concrete density, compressive strength, bending tensile strength, tensile strength, watertightness, concrete absorption, and abrasion resistance were determined using the Böhm method and wide wheel method. The test specimens were tested after 7, 28, and 90 days of maturation.
64

Acceleratorers påverkan för sprutbetongens tidiga hållfasthet / Accelerators affect on the early strength of shotcrete

Berndtsson, Filippa, Suleyman Bal, Harun January 2019 (has links)
Vid underhållsarbeten av trafikerade tunnlar stängs trafiken av. Därav sker dessa arbeten oftast nattetid. För att kunna släppa på trafiken igen så snabbt som möjligt eftersträvas effektiva förstärkningsarbeten. Av säkerhetsskäl kan utökade hållfasthetskrav förekomma för sprutbetong som förstärkningsmetod. Om betongen hinner uppnå det krav som ställs för hållfastheten snabbare kan antal nätter som tillägnas förstärkningsarbeten reduceras. Detta examensarbete ska undersöka hur olika tillsatser av typen acceleratorer kan påskynda den tidiga hållfasthetsutvecklingen för sprutbetong. Utav de acceleratorer som utreds ska en slutsats kunna dras om dessa typer av tillsatser lämpar sig för förstärkningsmetoden våt sprutbetong. För att utreda acceleratorernas påverkan på sprutbetong har fullskaliga tester utförts. Vid testning sprutades olika betongrecept i testlådor. På lådorna kunde sedan hållfasthetstester utföras enligt gällande standarder. Testerna undersöker endast betongens tidiga hållfasthet, vilket blir en av arbetets avgränsningar. Resultatet av testerna visas i form av grafer och diagram. Därefter diskuteras metodernas osäkerhet och hur skiljande parametrar påverkar resultatet. Ur graferna kan en positiv effekt utläsas för recepten med tillsatt hållfasthetsaccelerator jämfört med recepten där endast sprutbetongaccelerator användes. Den positiva trenden syns tydligast inom de första fyra timmarna, efter detta framträder osäkerheten i mätvärdena. Slutsatser om acceleratorernas verkan för hela testet kan inte dras utan en statistisk hypotesprövning mellan de olika recepten. En sådan prövning utesluter om det statistiskt går att skilja resultaten åt. Dessutom rekommenderas företaget utföra mindre kompletterande tester på provkroppar i laborativ miljö, där skiljande parametrar kan elimineras och säkrare utdata erhållas. / During maintenance work in trafficked tunnels, the traffic must be halted. Therefore, such efforts often take place night-time. In order to enable a quick release of traffic again, it is crucial to have an effective reinforcement work. Due to the safety risks of using shotcrete as a reinforce method, there is a chance of adding additional strength-requirement can exist due to safety risks. If the concrete achieves the strength requirements sooner than expected, the number of nights dedicated to maintenance work can be reduced. This study intends to investigate how different types of admixtures, so called accelerators, can expedite the shotcrete’s initial strength development. Furthermore, the study will include a conclusion of the suitability for the accelerators that have been applied in the shotcrete. To investigate the effects of these accelerators, extensive tests has taken place. During these tests, shotcretes with different recipes were sprinkled into test boxes. Thereafter, tests of strength development could be performed on these boxes in agreement with prevailing standards. To delimitate the study, the selected methods only show the early strength-development of shotcrete. The results from these tests will be presented in graphs. Uncertainties regarding measurement data and how separated physical parameters affect the test results will be discussed as well. By reading the data presented in the graphs, a positive development can be identified in recipes with added hardening accelerators compared to recipes containing only shotcrete accelerators within the first four hours. Following the first four hours, a significant uncertainty in measurements will be noticed. Finally, due to high irregularity in measured values, conclusions of the accelerators’ effect cannot be confirmed solely by the results from these tests. Therefore, a hypothesis trial is necessary as it would exclude if the recipes statically can be separated. Furthermore, the company recommends performing additional small-scale tests in a laboratory environment. Through laboratory tests, a more certain result can be received.
65

Étude de la diversité des populations historiques de Montréal et de Québec par l’analyse de la morphologie dentaire : le cimetière catholique de la première église Notre-Dame (1691-1796) et le cimetière protestant Saint-Matthew de Québec (1771-1860)

