Understanding the rheological properties of alkali-activated slag pastes from the cohesion and friction interactions

The workability and pumping performance of alkali-activated slag (AAS) concrete are affected by its rheological properties, which are related to the interactions between slag particles in the pastes. The rheological properties of AAS paste with different equivalent sodium oxide (Na2Oeq) dosage activated by sodium hydroxide (NaOH) and sodium silicate (waterglass) with different SiO2/Na2O molar ratios were investigated in this study. The rheological mechanism was studied from the cohesion and friction interactions by calculations from parameters such as the Zeta potential of particles in the pastes, surface energy, hydrogen bond, and friction coefficient of the alkaline activators. The results indicated that the yield stress of AAS pastes was lower than that of the paste made with slag and water, whereas the plastic viscosity was higher. The yield stress of AAS pastes was mainly determined by the friction interactions between particles. The plastic viscosity was mainly affected by attractive interactions, including van de Waals interactions and Lewis acid-base interactions. The electrostatic repulsion interactions were felt at a very short distance because the AAS pastes were systems with the high ionic strength, which means that the electric double layer were severely compressed, therefore, the attractive interactions were predominant. Taken together, these results suggest that the improvement of plastic viscosity of AAS pastes should be achieved by changing the attractive interactions. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The rheological properties of alkali-activated slag (AAS) paste are affected by the interactions between slag particles, where the yield stress is determined by friction interactions and the plastic viscosity is mainly influenced by attractive interactions. The attractive interactions, including van der Waals forces and Lewis acid-base interactions, play a predominant role in the high ionic strength systems of AAS paste. The improvement of plastic viscosity in AAS paste should focus on modifying these attractive interactions.