Title: Fresh Properties of Alkali-Activated Slag Pastes with Sodium and Potassium Hydroxide
Author(s): Vlastimil Bílek Jr., Lukáš Kalina, David Markusík
Publication: Symposium Paper
Appears on pages(s): 19-28
Keywords: Alkali-activated slag, rheology, activator type, concentration, hydroxide, flow curve, flow table test, oscillatory test, yield stress
The rheology of alkali-activated materials is a very complex issue that is strongly influenced, among others, by the chemical nature of the alkaline activator. The most widely used are sodium and potassium compounds, but it is well-known that Na+ and K+ have different impacts on rheology, causing different behaviors of fresh mixtures. Therefore, in this study, the rheological parameters of NaOH and KOH activated slag were investigated, especially with respect to various hydroxide concentrations that ranged from 0 to 40% for both hydroxides. The pastes were tested in terms of flow table test and using a rotational rheometer equipped with a vane in cup geometry in both rotation and oscillation mode. Increasing concentrations of both hydroxides up to 20-25% resulted in a similar evolution of rheological properties in terms of increased flowability, but differed greatly for higher concentrations, as the beneficial effect of KOH was observed throughout the concentration range, while high concentrations of NaOH resulted in a dramatic increase in all rheological parameters, such as yield stress, consistency index, viscoelastic moduli or stresses corresponding to the limit of the viscoelastic region and flow point. The paper shows the potential of oscillatory tests to study the structural breakdown of inorganic binders.