Retention of alkali ions by hydrated low-pH cements: Mechanism and Na+/K+ selectivity

Low-pH cements, also referred to as low-alkalinity cements, can be designed by replacing significant amounts of Portland cement by pozzolanic materials. Their pore solution is characterized by a pH near 11, and an alkali concentration much lower than that of Portland cement. This work investigates t...

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Veröffentlicht in:Cement and concrete research 2013-09, Vol.51, p.14-21
Hauptverfasser: Bach, T.T.H., Chabas, E., Pochard, I., Cau Dit Coumes, C., Haas, J., Frizon, F., Nonat, A.
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Sprache:eng
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Zusammenfassung:Low-pH cements, also referred to as low-alkalinity cements, can be designed by replacing significant amounts of Portland cement by pozzolanic materials. Their pore solution is characterized by a pH near 11, and an alkali concentration much lower than that of Portland cement. This work investigates the retention of sodium and potassium by a hydrated low-pH cement comprising 60% Portland cement and 40% silica fume. It is shown that sorption of potassium is higher than that of sodium and mainly results from counterion charge balancing of the C-S-H negative surface charge. To explain the greater retention of potassium compared to sodium, it is postulated that potassium, unlike sodium, may enter the interlayer of C-S-H to compensate the negative charges in the interlayer, in addition to the external surfaces. This assumption is supported by structural characterization of C-S-H using X-ray diffraction.
ISSN:0008-8846
1873-3948
DOI:10.1016/j.cemconres.2013.04.010