Portlandite solubility and Ca2+ activity in presence of gluconate and hexitols

The current paper investigates the impact of gluconate, D-sorbitol, d-mannitol and D-galactitol on calcium speciation at high pH values by i) solubility measurements of portlandite (Ca(OH)2) and ii) potentiometric titration measurements of calcium salt solutions. Thermodynamic modelling was used to...

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Bibliographic Details
Published in:Cement and concrete research 2021-11, Vol.149, p.106563, Article 106563
Main Authors: Bouzouaid, Lina, Lothenbach, Barbara, Fernandez-Martinez, Alejandro, Labbez, Christophe
Format: Article
Language:English
Subjects:
Calcium ions
Complex formation
Complexation
Gluconate
Hexitols
Mannitol
Portland cements
Portlandite solubility
Saline solutions
Slaked lime
Solubility
Sorbitol
Speciation
Thermodynamic modelling
Thermodynamic models
Titration
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Summary:The current paper investigates the impact of gluconate, D-sorbitol, d-mannitol and D-galactitol on calcium speciation at high pH values by i) solubility measurements of portlandite (Ca(OH)2) and ii) potentiometric titration measurements of calcium salt solutions. Thermodynamic modelling was used to fit the chemical activities of Ca2+ and OH− ions and thus to determine the strength and kind of the different Ca-organic-hydroxide complexes. The strength of complex formation with Ca2+ decreases in the order gluconate ≫ sorbitol > mannitol > galactitol, which follows the same order as sorption on portlandite. Heteropolynuclear gluconate complexes with calcium and hydroxide dominate the Ca-speciation in the presence of portlandite, while for sorbitol ternary CaSorbOH+ complexes were dominant under alkaline conditions. We expect that these results will help in better understanding the influence of gluconate and hexitols on the hydration of alite and Portland cement.
ISSN:0008-8846
1873-3948
DOI:10.1016/j.cemconres.2021.106563