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Ajouter le résultat dans votre panierChanges in C3S hydration in the presence of cellulose ethers / J. Pourchez in Cement and concrete research, Vol. 40 N° 2 (02 ex.) (Fevrier 2010)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 179-188
Titre : Changes in C3S hydration in the presence of cellulose ethers Type de document : texte imprimé Auteurs : J. Pourchez, Auteur ; P. Grosseau, Auteur ; B. Ruot, Auteur Année de publication : 2010 Article en page(s) : pp. 179-188 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Cellulose ethers Hydration Adsorption Dissolution Nucleation Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The influence of cellulose ethers (CE) on C3S hydration processes was examined in order to improve our knowledge of the retarding effect of cellulose ethers on the cement hydration kinetics. In this frame, the impacts of various cellulose ethers on C3S dissolution, C-S-H nucleation-growth process and portlandite precipitation were investigated. A weak influence of cellulose ethers on the dissolution kinetics of pure C3S phase was observed. In contrast, a significant decrease of the initial amount of C-S-H nuclei and a strong modification of the growth rate of C-S-H were noticed. A slowing down of the portlandite precipitation was also demonstrated in the case of both cement and C3S hydration. CE adsorption behavior clearly highlighted a chemical structure dependence as well as a cement phase dependence. Finally, we supported the conclusion that CE adsorption is doubtless responsible for the various retarding effect observed as a function of CE types.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XK31Y3-2&_user=6 [...] [article] Changes in C3S hydration in the presence of cellulose ethers [texte imprimé] / J. Pourchez, Auteur ; P. Grosseau, Auteur ; B. Ruot, Auteur . - 2010 . - pp. 179-188.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 179-188
Mots-clés : Cellulose ethers Hydration Adsorption Dissolution Nucleation Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The influence of cellulose ethers (CE) on C3S hydration processes was examined in order to improve our knowledge of the retarding effect of cellulose ethers on the cement hydration kinetics. In this frame, the impacts of various cellulose ethers on C3S dissolution, C-S-H nucleation-growth process and portlandite precipitation were investigated. A weak influence of cellulose ethers on the dissolution kinetics of pure C3S phase was observed. In contrast, a significant decrease of the initial amount of C-S-H nuclei and a strong modification of the growth rate of C-S-H were noticed. A slowing down of the portlandite precipitation was also demonstrated in the case of both cement and C3S hydration. CE adsorption behavior clearly highlighted a chemical structure dependence as well as a cement phase dependence. Finally, we supported the conclusion that CE adsorption is doubtless responsible for the various retarding effect observed as a function of CE types.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XK31Y3-2&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 189-196
Titre : The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers Type de document : texte imprimé Auteurs : Jae Eun Oh, Auteur ; Paulo J.M. Monteiro, Auteur ; Ssang Sun Jun, Auteur Année de publication : 2010 Article en page(s) : pp. 189-196 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Alkali-activated cement Geopolymer X-ray diffraction Fly ash Granulated blast furnace slag Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The increase in strength and evolution of crystalline phases in inorganic polymer cement, made by the alkali activation of slag, Class C and Class F fly ashes, was followed using compressive strength test and synchrotron X-ray diffraction. In order to increase the crystallinity of the product the reactions were carried out at 80 °C. We found that hydrotalcite formed in both the alkali-activated slag cements and the fly ash-based geopolymers. Hydroxycancrinite, one member of the ABC-6 family of zeolites, was found only in the fly ash geopolymers. Assuming that the predominantly amorphous geopolymer formed under ambient conditions relates to the crystalline phases found when the mixture is cured at high temperature, we propose that the structure of this zeolitic precursor formed in Na-based high alkaline environment can be regarded as a disordered form of the basic building unit of the ABC-6 group of zeolites which includes poly-types such as hydroxycancrinite, hydroxysodalite and chabazite-Na.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XNVTFP-1&_user=6 [...] [article] The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers [texte imprimé] / Jae Eun Oh, Auteur ; Paulo J.M. Monteiro, Auteur ; Ssang Sun Jun, Auteur . - 2010 . - pp. 189-196.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 189-196
Mots-clés : Alkali-activated cement Geopolymer X-ray diffraction Fly ash Granulated blast furnace slag Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The increase in strength and evolution of crystalline phases in inorganic polymer cement, made by the alkali activation of slag, Class C and Class F fly ashes, was followed using compressive strength test and synchrotron X-ray diffraction. In order to increase the crystallinity of the product the reactions were carried out at 80 °C. We found that hydrotalcite formed in both the alkali-activated slag cements and the fly ash-based geopolymers. Hydroxycancrinite, one member of the ABC-6 family of zeolites, was found only in the fly ash geopolymers. Assuming that the predominantly amorphous geopolymer formed under ambient conditions relates to the crystalline phases found when the mixture is cured at high temperature, we propose that the structure of this zeolitic precursor formed in Na-based high alkaline environment can be regarded as a disordered form of the basic building unit of the ABC-6 group of zeolites which includes poly-types such as hydroxycancrinite, hydroxysodalite and chabazite-Na.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XNVTFP-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 197-207
Titre : Identification of viscoelastic C-S-H behavior in mature cement paste by FFT-based homogenization method Type de document : texte imprimé Auteurs : Vít Smilauer, Auteur ; Zdenek P. Bazant, Auteur Année de publication : 2010 Article en page(s) : pp. 197-207 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Micromechanics Creep Cement paste Microprestress Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : A powerful and robust numerical homogenization method based on fast Fourier transform (FFT) is formulated to identify the viscoelastic behavior of calcium silicate hydrates (C-S-H) in hardened cement paste from its heterogeneous composition. The identification is contingent upon the linearity of the creep law. To characterize cement paste microstructure, the model developed by Bentz at the National Institute of Standards and Technology, which has the resolution of 1 μm, is adopted. Model B3 for concrete creep is adapted to characterize the creep of C-S-H in cement paste. It is found that the adaptation requires increasing the exponent of power law asymptote of creep compliance. This modification means that the rate of attenuation of creep with time is lower in C-S-H than in cement paste, and is explained by differences in stress redistribution. In cement paste, the stress is gradually transferred from the creeping C-S-H to the non-creeping components. The viscoelastic properties of C-S-H at the resolution of 1 μm were identified from creep experiments on cement pastes 2 and 30 years old, having the water–cement ratio of 0.5. The irreversible part of C-S-H creep, obtained from these old specimens at almost saturated state, is found to be negligible unless the specimens undergo drying and resaturation prior to the creep test.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XP8T93-1&_user=6 [...] [article] Identification of viscoelastic C-S-H behavior in mature cement paste by FFT-based homogenization method [texte imprimé] / Vít Smilauer, Auteur ; Zdenek P. Bazant, Auteur . - 2010 . - pp. 197-207.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 197-207
