Multi-technical characterization and correlations between properties of standard cured alkali-activated high-calcium FA binders with GGBS as additive

Abstract

In this study, ground granulated blast-furnace slag (GGBS) was introduced as an additive to improve the setting and hardened properties of alkali-activated high-calcium FA binders at standard curing condition. FA was partially replaced by GGBS with contents of 0, 10%, 20%, 30%, 40% and 50% by mass to form a binary blends, which were then activated by an alkaline solution consisting of Na2SiO3 and NaOH to produce alkali-activated binders. The performance of alkali-activated high-calcium FA binders modified by GGBS were evaluated by multi-technical characterization. Moreover, the correlations between multiple properties were also analysed. The results show that adding GGBS as an additive could accelerate the setting times of alkali-activated high-calcium FA binders. The viscosity increases with an increase in GGBS content and is closely related to the flowability. Increasing GGBS content significantly improves the compressive strength of the paste sample, especially its early compressive strength, but makes the material more brittle. The sorptivity coefficient of hardened paste has a strong correlation with its compressive strength. In addition, the microcosmic improvement mechanism of GGBS as an additive was also discussed. The improvement in strength is owing to the generation of additional C-(A)-S-H gel in the presence of GGBS, which fills the pores in the matrix, transforming the large capillary pores into small gel pores, resulting in a denser and more uniform structure. The resulting decrease of threshold and critical diameters may be the main reason for the decrease of sorptivity coefficient.