Title: Cement-Superplasticizers Interaction: The Influence of Superplasticizers on the Formation of Syngenite

Author(s): H. Kucerova and C. Robler

Publication: Symposium Paper

Volume: 239

Issue:

Appears on pages(s): 269-284

Keywords: alkali sulphate; cement; fluidity; superplasticizer; syngenite

DOI: 10.14359/18384

Date: 10/1/2006

Abstract:
Interaction of Portland cement and superplasticizer is significantly influenced by the alkali sulphate content of the cement. It is widely recognized that the alkali sulphates are a fast source of sulphate ions that slow down the amount of superplasticizers molecules that are adsorbed on cement particles. Potassium sulphate occurs widely as an alkali sulphate in European cements and its higher content leads to the crystallisation of syngenite immediately after mixing of the cement paste. However the formation of syngenite influences the rheological behaviour of cement pastes and this factor has been generally overlooked in subsequent studies of incompatibility between cement and superplasticizers. The aim of this study was to reveal the influence of potassium and sodium sulphates on the dispersing effect of superplasticizers. Two types of superplasticizers have been used for investigations: polycarboxylate (PC) based and a naphthalene sulphonate formaldehyde condensate (PNS). By using the combination of rheological testing, quantitative X-ray diffraction analysis, environmental scanning electron microscopy and measuring the superplasticizer adsorption, it was possible to investigate the different influence of K2SO4 and Na2SO4 on the fluidity of cement pastes. Thereby it can be proven that syngenite formation is an important factor that changes the rheological behaviour of cement pastes and that it is specifically influenced by superplasticizers.