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ESEM evidence for through-solution transport during brownmillerite hydration
In portland cements, there are two non-silicate clinker minerals which contain aluminum: calcium aluminate C3A and calcium aluminoferrite, having the approximate composition of the mineral brownmillerite C4AF (here we use the standard notation C = CaO, A = A12O3, S = SO3, H = H2O). In oil well cements, which are iron-rich, the aluminoferrite is always the predominant and usually the only aluminum-containing phase. Brownmillerite has frequently been used as a model of the aluminoferrite phase in cements. When placed in contact with water, brownmillerite forms solid hydration products within a few minutes. The metastable hexagonal C-A-H and ettringite can form by interdiffusion of calcium and aluminate ions moving through the solution away from the source mineral. In the case of C4AF the iron content of solid products formed in this way is negligible as iron does not go into the solution during hydration. It should be noted that the experiments here have high water-to-solid ratios: hence there are large fluid volumes in which soluble ions may move around freely. The situation in a dense paste is somewhat different. What is certain is that the hydration products of C4AF do not necessarily nucleate on the surface of hydrated C4AF but may grow on the surface of other clinker or hydrate phases.
ESEM evidence for through-solution transport during brownmillerite hydration
In portland cements, there are two non-silicate clinker minerals which contain aluminum: calcium aluminate C3A and calcium aluminoferrite, having the approximate composition of the mineral brownmillerite C4AF (here we use the standard notation C = CaO, A = A12O3, S = SO3, H = H2O). In oil well cements, which are iron-rich, the aluminoferrite is always the predominant and usually the only aluminum-containing phase. Brownmillerite has frequently been used as a model of the aluminoferrite phase in cements. When placed in contact with water, brownmillerite forms solid hydration products within a few minutes. The metastable hexagonal C-A-H and ettringite can form by interdiffusion of calcium and aluminate ions moving through the solution away from the source mineral. In the case of C4AF the iron content of solid products formed in this way is negligible as iron does not go into the solution during hydration. It should be noted that the experiments here have high water-to-solid ratios: hence there are large fluid volumes in which soluble ions may move around freely. The situation in a dense paste is somewhat different. What is certain is that the hydration products of C4AF do not necessarily nucleate on the surface of hydrated C4AF but may grow on the surface of other clinker or hydrate phases.
ESEM evidence for through-solution transport during brownmillerite hydration
ESEM-Nachweis für Transport durch die Lösung während der Brownmillerit-Hydratation
Meller, N. (author) / Hall, C. (author) / Crawshaw, J. (author)
Journal of Materials Science ; 39 ; 6611-6614
2004
4 Seiten, 4 Bilder, 1 Tabelle, 19 Quellen
Article (Journal)
English
ESEM evidence for through-solution transport during brownmillerite hydration
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