Analysis of Hydration Mechanism of Steel Slag-Based Cementitious Materials under Saline–Alkaline-Coupled Excitation

In order to realize the resourceful, large-scale, and high-value utilization of steel slag, which is a bulk industrial solid waste, and to reduce the use of cement-based cementitious materials, this study adopted the coupled excitation effect of sodium carbonate–magnesium oxide–desulfurization gypsum to excite steel slag-based cementitious materials, and it preliminarily investigated the hydration process of the steel slag-based cementitious system by the analysis of the heat of hydration of the cementitious materials and the pH value of the pore solution. The hydration products and microscopic morphology of the steel slag-based gelling material were initially investigated by XRD and SEM technical means on the gelling system. The results showed that the hydrolysis of the exciter and the dissociation of the active components in the steel slag provided an alkaline environment and relevant ions for the gelling system, which promoted the generation of the AFt and hydrotalcite phases. Subsequently, the AFt provided ungenerated sites for C-S-H gels as well as calcites, and the hydrotalcite phase accelerated the transformation of the carbonate phase in the gelling system, which promoted the synergistic effect of the hydration of the steel slag and mineral slag. Eventually, a large number of C-S-H gels, calcites, and other hydration products were generated in the gelling system under the synergistic effect of the hydration of the steel slag and slag, which was manifested in the improvement in the mechanical properties at the macrolevel. In addition, this study also standardized 28 d steel slag-based gelling for carbonization maintenance, and the data show that a carbonization temperature of 70 °C, CO2 pressure of 0.7 MPa, and carbonization time of 30 min achieved the best results, with a strength of up to 51.22 MPa, illustrating that steel slag-based gelling materials are safe and can be used for the green storage of CO2.