Optimizing Potassium-Based Activator Formulation for Balanced Reactivity, Flowability, Setting Time and Mechanical Performance of Alkali-Activated Materials

Alkali-activated materials (AAMs) based on industrial by-products, such as ground granulated blast furnace slag (GGBFS), are increasingly considered sustainable alternatives to Ordinary Portland Cement (OPC) due to their lower environmental impact and favorable mechanical performance. Among the key parameters controlling the behavior of alkali-activated systems, the chemical composition and modulus of the alkaline activator play critical roles in determining the reaction kinetics and material properties. This study investigates the influence of potassium silicate modulus (Ms), defined as the molar ratio of silica to alkali oxide (SiO2/K2O), on the reactivity, setting time, flowability, and mechanical properties of alkali-activated slag pastes. Potassium silicate solutions with moduli ranging from 1.0 to 2.5 were used as activators for GGBFS. Paste specimens with different activator moduli were prepared and cured at 20 °C and 75% relative humidity for mechanical testing. The results show that the activator modulus significantly affects the fresh properties, particularly at higher modulus values. Increasing the modulus delays reactivity and prolongs the setting time, whereas the flowability of the fresh paste decreases. Nevertheless, the flowability of the mixtures remained sufficient to allow proper penetration between open textile meshes, which is essential for textile-reinforced cement/concrete (TRC) applications. No clear systematic trends were observed in the mechanical properties, including the elastic modulus, flexural strength, and compressive strength.