Novel zwitterionic PCE superplasticizers for calcined clays and their application in calcined clay blended cements

Calcined (thermally activated) clays are the most promising source for supplementary cementitious materials (SCMs) which can contribute to lower the environmental impact of cement and concrete. To make such substitution applicable, the interaction of calcined clays with superplasticizers must be known. In this study, three different pure calcined clays – a meta illite, a meta kaolin and a meta muscovite – were prepared via flash calcination and in a laboratory-scale muffle furnace at temperatures ranging from 550–800 °C. Their mineralogical composition was assessed by Q-XRD. A series of zwitterionic (amphoteric) polycarboxylate (PCE) superplasticizers was successfully synthesized and characterized. The dispersibility of the abovementioned pure calcined clays with these novel superplasticizers (PCEs) was proven both in pastes and mortars prepared from 80:20 wt./wt. blends of OPC and the calcined clays. Furthermore, heat flow calorimetry and strength tests evidenced that the amphoteric superplasticizers do not retard cement hydration, as is observed for most of the common PCE products. The results suggest that depending on the different composition and surface charges of the calcined clays, novel zwitterionic terpolymers are a powerful and auspicious alternative to standard anionic polycarboxylate superplasticizers to combine both fluidity and a partially improved early strength of cements blended with calcined clays.

Author: M. Schmid, R. Sposito, K.-C. Thienel, J. Plank

Section: Science and production

Keywords: calcined clay, supplementary cementitious material, superplasticizer, zwitterionic polycarboxylate superplasticizer