Reaction Kinetics and Fresh State Properties of Alkali-Activated Slag Mixtures with Secondary Precursors

Abstract

In this study, the effects of the incorporation of various supplementary materials such as fly ash, limestone powder, silica fume, and portland cement as the secondary precursor on the early age reaction, structural buildup, rheology, and microstructure of alkali-activated slag cements (AAC) in the presence of two different activators (sodium hydroxide and sodium silicate) have been investigated. Test results showed that the activator type influenced the reaction process and the setting time of AAC pastes could be estimated by the specific cumulative heat release or ultrasonic pulse velocity range. AAC pastes containing the investigated secondary precursors showed Bingham fluid behavior. Early structural buildup tests suggested that the silica fume or portland cement addition seems beneficial for 3D printing applications, while the fly ash or limestone addition could be preferred for multilayer casting. The main reaction products for the AAC pastes incorporating various secondary precursors were characterized as a chain-like C-(N)-A-S-H/C-(A)-S-H or C-S-H using SEM/EDX analyses.