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Correlating Self-Consolidating Concrete mixture composition to its rheological propertiesOdeh, Joud January 2018 (has links)
Self-Consolidating concrete (SCC), a highly flowable concrete, is gaining wide acceptance in the concrete industries due to a higher productivity, lower energy consumption, improved working environment and increase quality. SCC is susceptible to segregation and therefore a balance between flow-ability and stability is required. The absence of a comprehensive SCC mixture composition design guidelines merits investigating the effects of SCC mixture variables on the properties affecting its performance, namely flow and stability.
An experimental and analytical study were carried out to study the influence of 5 design variables, namely water to binder ratio (w/b), percent addition of silica fume (SF), percent addition of Ground Granulated Blast Furnace Slag (GGBFS), bulk volume of coarse aggregates and binder content, on the workability and rheology of SCC. Workability measurements, specifically the slump flow, T50, L-Box and segregation column, and rheological properties, namely plastic viscosity, yield stress, and thixotropy were measured to evaluate SCC’s performance. A revised modified Bingham model was proposed to adequately account for the linear and non-linear responses of the concrete flow. It postulates that the flow is divided into a linear and non-linear part. The revised model is found to provide more consistent and precise estimate of the rheological properties. Using regression analyses, yield stress and plastic viscosity models that account for the statistically significant variables were derived from experimental test data. Yield stress is found to depend on the bulk volume fraction of the coarse aggregate, Silica Fume content, High Range Water Reducing Agent (HRWRA) and Viscosity Modifying Agent (VMA), and plastic viscosity on w/b, HRWRA and Average Paste Thickness (APT). / Thesis / Master of Applied Science (MASc)
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Performance des bétons autoplaçants développés pour la préfabrication d'éléments de ponts précontraints / Performance-based specifications of self-consolidating concrete designated for precast/prestressed bridge girder applicationsLong, Wu Jian January 2008 (has links)
In the precast construction market, the competitive situation is significantly affected by price, cost, productivity, and quality factors. Since self-consolidating concrete (SCC) was first introduced to the concrete industry in the late 1980s, it has been used worldwide in variety of applications. Despite the documented technical and economic advantages of SCC in precast, prestressed applications, the use of SCC has been limited in some countries due to some technical uncertainties of such innovative material. To explore some unsolved issues related to SCC and to contribute to a wider acceptance of SCC in precast, prestressed applications, this study was undertaken to assess the effect of mixture proportioning and material characteristics on the performance of SCC and recommend performance-based specifications for use of SCC in the precast, prestressed applications. The thesis presents an experimental program that contains four parts: (1) a parametric study to evaluate the influence of binder type, w/cm, coarse aggregate type, and coarse aggregate nominal size on the modulus of elasticity and compressive strength developments; (2) a parametric study to evaluate the effect of mixture proportioning and material characteristics on fresh and hardened properties of SCC; (3) a fractional factorial design to identify the relative significance of primary mixture parameters and their coupled effects on SCC properties; and (4) a field validation using full-scale AASHTO Type II girders cast to investigate constructability, material properties, and structural performance (the latter part was carried out by the research team of Professor Denis Mitchell at McGill University). Based on the experimental test results, SCC exhibits similar compressive strength and modulus of elasticity to that of conventional high-performance concrete (HPC) of normal slump consistency. SCC and HPC mixtures made of a given binder type exhibit similar autogenous shrinkage. However, SCC exhibits up to 30% and 20% higher drying shrinkage and creep, respectively, at 300 days compared to HPC made with similar w/cm but different paste volume. The results of the experiment program show that among the investigated material constituents and mix design parameters, the w/cm has the most significant effect on mechanical and visco-elastic properties. The binder content, binder type, and sand-to-total aggregate ratio (S/A) also have considerable