Dépouillements

Experimental determination of the effective anionic charge density of polycarboxylate superplasticizers in cement pore solution / J. Plank in Cement and concrete research, Vol. 39 N° 1 (Janvier 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 1–5 Titre : Experimental determination of the effective anionic charge density of polycarboxylate superplasticizers in cement pore solution Type de document : texte imprimé Auteurs : J. Plank, Auteur ; B. Sachsenhauser, Auteur Année de publication : 2009 Article en page(s) : pp. 1–5 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Pore  solution  ;  Adsorption  ;  Cement  ;  Polymers  ;  Polycarboxylate Résumé : The specific anionic charge density of polycarboxylate superplasticizers can be determined experimentally by titration with a cationic polyelectrolyte. In this study, the anionic charge densities of several polycarboxylates based on methacrylate ester chemistry were measured in aqueous solution at pH 7 and 12.6, resp., and in cement pore solution. The anionic charge of the polycarboxylates increases with increasing pH value as a result of deprotonation of the carboxylate groups in the polymer backbone. Addition of Ca2+ ions generally causes a decrease of the anionic charge density. The reduction in anionic charge varies and depends on the architecture of the polycarboxylate. The effect results from the binding of calcium ions by the carboxylate groups, both through complexation and counter-ion condensation. Consequently, the effective anionic charge density of polycarboxylates in cement pore solution can differ significantly from the charge density which is calculated based on the chemical composition. Generally the –COO− functionality may coordinate Ca2+ as a monodentate or bidentate ligand. The type of coordination depends on the steric accessibility of the carboxyl group. In PC molecules possessing high side chain density, the –COO− group is shielded by the side chains and coordinates as bidentate ligand, producing a neutral Ca2+–PC complex. Accordingly, this type of PC shows almost no anionic charge anymore in cement pore solution. In PCs possessing high amount of –COO−, Ca2+ is coordinated monodentate, resulting in an anionic complex. Consequently, this type of PC shows significant anionic character in pore solution. Its adsorption behaviour is determined by a gain in enthalpy which derives from the electrostatic attraction between the PC and the surface of cement. This way, by utilizing the relatively simple method of charge titration, it is possible to assess the electrostatic attraction which, besides entropy gains, is the driving force behind the adsorption of polycarboxylates on the cement surface and thus determines their effectiveness as dispersing agent. The findings are generally applicable to other anionic admixtures used in cement. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001579 [article] Experimental determination of the effective anionic charge density of polycarboxylate superplasticizers in cement pore solution [texte imprimé] / J. Plank, Auteur ; B. Sachsenhauser, Auteur . - 2009 . - pp. 1–5. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 1–5 Mots-clés : Pore  solution  ;  Adsorption  ;  Cement  ;  Polymers  ;  Polycarboxylate Résumé : The specific anionic charge density of polycarboxylate superplasticizers can be determined experimentally by titration with a cationic polyelectrolyte. In this study, the anionic charge densities of several polycarboxylates based on methacrylate ester chemistry were measured in aqueous solution at pH 7 and 12.6, resp., and in cement pore solution. The anionic charge of the polycarboxylates increases with increasing pH value as a result of deprotonation of the carboxylate groups in the polymer backbone. Addition of Ca2+ ions generally causes a decrease of the anionic charge density. The reduction in anionic charge varies and depends on the architecture of the polycarboxylate. The effect results from the binding of calcium ions by the carboxylate groups, both through complexation and counter-ion condensation. Consequently, the effective anionic charge density of polycarboxylates in cement pore solution can differ significantly from the charge density which is calculated based on the chemical composition. Generally the –COO− functionality may coordinate Ca2+ as a monodentate or bidentate ligand. The type of coordination depends on the steric accessibility of the carboxyl group. In PC molecules possessing high side chain density, the –COO− group is shielded by the side chains and coordinates as bidentate ligand, producing a neutral Ca2+–PC complex. Accordingly, this type of PC shows almost no anionic charge anymore in cement pore solution. In PCs possessing high amount of –COO−, Ca2+ is coordinated monodentate, resulting in an anionic complex. Consequently, this type of PC shows significant anionic character in pore solution. Its adsorption behaviour is determined by a gain in enthalpy which derives from the electrostatic attraction between the PC and the surface of cement. This way, by utilizing the relatively simple method of charge titration, it is possible to assess the electrostatic attraction which, besides entropy gains, is the driving force behind the adsorption of polycarboxylates on the cement surface and thus determines their effectiveness as dispersing agent. The findings are generally applicable to other anionic admixtures used in cement. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001579