B-Hardy, Marie-Hélène 12 1900 (has links)
Deux principaux événements colonisateurs ont apporté de nouvelles vagues de migration au Québec : La fondation de la Nouvelle France, de 1608 à 1763 et la conquête du territoire par les Britanniques après 1763. Afin d’étudier les différences et similarités entre ces dernières et les interactions possibles entre les migrants et les communautés locales déjà présentes sur le territoire, la morphologie dentaire, un outil permettant de proposer des interprétations d’ordre paléogénétique sur l’origine des populations passées, a été analysée pour les deux groupes suivants: 37 individus provenant du cimetière de la première église Notre-Dame à Montréal (1691-1796); et 61 individus provenant du cimetière de Saint-Matthew à Québec (1771-1860). À cette fin, le protocole de l’Arizona State University -Dental Anthropology System a été utilisé pour la collecte de données. La mesure moyenne de divergence et une analyse d’hétérogénéité des populations (Matrice R et Fst modifiés pour les données non-métriques) ont été ensuite calculées. Les valeurs de biodistance confirment que la majorité des individus observés pour les deux collections sont d’ascendance européenne. L’analyse intra-populationnelle a aussi permis d’identifier certains individus, probablement métis, qui s’approchent de la variation amérindienne. Il semble aussi, selon la matrice R et les valeurs Fst calculées pour les deux échantillons, que Notre-Dame est légèrement plus hétérogène et semble avoir incorporé une composante amérindienne un peu plus importante que Saint-Matthew, probablement par métissage, faisant suite, par exemple, à l’incorporation d’individus Amérindiens convertis dans les premières sociétés coloniales. Bien que nos résultats soient très préliminaires, la relation qu’ont entretenue ces deux populations d’origine européenne avec les populations locales, semble avoir varié au cours du temps, en fonction du contexte politique et économique des différentes vagues de migration européenne. Le degré de métissage plus élevé à Montréal au XVIIIe siècle qu’à Québec au XIXe siècle pourrait ainsi refléter un besoin plus pressant de la part des premiers migrants européens de se faire des alliés amérindiens en vue de la réussite du projet colonisateur. / Two colonisation events occurred in Quebec, from 1608 to 1763 (New France), and after 1763 (British Regime), providing new waves of immigrants. In order to examine differences and similarities between the latter waves and the possible interactions between the immigrants and the local communities already living on the territory, dental morphology, which allows us to propose paleogenetic interpretations on the ancestry of past populations, has been analysed for the following two groups: 37 individuals from the cemetery of the Première Église Notre-Dame in Montreal (1691-1796); and 61 individuals from the cemetery of Saint-Matthew in Quebec City (1771-1860). We used the Arizona State University’s -Dental Anthropology System protocol for the observation of dental traits. Mean measures of divergence and population heterogeneity analysis (R Matrix and Fst modified for non-metric data) were calculated. Biodistance values confirm that the majority of the analysed individuals from both collections were of European ancestry. However, intra-population analysis was able to identify certain individuals who were closer to Native American variation. Furthermore, results of R matrix and Fst tests showed that Notre-Dame sample was slightly more heterogeneous. It seemed to have incorporated more of a Native American component than Saint-Matthew, probably through admixture, which was a consequence of the assimilation of “Christianised” Native Americans within the early colonial society. Therefore, although our results are preliminary, interactions between Europeans and local groups seem to have changed through time as a result of colonisation. The higher levels of admixture in the 18th century Montreal (in comparison to the 19th century Quebec City) might reflect a rather urgent need from the first European migrants to set up alliances with Native Americans for the long-term viability of the colony.
66

Komparativna analiza osnovnih svojstava konstrukcijskih betona spravljenih sa različitim vrstama lakih agregata / A comparative analysis of the basic properties of structural concrete made with different types of lightweight aggregates