effect on those properties. The thickening-type viscosity modifying admixture (VMA) content (0 to 150 ml/100 kg CM) does not significantly affect mechanical and visco-elastic properties. Based on the findings, some mixture parameters regarding the overall performance of SCC designated for precast and prestressed applications can be recommended: SCC made with relatively low w/cm (such as 0.34 vs. 0.40) should be selected to ensure desirable compressive strength, modulus of elasticity (MOE), flexural strength, as well as less drying shrinkage and creep; the use of crushed aggregate with 12.5 mm MSA is suggested since it provides better mechanical properties of SCC compared to gravel; the use of low S/A (such as 0.46 vs. 0.54) to secure adequate mechanical and visco-elastic properties is recommended; the use of thickening-type VMA can help to secure robustness and stability of the concrete in the case of SCC proportioned with moderate and relatively high w/cm; and the use of Type MS cement can lead to lower creep and shrinkage than Type HE cement and 20% Class F fly ash. However, SCC mixtures made with Type HE cement and 20% Class F fly ash can result in better workability and mechanical properties. Therefore, it is recommended to use Type HE cement and 20% Class F fly ash and reduce binder content (such as 440 kg/m[exposant 3] vs. 500 kg/m[exposant 3]) to assure better overall performance of SCC. Validation on full-scale AASHTO-Type II girders using two HPC and two SCC mixtures show that girders casting with SCC can be successfully carried out without segregation and blocking for the selected optimized mixtures. The surface quality of the girders cast with SCC is quite satisfactory and of greater uniformity than girders cast with HPC. Both HPC and SCC mixtures develop similar autogenous shrinkage for mixtures made with similar w/cm. Again, the two evaluated SCC mixtures develop about 20% greater drying shrinkage than comparable HPC mixtures. Modifications of existing models to assess mechanical and visco-elastic properties of SCC used in the precast, prestressed applications are proposed. Based on the comparisons of various code provisions, the ACI 209 and CEB-FIP codes with suggested material coefficients can be recommended to estimate compressive strength. The modified AASHTO 2007 model can be used for predicting the elastic modulus and flexural strength. The AASHTO 2004 and 2007 models with suggested material coefficients can be used to estimate drying shrinkage and creep, respectively. The CEB-FIP 90 code model can be used to predict both drying shrinkage and creep. Finally, the modified Tazawa and Miyazawa 1997 model with material modifications can be used to estimate autogenous shrinkage of SCC.
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Friskvård på arbetsplatsen : -medarbetarens inställning till friskvårdJonsson, Helene, Wagner, Nina January 2008 (has links)
<p><p> </p><p> </p><p> </p></p><p><p><strong><p>Sammanfattning</p></strong><p>Syftet med denna uppsats var att belysa hur fenomenet friskvård på en arbetsplats uppfattas av enskilda individer och vilken betydelse det kan få med avseende på såväl hälsan som välbefinnandet i stort. Utifrån denna fråga ville vi även se om det fanns skillnader i upplevelser av friskvård i de olika yrkeskategorierna från arbetsledning till arbetstagare. Inställningen till friskvård som prevention på en arbetsplats och vardagsmotion för den enskilde individen är individuell. En del människor varken vill eller tror sig kunna utöva friskvård och håller sig friska ändå. Den empiriska undersökningen bygger på kvalitativ metod. Vi har genomfört en intervjuundersökning med sju intervjupersoner från olika yrkeskategorier vilka har bidragit med sina tankar kring friskvården. Vi har använt oss av Antonovsky teori KASAM. Intervjuerna har tolkats enligt hermeneutiska principer. Resultaten visar bland annat att friskvård är betydelsefull på många sätt för medarbetare. Friskvård handlar om så mycket mer än fysisk aktivitet.</p><em><em><p> </p></em><em><p> </p></em><p> </p></em> </p></p>
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Pasta de gesso com incorporação de resíduo de gesso e aditivo retardador de pega / Gypsum plaster with gypsum residue incorporation and setting retardant additiveTrovão, Ana Paula Milagres 10 August 2012 (has links)
