Dicalcium silicate is one of the main mineral phases of steel slag. Ascribed to the characteristics of hydration and carbonation, the application of slag in cement production and carbon dioxide sequestration has been confirmed as feasible. In the current study, the precipitation process of the dicalcium silicate phase in steel slag was discussed. Meanwhile, the study put emphasis on the influence of different crystal forms of dicalcium silicate on the hydration activity and carbonation characteristics of steel slag. It indicates that most of the dicalcium silicate phase in steel slag is the γ phase with the weakest hydration activity. The hydration activity of γ-C₂S is improved to a certain extent by means of mechanical, high temperature, and chemical activation. However, the carbonation activity of γ-C₂S is about two times higher than that of β-C₂S. Direct and indirect carbonation can effectively capture carbon dioxide. This paper also summarizes the research status of the application of steel slag in cement production and carbon dioxide sequestration. Further development of the potential of dicalcium silicate hydration activity and simplifying the carbonation process are important focuses for the future.

During the slow cooling process of steel slag, the crystals of inert mineral phases (C2F, RO phases) and active mineral phases (C2S, C3S) adhere and grow, and the irregular interlocking, embedding, filling, stacking, and coating between mineral phases seriously affect the hydration activity of active mineral phases in steel slag. Therefore, this article selects glycerol (C3H8O3) as a grinding aid to mechanically excite steel slag, exploring the mineral phase evolution and hydration activity excitation mechanism of steel slag under different process parameters. C3H8O3 mechanical excitation refined the steel slag particles, increased porosity, increased specific surface area, and caused peeling behavior between the rough surface active mineral phases (C2S, C3S) of the steel slag particles and the smooth surface inert mineral phase C2F with sharp angular protrusions. When the addition amount of C3H8O3 is 0.24 wt% and the ball milling time is 90 minutes, the mechanical excitation effect of steel slag is the best. The total mass fraction of C2S and C3S increases by 14.3 wt%, while the mass fraction of C2F decreases by 19.3 wt%. The mechanical excitation of C3H8O3 can cause the steel slag to germinate cracks at the interface of each phase, and a porous honeycomb structure composed of calcium hydroxide (CH) and calcium silicon hydrogel (C-S-H) appears during the hydration process, producing a large number of acicular ettringite (AFt), effectively improving the early hydration activity of steel slag.