Lukić Ivan 09 April 2015 (has links)
<p>U disertaciji su prikazani rezultati sopstvenog eksperimentalnog istraživanja na osnovu kojih je izvršena komparativna analiza uticaja različitih vrsta lakih agregata i vrste i količine cementa na osnovna fizičko-mehanička svojstva lakoagregatnih betona. Takođe, analizirana je i mogućnost zamene dela cementa mineralnim dodacima u cilju smanjenja negativnih uticaja proizvodnje betona na životnu sredinu. Rezultati su pokazali da je primenom svih analiziranih vrsta agregata moguće dobiti konstrukcijski lakoagregatni beton, čak i sa manjim količinama cementa, odnosno sa zamenom dela cementa mineralnim dodacima, kao i da je moguće uspostaviti pouzdane korelacione veze između pojedinih svojstava betona i primenjenih komponentnih materijala.</p> / <p>In dissertation are presented results of own experimental research of a<br />comparative analysis of the impact of different types of lightweight<br />aggregates and the type and quantity of cement on basic physical and<br />mechanical properties of structural lightweight concrete. Also, the possibility<br />of replacing part of cement with mineral admixtures is analyzed in order to<br />reduce the negative impact of concrete production on the environment. The<br />results showed that it is possible to obtain structural lightweight aggregate<br />concrete with all types of lightweight aggregates and even with lower<br />quantities of cement or with a replacement of part of a cement with mineral<br />admixtures. Also, it is possible to establish a reliable correlation between<br />certain properties of concrete and used component materials.</p>
67

L’impact du séchage au jeune âge sur la carbonatation des matériaux cimentaires avec additions minérales / The impact of drying at the early age of the carbonation cementitious materials with mineral admixtures

