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A new aluminium-hydrate species in hydrated Portland cements characterized by 27Al and 29Si MAS NMR spectroscopy
Recent 27Al MAS NMR studies of hydrated Portland cements and calcium-silicate-hydrate (C-S-H) phases have shown a resonance from Al in octahedral coordination, which cannot be assigned to the well-known aluminate species in hydrated Portland cements. This resonance, which exhibits the isotropic chemical shift deltaiso = 5.0 ppm and the quadrupole product parameter PQ = 1.2 MHz, has been characterized in detail by 27Al MAS and 27Al(1H ) CP/MAS NMR for different hydrated white Portland cements and C-S-H phases. These experiments demonstrate that the resonance originates from an amorphous or disordered aluminate hydrate which contains Al(OH)63- or OxAl(OH) 6-x(3+x)- units. The formation of the new aluminate hydrate is related to the formation of C-S-H at ambient temperatures, however, it decomposes by thermal treatment at temperatures of 70-90 degree C. From the experiments in this work it is proposed that the new aluminate hydrate is either an amorphous/disordered aluminate hydroxide or a calcium aluminate hydrate, produced as a separate phase or as a nanostructured surface precipitate on the C-S-H phase. Finally, the possibilities of Al3+ for Ca2+ substitution in the principal layers and interlayers of the C-S-H structure are discussed.
A new aluminium-hydrate species in hydrated Portland cements characterized by 27Al and 29Si MAS NMR spectroscopy
Recent 27Al MAS NMR studies of hydrated Portland cements and calcium-silicate-hydrate (C-S-H) phases have shown a resonance from Al in octahedral coordination, which cannot be assigned to the well-known aluminate species in hydrated Portland cements. This resonance, which exhibits the isotropic chemical shift deltaiso = 5.0 ppm and the quadrupole product parameter PQ = 1.2 MHz, has been characterized in detail by 27Al MAS and 27Al(1H ) CP/MAS NMR for different hydrated white Portland cements and C-S-H phases. These experiments demonstrate that the resonance originates from an amorphous or disordered aluminate hydrate which contains Al(OH)63- or OxAl(OH) 6-x(3+x)- units. The formation of the new aluminate hydrate is related to the formation of C-S-H at ambient temperatures, however, it decomposes by thermal treatment at temperatures of 70-90 degree C. From the experiments in this work it is proposed that the new aluminate hydrate is either an amorphous/disordered aluminate hydroxide or a calcium aluminate hydrate, produced as a separate phase or as a nanostructured surface precipitate on the C-S-H phase. Finally, the possibilities of Al3+ for Ca2+ substitution in the principal layers and interlayers of the C-S-H structure are discussed.
A new aluminium-hydrate species in hydrated Portland cements characterized by 27Al and 29Si MAS NMR spectroscopy
Andersen, Morten Daugaard (author) / Jakobsen, Hans J. (author) / Skibsted, Jörgen (author)
Cement and Concrete Research ; 36 ; 3-17
2006
15 Seiten, 44 Quellen
Article (Journal)
English
| British Library Online Contents | 2006
Reactivation of prematurely hydrated Portland cements
| Engineering Index Backfile | 1962