Cement hydration and microstructure formation in the presence of water-soluble polymers / E. Knapen in Cement and concrete research, Vol. 39 N° 1 (Janvier 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 6–13 Titre : Cement hydration and microstructure formation in the presence of water-soluble polymers Type de document : texte imprimé Auteurs : E. Knapen, Auteur ; D. Van Gemert, Auteur Année de publication : 2009 Article en page(s) : pp. 6–13 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Retardation  ;  Hydration  products  ;  Microstructure  ;SEM  ;  Polymers Résumé : Hardening of cement mortars modified with small amounts of water-soluble polymers implies both cement hydration and polymer film formation. In this paper, the effect of the presence of water-soluble polymers on the cement hydration reactions is investigated by means of isothermal calorimetry, thermal analysis, FT-IR spectroscopy and SEM investigation. In spite of an initial retardation of the hydration reactions, a higher degree of hydration is found after 90 days for 1% PVAA, MC and HEC modified mortars, due to a better dispersion of the cement particles in the mixing water. MC also affects the morphology of the Ca(OH)2 crystals. Polymer bridges are detected between the layered crystals, gluing the layers together and strengthening the microstructure. Additionally, the internal cohesion of all bulk polymer modified cement pastes is improved. In the presence of the polymers, a more cohesive microstructure with a smaller amount of microcracks is created. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001774 [article] Cement hydration and microstructure formation in the presence of water-soluble polymers [texte imprimé] / E. Knapen, Auteur ; D. Van Gemert, Auteur . - 2009 . - pp. 6–13. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 6–13 Mots-clés : Retardation  ;  Hydration  products  ;  Microstructure  ;SEM  ;  Polymers Résumé : Hardening of cement mortars modified with small amounts of water-soluble polymers implies both cement hydration and polymer film formation. In this paper, the effect of the presence of water-soluble polymers on the cement hydration reactions is investigated by means of isothermal calorimetry, thermal analysis, FT-IR spectroscopy and SEM investigation. In spite of an initial retardation of the hydration reactions, a higher degree of hydration is found after 90 days for 1% PVAA, MC and HEC modified mortars, due to a better dispersion of the cement particles in the mixing water. MC also affects the morphology of the Ca(OH)2 crystals. Polymer bridges are detected between the layered crystals, gluing the layers together and strengthening the microstructure. Additionally, the internal cohesion of all bulk polymer modified cement pastes is improved. In the presence of the polymers, a more cohesive microstructure with a smaller amount of microcracks is created. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001774

