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Alkali binding in cement pastes: Part I. The C-S-H phase
The binding of sodium and potassium into cement paste influences the performance of concrete: for example, alkali balances between solid and paste constituents and pore fluid affect the potential for reaction with alkali-susceptible aggregates. However, quantification of the binding potential into paste solids has proven to be difficult, although much empirical data are available from pore fluid analyses. In this study, single-phase homogeneous C-S-H phases have been prepared at Ca:Si molar ratios of 1.8, 1.5, 1.2, and 0.85 and reacted with six alkali hydroxide concentrations, both NaOH and KOH, between 1 and 300 mM, giving a grid of 48 alkali concentrations and Ca:Si ratios. A steady-state alkali partition is attained in less than 48 h. A distribution coefficient, Rd, was calculated to express the partition of alkali between solid and aqueous phases at 20 degree C. The numerical value of Rd is independent of alkali hydroxide concentration and depends only on Ca:Si ratio. Approximate reversibility is demonstrated, so the Rd values are constants of a C-S-H over wide ranges of alkali concentration. The trend of Rd values indicates that alkali binding into the solid improves as its Ca:Si ratio decreases.
Alkali binding in cement pastes: Part I. The C-S-H phase
The binding of sodium and potassium into cement paste influences the performance of concrete: for example, alkali balances between solid and paste constituents and pore fluid affect the potential for reaction with alkali-susceptible aggregates. However, quantification of the binding potential into paste solids has proven to be difficult, although much empirical data are available from pore fluid analyses. In this study, single-phase homogeneous C-S-H phases have been prepared at Ca:Si molar ratios of 1.8, 1.5, 1.2, and 0.85 and reacted with six alkali hydroxide concentrations, both NaOH and KOH, between 1 and 300 mM, giving a grid of 48 alkali concentrations and Ca:Si ratios. A steady-state alkali partition is attained in less than 48 h. A distribution coefficient, Rd, was calculated to express the partition of alkali between solid and aqueous phases at 20 degree C. The numerical value of Rd is independent of alkali hydroxide concentration and depends only on Ca:Si ratio. Approximate reversibility is demonstrated, so the Rd values are constants of a C-S-H over wide ranges of alkali concentration. The trend of Rd values indicates that alkali binding into the solid improves as its Ca:Si ratio decreases.
Alkali binding in cement pastes: Part I. The C-S-H phase
Hong, Sung-Yoon (author) / Glasser, F.P. (author)
Cement and Concrete Research ; 29 ; 1893-1903
1999
11 Seiten, 17 Quellen
Article (Journal)
English
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