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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