Rheological properties of cement paste: thixotropic behavior and structural breakdown / Jon Elvar Wallevik in Cement and concrete research, Vol. 39 N° 1 (Janvier 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp.14–29 Titre : Rheological properties of cement paste: thixotropic behavior and structural breakdown Type de document : texte imprimé Auteurs : Jon Elvar Wallevik, Auteur Année de publication : 2009 Article en page(s) : pp.14–29 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Cement  paste;  Rheology;  Thixotropy;  Structural  breakdown Résumé : In this work, a new material model is presented to simulate rheological behavior of cement paste. This material model is among others based on combined concepts by Hattori and Izumi and by Tattersall and Banfill. More precisely, coagulation, dispersion and re-coagulation of the cement particles (giving a true thixotropic behavior) in combination with the breaking of certain chemically formed linkages between the particles (giving a so-called structural breakdown behavior) are assumed to play an important role in generating the overall time-dependent behavior of the cement paste. The model evaluation is done by comparing experimental data with model prediction. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001919 [article] Rheological properties of cement paste: thixotropic behavior and structural breakdown [texte imprimé] / Jon Elvar Wallevik, Auteur . - 2009 . - pp.14–29. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp.14–29 Mots-clés : Cement  paste;  Rheology;  Thixotropy;  Structural  breakdown Résumé : In this work, a new material model is presented to simulate rheological behavior of cement paste. This material model is among others based on combined concepts by Hattori and Izumi and by Tattersall and Banfill. More precisely, coagulation, dispersion and re-coagulation of the cement particles (giving a true thixotropic behavior) in combination with the breaking of certain chemically formed linkages between the particles (giving a so-called structural breakdown behavior) are assumed to play an important role in generating the overall time-dependent behavior of the cement paste. The model evaluation is done by comparing experimental data with model prediction. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001919

Contribution of granular interactions to self compacting concrete stability: Development of a new device / S. Bethmont in Cement and concrete research, Vol. 39 N° 1 (Janvier 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 30–35 Titre : Contribution of granular interactions to self compacting concrete stability: Development of a new device Type de document : texte imprimé Auteurs : S. Bethmont, Auteur ; L. D'Aloia Schwartzentruber, Auteur ; C. E. Stefani, Auteur Année de publication : 2009 Article en page(s) : pp. 30–35 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Rheology;  Cement  paste;  Aggregate;  Concrete;  Self  Compacting  Concrete  (SCC) Résumé : Understanding the SCC behaviour is essential for resolving placement and consolidation problems in the field. As far as segregation is concerned, one of the main remaining obstacles is the design of a concrete mixture suitable for given casting conditions. Physical approaches which consist in studying the sedimentation of a single particle in a yield stress fluid failed to describe SCC static segregation. Segregation is a more complex phenomenon and the interactions between coarse aggregates have to be taken into account. They contribute to the stability of fresh SCC and this contribution should only depend on the solid fraction of the granular skeleton. A new experimental device has been developed in order to highlight and quantify the combined effects of coarse aggregates. This device allows studying lattices of particles. These latter are organised according to a cubic centred pattern and are immersed in a yield stress fluid. The experimental device and the test procedure are described in this paper. The validity of measurements has been demonstrated by performing a first series of tests and numerical simulations. Repeatability is quite satisfactory and “wall effects” can be limited. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001956 [article] Contribution of granular interactions to self compacting concrete stability: Development of a new device [texte imprimé] / S. Bethmont, Auteur ; L. D'Aloia Schwartzentruber, Auteur ; C. E. Stefani, Auteur . - 2009 . - pp. 30–35. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 30–35 Mots-clés : Rheology;  Cement  paste;  Aggregate;  Concrete;  Self  Compacting  Concrete  (SCC) Résumé : Understanding the SCC behaviour is essential for resolving placement and consolidation problems in the field. As far as segregation is concerned, one of the main remaining obstacles is the design of a concrete mixture suitable for given casting conditions. Physical approaches which consist in studying the sedimentation of a single particle in a yield stress fluid failed to describe SCC static segregation. Segregation is a more complex phenomenon and the interactions between coarse aggregates have to be taken into account. They contribute to the stability of fresh SCC and this contribution should only depend on the solid fraction of the granular skeleton. A new experimental device has been developed in order to highlight and quantify the combined effects of coarse aggregates. This device allows studying lattices of particles. These latter are organised according to a cubic centred pattern and are immersed in a yield stress fluid. The experimental device and the test procedure are described in this paper. The validity of measurements has been demonstrated by performing a first series of tests and numerical simulations. Repeatability is quite satisfactory and “wall effects” can be limited. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001956

