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.