Bertin, Matthieu 27 November 2017 (has links)
De nos jours, l’utilisation de liants à faible teneur en clinker est de plus en plus courante. Or la cinétique de réaction des additions minérales utilisées est plus lente que celle du clinker. Si les conditions de cure ne sont pas adaptées, le matériau aura une structure poreuse plus importante, ce qui le rendra plus sensible à la pénétration des agents agressifs extérieurs comme le CO2 ou les Cl-. La carbonatation du béton est l’un des principaux phénomènes pouvant diminuer la durée de vie d’une structure en béton armé. En effet, elle entraine une diminution du pH de la solution interstitielle qui a pour conséquence une dépassivation des armatures, puis la corrosion de ces dernières si les conditions s’y prêtent.L’objectif de cette thèse est d’étudier l’impact de la carbonatation au jeune âge sur des liants à faible teneur en clinker. Pour cela l’étude se compose de deux aspects : le premier est l’étude de l’impact de l’hydratation et de la carbonatation sur les propriétés de transport et les isothermes de sorption hydrique, et le second est l’étude de l’impact du couplage hydratation-séchage-carbonatation sur la microstructure et la structure poreuse. Pour le premier aspect, les propriétés de transport étudiées sont la diffusion de l’O2, la diffusion de la vapeur d’eau, la perméabilité à l’eau liquide qui sont des données d’entrée dans les modèles de carbonatation ainsi que la perméabilité aux gaz qui est un indicateur de durabilité. Pour le second aspect, l’impact du couplage est mesuré par ATG et DRX pour déterminer l’assemblage de phases, de plus de la porosimétrie par intrusion de Mercure et des pesées hydrostatiques sont effectuées pour détecter le changement de la structure poreuse. Les matériaux étudiés sont des pâtes de ciment et des bétons avec un rapport eau/ liant de 0,57 avec l’un des trois liants suivants : CEM I, CEM I +30% de cendres volantes et CEM I +60% de laitiers.Pour le premier aspect, les résultats montrent que pour les pâtes de CEM I le temps de cure a un faible impact sur les isothermes de sorption de vapeur d’eau s’il est compris entre 3 jours et 6 mois. Alors que, pour les pâtes de CEM I + 60% de laitier, l’augmentation du temps de cure accroit significativement la teneur en eau (pour HR=65%, tcure=3 jours et pour tcure=6 mois ) dû à une augmentation de la teneur en C-S-H. D’autre part, la carbonatation entraine une diminution de la teneur en eau de l’échantillon, ainsi que l’amplitude de l’hystérésis. De plus, le gel a une porosité plus grossière. Par ailleurs, la carbonatation entraine une augmentation de la perméabilité aux gaz des matériaux. Pour le second aspect, les résultats montrent que l’utilisation d’additions minérales diminue la résistance à la carbonatation du matériau et que cette résistance augmente avec le temps de cure si l’échantillon contient des additions. La carbonatation de la portlandite, des C-S-H et des aluminates est concomitante. De plus, pour les matériaux aux laitiers, les résultats montrent qu’ils sont plus sensibles à la carbonatation des C-S-H et des aluminates que les CEM I. En effet quand le rapport variation molaire de CaCO3 sur variation molaire de Portlandite est calculé, il vaut 1.8 pour le CEM I et environ 3.5 pour les matériaux aux laitiers. Enfin, la carbonatation entraine une diminution du degré de saturation de l’échantillon. En effet, le degré de saturation à la surface de l’échantillon passe de 50% à 35% après carbonatation pour les échantillons de CEM I et de 50% à 5% pour les échantillons de CEM I + 60% de laitiers. Cette diminution peut s’expliquer par la diminution de la surface spécifique qui est divisée par 2 après carbonatation due à la décalcification des C-S-H. Même si la carbonatation entraine une diminution de porosité cette dernière est trop faible dans ce cas pour contrer cet effet / Nowaday, low clinker content binders are used more and more often. But the kinetics reactions of the supplementary cementitious materials (SCM) are slower than this one of clinker. If the curing conditions are not adapted, material will have a bigger pore structure and becomes more sensitive to the ingress of aggressive species from the environment like the CO2 or Cl-. Carbonation is one of main phenomena which can lead to decrease the life time of reinforced concrete structure. Indeed, it leads to a decrease of pore solution pH which leads to the depassivation of rebar. Then these rebars can be corroded if the conditions are appropriate.The aim of this thesis is to study the impact of carbonation at early age for binder with a low clinker content. This study was composed of two aspects: the first one is focus on the impact of hydration and carbonation on the transport properties and the water vapour sorption isotherms (WVSI), and the second one is focus on the impact of coupling hydration – drying-carbonation on the microstructure and the pore structure. For the first aspect, the studied transport properties was O2 diffusivity, water vapour diffusivity, water liquid permeability which are inputs for carbonation modelling and the intrinsic gas permeability which is a durability factor. For the second aspect, the coupling impact was measured by TGA and DRX to determine the phase assemblage; moreover Mercury intrusion porosimetry (MIP) and hydrostatic weigh were carried out to measure the change in the pore structure. The studied materials were cement pastes and concretes with water to binder ratio of 0.57 with one of the following binders: CEM I, CEM I +30% PFA and CEM I + 60% GGBS.For the first part, results show that a curing time between 3 days and 6 months has a low impact on the WVSI for the CEM I paste. Whereas, in the CEM I +60% GGBS paste, when the curing time increases, the water content increases (for a RH=65%, tcuring=3 days and for tcuring=6 months ), this is due to the increase of the C-S-H content. Moreover, carbonation leads to decrease the water content and the hysteresis becomes flat. Additionally, carbonation leads to increase the intrinsic gas permeability. For the second part, the results show that the use of SCM decreases the carbonation resistance and this resistance increases with the curing time. Carbonation of Portlandite, C-S-H and aluminates occurs in the same time. Moreover, the CEM I +60% GGBS paste are more sensitive to the carbonation of C-S-H and aluminates than the CEM I paste. Indeed, the molar variation of CaCO3 to the molar variation of Portlandite ratio has a value around 3.5 for the CEM I +60% GGBS and 1.8 for the CEM I. Finally, carbonation leads to decrease the water saturation degree at the surface of sample. Indeed, the degree of saturation at the surface of the sample increases from 50% to 35% after carbonation for the CEM I paste and from 50% to 5% for the CEm I +60% GGBS paste. This decrease can be explained by the decrease of the BET specific surface which is divided by 2 after carbonation. It is due to the decalcification of C-S-H. Although carbonation leads to a decrease of porosity, this one is too small in this case to counter this effect
68

Méthodes de factorisation matricielle pour la génomique des populations et les tests d'association / Matrix factorization methods for population genomics and association mapping

Caye, Kévin 11 December 2017 (has links)
Nous présentons des méthodes statistiques reposant sur des problèmes de factorisation matricielle. Une première méthode permet l'inférence rapide de la structure de populations à partir de données génétiques en incluant l'information de proximité géographique. Une deuxième méthode permet de corriger les études d'association pour les facteurs de confusion. Nous présentons dans ce manuscrit les modèles, ainsi que les aspects théoriques des algorithmes d'inférence. De plus, à l'aide de simulations numériques, nous comparons les performances de nos méthodes à celles des méthodes existantes. Enfin, nous utilisons nos méthodes sur des données biologiques réelles. Nos méthodes ont été implémentées et distribuées sous la forme de packages R : tess3r et lfmm. / We present statistical methods based on matrix factorization problems. A first method allows efficient inference of population structure from genetic data and including geographic proximity information. A second method corrects the association studies for confounding factors. We present in this manuscript the models, as well as the theoretical aspects of the inference algorithms. Moreover, using numerical simulations, we compare the performance of our methods with those of existing methods. Finally, we use our methods on real biological data. Our methods have been implemented and distributed as R packages: tess3r and lfmm.
69