Water desorption and shrinkage in mortars and cement pastes: Experimental study and poromechanical model / Thomas Rougelota in Cement and concrete research, Vol. 39 N° 1 (Janvier 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 36–44 Titre : Water desorption and shrinkage in mortars and cement pastes: Experimental study and poromechanical model Type de document : texte imprimé Auteurs : Thomas Rougelota, Auteur ; Frédéric Skoczylas, Auteur ; Nicolas Burlion, Auteur Année de publication : 2009 Article en page(s) : pp. 36–44 Langues : Anglais (eng) Mots-clés : Water  desorption  curves;  Cement  paste;  Mortar;  Shrinkage;Modelling Résumé : The aim of the present research was to study moisture changes and strains induced by smooth water desorption of several cement based materials. The main advantage of this small-steps drying is to dramatically limit the structural effect within tested samples, by lowering moisture gradients and therefore cracking due to differential shrinkage. Resulting data are of importance as they allow water retention curves, porosity distribution and desiccation shrinkage to be determined versus a large range of relative humidity. Experiments were conducted on ordinary mortars and cement pastes with water-to-cement ratio of 0.5 and 0.8. The role of the cementitious matrix and of aggregates over water-related behaviour of these materials can also be studied. Finally, a simple numerical model, based on experimental poromechanical results, was proposed to predict the shrinkage when the material is submitted to drying. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001944 [article] Water desorption and shrinkage in mortars and cement pastes: Experimental study and poromechanical model [texte imprimé] / Thomas Rougelota, Auteur ; Frédéric Skoczylas, Auteur ; Nicolas Burlion, Auteur . - 2009 . - pp. 36–44. Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 36–44 Mots-clés : Water  desorption  curves;  Cement  paste;  Mortar;  Shrinkage;Modelling Résumé : The aim of the present research was to study moisture changes and strains induced by smooth water desorption of several cement based materials. The main advantage of this small-steps drying is to dramatically limit the structural effect within tested samples, by lowering moisture gradients and therefore cracking due to differential shrinkage. Resulting data are of importance as they allow water retention curves, porosity distribution and desiccation shrinkage to be determined versus a large range of relative humidity. Experiments were conducted on ordinary mortars and cement pastes with water-to-cement ratio of 0.5 and 0.8. The role of the cementitious matrix and of aggregates over water-related behaviour of these materials can also be studied. Finally, a simple numerical model, based on experimental poromechanical results, was proposed to predict the shrinkage when the material is submitted to drying. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001944

The mineralogy of the CaO–Al2O3–SiO2–H2O (CASH) hydroceramic system from 200 to 350 °C / Nicola Meller in Cement and concrete research, Vol. 39 N° 1 (Janvier 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. Titre : The mineralogy of the CaO–Al2O3–SiO2–H2O (CASH) hydroceramic system from 200 to 350 °C Type de document : texte imprimé Auteurs : Nicola Meller, Auteur ; Konstantinos Kyritsis, Auteur ; Christopher Hall, Auteur Année de publication : 2009 Article en page(s) : pp. Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hydration  products;X-ray  diffraction;Oil  well  cement;Geothermal  well  cement Résumé : We describe a quantitative mineralogical study of the hydrothermal reactions of an oil well cement with added silica and alumina, hydrated at temperatures from 200 to 350 °C. We compare the products with pure end member systems and find phase stability can be altered radically, even by small amounts of additive. The upper temperature limits of α-C2SH (< 250 °C), and 1.1 nm tobermorite C5S6H5 (< 300 °C) are increased. C8S5, reported in a cement-based system for the first time, is stable to 300 °C and is believed to prevent foshagite C4S3H formation below 350 °C. Hydrogarnet C3AS3−yH2y is the only aluminum bearing phase at < 300 °C but it coexists with C4A3H3 and bicchulite C8A4Si4H4 at higher temperatures. The presence of alumina increases the stability of 1.1 nm tobermorite greatly and also to a lesser degree of gyrolite. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001920 [article] The mineralogy of the CaO–Al2O3–SiO2–H2O (CASH) hydroceramic system from 200 to 350 °C [texte imprimé] / Nicola Meller, Auteur ; Konstantinos Kyritsis, Auteur ; Christopher Hall, Auteur . - 2009 . - pp. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. Mots-clés : Hydration  products;X-ray  diffraction;Oil  well  cement;Geothermal  well  cement Résumé : We describe a quantitative mineralogical study of the hydrothermal reactions of an oil well cement with added silica and alumina, hydrated at temperatures from 200 to 350 °C. We compare the products with pure end member systems and find phase stability can be altered radically, even by small amounts of additive. The upper temperature limits of α-C2SH (< 250 °C), and 1.1 nm tobermorite C5S6H5 (< 300 °C) are increased. C8S5, reported in a cement-based system for the first time, is stable to 300 °C and is believed to prevent foshagite C4S3H formation below 350 °C. Hydrogarnet C3AS3−yH2y is the only aluminum bearing phase at < 300 °C but it coexists with C4A3H3 and bicchulite C8A4Si4H4 at higher temperatures. The presence of alumina increases the stability of 1.1 nm tobermorite greatly and also to a lesser degree of gyrolite. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001920

