Effect of activator on rheological properties of alkali-activated slag-fly ash pastes

Abstract

The time-dependent rheological behaviors of alkali-activated cement (AAC) are expected to be precisely controlled, in order to meet the requirements of modern engineering practices. In this paper, the effects of activator, including the Na₂O concentration and SiO₂/Na₂O (S/N) molar ratio, on the rheological behavior of alkali-activated slag-fly ash pastes were investigated. The small amplitude oscillatory shear (SAOS) and shear test were used to evaluate the structural build-up and flowability of pastes. Besides, zeta potential measurement, calorimetric test and thermogravimetric analysis (TGA) were carried out to reveal the physico-chemical mechanisms behind the rheological evolution of fresh pastes. It was found that high Na₂O concentration and low S/N molar ratio improved the flowability and structural build-up rate of paste. Moreover, the structural build-up of alkali-activated slag-fly ash pastes consists of two stages, which is controlled by the dissolution of solid reactants and formation of C-(A)-S-H gels, respectively.

Keywords

alkali-activated slag-fly ash / activator / zeta potential / rheology / structural build-up

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