Dépouillements

Microstructural development of early age hydration shells around cement grains / E. Gallucci in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 4-13 Titre : Microstructural development of early age hydration shells around cement grains Type de document : texte imprimé Auteurs : E. Gallucci, Auteur ; P. Mathur, Auteur ; K. Scrivener, Auteur Année de publication : 2010 Article en page(s) : pp. 4-13 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : TEM  Early  age  Hydration  shells  Cement  microstructure  C–S–H Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : An important microstructural aspect of the early hydration of Portland cement (PC) is the formation of a shell of hydration products around cement grains. There is, at present, limited information on the mechanism of formation of the shell and of the chemistry of the phases that constitute the shells. Through the use of STEM imaging of early age hydrated cement pastes as early as 2 h, the present work shows that the shells correspond to the first C–S–H type product formed which has a distinct morphology compared to C–S–H formed later when the main reaction occurs (nucleation and growth stage at setting time). The shells form only around the silicate part of the grain and are not empty but filled with a fragile fibrous C–S–H which appears to have a lower (packing) density than the rest of the hydration products. The cement grains underneath the shells are seen to react unevenly and the hydration seems to follow a reaction front, leaving striations up to 1 µm deep on the grains. Over the long term, the original fragile product seems to densify and gives rise to the usual inner C–S–H. High resolution EDS chemical analysis and mappings were used to get insight into the chemistry associated with the formation of these early age products. The C/S ratio of all C–S–H (inner and outer shell) is the same (within the limits of the analysis accuracy) and evolves insignificantly over the first 24 h of hydration. High concentrations of sulfate are associated with the C–S–H formed during the early development of the microstructure, but these decrease later, the sulfate being mainly incorporated into ettringite. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XG90C3-2&_user=6 [...] [article] Microstructural development of early age hydration shells around cement grains [texte imprimé] / E. Gallucci, Auteur ; P. Mathur, Auteur ; K. Scrivener, Auteur . - 2010 . - pp. 4-13. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 4-13 Mots-clés : TEM  Early  age  Hydration  shells  Cement  microstructure  C–S–H Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : An important microstructural aspect of the early hydration of Portland cement (PC) is the formation of a shell of hydration products around cement grains. There is, at present, limited information on the mechanism of formation of the shell and of the chemistry of the phases that constitute the shells. Through the use of STEM imaging of early age hydrated cement pastes as early as 2 h, the present work shows that the shells correspond to the first C–S–H type product formed which has a distinct morphology compared to C–S–H formed later when the main reaction occurs (nucleation and growth stage at setting time). The shells form only around the silicate part of the grain and are not empty but filled with a fragile fibrous C–S–H which appears to have a lower (packing) density than the rest of the hydration products. The cement grains underneath the shells are seen to react unevenly and the hydration seems to follow a reaction front, leaving striations up to 1 µm deep on the grains. Over the long term, the original fragile product seems to densify and gives rise to the usual inner C–S–H. High resolution EDS chemical analysis and mappings were used to get insight into the chemistry associated with the formation of these early age products. The C/S ratio of all C–S–H (inner and outer shell) is the same (within the limits of the analysis accuracy) and evolves insignificantly over the first 24 h of hydration. High concentrations of sulfate are associated with the C–S–H formed during the early development of the microstructure, but these decrease later, the sulfate being mainly incorporated into ettringite. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XG90C3-2&_user=6 [...]

Nanogranular packing of C–S–H at substochiometric conditions / Matthieu Vandamme in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 14-26 Titre : Nanogranular packing of C–S–H at substochiometric conditions Type de document : texte imprimé Auteurs : Matthieu Vandamme, Auteur ; Ulm, Franz-Josef, Auteur ; Philip Fonollosa, Auteur Article en page(s) : pp. 14-26 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Nanoindentation  C–S–H  packing  density  Mix  compositions  Heat  treatment  Microstructure Résumé : Herein, we present a comprehensive nanoindentation investigation of cement pastes prepared at substoichiometric water-to-cement (w/c) mass ratios between 0.15 and 0.4 with and without heat treatment. Based on a statistical indentation technique, we provide strong evidence of the existence of a statistically significant third hydrated mechanical phase in addition to the already known Low-Density (LD) and High-Density (HD) C–S–H phases. The nanomechanical properties of this third phase are found to follow similar packing density scaling relations as LD C–S–H and HD C–S–H, while being significantly greater. This third phase, whose nano-packing density is measured at 0.83 ± 0.01, is therefore termed Ultra-High-Density (UHD) phase. All three phases are present in concrete materials in different volume proportions: LD dominates cement-based materials prepared at high w/c mass ratios; HD and UHD control the microstructure of low w/c ratio materials. In addition, heat treatment favors the formation of HD and UHD. The insight thus gained into the link between composition, processing and microstructure makes it possible to monitor packing density distributions of the hydration products at the nanoscale. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XGCHXD-1&_user=6 [...] [article] Nanogranular packing of C–S–H at substochiometric conditions [texte imprimé] / Matthieu Vandamme, Auteur ; Ulm, Franz-Josef, Auteur ; Philip Fonollosa, Auteur . - pp. 14-26. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 14-26 Mots-clés : Nanoindentation  C–S–H  packing  density  Mix  compositions  Heat  treatment  Microstructure Résumé : Herein, we present a comprehensive nanoindentation investigation of cement pastes prepared at substoichiometric water-to-cement (w/c) mass ratios between 0.15 and 0.4 with and without heat treatment. Based on a statistical indentation technique, we provide strong evidence of the existence of a statistically significant third hydrated mechanical phase in addition to the already known Low-Density (LD) and High-Density (HD) C–S–H phases. The nanomechanical properties of this third phase are found to follow similar packing density scaling relations as LD C–S–H and HD C–S–H, while being significantly greater. This third phase, whose nano-packing density is measured at 0.83 ± 0.01, is therefore termed Ultra-High-Density (UHD) phase. All three phases are present in concrete materials in different volume proportions: LD dominates cement-based materials prepared at high w/c mass ratios; HD and UHD control the microstructure of low w/c ratio materials. In addition, heat treatment favors the formation of HD and UHD. The insight thus gained into the link between composition, processing and microstructure makes it possible to monitor packing density distributions of the hydration products at the nanoscale. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XGCHXD-1&_user=6 [...]

