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

Polycarboxylate ether (PCE) admixtures are generally used in concrete at relatively low concentrations, enabling the reduction of mixture cost and enhanced flow properties due to reduction of cement content and significant enhancement of rheology, respectively. 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 consumption 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 (M), 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 M 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.