Effect of an Alkaline Set Accelerator on Normal Portland Cement Paste in the Presence of a Superplasticizer

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Title: Effect of an Alkaline Set Accelerator on Normal Portland Cement Paste in the Presence of a Superplasticizer

Author(s): Q Xu, C. Roessler, J. Stark, and P. Wang

Publication: Special Publication

Volume: 217

Issue:

Appears on pages(s): 409-422

Keywords: accelerator; calcium aluminate hydrate; ettringite; heat release; hydrate phases; hydration; pore solution; set time; superplasticizer

Date: 9/1/2003

Abstract:
The effect of an alkaline set accelerator on the setting of the cement paste without and with a superplasticizer is compared. The results show that the presence of the superplasticizer weakens the effect of the set accelerator. In order to attain the demanded rapid setting a higher content of the accelerator is needed. The early hydration process of the cement is largely changed by the two admixtures. It can be shown that the superplasticizer restrained the formation of the calcium aluminate hydrate phases whereas the accelerator increases the rate of formation of the calcium aluminate phases in the paste. Furthermore, due to superplasticizer-accelerator interaction the morphology of the calcium aluminate hydrate phases is changed. The calcium aluminate hydrate phases precipitate as clusters with a spheroid shape. We state that the cluster formation of the calcium aluminate hydrate phases is the reason for the reduced acceleration of the setting of the superplasticizer/accelerator containing paste.