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Alkali binding in hydrated Portland cement paste / W. Chen in Cement and concrete research, Vol. 40 N° 5 (Mai 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. 716–722 Titre : Alkali binding in hydrated Portland cement paste Type de document : texte imprimé Auteurs : W. Chen, Auteur ; H. J. H. Brouwers, Auteur Année de publication : 2012 Article en page(s) : pp. 716–722 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Alkalis  ;  Hydration  products  ;  Modeling  ;  Pore  solution  ;  Portland  cement Résumé : The alkali-binding capacity of C–S–H in hydrated Portland cement pastes is addressed in this study. The amount of bound alkalis in C–S–H is computed based on the alkali partition theories firstly proposed by Taylor (1987) and later further developed by Brouwers and Van Eijk (2003). Experimental data reported in literatures concerning thirteen different recipes are analyzed and used as references. A three-dimensional computer-based cement hydration model (CEMHYD3D) is used to simulate the hydration of Portland cement pastes. These model predictions are used as inputs for deriving the alkali-binding capacity of the hydration product C–S–H in hydrated Portland cement pastes. It is found that the relation of Na+ between the moles bound in C–S–H and its concentration in the pore solution is linear, while the binding of K+ in C–S–H complies with the Freundlich isotherm. New models are proposed for determining the alkali-binding capacities of C–S–H in hydrated Portland cement paste. An updated method for predicting the alkali concentrations in the pore solution of hydrated Portland cement pastes is developed. It is also used to investigate the effects of various factors (such as the water to cement ratio, clinker composition and alkali types) on the alkali concentrations. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884610000025 [article] Alkali binding in hydrated Portland cement paste [texte imprimé] / W. Chen, Auteur ; H. J. H. Brouwers, Auteur . - 2012 . - pp. 716–722. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. 716–722 Mots-clés : Alkalis  ;  Hydration  products  ;  Modeling  ;  Pore  solution  ;  Portland  cement Résumé : The alkali-binding capacity of C–S–H in hydrated Portland cement pastes is addressed in this study. The amount of bound alkalis in C–S–H is computed based on the alkali partition theories firstly proposed by Taylor (1987) and later further developed by Brouwers and Van Eijk (2003). Experimental data reported in literatures concerning thirteen different recipes are analyzed and used as references. A three-dimensional computer-based cement hydration model (CEMHYD3D) is used to simulate the hydration of Portland cement pastes. These model predictions are used as inputs for deriving the alkali-binding capacity of the hydration product C–S–H in hydrated Portland cement pastes. It is found that the relation of Na+ between the moles bound in C–S–H and its concentration in the pore solution is linear, while the binding of K+ in C–S–H complies with the Freundlich isotherm. New models are proposed for determining the alkali-binding capacities of C–S–H in hydrated Portland cement paste. An updated method for predicting the alkali concentrations in the pore solution of hydrated Portland cement pastes is developed. It is also used to investigate the effects of various factors (such as the water to cement ratio, clinker composition and alkali types) on the alkali concentrations. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884610000025

Photocatalytic degradation of air pollutants — From modeling to large scale application / M. Hunger in Cement and concrete research, Vol. 40 N° 2 (02 ex.) (Fevrier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 313-320 Titre : Photocatalytic degradation of air pollutants — From modeling to large scale application Type de document : texte imprimé Auteurs : M. Hunger, Auteur ; G. Hüsken, Auteur ; H. J. H. Brouwers, Auteur Année de publication : 2010 Article en page(s) : pp. 313-320 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Photocatalysis  Reaction  Kinetics  Diffusion  Modeling Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Indoor as well as outdoor air quality and their limiting values remain a major problem to our present-day society. This paper addresses the modeling of the decomposition process of nitrogen monoxide (NO) on reactive concrete surfaces under the controlled exposition of a UV source. Within this model the external mass transfer of the pollutant and the internal molecule diffusion-reaction were considered. A first-order kinetics equation is derived with respect to the NO concentration and a site-competitive adsorption between NO/NO2 and water molecules, resulting in a dependence of the reaction kinetics on the relative humidity. Using the proposed model, a reaction rate constant k and an adsorption equilibrium constant Kd can be derived which describe an active paving stone accurately. Experimental results from a self-developed photoreactor with continuous flow mode were used to validate the proposed kinetic expression. Furthermore, the effect of variations in process conditions such as irradiance and relative humidity on the two constants k and Kd is investigated. All modeling work provides a sound foundation for the translation of this process to real outside conditions. In this regard an upcoming project in a Dutch city is described in brief. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJW020-1&_user=6 [...] [article] Photocatalytic degradation of air pollutants — From modeling to large scale application [texte imprimé] / M. Hunger, Auteur ; G. Hüsken, Auteur ; H. J. H. Brouwers, Auteur . - 2010 . - pp. 313-320. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 313-320 Mots-clés : Photocatalysis  Reaction  Kinetics  Diffusion  Modeling Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Indoor as well as outdoor air quality and their limiting values remain a major problem to our present-day society. This paper addresses the modeling of the decomposition process of nitrogen monoxide (NO) on reactive concrete surfaces under the controlled exposition of a UV source. Within this model the external mass transfer of the pollutant and the internal molecule diffusion-reaction were considered. A first-order kinetics equation is derived with respect to the NO concentration and a site-competitive adsorption between NO/NO2 and water molecules, resulting in a dependence of the reaction kinetics on the relative humidity. Using the proposed model, a reaction rate constant k and an adsorption equilibrium constant Kd can be derived which describe an active paving stone accurately. Experimental results from a self-developed photoreactor with continuous flow mode were used to validate the proposed kinetic expression. Furthermore, the effect of variations in process conditions such as irradiance and relative humidity on the two constants k and Kd is investigated. All modeling work provides a sound foundation for the translation of this process to real outside conditions. In this regard an upcoming project in a Dutch city is described in brief. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJW020-1&_user=6 [...]