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Previous issue date: 2012-08-10 / The use of plaster in civil construction generates a large amount of waste, but it is a material that posses properties that makes it a highly competitive product. The main cause of the generation of this waste is the rapid hardening of the pastes. The incorporation of waste gypsum into the gypsum pastes results in an acceleration of the hardening process, which might increase the volume of residues generated. This dissertation aimed to develop procedure to incorporate the gypsum residue into plaster pastes without compromising the paste mechanical properties and, especially without accelerating its hardening process. Tests have been developed to evaluate the plaster pastes setting time, consistency, workability and temperature reading in the plaster pastes in the fresh state and evaluate the hardness and axial compressive strength in the hardened state. Tests results showed the viability of the incorporation of 5% gypsum waste in substitution of gypsum in the plaster paste when combined with borax retardant additive, which promoted extension of the workable time of the paste and an increase in the pastes mechanical properties / A utilização do gesso pela construção civil gera um grande volume de resíduos, no entanto é um material que apresenta propriedades que o torna altamente competitivo no mercado. A principal causa da geração desse resíduo é o rápido endurecimento das pastas. A incorporação de resíduo de gesso às pastas provoca a aceleração no processo de endurecimento, podendo aumentar ainda mais o volume de resíduos gerados. Essa dissertação teve como objetivo buscar a forma de incorporação do resíduo às pastas de gesso para revestimento de parede, sem comprometer suas propriedades mecânicas e principalmente não acelerar seu endurecimento. Foram realizados os ensaios de tempo de pega, consistência, consistência útil e leitura de temperatura nas pastas em seu estado fresco além dos ensaios de dureza e compressão axial destas no estado endurecido. Os ensaios apontaram a viabilidade da incorporação de 5% de resíduo de gesso em substituição do gesso quando associado ao aditivo retardador bórax, que promoveu ampliação do tempo de utilização da pasta e o aumento nas propriedades mecânicas ensaiadas
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Comportements rhéologique, Ouvrabilité et Durabilité des Mortiers à Base de Résine Epoxyde / Rheological behavior, Workability and Durability of Mortars Based on Epoxy ResinBourguiba, Amal 05 November 2016 (has links)
Cette étude concerne le comportement de mortiers constitués par une matrice résineuse à base d’époxyde désignés dans ce qui suit par mortier de résine, MR.Des études antérieures ont montré que l’ouvrabilité des MR élaborés avec un taux de polymère en masse mp≤12%, afin de baisser leur coût considéré élevé par comparaison à celui des mortiers hydrauliques MH, est médiocre et constitue un frein majeur au développement de ces matériaux dans le domaine de la préfabrication et de la réparation.Un moyen de favoriser le développement des MR consiste, donc, à faciliter leur mise en œuvre. Or le fait de diminuer le taux de polymère afin de diminuer le coût rend la mise en œuvre du mortier encore plus difficile. Par ailleurs l’utilisation de sable recyclé « SR » en substitution au sable naturel « SN »pour répondre à des exigences environnementales en matière d’épuisement de ressources naturelles exacerbe cette difficulté.L’objectif de cette thèse est, donc, de trouver un diluant à incorporer dans les formulations des MR, destinées soit à la préfabrication (2 formulations avec des taux massique de liant à base d’époxyde mp= 9% et 12%) ou à la réparation (mp= 20%). Le but ultime consiste à améliorer leur ouvrabilité tout en assurant leurs propriétés mécaniques et leur durabilité vis-à-vis de la diffusion des ions chlorure. Une comparaison systématique avec des mortiers hydrauliques, MH, est réalisée.Différents diluants ont été sélectionnés. Leur influence sur le point de gel, sur le temps de réticulation et sur les propriétés mécaniques et physiques des époxydes a fait l’objet d’une étude détaillée. Il en ressort que l’octanoate de méthyle permet de diminuer la viscosité de la résine époxyde sans affecter le point de gel et les cinétiques de durcissement de façon significative. Cependant, il joue un rôle de plastifiant à l’origine de l’augmentation de la ductilité et de la diminution des résistances et des rigidités des époxydes à l’état réticulé. Le taux optimal de diluant (md) à incorporer dans la formulation des mortiers de résine a été estimé à 5%.L’incorporation du diluant, avec md= 5%, dans les MR a amélioré leur ouvrabilité, modifié leur microstructure et leurs propriétés de transfert mais a généré une baisse des résistances mécaniques. En effet une baisse de 31% est observée pour MR-SN formulé avec mp= 20%. La substitution du SN par le SR dans les mortiers de réparation (MR avec mp= 20%) engendre, également, une diminution des propriétés mécaniques et une modification des propriétés rhéologiques. Toutefois, ces résistances mécaniques demeurent nettement plus élevées que celles des mortiers