Mots-clés : Micromechanics Creep Cement paste Microprestress Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : A powerful and robust numerical homogenization method based on fast Fourier transform (FFT) is formulated to identify the viscoelastic behavior of calcium silicate hydrates (C-S-H) in hardened cement paste from its heterogeneous composition. The identification is contingent upon the linearity of the creep law. To characterize cement paste microstructure, the model developed by Bentz at the National Institute of Standards and Technology, which has the resolution of 1 μm, is adopted. Model B3 for concrete creep is adapted to characterize the creep of C-S-H in cement paste. It is found that the adaptation requires increasing the exponent of power law asymptote of creep compliance. This modification means that the rate of attenuation of creep with time is lower in C-S-H than in cement paste, and is explained by differences in stress redistribution. In cement paste, the stress is gradually transferred from the creeping C-S-H to the non-creeping components. The viscoelastic properties of C-S-H at the resolution of 1 μm were identified from creep experiments on cement pastes 2 and 30 years old, having the water–cement ratio of 0.5. The irreversible part of C-S-H creep, obtained from these old specimens at almost saturated state, is found to be negligible unless the specimens undergo drying and resaturation prior to the creep test.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XP8T93-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 208-219
Titre : Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes Type de document : texte imprimé Auteurs : F. Brunet, Auteur ; T. Charpentier, Auteur ; C. N. Chao, Auteur Année de publication : 2010 Article en page(s) : pp. 208-219 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hydration Amorphous material Blended cement NMR spectroscopy Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C3S, C2S, C3A and C4AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experimental 29Si and 27Al MAS NMR spectra has allowed us to follow the hydration of recent (28 days) and old (10 years) samples that constitutes a basis of experimental data for the prediction of hydration model.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJN4W8-3&_user=6 [...] [article] Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes [texte imprimé] / F. Brunet, Auteur ; T. Charpentier, Auteur ; C. N. Chao, Auteur . - 2010 . - pp. 208-219.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 208-219
Mots-clés : Hydration Amorphous material Blended cement NMR spectroscopy Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C3S, C2S, C3A and C4AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experimental 29Si and 27Al MAS NMR spectra has allowed us to follow the hydration of recent (28 days) and old (10 years) samples that constitutes a basis of experimental data for the prediction of hydration model.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJN4W8-3&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 220-225
Titre : Influence of bleed water reabsorption on cement paste autogenous deformation Type de document : texte imprimé Auteurs : B.J. Mohr, Auteur ; K.L. Hood, Auteur Année de publication : 2010 Article en page(s) : pp. 220-225 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Shrinkage Expansion Stability Bleeding Admixture Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The effects of bleed water reabsorption and subsequent early age expansion on observed autogenous deformation are investigated in this research. Bleeding was induced by varying superplasticizer and shrinkage-reducing admixture dosages and by increasing the water-to-cement ratio. This research revealed that significant early age expansion occurs with increasing chemical admixture dosages and higher water-to-cement ratios, as expected, due to increasing bleeding of those samples. When samples were rotated, negligible early age expansion was observed. Thus, bleed water reabsorption is shown to be the primary mechanism causing initial expansion in sealed autogenous deformation samples. Thermal dilation and ettringite growth appear to have a minimal influence on the observed expansion. Rotating the samples during setting eliminates the potential for bleed water reabsorption and is recommended for all autogenous deformation testing.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMC05Y-2&_user=6 [...] [article] Influence of bleed water reabsorption on cement paste autogenous deformation [texte imprimé] / B.J. Mohr, Auteur ; K.L. Hood, Auteur . - 2010 . - pp. 220-225.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 220-225
Mots-clés : Shrinkage Expansion Stability Bleeding Admixture Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The effects of bleed water reabsorption and subsequent early age expansion on observed autogenous deformation are investigated in this research. Bleeding was induced by varying superplasticizer and shrinkage-reducing admixture dosages and by increasing the water-to-cement ratio. This research revealed that significant early age expansion occurs with increasing chemical admixture dosages and higher water-to-cement ratios, as expected, due to increasing bleeding of those samples. When samples were rotated, negligible early age expansion was observed. Thus, bleed water reabsorption is shown to be the primary mechanism causing initial expansion in sealed autogenous deformation samples. Thermal dilation and ettringite growth appear to have a minimal influence on the observed expansion. Rotating the samples during setting eliminates the potential for bleed water reabsorption and is recommended for all autogenous deformation testing.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMC05Y-2&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 226-234