Effect on fresh C-S-H gels of the simultaneous addition of alkali and aluminium / I. García Lodeiro in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 27-32 Titre : Effect on fresh C-S-H gels of the simultaneous addition of alkali and aluminium Type de document : texte imprimé Auteurs : I. García Lodeiro, Auteur ; A. Fernandez-Jimenez, Auteur ; A. Palomo, Auteur Article en page(s) : pp. 27-32 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Calcium-Silicate-Hydrate  (C-S-H)  Spectroscopy  TEM  Stratlingite Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Reducing Portland cement content in cementitious binders offers a means to address the adverse environmental impacts of Portland cement manufacture. This paper investigates the impacts on hydration product chemistry of partially replacing Portland cement with alkali-activated aluminosilicates. Here, short-term effects of soluble alkali and aluminium, likely to be available in an alkali-activated system, on the structure of synthetic C-S-H gels are assessed. .C-S-H gels (synthesized at pH values of over 13) were mixed with different concentrations of aluminium nitrate and sodium hydroxide. The gels were characterized by FTIR, TEM/EDX and XRD 72 h later. The results showed that both alkali and aluminium increased the degree of silicate polymerisation in the C-S-H gels and precipitated a crystalline calcium aluminosilicate phase. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4X5YWSN-2&_user=6 [...] [article] Effect on fresh C-S-H gels of the simultaneous addition of alkali and aluminium [texte imprimé] / I. García Lodeiro, Auteur ; A. Fernandez-Jimenez, Auteur ; A. Palomo, Auteur . - pp. 27-32. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 27-32 Mots-clés : Calcium-Silicate-Hydrate  (C-S-H)  Spectroscopy  TEM  Stratlingite Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Reducing Portland cement content in cementitious binders offers a means to address the adverse environmental impacts of Portland cement manufacture. This paper investigates the impacts on hydration product chemistry of partially replacing Portland cement with alkali-activated aluminosilicates. Here, short-term effects of soluble alkali and aluminium, likely to be available in an alkali-activated system, on the structure of synthetic C-S-H gels are assessed. .C-S-H gels (synthesized at pH values of over 13) were mixed with different concentrations of aluminium nitrate and sodium hydroxide. The gels were characterized by FTIR, TEM/EDX and XRD 72 h later. The results showed that both alkali and aluminium increased the degree of silicate polymerisation in the C-S-H gels and precipitated a crystalline calcium aluminosilicate phase. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4X5YWSN-2&_user=6 [...]

An investigation of microstructure evolution in cement paste through setting using ultrasonic and rheological measurements / Kolluru V. Subramaniam in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 33-44 Titre : An investigation of microstructure evolution in cement paste through setting using ultrasonic and rheological measurements Type de document : texte imprimé Auteurs : Kolluru V. Subramaniam, Auteur ; Xiaojun Wang, Auteur Article en page(s) : pp. 33-44 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Microstructure  Porosity  Rheology  Ultrasonic  Testing  Setting Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The response of hydrating cement paste through setting are monitored using rheological measurements and ultrasonic reflection measurements. Increases in the elastic modulus and yield stress of cement paste with time are obtained from the rheological measurements. Ultrasonic measurements are performed using horizontally polarized shear waves (SH) reflected off of the hydrating cement paste. Changes in the ultrasonic signal through setting are related with changes in the porosity and stiffness of an equivalent water-filled poroelastic material, which provides identical acoustic impedance. The measured changes in the shear modulus obtained from ultrasonic measurement are shown to correlate well with increase in elastic modulus obtained from rheological measurements. The increase in the shear modulus of the porous material obtained from the ultrasonic measurements is shown to correspond well with the observed increase in the yield stress of the cement paste. By combining the information from rheological and ultrasonic measurements, it is found that even in the fluid stage there is sufficient structural integrity in the arrangement of cement grains to support low-amplitude shear stress and the evolution of a continuously connected network of cement particles within the paste is coincident with a rapid increase in the shear modulus of the porous skeleton. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XHJX8K-1&_user=6 [...] [article] An investigation of microstructure evolution in cement paste through setting using ultrasonic and rheological measurements [texte imprimé] / Kolluru V. Subramaniam, Auteur ; Xiaojun Wang, Auteur . - pp. 33-44. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 33-44 Mots-clés : Microstructure  Porosity  Rheology  Ultrasonic  Testing  Setting Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The response of hydrating cement paste through setting are monitored using rheological measurements and ultrasonic reflection measurements. Increases in the elastic modulus and yield stress of cement paste with time are obtained from the rheological measurements. Ultrasonic measurements are performed using horizontally polarized shear waves (SH) reflected off of the hydrating cement paste. Changes in the ultrasonic signal through setting are related with changes in the porosity and stiffness of an equivalent water-filled poroelastic material, which provides identical acoustic impedance. The measured changes in the shear modulus obtained from ultrasonic measurement are shown to correlate well with increase in elastic modulus obtained from rheological measurements. The increase in the shear modulus of the porous material obtained from the ultrasonic measurements is shown to correspond well with the observed increase in the yield stress of the cement paste. By combining the information from rheological and ultrasonic measurements, it is found that even in the fluid stage there is sufficient structural integrity in the arrangement of cement grains to support low-amplitude shear stress and the evolution of a continuously connected network of cement particles within the paste is coincident with a rapid increase in the shear modulus of the porous skeleton. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4XHJX8K-1&_user=6 [...]

