Abstract
The changes occurring in the crystallised phases during degradation of an ordinary Portland cement have been studied. Leaching of cement paste with demineralised water generates a series of dissolution boundaries. Portlandite, then AFm, ettringite and calcite dissolve successively. In the zones with no change in mineralogy, local chemical equilibrium and decreasing gradients in calcium and hydroxyls between the core and the surface explain the precipitation of the secondary phases, like AFm, ettingite and calcite. Hydrogarnets in the surface layer in contact with the aggressive solution only dissolved slightly, or not at all. The very low solubility of hydrotalcites at pH values near neutrality explains the preciptation of these magnesium-containing phases in the surface layer.
Résumé
L’évolution des phases cristallisées durant la dégradation d’un ciment Portland ordinaire a été étudiée. La lixiviation d’une pâte de ciment par une eau déminéralisée provoque une série de dissolutions: la portlandite se dissout la première, puis les AFm, l’ettringite et la calcite. Dans des zones de minéralogie constante, l’équilibre chimique local et les gradients décroissants en calcium et hydroxyles entre le cœur et la surface explique les précipitations secondaires des phases présentes (AFm, ettringite, calcite). Les hydrogranats dans la couche de surface en contact avec une solution agressive se dissolvent peu ou pas de tout. La faible solubilité des hydrotalcites à des pH proches de la neutralité explique la précipitation des ces phases magnésiennes dans les couches de surface.
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Editorial note Prof. Richard Cabrillac is a RILEM Senior Member, P. Faucon and F. Adenot work at the CEA (French Atomic Energy Commission), a RILEM Titular Member.
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Faucon, P., Adenot, F., Jorda, M. et al. Behaviour of crystallised phases of Portland cement upon water attack. Mat. Struct. 30, 480–485 (1997). https://doi.org/10.1007/BF02524776
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DOI: https://doi.org/10.1007/BF02524776