Evaluating reactivity and sorptivity of fly ash for use in concrete construction

Islam, G. January 2012 (has links)
This thesis describes research carried out to investigate techniques for (i) rapidly assessing the reactivity of fly ash; and (ii) evaluating its interaction with air-entraining admixtures (AEAs), both with regard to use in concrete. The materials considered for the project included, 54 fly ashes from 8 UK sources, and an additional three materials from Bangladesh, covering a range of fineness, loss-on-ignition (LOI) and production conditions (run-of-station, carbon removed, air-classified, co-combustion, oxy-fuel technology); Portland Cements (PCs) from five UK sources with various properties (strength classes 32.5 R, 42.5 N and 52.5 N); laboratory grade hydrated and quick limes; and three commercial AEAs and a standard laboratory grade reagent (surfactant). The research examining fly ash reactivity considered activity index tests to BS EN 450 (BSI, 2005c) as the reference and investigated tests covering fly ash properties/providing measures of fly ash behaviour to rapidly assess this. These included (i) fly ash fineness (45 µm sieve residue, or LASER particle size distribution (PSD) parameters), LOI and flow properties; (ii) accelerated curing of PC and lime-based mortars (iii) lime consumption by fly ash when combined with PC in paste or suspension (Frattini) or from a saturated lime solution; (iv) various measures of fly ash chemical composition (based on oxide/mineralogical analysis); and (v) a quicklime slaking test. The test results were validated by strength tests with 100 mm concrete cube. Results of the above indicated good correlations between fly ash fineness, mortar flow/water requirement and (pozzolanic) activity index (standard or accelerated curing). However, fly ash reactivity and fresh properties appeared to be influenced by the properties of the test PC (e.g. chemical composition and fineness) and there is a need to take this into account during assessment. Generally, finer fly ashes gave better flow; however, there is an optimum fineness (d90 ~40 µm) for best performance, and which is similar to the fineness of the test PC. Strong correlations between the accelerated and standard cured PC-based mortar indicate the latter can be used to estimate the former taking account of the fly ash properties. In view of eliminating the effect of PC properties on reactivity, mortar tests with laboratory grade hydrated lime suggested potential for this. However, for better assessment, this approach requires further work to address issues relating to slower rates of strength gain and increased time requirements, although high temperature conditions were used for curing. Measuring Ca(OH)2 consumption from fly ash/PC paste or suspension agreed with the behaviour in mortar, but needs special instruments (e.g. TGA or XRF). A similar approach with saturated lime did not work well, despite several measures being taken to try and improve this. The oxide and mineralogical analysis results of fly ash did not give good correlations with activity index, but improved when a factor combining them with fineness was considered. The test results were validated in concrete and with air-classified fly ashes from single sources which gave clear trend/behaviour. The lime slaking test was found to be ineffective for identifying fly ash reactivity. The reactivity assessment results were validated by carrying out concrete strength tests. In general, more consistent trends were obtained for fly ash from single source as noted with mortar earlier. Methods adopted/developed to assess the interaction of fly ash with AEA included (i) the foam index test; (ii) acid blue 80 (AB80) dye adsorption test (spectroscopic method); and (iii) methylene blue test. High variability in foam index test results between different operators were noted, which reflected differences in the degree of shaking applied and difficulties in identification of the test end point. Adoption of an automatic shaker and determination of suitable test conditions reduced this by more than 50%. Reliable test procedures were also established for the AB80 dye adsorption method. The results obtained from these tests gave very good correlations with fly ash specific surface area and the AEA dose required (both with commercial AEAs and standard reagent) for achieving target air contents in mortar and concrete. The methylene blue dye test also gave good correlations with these parameters, but was less effective for low LOI fly ashes. Between laboratory tests were carried out at three UKQAA members and considered, LOI, fineness (45 µm sieve and LASER PSD), and activity index. The results gave good agreement with those obtained at the Concrete Technology Unit for this work and again emphasized the role of fly ash fineness on its reactivity. Overall, fly ash fineness was found to be the best means of rapidly assessing its reactivity. Some of the other methods considered gave promising behaviour but require further refinements. Therefore, it is suggested that in addition to 45 µm sieve residue, other types of fineness measurement (e.g. sub 10 µm quantities, d50 and d90) can be considered suitable alternatives to activity index. Similarly, foam index tests with the automatic shaker or the AB80 test method could both be used as fly ash physical requirement tests, or in production control for air-entrained concrete.
70