Fundamental mechanisms for polycarboxylate intercalation into C3A hydrate phases and the role of sulfate present in cement / Johann Plank in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 45-57 Titre : Fundamental mechanisms for polycarboxylate intercalation into C3A hydrate phases and the role of sulfate present in cement Type de document : texte imprimé Auteurs : Johann Plank, Auteur ; Dai Zhimin, Auteur ; Helena Keller, Auteur Article en page(s) : pp. 45-57 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Cement  Polymers  Concrete  Admixture  Organo-mineral  phase Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The fundamental reactions leading to the intercalation of polycarboxylate (PC) superplasticizers into calcium aluminum hydrates were studied by hydration of pure C3A in the presence of PC at 75 °C. It was found that the amount of dissolved sulfate present in cement pore solution determines whether organo-mineral phases are formed or not. In the absence of sulfate, PCs easily intercalate during C3A hydration in alkaline solution. Under these conditions, only excessive steric size of the PC will prevent intercalation. At low sulfate concentrations (SO42−/C3A molar ratios of 0.1–0.35), PC intercalates with intersalated alkali sulfate, are formed. At high sulfate concentrations (SO42−/C3A molar ratios of 0.7–2), PC can no longer intercalate. Instead, sulfate, because of its higher negative charge density, fills the interlayer space and monosulfoaluminates with different water contents are formed. Anion exchange experiments confirm that from the initially formed C4AH13, PC will exchange the interlayer OH− anion whereas with monosulfoaluminates, no replacement of sulfate by PC was found. Consequently, in alkaline solution, PC intercalates will not exchange their PC against OH− anions whereas sulfate will gradually replace the PC. Generally, intercalation of PC is an unwanted process because it consumes superplasticizer which is effective only when it adsorbs onto the cationic surfaces of AFm and AFt phases. Our experiments demonstrate that intercalation can be avoided by using PCs with long side chains or highly sulfated cements (SO42−/C3A molar ratio ≥ 0.75) containing alkali or calcium sulfates which dissolve fast. In undersulfated cements, however, PC intercalates can be formed, either directly during the stacking process of the [Ca2Al(OH)6]+ main layer, with PC acting as the template which determines the interlayer distance, or by anion exchange between initially formed aluminate hydrates (e.g. C4AH13 or C2AH8) and the PC anion. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4X7FRPX-3&_user=6 [...] [article] Fundamental mechanisms for polycarboxylate intercalation into C3A hydrate phases and the role of sulfate present in cement [texte imprimé] / Johann Plank, Auteur ; Dai Zhimin, Auteur ; Helena Keller, Auteur . - pp. 45-57. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 45-57 Mots-clés : Cement  Polymers  Concrete  Admixture  Organo-mineral  phase Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The fundamental reactions leading to the intercalation of polycarboxylate (PC) superplasticizers into calcium aluminum hydrates were studied by hydration of pure C3A in the presence of PC at 75 °C. It was found that the amount of dissolved sulfate present in cement pore solution determines whether organo-mineral phases are formed or not. In the absence of sulfate, PCs easily intercalate during C3A hydration in alkaline solution. Under these conditions, only excessive steric size of the PC will prevent intercalation. At low sulfate concentrations (SO42−/C3A molar ratios of 0.1–0.35), PC intercalates with intersalated alkali sulfate, are formed. At high sulfate concentrations (SO42−/C3A molar ratios of 0.7–2), PC can no longer intercalate. Instead, sulfate, because of its higher negative charge density, fills the interlayer space and monosulfoaluminates with different water contents are formed. Anion exchange experiments confirm that from the initially formed C4AH13, PC will exchange the interlayer OH− anion whereas with monosulfoaluminates, no replacement of sulfate by PC was found. Consequently, in alkaline solution, PC intercalates will not exchange their PC against OH− anions whereas sulfate will gradually replace the PC. Generally, intercalation of PC is an unwanted process because it consumes superplasticizer which is effective only when it adsorbs onto the cationic surfaces of AFm and AFt phases. Our experiments demonstrate that intercalation can be avoided by using PCs with long side chains or highly sulfated cements (SO42−/C3A molar ratio ≥ 0.75) containing alkali or calcium sulfates which dissolve fast. In undersulfated cements, however, PC intercalates can be formed, either directly during the stacking process of the [Ca2Al(OH)6]+ main layer, with PC acting as the template which determines the interlayer distance, or by anion exchange between initially formed aluminate hydrates (e.g. C4AH13 or C2AH8) and the PC anion. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4X7FRPX-3&_user=6 [...]

Unified modeling of setting and strength development / R.C.A. Pinto in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 58-65 Titre : Unified modeling of setting and strength development Type de document : texte imprimé Auteurs : R.C.A. Pinto, Auteur ; A.K. Schindler, Auteur Article en page(s) : pp. 58-65 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Maturity  method  Aging  Compressive  strength  Temperature Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The effect of temperature on the development of concrete compressive strength can be modeled by the maturity approach once the temperature sensitivity of the mixture, quantified by the activation energy (Ea) of its chemical reactions, is known. It is common in maturity applications to use a unique value of Ea obtained for the hardening period, even though the effect of temperature is different on the rate of setting and hardening. Ea-values presented in the literature suggest that the temperature sensitivity is lower before hardening. This paper proposes a new approach to the traditional maturity method unifying the distinctly different temperature sensitivities before final setting and during hardening. Results of setting and compressive strength of mixtures with different cementitious materials were analyzed with activation energy values calculated for the periods before final setting and during hardening. For the investigated mixtures, the new approach led to improved strength predictions, suggesting that it is useful to take into account setting behavior in the development of the strength–maturity relationship. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4X6DBN1-2&_user=6 [...] [article] Unified modeling of setting and strength development [texte imprimé] / R.C.A. Pinto, Auteur ; A.K. Schindler, Auteur . - pp. 58-65. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 58-65 Mots-clés : Maturity  method  Aging  Compressive  strength  Temperature Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The effect of temperature on the development of concrete compressive strength can be modeled by the maturity approach once the temperature sensitivity of the mixture, quantified by the activation energy (Ea) of its chemical reactions, is known. It is common in maturity applications to use a unique value of Ea obtained for the hardening period, even though the effect of temperature is different on the rate of setting and hardening. Ea-values presented in the literature suggest that the temperature sensitivity is lower before hardening. This paper proposes a new approach to the traditional maturity method unifying the distinctly different temperature sensitivities before final setting and during hardening. Results of setting and compressive strength of mixtures with different cementitious materials were analyzed with activation energy values calculated for the periods before final setting and during hardening. For the investigated mixtures, the new approach led to improved strength predictions, suggesting that it is useful to take into account setting behavior in the development of the strength–maturity relationship. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWG-4X6DBN1-2&_user=6 [...]