hydrauliques à sable naturel (MH-SN) et recyclé (MH-SR). En compression, le mortier MR-SR fabriqué avec mp=20% présente une résistance supérieure de 44% par rapport à celle du MH-SN et de 53% par rapport à celle du MH-SR.La résistance des mortiers à la diffusion des ions chlorure a été appréhendée par un essai de migration en régime transitoire (Non Steady State Migration) et le coefficient de diffusion apparent Dnssm a été calculé pour 10 formulations de mortiers : 1 MH-SR, 1 MH-SN, 2 MR-SR et 6 MR-SN. Il en ressort que les bétons de résine ont une résistance à la diffusion des ions chlorure nettement plus élevée que celle des mortiers hydrauliques. Les coefficients Dnssm des mortiers MH-SN et MH-SR sont respectivement 100 et 200 fois plus élevés que celui du MR-SN (mp= 20%).Le mortier MR-SN destiné à la réparation (avec mp= 20% et md=5%) est caractérisé par une très bonne ouvrabilité et des résistances mécaniques et à la diffusion des ions chlorure les plus élevées. On montre que son adhérence à un support constitué d’un MH-SN dépend de l’état de surface du support (lisse sec, lisse saturé, rugueux sec et rugueux saturé). Le mortier de réparation n’adhère pas aux supports à surface saturée en eau alors qu’une bonne adhérence est observée pour les surfaces sèches. Cette adhérence est meilleure lorsque la surface est lisse. / This study concerns the behavior of mortars constituted by epoxy-based resinous matrix and sand designated in what follows by resin mortar, RM.Previous studies have shown that the workability of RM made with a polymer rate by weight mp≤12% in order to reduce their cost which is considered high compared to that of hydraulic mortars HM, is poor and is a major obstacle to the development of these materials in the area of prefabrication and repair. However decreasing the polymer content to reduce the cost makes the mortar implementation even more difficult. Furthermore the use of recycled sand "RS" to substitute natural sand "NS" to answer environmental requirements regarding natural resource depletion exacerbates this difficulty.The objective of this work is, therefore, to find a thinner to incorporate into RM formulations, intended either to prefabrication (2 formulations with mass rate of epoxy based binder mp= 9% and 12%) or repair (mp = 20%). The ultimate goal is to improve their workability while maintaining their mechanical properties and their sustainability to chloride ion diffusion. A systematic comparison with hydraulic mortars, HM, is performed.Various thinners were selected. Their influence on the gel point, on the time of crosslinking and mechanical and physical properties of the epoxy resin has been the subject of detailed study. It shows that methyl octanoate reduces the viscosity of the epoxy resin without affecting significantly the gel point and curing kinetics.However, it acts as a plasticizer which represents the origin of the increased ductility and reduced resistance and rigidity of the epoxy resin in the cured state.The optimal rate of the thinner (md) to be incorporated in the formulation of resin mortar was estimated at 5%.The incorporation of thinner, with md=5% in the RM improved their workability, changed their microstructure and their transfer properties but generated lower mechanical strength. Indeed a decrease of 31% was observed for RM-NS formulated with mp=20%. The substitution of NS by the RS in repair mortars (RM with mp=20%), leads also, to decreased mechanical properties and modified rheological ones.However, these strengths remain significantly higher than those of hydraulic natural sand (HM-NS)and recycled (HM-RS) mortars. In compression, the RM-RS mortar manufactured with mp=20% has a higher resistance by 44% compared to the HM-NS and 53% compared to that of HM-RS.The resistance of mortars to chloride ions diffusion was apprehended by non Steady state migration test and apparent diffusion coefficient "Dnssm" was calculated for 10 mortar formulations: 1 HM-RS, 1 HM-NS, 2 RM-RS and 6 RM-NS. It follows that the resin concrete has a resistance to chloride ions diffusion considerably higher than that of hydraulic mortars. The "Dnssm" coefficients of HM-NS and HM-RS mortars are respectively 100 and 200 times higher than that of RM-NS (mp= 20%).The RM-NS mortar intended for repair (with mp=20% and md=5%) is characterized by very good workability and the highest mechanical strength and resistance to chloride ions diffusion. We show that adhesion to a support consisting of a HM-NS depends on the surface condition of the support (smooth dry , smooth saturated, rough dry and rough saturated). The repair mortar does not adhere to the surface saturated on water while a good adhesion was observed for dry surfaces. This adhesion is better when the surface is smooth.
