Effects of anionic species of activators on the rheological properties and early gel characteristics of alkali-activated slag paste

Abstract

The effects of anionic species of Na2O·2SiO2-NaOH-Na2CO3 ternary activator on the rheology of alkali-activated slag (AAS) pastes are studied to obtain quantitative relationships between composition of activator and rheological parameters. The interstitial fluid chemistry, especially silicate species, OH− and CO32− ions, controls the precipitation of early gels and structural build-up by affecting the competition between dissolution and polymerization kinetics. Abundant Al3+, Ca2+ and Na+ in the interstitial solution participate into silicate oligomer structures, reducing polymerization degree of silicate species. This results in reduced concentration of Si-O-Si structure and increased Si-O-NB, while the later precipitates to form gel nano particles which are attractive, leading to yield stress-spurt, great flowability loss and rapid setting. The mixture activated by the blended of Na2O·2SiO2 and Na2CO3 tends to form C-A-S-H gel with lower Ca/Si due to the competitive effect of CO32−. This study provides essential information towards better control fresh properties of AAS mixtures.