EFFECT OF ACTIVATOR TYPE AND MOLARITY ON RHEOLOGY AND SURFACE CHEMISTRY OF ALKALI-ACTIVATED SLAG

presentation, poster

English

Alkali-activated materials (AAM) can be a sustainable low CO2 alternative to conventional Portland cement (PC) based binders. Although these materials are not direct replacements for commercial PC-based products, they can be used in specific cases, such as during alkaline activation of the precursor with a varying doses of recycled material from disposed building materials. However, understanding the effect of concentration and choice of alkali activator on the rheological behavior and associated processability of the basic materials, without additional admixtures, is key to the applicability of AAM in more complex systems. Therefore, this study focuses on the influence of a wide range of alkaline activators and their concentrations (37 systems) on the rheology of alkali-activated slag pastes. A consistent volume fraction of 0.50 slag was used in all pastes. The focus of the research is on unconventional oscillatory measurements with controlled strain or controlled stress. From these measurements, the stresses corresponding to the end of the linear viscoelastic region (LVR, yield point) and to the crossover of storage and loss modulus (flow point) were evaluated. Subsequently, the dependence of the observed parameter (oscillation stress) on concentration was evaluated for the activators used at the yield point (Figure 1). The results indicate a significant effect of activator type and concentration on AAM rheology. Sodium-based activators generally cause a higher yield stress compared to potassium-based activators. It is also evident from the experimental results that, for most activators, there is a certain concentration value beyond which the trend in rheological properties changes, potentially affecting the alkali activation process. For instance, a significant increase in yield stress was observed in sodium hydroxide-activated pastes for molarities above 7.5 M. These phenomena are related to the smaller Na+ ions, which have a higher charge density and strongly attract and retain their hydration layer of water molecules. In contrast, K+ ions exhibit weaker binding to water. Additionally, alkali silicate-activated pastes showed a significant decrease in the yield point compared to those activated by other activators. This may be due to the plasticizing and deflocculating effects of the silicate ions. The rheological results are supported by zeta potential analysis and mini slump test and may be promising for monitoring the evolution of viscoelastic parameters during hydration using different blending systems.

Alkali-activated materials, activator, oscillatory measurements, yield stress

MARKUSÍK, D.; BÍLEK, V.

20. 5. 2025

Engineering Conferences International

Espoo, Finaland

https://engconf.us/wp-content/uploads/2025/05/Final-Program-and-Posters-25-AG-WEB.pdf