Assessment of phase formation in lime-based mortars with added metakaolin, Portland cement and sepiolite, for grouting of historic masonry / Alberto Sepulcre-Aguilar in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 66-76 Titre : Assessment of phase formation in lime-based mortars with added metakaolin, Portland cement and sepiolite, for grouting of historic masonry Type de document : texte imprimé Auteurs : Alberto Sepulcre-Aguilar, Auteur ; Francisco Hernandez-Olivares, Auteur Article en page(s) : pp. 66-76 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Blended  lime–cement  mortars  Restoration  mortars  Pozzolanic  additions  Metakaolin  Thermal  analysis Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Lime-based mortars containing pozzolanic additions of metakaolin, sepiolite and white Portland cement are studied in order to determine their performance as historic masonry conservation mortars. Hydration products on metakaolin–lime blended mortars include stable and metastable phases. The presence of such products has been studied by means of DTA and XRD analysis, concluding that the selection between them is mainly related with the water–lime ratio. Sepiolite addition to metakaolin–lime mortars has shown to inhibit C4AH13 formation. Therefore, the influence of phase distribution on the mechanical resistance is considered. Finally, compounds production on blended lime–white Portland cement was compared to natural hydraulic lime ones, and as a result, no remarkable differences appeared, apart from traces of possible cement Portland addition to the latter, usually not mentioned in the nominal composition supplied by the manufacturers of lime binders. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Assessment of phase formation in lime-based mortars with added metakaolin, Portland cement and sepiolite, for grouting of historic masonry [texte imprimé] / Alberto Sepulcre-Aguilar, Auteur ; Francisco Hernandez-Olivares, Auteur . - pp. 66-76. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 66-76 Mots-clés : Blended  lime–cement  mortars  Restoration  mortars  Pozzolanic  additions  Metakaolin  Thermal  analysis Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Lime-based mortars containing pozzolanic additions of metakaolin, sepiolite and white Portland cement are studied in order to determine their performance as historic masonry conservation mortars. Hydration products on metakaolin–lime blended mortars include stable and metastable phases. The presence of such products has been studied by means of DTA and XRD analysis, concluding that the selection between them is mainly related with the water–lime ratio. Sepiolite addition to metakaolin–lime mortars has shown to inhibit C4AH13 formation. Therefore, the influence of phase distribution on the mechanical resistance is considered. Finally, compounds production on blended lime–white Portland cement was compared to natural hydraulic lime ones, and as a result, no remarkable differences appeared, apart from traces of possible cement Portland addition to the latter, usually not mentioned in the nominal composition supplied by the manufacturers of lime binders. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Steady state flow of cement suspensions / Nicolas Roussel in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 77-84 Titre : Steady state flow of cement suspensions : a micromechanical state of the art Type de document : texte imprimé Auteurs : Nicolas Roussel, Auteur ; Anael Lemaître, Auteur ; Robert J. Flatt, Auteur Article en page(s) : pp. 77-84 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Admixture  Particles  Rheology  Shear  thickening  Yield  stress Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Fresh cementitious pastes can be viewed as suspensions of particles of many different sizes (from several tens of nm to 100 μm) in a continuous fluid phase. This broad poly-dispersity implies that various interactions such as surface forces (or colloidal interactions), Brownian forces, hydrodynamic forces or various contact forces between particles interplay. Depending on the volume fraction of the particles in the mixture, the use of admixtures or the magnitude of either the applied stress or strain rate, one or several of these interactions dominate. Our objective here is not to quantitatively predict rheology of cement pastes but rather to understand and classify the situations where, depending on composition and processing, one or other of the physical phenomena will control the macroscopic behavior. The result of this analysis is a conceptual diagram of predominant interactions in flowing cementitious suspensions under simple shear, as a function of shear rate and solid fraction. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Steady state flow of cement suspensions : a micromechanical state of the art [texte imprimé] / Nicolas Roussel, Auteur ; Anael Lemaître, Auteur ; Robert J. Flatt, Auteur . - pp. 77-84. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 77-84 Mots-clés : Admixture  Particles  Rheology  Shear  thickening  Yield  stress Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Fresh cementitious pastes can be viewed as suspensions of particles of many different sizes (from several tens of nm to 100 μm) in a continuous fluid phase. This broad poly-dispersity implies that various interactions such as surface forces (or colloidal interactions), Brownian forces, hydrodynamic forces or various contact forces between particles interplay. Depending on the volume fraction of the particles in the mixture, the use of admixtures or the magnitude of either the applied stress or strain rate, one or several of these interactions dominate. Our objective here is not to quantitatively predict rheology of cement pastes but rather to understand and classify the situations where, depending on composition and processing, one or other of the physical phenomena will control the macroscopic behavior. The result of this analysis is a conceptual diagram of predominant interactions in flowing cementitious suspensions under simple shear, as a function of shear rate and solid fraction. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar / Peter Grassl in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 85-93 Titre : Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar Type de document : texte imprimé Auteurs : Peter Grassl, Auteur ; Hong S. Wong, Auteur ; Nick R. Buenfeld, Auteur Article en page(s) : pp. 85-93 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Microcracking  Interfacial  transition  zone  Transport  properties  Shrinkage  Aggregate  Lattice  modelling Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In this paper, the influence of aggregate size and volume fraction on shrinkage induced micro-cracking and permeability of concrete and mortar was investigated. Nonlinear finite element analyses of model concrete and mortar specimens with regular and random aggregate arrangements were performed. The aggregate diameter was varied between 2 and 16 mm. Furthermore, a range of volume fractions between 0.1 and 0.5 was studied. The nonlinear analyses were based on a 2D lattice approach in which aggregates were simplified as monosized cylindrical inclusions. The analysis results were interpreted by means of crack length, crack width and change of permeability. The results show that increasing aggregate diameter (at equal volume fraction) and decreasing volume fraction (at equal aggregate diameter) increase crack width and consequently greatly increases permeability. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar [texte imprimé] / Peter Grassl, Auteur ; Hong S. Wong, Auteur ; Nick R. Buenfeld, Auteur . - pp. 85-93. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 85-93 Mots-clés : Microcracking  Interfacial  transition  zone  Transport  properties  Shrinkage  Aggregate  Lattice  modelling Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In this paper, the influence of aggregate size and volume fraction on shrinkage induced micro-cracking and permeability of concrete and mortar was investigated. Nonlinear finite element analyses of model concrete and mortar specimens with regular and random aggregate arrangements were performed. The aggregate diameter was varied between 2 and 16 mm. Furthermore, a range of volume fractions between 0.1 and 0.5 was studied. The nonlinear analyses were based on a 2D lattice approach in which aggregates were simplified as monosized cylindrical inclusions. The analysis results were interpreted by means of crack length, crack width and change of permeability. The results show that increasing aggregate diameter (at equal volume fraction) and decreasing volume fraction (at equal aggregate diameter) increase crack width and consequently greatly increases permeability. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