Mitigação da retração autógena em concretos de alta resistência contendo aditivo redutor de retração e seus efeitos na macro e microestrutura / Mitigation of autogenous shrinkage in high strength concrete using shrinkage-reducing admixture and its macro and microstructural effects

Lopes, Anne Neiry de Mendonça January 2011 (has links)
O desenvolvimento do concreto de alta resistência - CAR foi um importante avanço na tecnologia de concreto, entretanto, a despeito de suas inúmeras vantagens como material estrutural, o seu emprego tem sido limitado, por ter se revelado mais susceptível à fissuração nas primeiras idades. Isto se deve à ocorrência do fenômeno da retração autógena, particularmente mais intenso nestes concretos que nos de resistência normal, uma vez que no CAR, há significativamente maior quantidade de material cimentício e menor quantidade de água, o que dá origem a uma estrutura porosa muito refinada logo nas primeiras idades, gerando altas magnitudes de tensões capilares. Além do estudo sobre o entendimento do fenômeno, as pesquisas atualmente têm buscado formas de mitigá-lo a fim de contribuir para estruturas mais duráveis. Diante do exposto, esta pesquisa investigou o comportamento do CAR, no tocante às propriedades mecânicas, elásticas e viscoelásticas e à durabilidade, quando empregado um aditivo redutor de retração - ARR que pode se configurar como estratégia mitigadora para a redução da retração autógena, bem como verificar a sua influência sobre a microestrutura e hidratação da pasta de cimento. Os resultados indicam que o ARR é eficaz na redução da retração autógena e retração por secagem, sem alterar de forma relevante as propriedades mecânicas e elásticas: a resistência à compressão sofre uma pequena queda de 5% com o uso de 2% de ARR em relação ao concreto referência, contudo, as demais propriedades não são alteradas com o uso do ARR. Quanto ao efeito sobre a fluência, não se obtiveram resultados conclusivos. A durabilidade, medida pelos ensaios de penetrabilidade a íons cloretos, permeabilidade à água, carbonatação natural e absorção capilar e por imersão, não é comprometida com a incorporação do aditivo redutor de retração. Do ponto de vista microestrutural, observou-se que o ARR altera o volume total de poros, embora de uma forma não muito expressiva; e ainda constatou-se que este aditivo afeta a velocidade de hidratação das pastas de cimento, e que possivelmente interage com compostos de hidratados da pasta, sem, no entanto, alterar as características macroestruturais do material. / The development of high strength concrete - HSC represented an important advance in concrete technology. However, even knowing that this kind of concrete has several advantages as a structural material, its application is limited by the early ages cracking. This occurrence is due to the autogenous shrinkage phenomenon, once HSC has a greater amount of cementitious material and a lower amount of water in relation to a normal-strength concrete. This condition implies in a greatly refinement of pore structure at early ages which lead to a higher magnitudes of capillary tension than the one observed in a normal-strength concrete. Beyond to study the phenomenon, much research has been conducted in many countries in order to reduce autogenous shrinkage and contribute to more durable structures. So, this research aims to investigate the effectiveness of shrinkage-reducing admixtures – SRA in decreasing the autogenous shrinkage of HSC, and mainly, verify its influence on viscoelastic, elastic and mechanicals properties and durability. The effect of SRA on microstructure and on the cement paste hydration was also investigated. The results show that SRA is effective in reducing the autogenous shrinkage and drying shrinkage without remarkable changes in elastic and mechanical properties. There were not conclusive results related to the creep property. The concrete durability under the action of aggressive agents (such as water, CO2 and chloride) was not influenced by the SRA, information provided by the results of chloride penetration, natural carbonation, water permeability, capillary absorption and absorption of water tests. In a microstructural point of view, it was observed that the addition of SRA results in a small rise in total pore volume. Besides, the results suggest that the SRA affects the rate of cement hydration and it can interact to the hydrated products of paste without implying in great influences on the macrostructural characteristics of the material.

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