Influence of sodium borate on the early age hydration of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements are potential candidates for the conditioning of radioactive wastes with high sodium borate concentrations. This work thus investigates early age hydration of two CSA cements with different gypsum contents (0 to 20%) as a function of the mixing solution compositi...

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Bibliographic Details
Published in:Cement and concrete research 2015-04, Vol.70, p.83-93
Main Authors: Champenois, Jean-Baptiste, Dhoury, Mélanie, Cau Dit Coumes, Céline, Mercier, Cyrille, Revel, Bertrand, Le Bescop, Patrick, Damidot, Denis
Format: Article
Language:English
Subjects:
BINDERS
BORATES
Calcium
CALCIUM COMPOUNDS
CEMENTS
Concentration (composition)
CONCENTRATION RATIO
CORRELATIONS
Delay
GYPSUM
HYDRATION
Hydration (A)
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
MATERIALS SCIENCE
MATHEMATICAL SOLUTIONS
PH VALUE
PHASE STABILITY
PRECIPITATION
REACTIVITY
Retardation (A)
Sodium borates
SODIUM COMPOUNDS
SODIUM HYDROXIDES
Sulfoaluminate (D)
Waste management (E)
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Summary:Calcium sulfoaluminate (CSA) cements are potential candidates for the conditioning of radioactive wastes with high sodium borate concentrations. This work thus investigates early age hydration of two CSA cements with different gypsum contents (0 to 20%) as a function of the mixing solution composition (borate and NaOH concentrations). Gypsum plays a key role in controlling the reactivity of cement. When the mixing solution is pure water, increasing the gypsum concentration accelerates cement hydration. However, the reverse is observed when the mixing solution contains sodium borate. Until gypsum exhaustion, the pore solution pH remains constant at ~10.8, and a poorly crystallized borate compound (ulexite) precipitates. A correlation is established between this transient precipitation and the hydration delay. Decreasing the gypsum content in the binder, or increasing the sodium content in the mixing solution, are two ways of reducing the stability of ulexite, thus decreasing the hydration delay.
ISSN:0008-8846
1873-3948
DOI:10.1016/j.cemconres.2014.12.010