New observations on the mechanism of lithium nitrate against alkali silica reaction (ASR) / X. Feng in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 94-101 Titre : New observations on the mechanism of lithium nitrate against alkali silica reaction (ASR) Type de document : texte imprimé Auteurs : X. Feng, Auteur ; M.D.A. Thomas, Auteur ; T. W. Bremner, Auteur Article en page(s) : pp. 94-101 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Lithium  nitrate  Alkali  silica  reaction  (ASR)  Vycor  glass  Mechanism Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In the current study, in order to elucidate the mechanisms for the favorable effects of lithium nitrate in controlling alkali silica reaction (ASR), vycor glass disk immersion specimens and glass disk–cement paste sandwich specimens were prepared and examined by XRD, SEM and Laser Ablation Induction Coupled Plasma Mass Spectrometry (LA-ICP-MS). Results showed that when glass disk was immersed in only NaOH solution, the glass was attacked by hydroxyl ions but no solid reaction product was found, thus the presence of calcium was essential for the formation of ASR gel. In the presence of lithium, the glass surface was covered by a thick layer of Li–Si crystal. With the addition of Ca(OH)2, the glass surface was completely covered by Li–Si crystal and a lithium-bearing low Ca–Na–(K)–Si gel. These two phases either form a dense matrix with Li–Si crystal serving as the framework, and the gel filling in the void space, or the Li–Si crystal serving as the foundation to completely cover the entire reactive SiO2 surface, and the gel sitting on top of these crystal particles. Hence, the suppressive effects of LiNO3 were attributed to the formation of a layer of Li–Si crystals intimately at the reactive SiO2 particle surface and the formation of Li-bearing low-Ca ASR gel products. The Li-bearing low-Ca ASR gels may have a dense and rigid structure, thus having low capacity to absorb moisture from the surrounding paste, and exhibiting a non-swelling property. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] New observations on the mechanism of lithium nitrate against alkali silica reaction (ASR) [texte imprimé] / X. Feng, Auteur ; M.D.A. Thomas, Auteur ; T. W. Bremner, Auteur . - pp. 94-101. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 94-101 Mots-clés : Lithium  nitrate  Alkali  silica  reaction  (ASR)  Vycor  glass  Mechanism Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In the current study, in order to elucidate the mechanisms for the favorable effects of lithium nitrate in controlling alkali silica reaction (ASR), vycor glass disk immersion specimens and glass disk–cement paste sandwich specimens were prepared and examined by XRD, SEM and Laser Ablation Induction Coupled Plasma Mass Spectrometry (LA-ICP-MS). Results showed that when glass disk was immersed in only NaOH solution, the glass was attacked by hydroxyl ions but no solid reaction product was found, thus the presence of calcium was essential for the formation of ASR gel. In the presence of lithium, the glass surface was covered by a thick layer of Li–Si crystal. With the addition of Ca(OH)2, the glass surface was completely covered by Li–Si crystal and a lithium-bearing low Ca–Na–(K)–Si gel. These two phases either form a dense matrix with Li–Si crystal serving as the framework, and the gel filling in the void space, or the Li–Si crystal serving as the foundation to completely cover the entire reactive SiO2 surface, and the gel sitting on top of these crystal particles. Hence, the suppressive effects of LiNO3 were attributed to the formation of a layer of Li–Si crystals intimately at the reactive SiO2 particle surface and the formation of Li-bearing low-Ca ASR gel products. The Li-bearing low-Ca ASR gels may have a dense and rigid structure, thus having low capacity to absorb moisture from the surrounding paste, and exhibiting a non-swelling property. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Effect of moisture content of concrete on water uptake / P. Rucker-Gramm in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 102-108 Titre : Effect of moisture content of concrete on water uptake Type de document : texte imprimé Auteurs : P. Rucker-Gramm, Auteur ; R. E. Beddoe, Auteur Article en page(s) : pp. 102-108 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Water  penetration  Permeability  Transport  properties Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The penetration of water and non-polar hexane in Portland cement mortar prisms with different initial moisture contents was investigated using nuclear magnetic resonance (1H NMR). The amount of water in gel pores strongly affects the penetration of water in much larger capillary pores. Water penetration is reduced by the self-sealing effect as characterized by non-√t dependence of capillary uptake and penetration depth. This is explained by the ongoing redistribution of water from capillaries into gel pores which results in internal swelling and loss of continuity of the capillary pore system; a correlation was observed between the amount of redistributed water and departure from √t behaviour. A descriptive model is used to explain the dependence of water uptake and penetration on moisture content. For increasing initial moisture contents up to a critical value equivalent to equilibrium with a relative humidity between 65 and 80%, less penetrating water is able to redistribute. Thus more penetrating water is in larger capillaries with less viscous resistance; uptake and penetration depth increase. Above the critical initial moisture content, uptake and penetration depth decrease towards zero. This is explained by (a) an overall reduction in capillary pressure because transport takes places in fewer and larger pores and (b) an increase in viscous resistance due to the connection of penetrating capillary water with pores already containing water. Less capillary pore space is available for transport. The surface region of concrete placed in contact with water is not instantaneously saturated. Water content increases with time depending on the degree of surface saturation. A new transition coefficient for capillary suction γ is defined for the calculation of surface flux. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Effect of moisture content of concrete on water uptake [texte imprimé] / P. Rucker-Gramm, Auteur ; R. E. Beddoe, Auteur . - pp. 102-108. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 102-108 Mots-clés : Water  penetration  Permeability  Transport  properties Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : The penetration of water and non-polar hexane in Portland cement mortar prisms with different initial moisture contents was investigated using nuclear magnetic resonance (1H NMR). The amount of water in gel pores strongly affects the penetration of water in much larger capillary pores. Water penetration is reduced by the self-sealing effect as characterized by non-√t dependence of capillary uptake and penetration depth. This is explained by the ongoing redistribution of water from capillaries into gel pores which results in internal swelling and loss of continuity of the capillary pore system; a correlation was observed between the amount of redistributed water and departure from √t behaviour. A descriptive model is used to explain the dependence of water uptake and penetration on moisture content. For increasing initial moisture contents up to a critical value equivalent to equilibrium with a relative humidity between 65 and 80%, less penetrating water is able to redistribute. Thus more penetrating water is in larger capillaries with less viscous resistance; uptake and penetration depth increase. Above the critical initial moisture content, uptake and penetration depth decrease towards zero. This is explained by (a) an overall reduction in capillary pressure because transport takes places in fewer and larger pores and (b) an increase in viscous resistance due to the connection of penetrating capillary water with pores already containing water. Less capillary pore space is available for transport. The surface region of concrete placed in contact with water is not instantaneously saturated. Water content increases with time depending on the degree of surface saturation. A new transition coefficient for capillary suction γ is defined for the calculation of surface flux. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Comprehensive modeling of chloride ion and water ingress into concrete considering thermal and carbonation state for real climate / David Conciatori in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 109-118 Titre : Comprehensive modeling of chloride ion and water ingress into concrete considering thermal and carbonation state for real climate Type de document : texte imprimé Auteurs : David Conciatori, Auteur ; Francine Laferrière, Auteur ; Eugen Brühwiler, Auteur Article en page(s) : pp. 109-118 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Adsorption  Carbonation  Diffusion  Chloride  Thermal  analysis  Finite  element  analysis Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : This article presents a comprehensive modeling of temperature, carbonation, water and chloride ions transport in cover concrete using the transport model “TransChlor”. The TransChlor transport model employs weather data and chloride ion concentrations present on the concrete surface to predict the temporal and spatial evolution of the presence of chloride ion concentrations in the cover concrete pores. The main features of the TransChlor model are presented and validated. The TransChlor model has been calibrated using experimental data on liquid water movement in concrete of different permeabilities under realistic microclimatic conditions. Chloride ion transport is validated by means of experimental results obtained from a newly developed chloride ion optical fiber based sensor. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Comprehensive modeling of chloride ion and water ingress into concrete considering thermal and carbonation state for real climate [texte imprimé] / David Conciatori, Auteur ; Francine Laferrière, Auteur ; Eugen Brühwiler, Auteur . - pp. 109-118. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 109-118 Mots-clés : Adsorption  Carbonation  Diffusion  Chloride  Thermal  analysis  Finite  element  analysis Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : This article presents a comprehensive modeling of temperature, carbonation, water and chloride ions transport in cover concrete using the transport model “TransChlor”. The TransChlor transport model employs weather data and chloride ion concentrations present on the concrete surface to predict the temporal and spatial evolution of the presence of chloride ion concentrations in the cover concrete pores. The main features of the TransChlor model are presented and validated. The TransChlor model has been calibrated using experimental data on liquid water movement in concrete of different permeabilities under realistic microclimatic conditions. Chloride ion transport is validated by means of experimental results obtained from a newly developed chloride ion optical fiber based sensor. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Analysis of carbonation behavior in concrete using neural network algorithm and carbonation modeling / Seung-Jun Kwon in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 119-127 Titre : Analysis of carbonation behavior in concrete using neural network algorithm and carbonation modeling Type de document : texte imprimé Auteurs : Seung-Jun Kwon, Auteur ; Ha-Won Song, Auteur Article en page(s) : pp. 119-127 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Carbonation  Modeling  Diffusion  coefficient  Neural  network  Porosity Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Carbonation on concrete structures in underground sites or metropolitan cities is one of the major causes of steel corrosion in RC (Reinforced Concrete) structures. For quantitative evaluation of carbonation, physico-chemo modeling for reaction with dissolved CO2 and hydrates is necessary. Amount of hydrates and CO2 diffusion coefficient play an important role in evaluation of carbonation behavior, however, it is difficult to obtain a various CO2 diffusion coefficient from experiments due to limited time and cost. In this paper, a numerical technique for carbonation behavior using neural network algorithm and carbonation modeling is developed. To obtain the comparable data set of CO2 diffusion coefficient, experimental results which were performed previously are analyzed. Mix design components such as cement content, water to cement ratio, and volume of aggregate including exposure condition of relative humidity are selected as neurons. Training of learning for neural network is carried out using back propagation algorithm. The diffusion coefficient of CO2 from neural network are in good agreement with experimental data considering various conditions such as water to cement ratios (w/c: 0.42, 0.50, and 0.58) and relative humidities (R.H.: 10%, 45%, 75%, and 90%). Furthermore, mercury intrusion porosimetry (MIP) test is also performed to evaluate the change in porosity under carbonation. Finally, the numerical technique which is based on behavior in early-aged concrete such as hydration and pore structure is developed considering CO2 diffusion coefficient from neural network and changing effect on porosity under carbonation. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Analysis of carbonation behavior in concrete using neural network algorithm and carbonation modeling [texte imprimé] / Seung-Jun Kwon, Auteur ; Ha-Won Song, Auteur . - pp. 119-127. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 119-127 Mots-clés : Carbonation  Modeling  Diffusion  coefficient  Neural  network  Porosity Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Carbonation on concrete structures in underground sites or metropolitan cities is one of the major causes of steel corrosion in RC (Reinforced Concrete) structures. For quantitative evaluation of carbonation, physico-chemo modeling for reaction with dissolved CO2 and hydrates is necessary. Amount of hydrates and CO2 diffusion coefficient play an important role in evaluation of carbonation behavior, however, it is difficult to obtain a various CO2 diffusion coefficient from experiments due to limited time and cost. In this paper, a numerical technique for carbonation behavior using neural network algorithm and carbonation modeling is developed. To obtain the comparable data set of CO2 diffusion coefficient, experimental results which were performed previously are analyzed. Mix design components such as cement content, water to cement ratio, and volume of aggregate including exposure condition of relative humidity are selected as neurons. Training of learning for neural network is carried out using back propagation algorithm. The diffusion coefficient of CO2 from neural network are in good agreement with experimental data considering various conditions such as water to cement ratios (w/c: 0.42, 0.50, and 0.58) and relative humidities (R.H.: 10%, 45%, 75%, and 90%). Furthermore, mercury intrusion porosimetry (MIP) test is also performed to evaluate the change in porosity under carbonation. Finally, the numerical technique which is based on behavior in early-aged concrete such as hydration and pore structure is developed considering CO2 diffusion coefficient from neural network and changing effect on porosity under carbonation. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Thermal properties of hydrating calcium aluminate cement pastes / Neven Ukrainczyk in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 128-136 Titre : Thermal properties of hydrating calcium aluminate cement pastes Type de document : texte imprimé Auteurs : Neven Ukrainczyk, Auteur ; Tomislav Matusinovic, Auteur Article en page(s) : pp. 128-136 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Calcium  aluminate  cement  Hydration  Thermal  properties  Transient  hot  wire  method  Inverse  problem Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : As the hydration of calcium aluminate cements (CAC) is highly temperature dependent, yielding morphologically and structurally different hydration products that continuously alter material properties, a good knowledge of thermal properties at early stages of hydration is essential. Thermal diffusivity and thermal conductivity during CAC hydration was investigated by a transient method with a numerical approach and a transient hot wire method, respectively. For hydration at 15 °C (formation of mainly CAH10), thermal diffusivity shows a linear decrease as a function of hydration degree, while for hydration at 30 °C there is a linear increase of thermal diffusivity. Converted materials exhibited the highest values of thermal diffusivities. The results on sealed converted material indicated that thermal conductivity increased with an increase in temperature (20–80 °C), while thermal diffusivities marginally decreased with temperature. The Hashin–Shtrikman boundary conditions and a simple law of mixtures were successfully applied for estimating thermal conductivity and heat capacity, respectively, of fresh cement pastes. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Thermal properties of hydrating calcium aluminate cement pastes [texte imprimé] / Neven Ukrainczyk, Auteur ; Tomislav Matusinovic, Auteur . - pp. 128-136. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 128-136 Mots-clés : Calcium  aluminate  cement  Hydration  Thermal  properties  Transient  hot  wire  method  Inverse  problem Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : As the hydration of calcium aluminate cements (CAC) is highly temperature dependent, yielding morphologically and structurally different hydration products that continuously alter material properties, a good knowledge of thermal properties at early stages of hydration is essential. Thermal diffusivity and thermal conductivity during CAC hydration was investigated by a transient method with a numerical approach and a transient hot wire method, respectively. For hydration at 15 °C (formation of mainly CAH10), thermal diffusivity shows a linear decrease as a function of hydration degree, while for hydration at 30 °C there is a linear increase of thermal diffusivity. Converted materials exhibited the highest values of thermal diffusivities. The results on sealed converted material indicated that thermal conductivity increased with an increase in temperature (20–80 °C), while thermal diffusivities marginally decreased with temperature. The Hashin–Shtrikman boundary conditions and a simple law of mixtures were successfully applied for estimating thermal conductivity and heat capacity, respectively, of fresh cement pastes. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Electrical resistance tomography imaging of concrete / Kimmo Karhunen in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 137-145 Titre : Electrical resistance tomography imaging of concrete Type de document : texte imprimé Auteurs : Kimmo Karhunen, Auteur ; Aku Seppanen, Auteur ; Anssi Lehikoinen, Auteur Article en page(s) : pp. 137-145 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Concrete  Electrical  properties  Crack  detection  Non-destructive  testing Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : We apply Electrical Resistance Tomography (ERT) for three dimensional imaging of concrete. In ERT, alternating currents are injected into the target using an array of electrodes attached to the target surface, and the resulting voltages are measured using the same electrodes. These boundary measurements are used for reconstructing the internal (3D) conductivity distribution of the target. In reinforced concrete, the metallic phases (reinforcing bars and fibers), cracks and air voids, moisture gradients, and the chloride distribution in the matrix carry contrast with respect to conductivity. While electrical measurements have been widely used to characterize the properties of concrete, only preliminary results of applying ERT to concrete imaging have been published so far. The aim of this paper is to carry out a feasibility evaluation with specifically cast samples. The results indicate that ERT may be a feasible modality for non-destructive evaluation of concrete. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Electrical resistance tomography imaging of concrete [texte imprimé] / Kimmo Karhunen, Auteur ; Aku Seppanen, Auteur ; Anssi Lehikoinen, Auteur . - pp. 137-145. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 137-145 Mots-clés : Concrete  Electrical  properties  Crack  detection  Non-destructive  testing Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : We apply Electrical Resistance Tomography (ERT) for three dimensional imaging of concrete. In ERT, alternating currents are injected into the target using an array of electrodes attached to the target surface, and the resulting voltages are measured using the same electrodes. These boundary measurements are used for reconstructing the internal (3D) conductivity distribution of the target. In reinforced concrete, the metallic phases (reinforcing bars and fibers), cracks and air voids, moisture gradients, and the chloride distribution in the matrix carry contrast with respect to conductivity. While electrical measurements have been widely used to characterize the properties of concrete, only preliminary results of applying ERT to concrete imaging have been published so far. The aim of this paper is to carry out a feasibility evaluation with specifically cast samples. The results indicate that ERT may be a feasible modality for non-destructive evaluation of concrete. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Comprehensive phase characterization of crystalline and amorphous phases of a Class F fly ash / Ryan T. Chancey in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 146-156 Titre : Comprehensive phase characterization of crystalline and amorphous phases of a Class F fly ash Type de document : texte imprimé Auteurs : Ryan T. Chancey, Auteur ; Paul Stutzman, Auteur ; Maria C.G. Juenger, Auteur Article en page(s) : pp. 146-156 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Amorphous  material  Characterization  Image  analysis  Fly  ash  SEM  X-ray  powder  diffraction Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : A comprehensive approach to qualitative and quantitative characterization of crystalline and amorphous constituent phases of a largely heterogeneous Class F fly ash is presented. Traditionally, fly ash composition is expressed as bulk elemental oxide content, generally determined by X-ray fluorescence spectroscopy. However, such analysis does not discern between relatively inert crystalline phases and highly reactive amorphous phases of similar elemental composition. X-ray diffraction was used to identify the crystalline phases present in the fly ash, and the Rietveld quantitative phase analysis method was applied to determine the relative proportion of each of these phases. A synergistic method of X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and multispectral image analysis was developed to identify and quantify the amorphous phases present in the fly ash. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Comprehensive phase characterization of crystalline and amorphous phases of a Class F fly ash [texte imprimé] / Ryan T. Chancey, Auteur ; Paul Stutzman, Auteur ; Maria C.G. Juenger, Auteur . - pp. 146-156. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 146-156 Mots-clés : Amorphous  material  Characterization  Image  analysis  Fly  ash  SEM  X-ray  powder  diffraction Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : A comprehensive approach to qualitative and quantitative characterization of crystalline and amorphous constituent phases of a largely heterogeneous Class F fly ash is presented. Traditionally, fly ash composition is expressed as bulk elemental oxide content, generally determined by X-ray fluorescence spectroscopy. However, such analysis does not discern between relatively inert crystalline phases and highly reactive amorphous phases of similar elemental composition. X-ray diffraction was used to identify the crystalline phases present in the fly ash, and the Rietveld quantitative phase analysis method was applied to determine the relative proportion of each of these phases. A synergistic method of X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and multispectral image analysis was developed to identify and quantify the amorphous phases present in the fly ash. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Use of bacteria to repair cracks in concrete / Kim Van Tittelboom in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 157-166 Titre : Use of bacteria to repair cracks in concrete Type de document : texte imprimé Auteurs : Kim Van Tittelboom, Auteur ; Nele de Belie, Auteur ; Willem de Muynck, Auteur Article en page(s) : pp. 157-166 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Concrete  Microcracking  CaCO3  Bacteria Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique is investigated in this study. Ureolytic bacteria such as Bacillus sphaericus are able to precipitate CaCO3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated crystals can thus fill the cracks. The crack healing potential of bacteria and traditional repair techniques are compared in this research by means of water permeability tests, ultrasound transmission measurements and visual examination. Thermogravimetric analysis showed that bacteria were able to precipitate CaCO3 crystals inside the cracks. It was seen that pure bacteria cultures were not able to bridge the cracks. However, when bacteria were protected in silica gel, cracks were filled completely. DEWEY : 627 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Use of bacteria to repair cracks in concrete [texte imprimé] / Kim Van Tittelboom, Auteur ; Nele de Belie, Auteur ; Willem de Muynck, Auteur . - pp. 157-166. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 157-166 Mots-clés : Concrete  Microcracking  CaCO3  Bacteria Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique is investigated in this study. Ureolytic bacteria such as Bacillus sphaericus are able to precipitate CaCO3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated crystals can thus fill the cracks. The crack healing potential of bacteria and traditional repair techniques are compared in this research by means of water permeability tests, ultrasound transmission measurements and visual examination. Thermogravimetric analysis showed that bacteria were able to precipitate CaCO3 crystals inside the cracks. It was seen that pure bacteria cultures were not able to bridge the cracks. However, when bacteria were protected in silica gel, cracks were filled completely. DEWEY : 627 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Melt differentiation and crystallization of clinker minerals in a CaO–SiO2–Al2O3–Fe2O3 pseudoquaternary system / Koichiro Fukuda in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 167-170 Titre : Melt differentiation and crystallization of clinker minerals in a CaO–SiO2–Al2O3–Fe2O3 pseudoquaternary system Type de document : texte imprimé Auteurs : Koichiro Fukuda, Auteur ; Tomoyuki Iwata, Auteur ; Hideto Yoshida, Auteur Article en page(s) : pp. 167-170 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Microstructure  Clinker  Portland  Cement  Calcium  aluminoferrite  Melt  differentiation Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In the CaO–SiO2–Al2O3–Fe2O3 pseudoquaternary system, the solid solutions of Ca3SiO5 [C3S(ss)], Ca2SiO4 [C2S(ss)], Ca2(AlxFe1 − x)2O5 with 0.40 ≤ x ≤ 0.57 (ferrite) and Ca3Al2O6 [C3A(ss)] were crystallized out of a complete melt with 52.9 mass% CaO and Al2O3/Fe2O3 = 0.70. When the melt was cooled from 1673 K at 80 K/h, the crystals of ferrite with x = 0.40, C3S(ss) and C2S(ss) would start to nucleate from the melt at 1630 K. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.57 at 1613 K. The resulting ferrite crystals showed a zonal structure, the x value of which successively increased from the cores toward the rims. Actually, the x values of 0.43 and 0.52 were confirmed for, respectively, the cores and rims by EPMA. As the simultaneous crystallization of zoned ferrite, C3S(ss) and C2S(ss) proceeded, the coexisting melt would become progressively enriched in the Al2O3 component. After the termination of the ferrite crystallization, the C3A(ss), C3S(ss) and C2S(ss) crystallized out of the differentiated melt. The end result was the four phase mixture of ferrite, C3A(ss), C3S(ss) and C2S(ss), being free from the nucleation of Ca12Al14O33 solid solution. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Melt differentiation and crystallization of clinker minerals in a CaO–SiO2–Al2O3–Fe2O3 pseudoquaternary system [texte imprimé] / Koichiro Fukuda, Auteur ; Tomoyuki Iwata, Auteur ; Hideto Yoshida, Auteur . - pp. 167-170. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 167-170 Mots-clés : Microstructure  Clinker  Portland  Cement  Calcium  aluminoferrite  Melt  differentiation Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In the CaO–SiO2–Al2O3–Fe2O3 pseudoquaternary system, the solid solutions of Ca3SiO5 [C3S(ss)], Ca2SiO4 [C2S(ss)], Ca2(AlxFe1 − x)2O5 with 0.40 ≤ x ≤ 0.57 (ferrite) and Ca3Al2O6 [C3A(ss)] were crystallized out of a complete melt with 52.9 mass% CaO and Al2O3/Fe2O3 = 0.70. When the melt was cooled from 1673 K at 80 K/h, the crystals of ferrite with x = 0.40, C3S(ss) and C2S(ss) would start to nucleate from the melt at 1630 K. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.57 at 1613 K. The resulting ferrite crystals showed a zonal structure, the x value of which successively increased from the cores toward the rims. Actually, the x values of 0.43 and 0.52 were confirmed for, respectively, the cores and rims by EPMA. As the simultaneous crystallization of zoned ferrite, C3S(ss) and C2S(ss) proceeded, the coexisting melt would become progressively enriched in the Al2O3 component. After the termination of the ferrite crystallization, the C3A(ss), C3S(ss) and C2S(ss) crystallized out of the differentiated melt. The end result was the four phase mixture of ferrite, C3A(ss), C3S(ss) and C2S(ss), being free from the nucleation of Ca12Al14O33 solid solution. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Triaxial strength and failure criterion of plain high-strength and high-performance concrete before and after high temperatures / Zhen-jun He in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 171-178 Titre : Triaxial strength and failure criterion of plain high-strength and high-performance concrete before and after high temperatures Type de document : texte imprimé Auteurs : Zhen-jun He, Auteur ; Yu-pu Song, Auteur Article en page(s) : pp. 171-178 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : High-strength  high-performace  concrete  HSHPC  High  temperatures  Stress  ratios  Triaxial  strengths  Failure  criterion Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Triaxial tests were performed on 100 mm × 100 mm × 100 mm cubic specimens of plain high-strength and high-performace concrete (HSHPC) at all kinds of stress ratios after exposure to normal and high temperatures of 20, 200, 300, 400, 500, and 600 °C, using a large static–dynamic true triaxial machine. Friction-reducing pads, using three layers of plastic membrane with glycerine were placed between the compressive loading plate and the specimens; the tensile loading planes of concrete samples were processed by an attrition machine, and then the samples were glued-up with the loading plate with structural glue. The failure mode characteristic of the specimens and the direction of the crack were observed and described. The three principally static strengths in the corresponding stress state were measured. The influence of the temperatures and stress ratios on the triaxial strengths of HSHPC after exposure to high temperatures was also analyzed. The experimental results showed that the uniaxial compressive strength of plain HSHPC after exposure to high temperatures does not decrease completely with the increase in temperature, the ratios of the triaxial to its uniaxial compressive strength are dependent on the brittleness–stiffness of HSHPC after different temperatures and the stress ratios. On this basis, a new failure criterion with the temperature parameters is proposed for plain HSHPC under multiaxial stress states. It provides the experimental and theoretical foundations for strength analysis of HSHPC structures subject to complex loads after subjected to a high temperature environment. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Triaxial strength and failure criterion of plain high-strength and high-performance concrete before and after high temperatures [texte imprimé] / Zhen-jun He, Auteur ; Yu-pu Song, Auteur . - pp. 171-178. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 171-178 Mots-clés : High-strength  high-performace  concrete  HSHPC  High  temperatures  Stress  ratios  Triaxial  strengths  Failure  criterion Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : Triaxial tests were performed on 100 mm × 100 mm × 100 mm cubic specimens of plain high-strength and high-performace concrete (HSHPC) at all kinds of stress ratios after exposure to normal and high temperatures of 20, 200, 300, 400, 500, and 600 °C, using a large static–dynamic true triaxial machine. Friction-reducing pads, using three layers of plastic membrane with glycerine were placed between the compressive loading plate and the specimens; the tensile loading planes of concrete samples were processed by an attrition machine, and then the samples were glued-up with the loading plate with structural glue. The failure mode characteristic of the specimens and the direction of the crack were observed and described. The three principally static strengths in the corresponding stress state were measured. The influence of the temperatures and stress ratios on the triaxial strengths of HSHPC after exposure to high temperatures was also analyzed. The experimental results showed that the uniaxial compressive strength of plain HSHPC after exposure to high temperatures does not decrease completely with the increase in temperature, the ratios of the triaxial to its uniaxial compressive strength are dependent on the brittleness–stiffness of HSHPC after different temperatures and the stress ratios. On this basis, a new failure criterion with the temperature parameters is proposed for plain HSHPC under multiaxial stress states. It provides the experimental and theoretical foundations for strength analysis of HSHPC structures subject to complex loads after subjected to a high temperature environment. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]

Exemplaires

Bibliothèque Ecole Nationale Polytechnique d'Alger

Accueil

Se connecter

Météo

Adresse