Documents disponibles écrits par cet auteur

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

Experimental determination of the thermodynamic parameters affecting the adsorption behaviour and dispersion effectiveness of PCE superplasticizers / J. Plank in Cement and concrete research, Vol. 40 N° 5 (Mai 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. 699–709 Titre : Experimental determination of the thermodynamic parameters affecting the adsorption behaviour and dispersion effectiveness of PCE superplasticizers Type de document : texte imprimé Auteurs : J. Plank, Auteur ; B. Sachsenhauser, Auteur ; J. de Reese, Auteur Année de publication : 2012 Article en page(s) : pp. 699–709 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Adsorption  ;  Polycarboxylates;  CaCO3  ;  Thermodynamic  calculations  ;  Workability Résumé : For adsorption of three different allylether-based PCE superplasticizers on CaCO3 surface, the thermodynamic parameters ΔH, ΔS and ΔG were determined experimentally. The GIBBS standard free energy of adsorption ΔG0ads, the standard enthalpy of adsorption ΔH0ads and the standard entropy of adsorption ΔS0ads applying to an unoccupied CaCO3 surface were obtained via a linear regression of ln K (equilibrium constant) versus 1 / T (VAN'T HOFF plot). Additionally, the thermodynamic parameters characteristic for a CaCO3 surface loaded already with polymer (isosteric conditions) were determined using a modified CLAUSIUS–CLAPEYRON equation. For all PCE molecules, negative ΔG values were found, indicating that adsorption of these polymers is energetically favourable and a spontaneous process. Adsorption of PCEs possessing short side chains is mainly instigated by electrostatic attraction and a release of enthalpy. Contrary to this, adsorption of PCEs with long side chains occurs because of a huge gain in entropy. The gain in entropy results from the release of counter ions attached to the carboxylate groups of the polymer backbone and of water molecules and ions adsorbed on the CaCO3 surface. With increased surface loading, however, ΔGisosteric decreases and adsorption ceases when ΔG becomes 0. The presence of Ca2+ ions in the pore solution strongly impacts PCE adsorption, due to complexation of carboxylate groups and a reduced anionic charge amount of the molecule. In the presence of Ca2+, adsorption of allylether-based PCEs is almost exclusively driven by a gain in entropy. Consequently, PCEs should produce a strong entropic effect upon adsorption to be effective cement dispersants. Molecular architecture, anionic charge density and molecular weight as well as the type of anchor groups present in a superplasticizer determine whether enthalpy or entropy is the dominant force for superplasticizer adsorption. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003482 [article] Experimental determination of the thermodynamic parameters affecting the adsorption behaviour and dispersion effectiveness of PCE superplasticizers [texte imprimé] / J. Plank, Auteur ; B. Sachsenhauser, Auteur ; J. de Reese, Auteur . - 2012 . - pp. 699–709. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. 699–709 Mots-clés : Adsorption  ;  Polycarboxylates;  CaCO3  ;  Thermodynamic  calculations  ;  Workability Résumé : For adsorption of three different allylether-based PCE superplasticizers on CaCO3 surface, the thermodynamic parameters ΔH, ΔS and ΔG were determined experimentally. The GIBBS standard free energy of adsorption ΔG0ads, the standard enthalpy of adsorption ΔH0ads and the standard entropy of adsorption ΔS0ads applying to an unoccupied CaCO3 surface were obtained via a linear regression of ln K (equilibrium constant) versus 1 / T (VAN'T HOFF plot). Additionally, the thermodynamic parameters characteristic for a CaCO3 surface loaded already with polymer (isosteric conditions) were determined using a modified CLAUSIUS–CLAPEYRON equation. For all PCE molecules, negative ΔG values were found, indicating that adsorption of these polymers is energetically favourable and a spontaneous process. Adsorption of PCEs possessing short side chains is mainly instigated by electrostatic attraction and a release of enthalpy. Contrary to this, adsorption of PCEs with long side chains occurs because of a huge gain in entropy. The gain in entropy results from the release of counter ions attached to the carboxylate groups of the polymer backbone and of water molecules and ions adsorbed on the CaCO3 surface. With increased surface loading, however, ΔGisosteric decreases and adsorption ceases when ΔG becomes 0. The presence of Ca2+ ions in the pore solution strongly impacts PCE adsorption, due to complexation of carboxylate groups and a reduced anionic charge amount of the molecule. In the presence of Ca2+, adsorption of allylether-based PCEs is almost exclusively driven by a gain in entropy. Consequently, PCEs should produce a strong entropic effect upon adsorption to be effective cement dispersants. Molecular architecture, anionic charge density and molecular weight as well as the type of anchor groups present in a superplasticizer determine whether enthalpy or entropy is the dominant force for superplasticizer adsorption. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003482

Method to assess the quality of casein used as superplasticizer in self-levelling compounds / J. Plank in Cement and concrete research, Vol. 40 N° 5 (Mai 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. Titre : Method to assess the quality of casein used as superplasticizer in self-levelling compounds Type de document : texte imprimé Auteurs : J. Plank, Auteur ; H. Bian, Auteur Année de publication : 2012 Article en page(s) : pp. Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Mortar  ;  Admixture  ;  Workability  ;  Casein;  haracterization Résumé : A fast and accurate method of assessing the quality of casein superplasticizer is presented. The method is based on analysis of the content of α-, β- and κ-casein proteins contained in whole casein by ion exchange fast protein liquid chromatography (FPLC). The chromatographic profiles of six commercial casein samples were determined, revealing that the amount of κ-casein present in the biopolymer is the main assessment criteria for the quality of casein. For high dispersing effectiveness, the content of κ-casein needs to be high. The reason is that at pH ~ 12, a high content of κ-casein results in submicelles possessing smaller size (diameter ~ 10 nm), as was proven by dynamic light scattering measurement (DLS). These smaller submicelles are supposed to adsorb on cement in higher amount than large submicelles. Using this FPLC method, the dispersing performance of any casein sample can be determined very quickly without physical testing of mortar En ligne : http://www.sciencedirect.com/science/article/pii/S0008884610000074 [article] Method to assess the quality of casein used as superplasticizer in self-levelling compounds [texte imprimé] / J. Plank, Auteur ; H. Bian, Auteur . - 2012 . - pp. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. Mots-clés : Mortar  ;  Admixture  ;  Workability  ;  Casein;  haracterization Résumé : A fast and accurate method of assessing the quality of casein superplasticizer is presented. The method is based on analysis of the content of α-, β- and κ-casein proteins contained in whole casein by ion exchange fast protein liquid chromatography (FPLC). The chromatographic profiles of six commercial casein samples were determined, revealing that the amount of κ-casein present in the biopolymer is the main assessment criteria for the quality of casein. For high dispersing effectiveness, the content of κ-casein needs to be high. The reason is that at pH ~ 12, a high content of κ-casein results in submicelles possessing smaller size (diameter ~ 10 nm), as was proven by dynamic light scattering measurement (DLS). These smaller submicelles are supposed to adsorb on cement in higher amount than large submicelles. Using this FPLC method, the dispersing performance of any casein sample can be determined very quickly without physical testing of mortar En ligne : http://www.sciencedirect.com/science/article/pii/S0008884610000074