REACTION MECHANISM OF ORGANIC ADMIXTURES WITH HYDRATING CEMENT COMPOUNDS

This paper discusses the possible mechanismsby which organic compounds influence the setting properties of portland cement. From a consideration of the hydration mechanisms of tricalcium silicate and tricalcium aluminate, it is concluded that organic compounds influence the hydration of these compounds by their effect on the hydration products through complexing and nucleation processes, It is hypothesized that the hydration of tricalcium silicate is controlled by the nucleation and growth of calcium hydroxide. The poisoning of nuclei by soluble silica is responsible for the induction period. Adsorption of organic compounds onto clcium hydroxide nuclei, through a chelation process, inhibits crystal growth even more effectively and prolongs the induction period. Tricalcium aluminate is considered to hydrate rapidly because the protective hydrate layer is destroyed by conversion to the hydrate of triclcium aluminate. Organic retarders enter the interlayer region of the hexagonal hydrates to inhibit this conversion reaction and therefore maintain the integrity of the hydration barrier. A similar mechanism may hold in the presence of sulfate ions. In portland cement, adsorption of admixtures by the hydration products of tricalcium aluminate controls the supply of admixture to tricalcium silicate. This explains the enhanced retardation when the addition of admixtures is delayed after the first addition of water.

• Record URL:
  • http://onlinepubs.trb.org/Onlinepubs/trr/1976/564/564-001.pdf
• Summary URL:
  • https://scholar.google.com/scholar_lookup?title=REACTION+MECHANISM+OF+ORGANIC+ADMIXTURES+WITH+HYDRATING+CEMENT+COMPOUNDS&author=J.+Young&publication_year=1976
• Availability:
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• Supplemental Notes:
  • Publication of this paper sponsored by Committee on Chemical Additions and Admixtures for Concrete. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Authors:
  • Young, J F
• Conference:
  • 54th Annual Meeting of the Transportation Research Board
  • Location: Washington District of Columbia
  • Date: 1975-1-13 to 1975-1-17
• Publication Date: 1976

Media Info

• Media Type: Print
• Features: Figures; References; Tables;
• Pagination: pp 1-9
• Monograph Title: Concrete Admixtures
• Serial:
  • Transportation Research Record
  • Issue Number: 564
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Admixtures; Adsorption; Hydration; Organic compounds; Portland cement; Tricalcium aluminate; Tricalcium silicate
• Old TRIS Terms: Reaction
• Subject Areas: Highways; Materials;

Filing Info

• Accession Number: 00135022
• Record Type: Publication
• ISBN: 0309024749
• Files: TRIS, TRB
• Created Date: Jul 13 1976 12:00AM