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Övergångarnas Dilemma : En uppsats om kvinnors underrepresentation i andelen övergångar ifrån Samhall AB till den reguljära arbetsmarknaden / Transitional Difficulties : An essay about the factors behind female under representation in transitions from Samhall AB to the Swedish labour marketJonsson, Robin January 2008 (has links)
<p>With the ambitions to rehabilitate individuals with different kinds of work disabilities through work, the government owned Samhall AB has a long history as labour market measure in Sweden.</p><p>To show Samhall AB its importance, the company has requirements to fulfill the goal that around 5 percent of their employees, at Samhall AB, every year shall be transferred to an employment outside the company, which is called transition. Unfortunately since this goal was introduced it also created several dilemmas. One dilemma is the long lasting female under representation in transitions from Samhall AB to the regular labour market.</p><p>The essays main task is to investigate the factors behind the female under presentation in transition from Samhall AB through a genus perspective and by using quantitative and qualitative method.</p><p>The main conclusions are that female under representation in transitions from Samhall AB are basically caused by structural factors. Samhall AB’s strong industrial tradition and particularly the strong segregation between female and males on the regular Swedish labour market may inhibit females in their transitions. It also seems that Samhall AB has problems with transitions to the public service which bear a large female work force and probably is an important factor that inhibits female transitions. Even wages and employment may effect female representations in transitions. Typical female jobs on the regular labour market have in general both lower wages and lower length of service. This may lead to a bigger and smaller gap, a bigger and lower incentive to leave Samhall AB to the regular labour market which also may affect female and their representation in transition.</p> / <p>Med ambitionerna att rehabilitera arbetshandikappade genom arbete vilar det statligt ägda Samhall AB på en lång historia som arbetsmarknadspolitisk åtgärd i Sverige.</p><p>För att visa på företagets betydelse som ett arbetsinriktat rehabiliteringsinstrument på den svenska arbetsmarknaden har Samhall AB krav på sig att uppfylla målet att 5 procent av de anställda lämnar företaget för anställning utanför Samhall varje år, i det som inom Samhall kallas för övergång. Procentmålet har sedan dess uppkomst dragits med flera dilemman. En av dessa är den varaktiga underrepresentationen av kvinnor i övergångarna ifrån Samhall AB till den reguljära arbetsmarknaden.</p><p>Uppsatsens har med ett genusperspektiv och med hjälp av kvalitativ och kvantitativ metodik, utrett de faktorer som ligger till grund för den kvinnliga underrepresentationen i övergångar ifrån Samhall AB.</p><p>Av resultatet tycks den kvinnliga underrepresentationen främst bero på strukturella grunder. Här återkommer de tidigare uppfattningarna om Samhalls starka manliga industritradition och i synnerhet den könsuppdelning som råder mellan män och kvinnor på den svenska arbetsmarknaden vilket troligtvis hämmar övergångar bland kvinnor. Uppsatsen har även uppmärksammat de svårigheter Samhall AB tycks ha med övergångar till kvinnodominerade yrken inom den offentlig sektor, vilket tordes utgöra en betydelsefull faktor till kvinnors lägre övergångsandel. Även lönesättningar och anställningsformer kan efter enligt uppsatsens resultat påverka kvinnors incitament att söka sig till den reguljära arbetsmarknaden. Samhallanställda kvinnor som har ambitioner att söka sig till kvinnodominerade yrken möter i många fall en arbetsmarknad med generellt lägre löner och spridda anställningsformer. Detta förhållande skulle kunna leda till ett större och mindre gap mellan män och kvinnor, vilket i sin tur kan ge skillnader mellan könens incitament att söka sig till ett arbete på den reguljära arbetsmarknaden. Enligt uppsatsens resultat skulle alltså detta kunna vara en betydelsefull faktor som påverkar kvinnor och deras lägre övergångsandel inom Samhall AB.</p>
