00135022

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http://onlinepubs.trb.org...s/trr/1976/564/564-001.pdf

https://scholar.google.co...oung&publication_year=1976

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.

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.

01411422

pp 1-9

1976

Transportation Research Record

54th Annual Meeting of the Transportation Research Board

0309024749

Print

Figures (12) ; References (29) ; Tables (1)

Admixtures; Adsorption; Hydration; Organic compounds; Portland cement; Tricalcium aluminate; Tricalcium silicate

Highways; Materials

TRIS, TRB

Jul 13 1976 12:00AM

• A SETTING PROBLEM INVOLVING WHITE CEMENT AND ADMIXTURE
• USE OF ADMIXTURES IN CONCRETE PLACED AT HIGH TEMPERATURES
• USE OF ADMIXTURES IN PRODUCTION OF LOW-POROSITY PASTES AND CONCRETES