Influence of Mixing Sequence on Cement-Admixture Interaction

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Title: Influence of Mixing Sequence on Cement-Admixture Interaction

Author(s): Chun-Tao Chen and Leslie J. Struble

Publication: Materials Journal

Volume: 106

Issue: 6

Appears on pages(s): 503-508

Keywords: cement-admixture interaction; delayed addition; dynamic rheology; high-range water-reducing admixture; mixing sequence

DOI: 10.14359/51663332

Date: 11/1/2009

Abstract:
Cement pastes containing a high-range water-reducing admixture and prepared using various mixing sequences were investigated using dynamic rheology. Samples were prepared using delayed admixture addition, delayed water addition, double mixing, and vigorous mixing techniques. The effects of the mixing sequence varied with cement composition, admixture dosage, and time of addition. Of these mixing sequences, delayed admixture addition was the most effective way to enhance the dispersion. A delay time of 2.5 minutes was sufficient to disperse all the cement-admixture combinations. With delayed water addition, there exists an optimum amount of delayed water. With double mixing, pastes with longer time intervals between the mixing were dispersed more. With vigorous mixing, the pastes were, in general, dispersed by the admixture. The dispersing effect, however, was not apparent at low admixture dosages. Results of this study demonstrate that the batching sequence and mixing procedure must be taken into account when comparing different concrete batches, even though they have same mixture proportions and raw materials. Moreover, results in this study suggest a direction for optimizing the batching sequence and mixing procedure for both paste and concrete.


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