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Friskvård på arbetsplatsen : -medarbetarens inställning till friskvårdJonsson, Helene, Wagner, Nina January 2008 (has links)
Sammanfattning Syftet med denna uppsats var att belysa hur fenomenet friskvård på en arbetsplats uppfattas av enskilda individer och vilken betydelse det kan få med avseende på såväl hälsan som välbefinnandet i stort. Utifrån denna fråga ville vi även se om det fanns skillnader i upplevelser av friskvård i de olika yrkeskategorierna från arbetsledning till arbetstagare. Inställningen till friskvård som prevention på en arbetsplats och vardagsmotion för den enskilde individen är individuell. En del människor varken vill eller tror sig kunna utöva friskvård och håller sig friska ändå. Den empiriska undersökningen bygger på kvalitativ metod. Vi har genomfört en intervjuundersökning med sju intervjupersoner från olika yrkeskategorier vilka har bidragit med sina tankar kring friskvården. Vi har använt oss av Antonovsky teori KASAM. Intervjuerna har tolkats enligt hermeneutiska principer. Resultaten visar bland annat att friskvård är betydelsefull på många sätt för medarbetare. Friskvård handlar om så mycket mer än fysisk aktivitet.
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Övergångarnas Dilemma : En uppsats om kvinnors underrepresentation i andelen övergångar ifrån Samhall AB till den reguljära arbetsmarknaden / Transitional Difficulties : An essay about the factors behind female under representation in transitions from Samhall AB to the Swedish labour marketJonsson, Robin January 2008 (has links)
With the ambitions to rehabilitate individuals with different kinds of work disabilities through work, the government owned Samhall AB has a long history as labour market measure in Sweden. To show Samhall AB its importance, the company has requirements to fulfill the goal that around 5 percent of their employees, at Samhall AB, every year shall be transferred to an employment outside the company, which is called transition. Unfortunately since this goal was introduced it also created several dilemmas. One dilemma is the long lasting female under representation in transitions from Samhall AB to the regular labour market. The essays main task is to investigate the factors behind the female under presentation in transition from Samhall AB through a genus perspective and by using quantitative and qualitative method. The main conclusions are that female under representation in transitions from Samhall AB are basically caused by structural factors. Samhall AB’s strong industrial tradition and particularly the strong segregation between female and males on the regular Swedish labour market may inhibit females in their transitions. It also seems that Samhall AB has problems with transitions to the public service which bear a large female work force and probably is an important factor that inhibits female transitions. Even wages and employment may effect female representations in transitions. Typical female jobs on the regular labour market have in general both lower wages and lower length of service. This may lead to a bigger and smaller gap, a bigger and lower incentive to leave Samhall AB to the regular labour market which also may affect female and their representation in transition. / Med ambitionerna att rehabilitera arbetshandikappade genom arbete vilar det statligt ägda Samhall AB på en lång historia som arbetsmarknadspolitisk åtgärd i Sverige. För att visa på företagets betydelse som ett arbetsinriktat rehabiliteringsinstrument på den svenska arbetsmarknaden har Samhall AB krav på sig att uppfylla målet att 5 procent av de anställda lämnar företaget för anställning utanför Samhall varje år, i det som inom Samhall kallas för övergång. Procentmålet har sedan dess uppkomst dragits med flera dilemman. En av dessa är den varaktiga underrepresentationen av kvinnor i övergångarna ifrån Samhall AB till den reguljära arbetsmarknaden. Uppsatsens har med ett genusperspektiv och med hjälp av kvalitativ och kvantitativ metodik, utrett de faktorer som ligger till grund för den kvinnliga underrepresentationen