Titre : Rheology of fiber reinforced cementitious materials : classification and prediction Type de document : texte imprimé Auteurs : Laetitia Martinie, Auteur ; Pierre Rossi, Auteur ; Nicolas Roussel, Auteur Année de publication : 2010 Article en page(s) : pp. 226-234 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Rheology Mixture proportioning Fresh concrete Aggregate Fiber reinforcement Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In this paper, the effect of rigid straight fibers on the yield stress of cementitious materials is studied. A simple model describing the contact network between rigid fibers inside the material is first derived from the physical phenomena involved in the case of spherical inclusions. As soon as this contact network becomes percolated, the yield stress of the mixture increases by several orders of magnitude. A prediction of the critical fiber amount leading to a very strong increase of the yield stress of any cement paste, mortar or concrete is then derived. A simple and helpful mix design criterion for Ultra High Performance Fiber Reinforced Concretes is finally proposed and applied to several mix proportions from literature.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XDKCDW-1&_user=6 [...] [article] Rheology of fiber reinforced cementitious materials : classification and prediction [texte imprimé] / Laetitia Martinie, Auteur ; Pierre Rossi, Auteur ; Nicolas Roussel, Auteur . - 2010 . - pp. 226-234.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 226-234
Mots-clés : Rheology Mixture proportioning Fresh concrete Aggregate Fiber reinforcement Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In this paper, the effect of rigid straight fibers on the yield stress of cementitious materials is studied. A simple model describing the contact network between rigid fibers inside the material is first derived from the physical phenomena involved in the case of spherical inclusions. As soon as this contact network becomes percolated, the yield stress of the mixture increases by several orders of magnitude. A prediction of the critical fiber amount leading to a very strong increase of the yield stress of any cement paste, mortar or concrete is then derived. A simple and helpful mix design criterion for Ultra High Performance Fiber Reinforced Concretes is finally proposed and applied to several mix proportions from literature.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XDKCDW-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 235-241
Titre : Effect of limestone filler content and superplasticizer dosage on rheological parameters of highly flowable mortar under light pressure conditions Type de document : texte imprimé Auteurs : Jean-Yves Petit, Auteur ; Eric Wirquina, Auteur Année de publication : 2010 Article en page(s) : pp. 235-241 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Fresh concrete High range water reducers Rheology Filler Pressure Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The influence of pressure on the yield stress and plastic viscosity of SCC mortars was investigated using an adapted Marsh cone with cylindrical shear paddles. Nine mortars proportioned with various limestone filler content and high-range water-reducing admixture (HRWRA) dosage from 0.65% to 0.85% were prepared. Test results show that when a pressure is exerted on the mortars, the material does not behave as a homogeneous fluid, i.e. having a yield stress depending only on the specific gravity of the mixture and the height of poured mortars and a constant value of plastic viscosity, but as a separative multiphasic material which consolidates, leading to exponential variations of τ0 and lowering values of μ with pressure. The HRWRA dosage or the limestone filler content has only an effect on the initial value of the yield stress, but has more influence on the variation of plastic viscosity of the mortar with pressure.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMTFMS-1&_user=6 [...] [article] Effect of limestone filler content and superplasticizer dosage on rheological parameters of highly flowable mortar under light pressure conditions [texte imprimé] / Jean-Yves Petit, Auteur ; Eric Wirquina, Auteur . - 2010 . - pp. 235-241.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 235-241
Mots-clés : Fresh concrete High range water reducers Rheology Filler Pressure Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The influence of pressure on the yield stress and plastic viscosity of SCC mortars was investigated using an adapted Marsh cone with cylindrical shear paddles. Nine mortars proportioned with various limestone filler content and high-range water-reducing admixture (HRWRA) dosage from 0.65% to 0.85% were prepared. Test results show that when a pressure is exerted on the mortars, the material does not behave as a homogeneous fluid, i.e. having a yield stress depending only on the specific gravity of the mixture and the height of poured mortars and a constant value of plastic viscosity, but as a separative multiphasic material which consolidates, leading to exponential variations of τ0 and lowering values of μ with pressure. The HRWRA dosage or the limestone filler content has only an effect on the initial value of the yield stress, but has more influence on the variation of plastic viscosity of the mortar with pressure.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMTFMS-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 242-252
Titre : Some aspects of cellulose ethers influence on water transport and porous structure of cement-based materials Type de document : texte imprimé Auteurs : J. Pourchez, Auteur ; B. Ruot, Auteur ; J. Debayle, Auteur Année de publication : 2010 Article en page(s) : pp. 242-252 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Cellulose ethers Porous structure Water transport Microtomography Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : This paper evaluates and compares the impact of cellulose ethers (CE) on water transport and porous structure of cement-based materials in both fresh and hardened state. Investigations of the porous network (mercury intrusion porosimetry, apparent density, 2D and 3D observations) emphasize an air-entrained stabilisation depending on CE chemistry. We also highlight that CE chemistry leads to a gradual effect on characteristics of the water transport. The global tendencies brought by CE are: higher water retention, lower capillarity water absorption, lower liquid water permeability as well as higher water vapour permeability. All things considered, we demonstrate that CE chemistry is an important controlling factor on water transport and porous structure evolution.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJN4W8-2&_user=6 [...] [article] Some aspects of cellulose ethers influence on water transport and porous structure of cement-based materials [texte imprimé] / J. Pourchez, Auteur ; B. Ruot, Auteur ; J. Debayle, Auteur . - 2010 . - pp. 242-252.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 242-252
Mots-clés : Cellulose ethers Porous structure Water transport Microtomography Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : This paper evaluates and compares the impact of cellulose ethers (CE) on water transport and porous structure of cement-based materials in both fresh and hardened state. Investigations of the porous network (mercury intrusion porosimetry, apparent density, 2D and 3D observations) emphasize an air-entrained stabilisation depending on CE chemistry. We also highlight that CE chemistry leads to a gradual effect on characteristics of the water transport. The global tendencies brought by CE are: higher water retention, lower capillarity water absorption, lower liquid water permeability as well as higher water vapour permeability. All things considered, we demonstrate that CE chemistry is an important controlling factor on water transport and porous structure evolution.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJN4W8-2&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 253-259
