Evaluation of the flowability and non-linear rheological properties in alkali-activated concretes

Alkali-activated materials (AAMs) emerge as a sustainable alternative to Portland cement binders. Despite their potential, the rheological properties of alkali-activated concrete, particularly their non-linear behaviors, remain underexplored. To bridge this gap, a comparative study was conducted to examine the flow characteristics and shear thinning/thickening tendencies of alkali-activated slag (AAS) concrete. The research began with a detailed evaluation of the setting times of AAS mixtures, optimizing activator compositions to identify formulations suitable for concrete productions. Employing the Bingham and Herschel-Bulkley models, it was observed that AAS concrete with a lower silicate modulus (Ms) predominantly exhibited shear-thinning behavior. As the Ms increased, a shift toward shear-thickening behavior occurred, becoming more pronounced with higher concentrations of alkaline compounds in the activators. Furthermore, the fresh properties of AAS concrete significantly improved with increased alkali dosages in the activators, resulting in reduced dynamic yield stress and plastic viscosity, along with enhanced workability retention over time.