Study on the chloride ion binding rate of sulfoaluminate cement mortars containing different mineral admixtures

In this study, the chloride ion (Cl^-) binding rate of sulfoaluminate cement (SAC) mortars containing different mineral admixtures was investigated. This is essential to improve the durability of concrete structures in high Cl^- environments, especially where they are susceptible to Cl^- attack such as coastlines and marine structures. The effects of Cl^- concentration, curing age, and the type and amount of mineral admixture on the Cl^- binding rate of SAC mortars were analyzed. It was found that the content of water-soluble Cl^- in SAC mortars decreased with the increase of curing age, while the Cl^- binding ratio increased accordingly, indicating that its resistance to internal Cl^- permeation increased. The addition of fly ash (FA) and ground granulated blast furnace slag (GGBS) can significantly improve the Cl^- binding rate of SAC mortars, and the Cl^- binding rate increases to 46.6% with 20% of FA and 38.7% with 40% of GGBS. The effects of mineral admixtures on the microstructure and phase composition of SAC mortars were further investigated by X-ray diffraction (XRD) analysis. The results showed that the addition of FA and GGBS promoted the formation of C-S-H (calcium silicate hydrate) gels and improved the resistance of SAC mortars to Cl^- penetration. On the other hand, the excessive addition of silica fume (SF) decreased the Cl^- binding rate, whereas a moderate amount of limestone powder (LP) improved the Cl^- binding rate. The study of the Cl^- binding rate of SAC mortars can help to evaluate their resistance to Cl^- erosion in real projects, thus guiding the optimization of concrete formulations and the improvement of durability.