Development of Sodium Silicate-Activated Ground Granulated Blast Furnace Slag and Fly Ash Binder-Based Concrete for Pumping Applications

Alkali-activated materials are one of the alternative cementitious materials, but their extensive usage is constrained by certain limitations, such as quick setting and rapid loss of workability. By addressing these limitations, this study developed alkali-activated concrete formulations, with enhanced workable times and pumpable workability, comprising of precursors based on fly ash and blast furnace slag. The precursors were activated with sodium silicate activator of molar modulus 1.5 and activator dosage (% of Na₂O) of 8 and 10%. Zinc sulfate was incorporated as a retarder to prolong the workable times. The spread diameter of these concrete mixtures measured at 10th min was in the range of 650–745 mm. Several of the developed concrete mixtures could retain the spread diameters in the range of 430 – 655 mm for a duration longer than 90 min. These developed alkali-activated concrete mixtures with pumpable workability and prolonged workable times have exhibited compressive strengths in the range of M30 to M60 grade. The rheological behavior of these concrete mixtures was also assessed on their corresponding concrete equivalent mortar (CEM) mixtures. The yield stress and plastic viscosity of CEM mixtures were found to decrease with an increase in the proportion of fly ash and increase with an increase in the hydration time and retarder content. The evolution of yield stress and plastic viscosity of alkali-activated CEM mixtures were found to be in agreement with the obtained spread diameter values for concrete mixtures.