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Influence of citric acid on the hydration of Portland cement / Göril Möschner in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) Titre : Influence of citric acid on the hydration of Portland cement Type de document : texte imprimé Auteurs : Göril Möschner, Auteur ; Barbara Lothenbach, Auteur ; Renato Figi, Auteur Année de publication : 2009 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Retardation;  Hydration  products;  Thermodynamic  calculations;  Admixture;  Modeling Résumé : Citric acid can be used to retard the hydration of cement. Experiments were carried out to investigate the influence of citric acid on the composition of solid and liquid phases during cement hydration. Analyses of the solid phases showed that dissolution of alite and aluminate slowed down while analyses of the pore solution showed that citric acid was removed almost completely from the pore solution within the first hours of hydration. The complexation of the ions by citrate was weak, which could also be confirmed by thermodynamic calculations. Only 2% of the dissolved Ca and 0.001% of the dissolved K formed complexes with citrate during the first hours. Thus, citric acid retards cement hydration not by complex formation, but by slowing down the dissolution of the clinker grains. Thermodynamic calculations did not indicate precipitation of a crystalline citrate species. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000179 [article] Influence of citric acid on the hydration of Portland cement [texte imprimé] / Göril Möschner, Auteur ; Barbara Lothenbach, Auteur ; Renato Figi, Auteur . - 2009. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) Mots-clés : Retardation;  Hydration  products;  Thermodynamic  calculations;  Admixture;  Modeling Résumé : Citric acid can be used to retard the hydration of cement. Experiments were carried out to investigate the influence of citric acid on the composition of solid and liquid phases during cement hydration. Analyses of the solid phases showed that dissolution of alite and aluminate slowed down while analyses of the pore solution showed that citric acid was removed almost completely from the pore solution within the first hours of hydration. The complexation of the ions by citrate was weak, which could also be confirmed by thermodynamic calculations. Only 2% of the dissolved Ca and 0.001% of the dissolved K formed complexes with citrate during the first hours. Thus, citric acid retards cement hydration not by complex formation, but by slowing down the dissolution of the clinker grains. Thermodynamic calculations did not indicate precipitation of a crystalline citrate species. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000179

Solid solution between Al-ettringite and Fe-ettringite (Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O) / Göril Möschner in Cement and concrete research, Vol. 39 N° 6 (Juin 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 6 (Juin 2009) . - pp. 482–489 Titre : Solid solution between Al-ettringite and Fe-ettringite (Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O) Type de document : texte imprimé Auteurs : Göril Möschner, Auteur ; Barbara Lothenbach, Auteur ; Frank Winnefeld, Auteur Année de publication : 2009 Article en page(s) : pp. 482–489 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Ettringite;  Thermodynamic  calculations;  Hydration  products Résumé : The solid solution between Al- and Fe-ettringite Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O was investigated. Ettringite phases were synthesized at different Al/(Al + Fe)-ratios (= XAl,total), so that XAl increased from 0.0 to 1.0 in 0.1 unit steps. After 8 months of equilibration, the solid phases were analyzed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the aqueous solutions were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analyses of the solid phases indicated the existence of a miscibility gap between XAl,total = 0.3–0.6. Some of the XRD reflections showed two overlapping peaks at these molar ratios. The composition of the aqueous solutions, however, would have been in agreement with both, the existence of a miscibility gap or a continuous solid solution between Al- and Fe-ettringite, based on thermodynamic modeling, simulating the experimental conditions. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000490 [article] Solid solution between Al-ettringite and Fe-ettringite (Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O) [texte imprimé] / Göril Möschner, Auteur ; Barbara Lothenbach, Auteur ; Frank Winnefeld, Auteur . - 2009 . - pp. 482–489. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 6 (Juin 2009) . - pp. 482–489 Mots-clés : Ettringite;  Thermodynamic  calculations;  Hydration  products Résumé : The solid solution between Al- and Fe-ettringite Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O was investigated. Ettringite phases were synthesized at different Al/(Al + Fe)-ratios (= XAl,total), so that XAl increased from 0.0 to 1.0 in 0.1 unit steps. After 8 months of equilibration, the solid phases were analyzed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the aqueous solutions were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analyses of the solid phases indicated the existence of a miscibility gap between XAl,total = 0.3–0.6. Some of the XRD reflections showed two overlapping peaks at these molar ratios. The composition of the aqueous solutions, however, would have been in agreement with both, the existence of a miscibility gap or a continuous solid solution between Al- and Fe-ettringite, based on thermodynamic modeling, simulating the experimental conditions. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000490