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Dissertation
Contribution à l'étude de la structure et des propriétés de surface des silico-alumines amorphes

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Sustainable materialisation of residues from thermal processes into construction materials : construction materials from stainless steel slags
Authors: ---
ISBN: 9789460188602 Year: 2014 Publisher: Leuven Katholieke Universiteit Leuven

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The amount of slag generated is almost athird of the total stainless steel produced. Owing to its mineralogy, a large partof the slag is produced as fines, which has a very low valorisation potentialand has to be landfilled. The present work is aimed at exploring the potentialof these slags to produce construction materials of higher economic value.To address the issue, two valorisationroutes were applied: 1) alkali-activation initiating binding reactions in theslag by the addition of alkali hydroxides and silicates, 2) carbonation initiating hardening reaction in the slag by the formation of alkalicarbonates. Two stainless steel slags, continuous casting (CtCs) slag and Argonoxygen decarburisation (AOD) slag, were targeted for valorisation.Initiation of hardening reactions in theslag was found to occur only under a combined treatment of alkali (Na and K)hydroxides and high temperature (80 &#176;C) which was provided by steam curing. However,only a moderate strength in the mortar specimens was observed under suchconditions along with appearance of efflorescence with NaOH for molaritiesabove 5 M. The problem of low strength and efflorescence in the mortar sampleswas eliminated by the introduction of silicates in the system along with thealkali hydroxides. The compressive strength of the slag mortars was found toincrease with the increase in the amount of silicates in the activatingsolution and with the increase of the curing temperature. The reaction productfrom the activation was found to be C-S-H as confirmed by thermogravimetric,QXRD, FTIR and 29Si NMR analysis.The slag was also found to develop strengthunder acceleration carbonation conditions which was provided under two environments:i) in a carbonation chamber, maintained at atmospheric pressure, 22 &#176;C, 5 vol.%CO2 and 80% RH; and ii) in a carbonation reactor, where the CO2partial pressure (pCO2)and temperature could be further increased. It was found that in thecarbonation chamber the compressive strength of the samples and the CO2sequestration continued to increase up to 3 weeks whereas in the reactor theoptimum for strength and CO2 sequestration was found at 80 &#176;C, 8 barpressure in 2.5 h. The major reaction product was found to be calcite indifferent morphologies.Three types of masonry blocks were preparedform the slag with the two valorisation routes: alkali-activated solid bricks,perforated carbonated bricks and alkali-activated aerated bricks. Thecarbonated bricks were found to have the best resistance to freeze-thaw,whereas the aerated bricks were found to have superior thermal resistivity values.The LCA showed that the environmental impact of the bricks is lower (negativefor carbonated bricks) than the conventional clay fired bricks and the impactof the aerated bricks was found to be similar to the conventional aeratedblocks available in the market. A SWOTanalysis highlighted the advantage of using these bricks in the form of lowerenergy requirement in its production, reduction of stress on the use of prime materialsand ease of metal recovery from the residual slag.The results of the dissertation show that thebinding potential of the stainless steel slags can be exploited as valorisedapplications in the construction industry by novel thermo-alkali activation andcarbonation processes.


Dissertation
Online risico's bij jongeren in het buitengewoon secundair onderwijs.
Authors: ---
Year: 2013 Publisher: Leuven KU Leuven. Faculteit Sociale Wetenschappen,

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Jongeren in het BuSO worden vaker blootgesteld aan online risico's dan jongeren in het reguliere onderwijs. Met andere woorden: jongeren in het BuSO worden vaker blootgesteld aan cyberpesten, seksueel getinte beelden, negatieve UGC, contact met vreemde personen en sexting dan jongeren in het reguliere secundair onderwijs. In het reguliere onderwijs zijn jongeren vaker geschokt naar aanleiding van seksueel getinte beelden dan jongeren in het BuSO. Cyberpesten is het risico waar jongeren zowel in het BuSO als in het reguliere onderwijs het minst vaak aan worden blootgesteld, maar tegelijkertijd ervaren ze de blootstelling eraan het vaakst als negatief. Verder kunnen we over BuSO-jongeren het volgende concluderen: jongens hebben minder kans om in aanraking te komen met cyberpesten en negatieve UGC dan meisjes, maar komen wel vaker in contact met seksueel getinte beelden. Oudere kinderen hebben minder kans om slachtoffer te zijn van cyberpesten en meer kans om in aanraking te komen met seksueel getinte beelden. Hoe beter de relatie van het kind met de vader, hoe minder kans op blootstelling aan cyberpesten, negatieve UGC en misbruik van persoonlijke informatie. Jongens gebruiken minder actieve copingstrategieën dan meisjes en naarmate jongeren intenser geschokt raken als gevolg van een blootstelling aan een online risico, gaan ze zowel actieve als passieve copingstrategieën hanteren.