Titre : Interaction between α-calcium sulfate hemihydrate and superplasticizer from the point of adsorption characteristics, hydration and hardening process Type de document : texte imprimé Auteurs : Baohong Guan, Auteur ; Qingqing Ye, Auteur ; Jiali Zhang, Auteur Année de publication : 2010 Article en page(s) : pp. 253-259 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : α-calcium sulfate hemihydrate Superplasticizer Adsorption Hydration Hardening Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Superplasticizers (SPs), namely sulfonated melamine formaldehyde (SMF) and polycarboxylate (PC), were independently admixed with α-calcium sulfate hemihydrate based plaster to improve the material's performance. SMF and PC gave, respectively, 38% and 25% increases in the 2 h bending strength at the optimum dosages of 0.5 wt.% and 0.3 wt.%, which are determined essentially by the maximum water-reducing efficiency. The peak shift of binding energy of Ca2p3/2 detected by X-ray photoelectron spectroscopy (XPS) suggests that SPs are chemically adsorbed on gypsum surface. A careful examination of the strength development of set plaster allowed the hydration and hardening process to be divided roughly into five stages. SMF accelerates early hydration, while PC decelerates it. Both SPs allowed similar maximum water reductions, giving a more compact structure and a decrease in total pore volume and average pore diameter, and thus leading to higher strengths in the hardened plasters with SPs.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJF38H-1&_user=6 [...] [article] Interaction between α-calcium sulfate hemihydrate and superplasticizer from the point of adsorption characteristics, hydration and hardening process [texte imprimé] / Baohong Guan, Auteur ; Qingqing Ye, Auteur ; Jiali Zhang, Auteur . - 2010 . - pp. 253-259.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 253-259
Mots-clés : α-calcium sulfate hemihydrate Superplasticizer Adsorption Hydration Hardening Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Superplasticizers (SPs), namely sulfonated melamine formaldehyde (SMF) and polycarboxylate (PC), were independently admixed with α-calcium sulfate hemihydrate based plaster to improve the material's performance. SMF and PC gave, respectively, 38% and 25% increases in the 2 h bending strength at the optimum dosages of 0.5 wt.% and 0.3 wt.%, which are determined essentially by the maximum water-reducing efficiency. The peak shift of binding energy of Ca2p3/2 detected by X-ray photoelectron spectroscopy (XPS) suggests that SPs are chemically adsorbed on gypsum surface. A careful examination of the strength development of set plaster allowed the hydration and hardening process to be divided roughly into five stages. SMF accelerates early hydration, while PC decelerates it. Both SPs allowed similar maximum water reductions, giving a more compact structure and a decrease in total pore volume and average pore diameter, and thus leading to higher strengths in the hardened plasters with SPs.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJF38H-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 260-270
Titre : Effect of air voids on salt scaling and internal freezing Type de document : texte imprimé Auteurs : Zhenhua Sun, Auteur ; George W. Scherer, Auteur Année de publication : 2010 Article en page(s) : pp. 260-270 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Pore size distribution Freezing and Thawing Thermal analysis Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : By combining calorimetric measurements with dilatometry, it has been possible to calculate the contributions of thermal expansion, pore pressure, and crystallization pressure of ice to the strain observed in a mortar during freezing/thawing cycles. Air-entrained mortars contract upon freezing, while non-air-entrained mortars expand. The expansion of the latter is attributed primarily to hydraulic pressure, owing to the rapid growth of ice, which nucleates at low temperatures in laboratory samples. Poromechanical calculations account quantitatively for the contraction of samples with air entrainment, assuming that ice crystals form in the air voids. As originally proposed by Powers and Helmuth, those crystals create suction in the pore liquid that offsets the crystallization pressure of ice in the mesopores of the paste, resulting in a net contraction. Ice in the matrix also contributes significantly to the increase in the thermal expansion coefficient of the mortar.
The magnitude of the contraction in air-entrained mortar is shown to account for a reduction of salt scaling damage. According to the glue-spall theory, the damage results from cracking of the ice on the surface of concrete, when the thermal expansion mismatch stress exceeds the strength of the ice. The contraction of the mortar caused by air entrainment offsets the thermal expansion mismatch sufficiently to prevent cracking.
Based on observations of the nucleation temperature of ice in laboratory samples of various sizes, it is estimated that there is one site capable of nucleating ice at − 1 °C in a cube of mortar roughly 34 cm on an edge (or, one per square meter in a slab 3 cm thick). This suggests that ice nucleates in the field at high temperatures, compared to what is typically seen in the laboratory, and propagates slowly through the pores as the temperature drops. This mode of growth may lead to fatigue damage over many cycles, owing to local stresses from crystallization pressure, where the contribution of hydraulic pressure is insignificant.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJW020-3&_user=6 [...] [article] Effect of air voids on salt scaling and internal freezing [texte imprimé] / Zhenhua Sun, Auteur ; George W. Scherer, Auteur . - 2010 . - pp. 260-270.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 260-270
Mots-clés : Pore size distribution Freezing and Thawing Thermal analysis Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : By combining calorimetric measurements with dilatometry, it has been possible to calculate the contributions of thermal expansion, pore pressure, and crystallization pressure of ice to the strain observed in a mortar during freezing/thawing cycles. Air-entrained mortars contract upon freezing, while non-air-entrained mortars expand. The expansion of the latter is attributed primarily to hydraulic pressure, owing to the rapid growth of ice, which nucleates at low temperatures in laboratory samples. Poromechanical calculations account quantitatively for the contraction of samples with air entrainment, assuming that ice crystals form in the air voids. As originally proposed by Powers and Helmuth, those crystals create suction in the pore liquid that offsets the crystallization pressure of ice in the mesopores of the paste, resulting in a net contraction. Ice in the matrix also contributes significantly to the increase in the thermal expansion coefficient of the mortar.
The magnitude of the contraction in air-entrained mortar is shown to account for a reduction of salt scaling damage. According to the glue-spall theory, the damage results from cracking of the ice on the surface of concrete, when the thermal expansion mismatch stress exceeds the strength of the ice. The contraction of the mortar caused by air entrainment offsets the thermal expansion mismatch sufficiently to prevent cracking.