i övergångar ifrån Samhall AB. Av resultatet tycks den kvinnliga underrepresentationen främst bero på strukturella grunder. Här återkommer de tidigare uppfattningarna om Samhalls starka manliga industritradition och i synnerhet den könsuppdelning som råder mellan män och kvinnor på den svenska arbetsmarknaden vilket troligtvis hämmar övergångar bland kvinnor. Uppsatsen har även uppmärksammat de svårigheter Samhall AB tycks ha med övergångar till kvinnodominerade yrken inom den offentlig sektor, vilket tordes utgöra en betydelsefull faktor till kvinnors lägre övergångsandel. Även lönesättningar och anställningsformer kan efter enligt uppsatsens resultat påverka kvinnors incitament att söka sig till den reguljära arbetsmarknaden. Samhallanställda kvinnor som har ambitioner att söka sig till kvinnodominerade yrken möter i många fall en arbetsmarknad med generellt lägre löner och spridda anställningsformer. Detta förhållande skulle kunna leda till ett större och mindre gap mellan män och kvinnor, vilket i sin tur kan ge skillnader mellan könens incitament att söka sig till ett arbete på den reguljära arbetsmarknaden. Enligt uppsatsens resultat skulle alltså detta kunna vara en betydelsefull faktor som påverkar kvinnor och deras lägre övergångsandel inom Samhall AB.
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Study on the thermomechanical properties and workability of Mg-based bulk metallic glassesChang, Yu-Chen 10 July 2008 (has links)
In the near couple years, the applications of amorphous alloys have attracted great attention due to their characteristics and future potential. This research is intended to synthesis a lighter Mg-based amorphous alloy as the imprinting materials for micro-electromechanical system (MEMS) with a high glass forming ability (GFA) and lower glass transition temperature (Tg). Also, the workability of the Mg-based metallic glasses is examined in terms of several viscous flow behaviors and parameters obtained from the thermomechanical analysis (TMA).
The lighter Mg-based metallic glasses exhibit their superior glass forming ability, and can be cast into bulk metallic glasses (BMGs). Based on the thermal analysis of the Mg-Cu-Y glassy materials, the evaluation of the glass forming ability and thermal stability for searching the optimum alloy composition is conducted. By using Mg58Cu31Y11 amorphous alloy with the best composition as the micro-forming specimens, imprinting was made by hot pressing at 150oC with several applied compressive stresses to form the hexagonal micro-lens arrays. Finite element simulation using 3D Deform software is also applied to trace the microforming evolution, and to compare with the experimental observations. The results demonstrate that the imprinting is feasible and promising.
On the other hand, the Mg-Cu-Gd BMGs with even better GFA than Mg-Cu-Y are explored in terms of their thermomechanical properties. Extension of this study is performed partially by Cu replacing by Ag or B for the improvement of maximum diameter and thermal stability. And the workability of these Mg-Cu-(Ag, B)-Gd metallic glasses, namely, Mg65Cu25-xAgxGd10 (x = 0, 3, 10 at %) and Mg65Cu22B3Gd10 is evaluated in terming of the thermomechanical parameters, viscous flow behavior, deformability, and the deformation model. It is found the fragility for viscous deformation would increase with the replacement of Ag or B, leading to the negative factors for the micro-forming and nano-imprinting practices. This conclusion is supported by the many extracted parameters.
Thus, even the B-additive Mg based BMG has much higher hardness and Ag-additive Mg based BMG has the larger maximum rod diameter, they are more difficult to be formed, appearing as a negative factor in the micro-forming or nano-imprinting industry. The base Mg65Cu25Gd10 alloy stilly appears to be more promising than the Ag or B-containing alloys when the viscous forming is under consideration.
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Characterisation and Modelling of Asphalt Mastic and Their Effect on WorkabilityHesami, Ebrahim January 2014 (has links)
<p>QC 20140902</p>
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