Dissertation
Hoe vertellen we het de Kamer ? : een empirisch onderzoek naar de informatierelatie tussen regering en parlement.

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Dissertation
Online risico's bij jongeren in het buitengewoon secundair onderwijs.
Authors: ---
Year: 2013 Publisher: Leuven KU Leuven. Faculteit Sociale Wetenschappen,

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Jongeren in het BuSO worden vaker blootgesteld aan online risico's dan jongeren in het reguliere onderwijs. Met andere woorden: jongeren in het BuSO worden vaker blootgesteld aan cyberpesten, seksueel getinte beelden, negatieve UGC, contact met vreemde personen en sexting dan jongeren in het reguliere secundair onderwijs. In het reguliere onderwijs zijn jongeren vaker geschokt naar aanleiding van seksueel getinte beelden dan jongeren in het BuSO. Cyberpesten is het risico waar jongeren zowel in het BuSO als in het reguliere onderwijs het minst vaak aan worden blootgesteld, maar tegelijkertijd ervaren ze de blootstelling eraan het vaakst als negatief. Verder kunnen we over BuSO-jongeren het volgende concluderen: jongens hebben minder kans om in aanraking te komen met cyberpesten en negatieve UGC dan meisjes, maar komen wel vaker in contact met seksueel getinte beelden. Oudere kinderen hebben minder kans om slachtoffer te zijn van cyberpesten en meer kans om in aanraking te komen met seksueel getinte beelden. Hoe beter de relatie van het kind met de vader, hoe minder kans op blootstelling aan cyberpesten, negatieve UGC en misbruik van persoonlijke informatie. Jongens gebruiken minder actieve copingstrategieën dan meisjes en naarmate jongeren intenser geschokt raken als gevolg van een blootstelling aan een online risico, gaan ze zowel actieve als passieve copingstrategieën hanteren.


Multi
Interactions between cement and combined concrete admixtures : the influence on cement paste rheology
Authors: ---
ISBN: 9789460188589 Year: 2014 Publisher: Leuven Katholieke Universiteit Leuven

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During the last decades, innovative concrete applications have been the result of technological developments as new processing techniques, the use of concrete admixtures and advanced materials. All these improvements increase the demand for better performing concrete with enhanced workability. However, the lack of reliable engineering tools in traditional concrete production methods has led to some inconsistent control of the workability. Therefore, todays research is increasingly investigating advanced models that capture the flow behavior of fresh concrete as accurately as possible. These models are continuously improving but generally keep facing problems which are linked to the agglomeration of the cement particles and to the implementation of combined concrete admixtures. The objective of this work is to investigate the rheological mechanism in cement paste for the combined use of superplasticizer, retarder and accelerator. In particular, an effect on the particle agglomeration is aimed for in order to contribute to a more fundamental understanding of the concretes flow behavior. Concerning the superplasticizer impact on cement paste, thermodynamic modelling and mineralogy studies led to the conclusion that the superplasticizer can change the hydrate morphology to such an extent that the interparticle contact forces are modified. The extra addition of retarder led to a densified polymer layer at the cement grain surface which contributed to the steric stabilization of the cement paste. An additional electrostatic effect and the induced changes in hydrate morphology are also demonstrated to contribute to the low paste viscosity. With the extra addition of a calcium salt accelerator to the cement paste, an interstitial structure was assumed to diminish the rheological effect of the polymer layer.All the developed conceptual mechanisms were implemented in a coherent agglomeration model, based on measurable parameters. In this model, the internal and external hydrates in a cement agglomerate were defined and quantified. Generally, the cumulative amount of hydrates within the agglomerates influenced the agglomerate stability and the amount of external hydrates determined the reagglomeration rate. For the superplasticizer only, a proportional relation was found between the change in agglomeration rate and the external agglomerate connectivity while, for the extra addition of retarder and accelerator, a reverse relation was found. The latter was attributed to a mechanical contribution of the interstitial volume. On the one hand, the retarder creates a source of slowly hydrating nuclei and particles in that volume and, on the other hand, these particles are expected to coagulate due to the accelerator addition. In the second case, the interstitial volume also delivered a contribution to the stress resistance of the cement paste at rest.This fundamental research combines dedicated analytical methods and conceptual models to improve the understanding of particle agglomeration and contributes to a more extensive insight into the concrete rheology.


Dissertation
Beton- en lichtbeton technologie : economie van bekistingen
Authors: ---
Year: 1970 Publisher: Leuven KUL. Fakulteit toegepaste wetenschappen,

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Dissertation
Architektonisch beton
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Year: 1973 Publisher: Leuven KUL. Fakulteit toegepaste wetenschappen,

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