Based on observations of the nucleation temperature of ice in laboratory samples of various sizes, it is estimated that there is one site capable of nucleating ice at − 1 °C in a cube of mortar roughly 34 cm on an edge (or, one per square meter in a slab 3 cm thick). This suggests that ice nucleates in the field at high temperatures, compared to what is typically seen in the laboratory, and propagates slowly through the pores as the temperature drops. This mode of growth may lead to fatigue damage over many cycles, owing to local stresses from crystallization pressure, where the contribution of hydraulic pressure is insignificant.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJW020-3&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 271-283
Titre : About microcracking due to leaching in cementitious composites : x-ray microtomography description and numerical approach Type de document : texte imprimé Auteurs : Thomas Rougelot, Auteur ; Nicolas Burlion, Auteur ; Dominique Bernard, Auteur Année de publication : 2010 Article en page(s) : pp. 271-283 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Cementitious composites Endogenous and decalcification shrinkages Leaching Microcracking X-ray computed microtomography Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Chemical shock of cement based materials leads to significant degradation of their physical properties. A typical scenario is a calcium leaching due to water (water with very low pH compared with that of pore fluid). The main objective of this paper is to evaluate the evolution of microstructure induced by leaching of a cementitious composite using synchrotron X-ray micro tomography, mainly from an experimental point of view. In this particular case, it was possible to identify cracking induced by leaching. After a description of the degradation mechanism and the X-ray synchrotron microtomographic analysis, numerical simulations are performed in order to show that cracking is induced by an initial pre-stressing of the composite, coupled with decalcification shrinkage and dramatic decrease in tensile strength during leaching. X-ray microtomography analysis allowed to make evidence of an induced microcracking in cementitious material submitted to leaching.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XHT4G5-2&_user=6 [...] [article] About microcracking due to leaching in cementitious composites : x-ray microtomography description and numerical approach [texte imprimé] / Thomas Rougelot, Auteur ; Nicolas Burlion, Auteur ; Dominique Bernard, Auteur . - 2010 . - pp. 271-283.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 271-283
Mots-clés : Cementitious composites Endogenous and decalcification shrinkages Leaching Microcracking X-ray computed microtomography Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Chemical shock of cement based materials leads to significant degradation of their physical properties. A typical scenario is a calcium leaching due to water (water with very low pH compared with that of pore fluid). The main objective of this paper is to evaluate the evolution of microstructure induced by leaching of a cementitious composite using synchrotron X-ray micro tomography, mainly from an experimental point of view. In this particular case, it was possible to identify cracking induced by leaching. After a description of the degradation mechanism and the X-ray synchrotron microtomographic analysis, numerical simulations are performed in order to show that cracking is induced by an initial pre-stressing of the composite, coupled with decalcification shrinkage and dramatic decrease in tensile strength during leaching. X-ray microtomography analysis allowed to make evidence of an induced microcracking in cementitious material submitted to leaching.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XHT4G5-2&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 284-292
Titre : Carbonation of CH and C–S–H in composite cement pastes containing high amounts of BFS Type de document : texte imprimé Auteurs : Paulo H.R. Borges, Auteur ; Juliana O. Costa, Auteur ; Neil B. Milestone, Auteur Année de publication : 2010 Article en page(s) : pp. 284-292 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Calcium–silicate–hydrate (C–S–H) Thermal analysis Carbonation Granulated blast-furnace slag Résumé : 3:1 BFS:OPC, 9:1 BFS:OPC and 9:1 alkali activated BFS:OPC pastes cured at 20 °C and 60 °C for 90 days were submitted to accelerated carbonation under 5% CO2, 60% relative humidity and 25 ± 5 °C for 21 days. TGA/DTG was used to quantify the amounts of carbonates formed from calcium hydroxide (CH) and calcium silicate hydrate (C–S–H), based on the CH and carbonate contents before and after carbonation. Apparent dry density, apparent porosity and gas permeability were measured before and after accelerated carbonation testing, and the phenolphthalein method used to determine the accelerated carbonation rate. The results showed that samples cured at elevated temperature, i.e. 60 °C, were initially less porous and, therefore, had decreased levels of both total carbonation and C–S–H carbonation. In addition, the carbonation of C–S–H was significantly higher in pastes that contained less CH before carbonation. In the activated 9:1 BFS:OPC, the carbonation of C–S–H was extensive, despite a lower carbonation rate than the analogous non-activated system. In the particular case of activated 9:1 BFS:OPC, a shift in the DTG decarbonation pattern was observed and XRD showed that aragonite was present as one of the calcium carbonate polymorphs.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XRBH3Y-1&_user=6 [...] [article] Carbonation of CH and C–S–H in composite cement pastes containing high amounts of BFS [texte imprimé] / Paulo H.R. Borges, Auteur ; Juliana O. Costa, Auteur ; Neil B. Milestone, Auteur . - 2010 . - pp. 284-292.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 284-292
Mots-clés : Calcium–silicate–hydrate (C–S–H) Thermal analysis Carbonation Granulated blast-furnace slag Résumé : 3:1 BFS:OPC, 9:1 BFS:OPC and 9:1 alkali activated BFS:OPC pastes cured at 20 °C and 60 °C for 90 days were submitted to accelerated carbonation under 5% CO2, 60% relative humidity and 25 ± 5 °C for 21 days. TGA/DTG was used to quantify the amounts of carbonates formed from calcium hydroxide (CH) and calcium silicate hydrate (C–S–H), based on the CH and carbonate contents before and after carbonation. Apparent dry density, apparent porosity and gas permeability were measured before and after accelerated carbonation testing, and the phenolphthalein method used to determine the accelerated carbonation rate. The results showed that samples cured at elevated temperature, i.e. 60 °C, were initially less porous and, therefore, had decreased levels of both total carbonation and C–S–H carbonation. In addition, the carbonation of C–S–H was significantly higher in pastes that contained less CH before carbonation. In the activated 9:1 BFS:OPC, the carbonation of C–S–H was extensive, despite a lower carbonation rate than the analogous non-activated system. In the particular case of activated 9:1 BFS:OPC, a shift in the DTG decarbonation pattern was observed and XRD showed that aragonite was present as one of the calcium carbonate polymorphs.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XRBH3Y-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 293-301