The effect of undrained heating on a fluid-saturated hardened cement paste / Siavash Ghabezloo in Cement and concrete research, Vol. 39 N° 1 (Janvier 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 54–64 Titre : The effect of undrained heating on a fluid-saturated hardened cement paste Type de document : texte imprimé Auteurs : Siavash Ghabezloo, Auteur ; Jean Sulem, Auteur ; Jérémie Saint-Marc, Auteur Année de publication : 2009 Article en page(s) : pp. 54–64 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hardened  cement  paste;  Thermo-poro-elasticity;  Thermal  pressurization;  Pore  pressure;  Thermal  expansion Résumé : The effect of undrained heating on volume change and induced pore pressure increase is an important point to properly understand the behaviour and evaluate the integrity of an oil well cement sheath submitted to rapid temperature changes. This thermal pressurization of the pore fluid is due to the discrepancy between the thermal expansion coefficients of the pore fluid and of the solid matrix. The equations governing the undrained thermo-hydro-mechanical response of a porous material are presented and the effect of undrained heating is studied experimentally for a saturated hardened cement paste. The measured value of the thermal pressurization coefficient is equal to 0.6 MPa/°C. The drained and undrained thermal expansion coefficients of the hardened cement paste are also measured in the heating tests. The anomalous thermal behaviour of cement paste pore fluid is back analysed from the results of the undrained heating test. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001762 [article] The effect of undrained heating on a fluid-saturated hardened cement paste [texte imprimé] / Siavash Ghabezloo, Auteur ; Jean Sulem, Auteur ; Jérémie Saint-Marc, Auteur . - 2009 . - pp. 54–64. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 1 (Janvier 2009) . - pp. 54–64 Mots-clés : Hardened  cement  paste;  Thermo-poro-elasticity;  Thermal  pressurization;  Pore  pressure;  Thermal  expansion Résumé : The effect of undrained heating on volume change and induced pore pressure increase is an important point to properly understand the behaviour and evaluate the integrity of an oil well cement sheath submitted to rapid temperature changes. This thermal pressurization of the pore fluid is due to the discrepancy between the thermal expansion coefficients of the pore fluid and of the solid matrix. The equations governing the undrained thermo-hydro-mechanical response of a porous material are presented and the effect of undrained heating is studied experimentally for a saturated hardened cement paste. The measured value of the thermal pressurization coefficient is equal to 0.6 MPa/°C. The drained and undrained thermal expansion coefficients of the hardened cement paste are also measured in the heating tests. The anomalous thermal behaviour of cement paste pore fluid is back analysed from the results of the undrained heating test. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608001762

Exemplaires

Bibliothèque Ecole Nationale Polytechnique d'Alger

Accueil

Se connecter

Météo

Adresse