Influence of Sulfates Content in Cement on the Performances of Superplasticizers

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Title: Influence of Sulfates Content in Cement on the Performances of Superplasticizers

Author(s): R. Magarotto, F. Moratti, and N. Zeminian

Publication: Special Publication

Volume: 239

Issue:

Appears on pages(s): 215-230

Keywords: B-naphtalensulphonate; incompatibility; polycarboxylate; sulfates; superplasticizer

Date: 10/1/2006

Abstract:
Extreme performances are required in superplasticizers technology nowadays; the new generation of polymers makes it possible to reach a high water reduction together with a good workability retention, ensuring excellent properties to the hardened concrete. With most of the cements, outstanding performances are achieved with the right combination between cement and superplasticizer; on the other hand, high performing superplasticizer are inevitably highly sensitive to the materials used, and in particular to the cement. Among the parameters that characterize the chemical composition of cement, the sulfate amount and type are recognized as key factors for understanding the reasons of possible problems of incompatibility between cement and superplasticizer; however, little was done on the concrete scale. In this article, five samples of cement containing different amounts of sulfates were selected. The influence of the sulfate content on the performances of PNS- and polycarboxylate-type superplasticizers was evaluated by means of adsorption tests, minislump tests and mortar tests. In the case of addition of sulfates to cement, concrete tests were also made in order to check the results on the concrete scale. The results of this study highlight the importance of an adequate content and balance between the different types of sulfates in cement, in order to guarantee the right interaction with superplasticizers.