Titre : Biogenic sulfuric acid attack on different types of commercially produced concrete sewer pipes Type de document : texte imprimé Auteurs : Ma. Guadalupe D. Gutiérrez-Padilla, Auteur ; Angela Bielefeldt, Auteur ; Serguei Ovtchinnikov, Auteur Année de publication : 2010 Article en page(s) : pp. 293-301 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Microbial activity Sulfate attack Degradation Waste management Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Laboratory experiments were conducted to compare the degradation of low and high quality concrete under conditions simulating sewer pipes with and without bacteria. Small concrete samples were exposed to hydrogen sulfide, multiple species of bacteria found in corroding sewer pipes and artificial wastewater. Experiments without bacteria were used as controls. The corrosion rates of the concrete samples exposed to bacteria over 227 days were 0.08 mm/yr (millimeters per year) for the concrete from a domestic manufacturer with moderate strength and a lower water–cement ratio (Low-w/c) versus 0.208 mm/yr for the concrete samples from a foreign country with low strength and a higher water–cement ratio (High-w/c). The (Low-w/c) concrete was more resistant to the biodegradation even though a lower pH was attained for its bioactive systems. Experiments showed the influence of biogenic sulfuric acid production on short term corrosion rates.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMK21Y-1&_user=6 [...] [article] Biogenic sulfuric acid attack on different types of commercially produced concrete sewer pipes [texte imprimé] / Ma. Guadalupe D. Gutiérrez-Padilla, Auteur ; Angela Bielefeldt, Auteur ; Serguei Ovtchinnikov, Auteur . - 2010 . - pp. 293-301.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 293-301
Mots-clés : Microbial activity Sulfate attack Degradation Waste management Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Laboratory experiments were conducted to compare the degradation of low and high quality concrete under conditions simulating sewer pipes with and without bacteria. Small concrete samples were exposed to hydrogen sulfide, multiple species of bacteria found in corroding sewer pipes and artificial wastewater. Experiments without bacteria were used as controls. The corrosion rates of the concrete samples exposed to bacteria over 227 days were 0.08 mm/yr (millimeters per year) for the concrete from a domestic manufacturer with moderate strength and a lower water–cement ratio (Low-w/c) versus 0.208 mm/yr for the concrete samples from a foreign country with low strength and a higher water–cement ratio (High-w/c). The (Low-w/c) concrete was more resistant to the biodegradation even though a lower pH was attained for its bioactive systems. Experiments showed the influence of biogenic sulfuric acid production on short term corrosion rates.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMK21Y-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 302-312
Titre : Prediction of time dependent chloride transport in concrete structures exposed to a marine environment Type de document : texte imprimé Auteurs : Seung-Woo Pack, Auteur ; Min-Sun Jung, Auteur ; Ha-Won Song, Auteur Année de publication : 2010 Article en page(s) : pp. 302-312 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Chloride Diffusion Portland cement Granulated blast-furnace slag Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : A survey of 11 concrete bridges located in a marine environment at 0.65–48.65 years was examined in terms of chloride transport. As a result, the apparent diffusion coefficient (D) and the surface chloride concentration (CS) are time dependent; the D exponentially decreased with time and the CS increased in the form of a logarithm function to time. Using these data, governing equations for the D and CS were derived to predict the chloride transport in a long term. The time dependent model indicated the higher chloride ingresses in ordinary Portland cement (OPC) concrete than the time independent model, due to a build-up of the CS with time, but ground granulated blast furnace slag (GGBS) concrete indicated a similar range of the chloride ingresses, due to the rapid decrease in the D. To ensure the accuracy of the model that the present study suggested, the fitted model was compared to the well known model of the LIFE 365 together with a chloride profile obtained from an in-situ examination. Then it was found that the model in the present study well predicted the rate of chloride transport, while the LIFE 365 indicated a poor description of the chloride ingress in a long term, due to a constant CS and an overwhelming rapid decrease in the D.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XHJX8K-2&_user=6 [...] [article] Prediction of time dependent chloride transport in concrete structures exposed to a marine environment [texte imprimé] / Seung-Woo Pack, Auteur ; Min-Sun Jung, Auteur ; Ha-Won Song, Auteur . - 2010 . - pp. 302-312.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 302-312
Mots-clés : Chloride Diffusion Portland cement Granulated blast-furnace slag Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : A survey of 11 concrete bridges located in a marine environment at 0.65–48.65 years was examined in terms of chloride transport. As a result, the apparent diffusion coefficient (D) and the surface chloride concentration (CS) are time dependent; the D exponentially decreased with time and the CS increased in the form of a logarithm function to time. Using these data, governing equations for the D and CS were derived to predict the chloride transport in a long term. The time dependent model indicated the higher chloride ingresses in ordinary Portland cement (OPC) concrete than the time independent model, due to a build-up of the CS with time, but ground granulated blast furnace slag (GGBS) concrete indicated a similar range of the chloride ingresses, due to the rapid decrease in the D. To ensure the accuracy of the model that the present study suggested, the fitted model was compared to the well known model of the LIFE 365 together with a chloride profile obtained from an in-situ examination. Then it was found that the model in the present study well predicted the rate of chloride transport, while the LIFE 365 indicated a poor description of the chloride ingress in a long term, due to a constant CS and an overwhelming rapid decrease in the D.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XHJX8K-2&_user=6 [...]
