Dilatancy mitigation of cement powder paste by pozzolanic and inert fillers

Third generation polycarboxylate-based superplasticiser (SP) can easily extend the maximum concurrent design limits of strength and flowability of concrete or cement paste, but simultaneously creates unfavorable dilatancy (or shear thickening) that decreases mixing efficiency and pumping range of concrete. The dilatancy is created initially by clustering of free and adsorbed polymers of SP, but further addition of SP can conversely mitigate the dilatancy by improved wet packing density. Because of the negative correlation of packing density and dilatancy, it is believed that partial replacement of cement by finer pozzolanic or inert filler can decrease the dilatancy via improved filling effect. Herein, the dilatancy of cement powder paste with or without pozzolanic fly ash or inert limestone powder replacing partial cement was studied using a coaxial rheometer. The results revealed that there exists a threshold limit of SP, beyond which the effect on dilatancy reverses. At a given SP dosage, partial cement replacement by either filler decreases dilatancy via improved packing density up to an optimal ratio, after which the dilatancy increases because the packing density reverses.