BINDING OF CHLORIDE AND ALKALIS IN PORTLAND CEMENT SYSTEMS

Models predicting the phase equilibria of cement binder systems, and the diffusion of each of the species in these systems, would provide a powerful means of identifying the optimum binder composition in a given service environment. These models would be particularly useful because there are so many new binders that are being touted to help delay the onset of corrosion of steel reinforcement. In this article, the authors report the development of a thermodynamic model for describing the binding of chloride and alkalis in hydrated Portland cement pastes. The model is based on the phase rule, which for cement pastes in aggressive marine environment predicts multivariant conditions, even at constant temperature and pressure. The authors report on studies of the effect of the chloride and alkalis; experiments have been conducted on cement pastes prepared from white Portland cements containing 4% and 12% C3A, and a grey Portland cement containing 7% C3A. One weight percent calcite was added to all cements. The pastes prepared at w/s ratio of 0.70 were stored in solutions of different Cl (CaCl2) and Na (NaOH) concentrations. When equilibrium was reached, the pastes were analyzed by spectroscopy on the scanning electron microscope (SEM). Results showed a well-defined distribution of chloride was found between the pore solution, the C-S-H phase, and an AFm solid solution phase consisting of Friedel's salt and monocarbonate. The lower content of alkalis in white Portland cement results in higher chloride contents in the C-S-H phase. Alkalis have a negative impact on the binding of chlorides because they increase the concentration of chlorides in solution. The authors conclude that this model can be used to predict the performance of different types of Portland cement under different conditions of exposure.

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  • Find a library where document is available. Order URL: http://worldcat.org/issn/00088846
• Corporate Authors:

  Elsevier

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  Kidlington, Oxford  United Kingdom  OX5 1GB
• Authors:
  • Nielsen, E P
  • Herfort, D
  • Geiker, M R
• Publication Date: 2005-1

Language

• English

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 117-123
• Serial:
  • Cement and Concrete Research
  • Volume: 35
  • Issue Number: 1
  • Publisher: Elsevier
  • ISSN: 0008-8846
  • Serial URL: http://www.sciencedirect.com/science/journal/00088846

Subject/Index Terms

• TRT Terms: Binders; Calcium sulfates; Chloride content; Hydration; Phase equilibrium; Portland cement; Sodium; Solubility; Spectroscopy; Water cement ratio
• Uncontrolled Terms: Modeling
• Subject Areas: Highways; Materials; I32: Concrete;

Filing Info

• Accession Number: 00988989
• Record Type: Publication
• Files: TRIS
• Created Date: Apr 18 2005 12:00AM