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 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 321-333
Titre : Influence of free water on the quasi-static and dynamic strength of concrete in confined compression tests Type de document : texte imprimé Auteurs : P. Forquin, Auteur ; K. Safa, Auteur ; G. Gary, Auteur Année de publication : 2010 Article en page(s) : pp. 321-333 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Compressive strength Permeability Strain-rate effect Microconcrete Hopkinson pressure bar Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The behaviour of concrete under high pressure and dynamic loadings is experimentally investigated in the present paper. The specimen is confined in a cylindrical elastic steel ring that insures a quasi-uniaxial strain state of loading. It is subjected to static and dynamic (with strain rates in the range from 1e−6/s to 200/s) axial compressive loadings. Transverse gauges glued on the lateral surface of the ring allow for the measurement of the confining pressure so that the volumetric and the deviatoric response of the specimen can be computed. At high or intermediate strain rates, water saturated and dried specimens show strongly different results: i.e. a continuous increase of strength with pressure in dried specimens and a quasi nil strength enhancement in water-saturated specimens. This difference is not observed with quasi-static loadings. As explained through a basic poromechanics analysis, this dissimilarity is mainly attributed to an increase of pore pressure inside the saturated concrete during fast (quasi-static or dynamic) experiments.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XNMC04-1&_user=6 [...] [article] Influence of free water on the quasi-static and dynamic strength of concrete in confined compression tests [texte imprimé] / P. Forquin, Auteur ; K. Safa, Auteur ; G. Gary, Auteur . - 2010 . - pp. 321-333.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 321-333
Mots-clés : Compressive strength Permeability Strain-rate effect Microconcrete Hopkinson pressure bar Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The behaviour of concrete under high pressure and dynamic loadings is experimentally investigated in the present paper. The specimen is confined in a cylindrical elastic steel ring that insures a quasi-uniaxial strain state of loading. It is subjected to static and dynamic (with strain rates in the range from 1e−6/s to 200/s) axial compressive loadings. Transverse gauges glued on the lateral surface of the ring allow for the measurement of the confining pressure so that the volumetric and the deviatoric response of the specimen can be computed. At high or intermediate strain rates, water saturated and dried specimens show strongly different results: i.e. a continuous increase of strength with pressure in dried specimens and a quasi nil strength enhancement in water-saturated specimens. This difference is not observed with quasi-static loadings. As explained through a basic poromechanics analysis, this dissimilarity is mainly attributed to an increase of pore pressure inside the saturated concrete during fast (quasi-static or dynamic) experiments.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XNMC04-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 334-339
Titre : Effect of elevated temperatures on geopolymer paste, mortar and concrete Type de document : texte imprimé Auteurs : Daniel L. Y. Kong, Auteur ; Jay G. Sanjayan, Auteur Année de publication : 2010 Article en page(s) : pp. 334-339 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Geopolymer Fly ash Temperature Aggregates Concrete Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Geopolymers are generally believed to provide good fire resistance due to their ceramic-like properties. Previous experimental studies on geopolymer under elevated temperatures have mainly focused on metakaolin-based geopolymers. This paper presents the results of a study on the effect of elevated temperature on geopolymer paste, mortar and concrete made using fly ash as a precursor. The geopolymer was synthesized with sodium silicate and potassium hydroxide solutions. Various experimental parameters have been examined such as specimen sizing, aggregate sizing, aggregate type and superplasticizer type. The study identifies specimen size and aggregate size as the two main factors that govern geopolymer behavior at elevated temperatures (800 °C). Aggregate sizes larger than 10 mm resulted in good strength performances in both ambient and elevated temperatures. Strength loss in geopolymer concrete at elevated temperatures is attributed to the thermal mismatch between the geopolymer matrix and the aggregates.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XPXT87-1&_user=6 [...] [article] Effect of elevated temperatures on geopolymer paste, mortar and concrete [texte imprimé] / Daniel L. Y. Kong, Auteur ; Jay G. Sanjayan, Auteur . - 2010 . - pp. 334-339.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 334-339
Mots-clés : Geopolymer Fly ash Temperature Aggregates Concrete Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Geopolymers are generally believed to provide good fire resistance due to their ceramic-like properties. Previous experimental studies on geopolymer under elevated temperatures have mainly focused on metakaolin-based geopolymers. This paper presents the results of a study on the effect of elevated temperature on geopolymer paste, mortar and concrete made using fly ash as a precursor. The geopolymer was synthesized with sodium silicate and potassium hydroxide solutions. Various experimental parameters have been examined such as specimen sizing, aggregate sizing, aggregate type and superplasticizer type. The study identifies specimen size and aggregate size as the two main factors that govern geopolymer behavior at elevated temperatures (800 °C). Aggregate sizes larger than 10 mm resulted in good strength performances in both ambient and elevated temperatures. Strength loss in geopolymer concrete at elevated temperatures is attributed to the thermal mismatch between the geopolymer matrix and the aggregates.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XPXT87-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 340-346
Titre : Nonlinear ultrasonic evaluation of load effects on discontinuities in concrete Type de document : texte imprimé Auteurs : P. Antonaci, Auteur ; C. L. E. Bruno, Auteur ; P. G. Bocca, Auteur Année de publication : 2010 Article en page(s) : pp. 340-346 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Characterization Mechanical properties Microcracking Degradation Concrete Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The presence of discontinuity surfaces in concrete structures, i.e. two or more layers in contact, may be an existing situation with evident relapses on damage formation and progression. Differences occur depending on the type of discontinuity, which could be a thin weaker layer or a pre-existing crack. The behavior of pre-existing interfaces is here studied by means of the Scaling Subtraction Method, a Nonlinear Ultrasonic Non-Destructive Technique, that revealed to be effective in describing the mechanical evolution of concrete samples with discontinuity surfaces under the effects of compressive loads.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJN4W8-1&_user=6 [...] [article] Nonlinear ultrasonic evaluation of load effects on discontinuities in concrete [texte imprimé] / P. Antonaci, Auteur ; C. L. E. Bruno, Auteur ; P. G. Bocca, Auteur . - 2010 . - pp. 340-346.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 340-346
