Mapping the effects of activator type and molarity on the rheology of alkali-activated slag using oscillation amplitude testing

• AAS pastes investigated using wide concentration ranges of Na/K hydroxides, carbonates, and silicates. • Comparison of strain- and stress-controlled oscillation amplitude sweep rheological tests. • Workability increased with activator molarity up to a threshold of 5–7.5 M. • Unique effect of silicates: loss factor increased sharply with their concentration. • Full rheological profiling supported by zeta potential and mini-slump tests. This study investigates the effects of activator type and concentration, namely sodium and potassium hydroxides, carbonates, and silicates, on the rheological behaviour of alkali activated slag pastes. Oscillation amplitude sweep tests in both strain- and stress-controlled modes were conducted to evaluate key parameters such as yield point and break point. Increasing activator concentration generally improved workability up to a threshold between 5 and 7.5 M, beyond which rheological properties deteriorated due to changes in microstructure and viscosity. This threshold was less pronounced for KOH and K 2 CO 3 . Alkali silicates exhibited the strongest plasticizing effect and, uniquely, shifted the viscoelastic nature of the pastes from solid-like to liquid-like (significantly increased loss factor). Complementary mini-slump and zeta potential tests supported the oscillatory findings and revealed limitations at extreme concentrations. The results highlight the distinct impacts of different combinations of Na + and K + cations and various anions on the rheology of alkali-activated slag pastes.