Compound effect of CaCO₃ and CaSO₄·2H₂O on the strength of steel slag: cement binding materials

In this study, we replaced 30% of the cement with steel slag to prepare binding material; additionally, small amounts of CaCO₃ and CaSO₄·2H₂O were added. This was done to study the compound effect of CaCO₃ and CaSO₄·2H₂O on the strength of steel slag-cement binding materials. The hydration degree of the steel slag cementitious material was analyzed by XRD, TG and SEM. The results showed that the optimum proportions of CaCO₃ and CaSO₄·2H₂O were 3% and 2%, respectively. Compared with the steel slag-cement binders without adding CaCO₃ and CaSO₄·2H₂O, the compressive strength increased by 59.9% at 3 days and by 17.8% at 28 days. Acting as the nucleation matrix, CaCO₃ could accelerate the hydration of C₃S. In addition, CaCO₃ was involved in the hydration reaction, generating a new hydration product, which could stably exist in a slurry. Meanwhile, CaSO₄·2H₂O could increase the number of AFt. The compound effect of CaCO₃ and CaSO₄·2H₂O enhanced the intensity of steel slag-cement binding materials and improved the whole hydration behavior. (author)