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Calcium alumino-silicates hydrates (C-A-S-H) carbonation kinetics

Abstract : In this study, we intended to characterize the impact of carbonation on the main cement hydrate (C A S H) in terms of chemistry and kinetics of degradation as well as to provide a better understanding on the carbonation products’ properties. We synthetized C-A-S-H with increasing calcium content, i.e. Ca/Si ratios ranging from 0.80 to 1.40 and Al/ Si ratios of 0.05 and 0.10. Based on thermogravimetric, 27Al and 29Si magic angle spinnining nuclear magnetic resonance and x-ray diffraction preliminary results, it was observed that C-A-S-H and C-S-H generated, after carbonation, the same major and minor calcium carbonates polymorphs (vaterite and aragonite, respectively) and the same amorphous product (silica gel). For the C-S-H, the silica gel embedded the fraction of calcium not transformed in calcium carbonate and, it was also the case for C-A-S-H silica gel which incorporates also aluminium. It was also found that coupling a high aluminium content with a high calcium content, i.e. Ca/Si higher than 0.95, calcium aluminates hydrates of pentahedral and octahedral coordination (third aluminate hydrate, TAH) are produced. The pentahedral product is located in the C-A-S-H interlayers and the TAH on its surfaces. The presence of those species correlated with a lower kinetic of degradation for the C A S Hs. A proper understanding of the mechanisms involved requires further studies but from these preliminary results, the hypothesis of a CO2 access to the C-A-S-H limited by the calcium aluminates with Al in pentahedral environment and TAH seems acceptable.
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Submitted on : Thursday, April 29, 2021 - 11:00:06 AM
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  • HAL Id : cea-03211966, version 1

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Ekoé Kangni-Foli, Stéphane Poyet, Patrick Le Bescop, Thibault Charpentier, Alexandre Dauzeres, et al.. Calcium alumino-silicates hydrates (C-A-S-H) carbonation kinetics. ICCC 2019 - 15th International Congress on the Chemistry of Cement, Sep 2019, Prague, Czech Republic. ⟨cea-03211966⟩

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