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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 [...]