Title: Effects of Different Polycarboxylate Ether Structures on the Rheology of Alkali-Activated Slag Binders

Author(s): Alireza Kashani, John L. Provis, Jiangtao Xu, Adam Kilcullen, Peter Duxson, Greg G. Qiao, Jannie S.J. van Deventer

Publication: Symposium Paper

Volume: 288

Issue:

Appears on pages(s): 1-11

Keywords: admixtures; alkali-activated slag; plasticizer; polycarboxylate; rheology.

DOI: 10.14359/51684235

Date: 9/14/2012

Abstract:
Polycarboxylate ether (PCE) admixtures are generally used in concrete at rela¬tively low concentrations, enabling the reduction of mixture cost and enhanced flow prop¬erties due to reduction of cement content and significant enhancement of rheology, respec¬tively. However, typical PCE polymer structures that are used in Portland cement have little or no effect on alkali activated slag (AAS) binder rheology due to ineffective consump¬tion of polymer by a number of mechanisms, including degradation of the polymer chains within the high alkaline environments present in AAS systems. In this study, a range of PCEs with long and moderate PolyEthyleneGlycol (PEG) side chain lengths, and with high and low molecular weights (Mn), are examined. Co-polymers containing a higher density of backbone charges, as is typical for a Portland cement superplasticiser, increase the yield stress of alkali-activated slag. A co-polymer with longer side chains and lower Mn show a yield stress reduction, indicating a mild increase in workability compared to an unmodified AAS paste. It is suggested that in the high ionic strength environment of an AAS binder, a more charged polymer is consumed through interactions with other ions and charged particles, which can bring an increase in yield stress and plastic viscosity of AAS.