Mots-clés : Characterization Mechanical properties Microcracking Degradation Concrete Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The presence of discontinuity surfaces in concrete structures, i.e. two or more layers in contact, may be an existing situation with evident relapses on damage formation and progression. Differences occur depending on the type of discontinuity, which could be a thin weaker layer or a pre-existing crack. The behavior of pre-existing interfaces is here studied by means of the Scaling Subtraction Method, a Nonlinear Ultrasonic Non-Destructive Technique, that revealed to be effective in describing the mechanical evolution of concrete samples with discontinuity surfaces under the effects of compressive loads.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XJN4W8-1&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 347-351
Titre : Impact resistance of poly (vinyl alcohol) fiber reinforced high-performance organic aggregate cementitious material Type de document : texte imprimé Auteurs : Bo Xu, Auteur ; Houssam A. Toutanji, Auteur ; John Gilbert, Auteur Année de publication : 2010 Article en page(s) : pp. 347-351 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : PVB PVA fiber Impact energy Concrete Hydrogen bond Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Poly(vinyl butyral) (PVB) which has many special engineering aggregate properties such as super lightweight, physical toughness, adhesion to a variety of surfaces and energy-absorbing characteristics is utilized as the sole aggregate in this study to develop a novel cementitious composite reinforced with Poly(vinyl alcohol) (PVA) fiber. Impact energy absorption capacity is evaluated based on the Charpy impact test. The results show that PVB composite material has lower density but higher impact energy absorption capability compared with conventional lightweight concrete and regular concrete. The addition of PVA fiber improves the impact resistance with fiber volume fractions. The remarkable change in the interfacial bond strength contributed by the non-covalent bond such as hydrogen bond and ether interactions at the interfaces between fiber, aggregate and matrix contributes to the improvement of the impact resistant capacity. A model based on fiber bridging mechanics and the rule of mixtures is developed to characterize the impact energy. A good correlation was obtained for the materials tested when experimental results are compared to those predicted by the developed model.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XC3X9D-2&_user=6 [...] [article] Impact resistance of poly (vinyl alcohol) fiber reinforced high-performance organic aggregate cementitious material [texte imprimé] / Bo Xu, Auteur ; Houssam A. Toutanji, Auteur ; John Gilbert, Auteur . - 2010 . - pp. 347-351.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 347-351
Mots-clés : PVB PVA fiber Impact energy Concrete Hydrogen bond Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Poly(vinyl butyral) (PVB) which has many special engineering aggregate properties such as super lightweight, physical toughness, adhesion to a variety of surfaces and energy-absorbing characteristics is utilized as the sole aggregate in this study to develop a novel cementitious composite reinforced with Poly(vinyl alcohol) (PVA) fiber. Impact energy absorption capacity is evaluated based on the Charpy impact test. The results show that PVB composite material has lower density but higher impact energy absorption capability compared with conventional lightweight concrete and regular concrete. The addition of PVA fiber improves the impact resistance with fiber volume fractions. The remarkable change in the interfacial bond strength contributed by the non-covalent bond such as hydrogen bond and ether interactions at the interfaces between fiber, aggregate and matrix contributes to the improvement of the impact resistant capacity. A model based on fiber bridging mechanics and the rule of mixtures is developed to characterize the impact energy. A good correlation was obtained for the materials tested when experimental results are compared to those predicted by the developed model.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XC3X9D-2&_user=6 [...]
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 352-358
Titre : High porosity (> 90%) cementitious foams Type de document : texte imprimé Auteurs : F.K. Akthar, Auteur ; J.R.G. Evans, Auteur Année de publication : 2010 Article en page(s) : pp. 352-358 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Microstructure Compressive strength Transport properties Fibre reinforcement Foams Résumé : High porosity foams based on Portland limestone cement or gypsum plaster were prepared by a simple method of stirring and drying using low levels of the food additives: methyl cellulose and iota carageenan gum. Thermal conductivity of 0.11 W m− 1 K− 1 at 92% porosity was achieved but compressive strength was also very low. Foams were almost closed cell. Attempts to improve strength by incorporation of short staple glass fibre were only partially successful because of a change in the failure mode from progressive collapse to uniform fibre-cement debonding facilitated by the ability of the fibre network to transmit stress throughout the assembly. This approach to fire resistant insulation materials does not yet match the high strength/conductivity ratios of calcium silicate products but deserves exploring because of the simplicity of preparation and the compositional freedom for using mixtures of hydraulic cement and other powders.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMC05Y-1&_user=6 [...] [article] High porosity (> 90%) cementitious foams [texte imprimé] / F.K. Akthar, Auteur ; J.R.G. Evans, Auteur . - 2010 . - pp. 352-358.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 40 N° 2 (02 ex.) (Fevrier 2010) . - pp. 352-358
Mots-clés : Microstructure Compressive strength Transport properties Fibre reinforcement Foams Résumé : High porosity foams based on Portland limestone cement or gypsum plaster were prepared by a simple method of stirring and drying using low levels of the food additives: methyl cellulose and iota carageenan gum. Thermal conductivity of 0.11 W m− 1 K− 1 at 92% porosity was achieved but compressive strength was also very low. Foams were almost closed cell. Attempts to improve strength by incorporation of short staple glass fibre were only partially successful because of a change in the failure mode from progressive collapse to uniform fibre-cement debonding facilitated by the ability of the fibre network to transmit stress throughout the assembly. This approach to fire resistant insulation materials does not yet match the high strength/conductivity ratios of calcium silicate products but deserves exploring because of the simplicity of preparation and the compositional freedom for using mixtures of hydraulic cement and other powders.
DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XMC05Y-1&_user=6 [...]
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