| Steel slag is a solid waste from steel production, in which the main mineral is calcium silicate phase, therefore, the steel slag has a great potential for application in concrete. The main reason leading to the limited utilization of steel slag is volatile ingredients, the low strength and the poor stability problem. Study on how to improve the efficient use of steel slag to produce high value-added products has a important practically significance in promoting the development of circle economy steel production. In this paper, Xinyu hot stuffy steel slag was researched, the hydrated properties of steel slag cement binders under different curing conditions was studied; According to the Krustulovic-Dabic hydration kinetics model, the kinetic model for the hydration of steel slag cement was introduced; In addition, the effect of CaCO3 on the hydration of steel slag cement binders was also studied in this research. All of these research could provide theoretical foundation for the recycling use of steel slag as a cement admixture. The conclusions are as follows:High temperature curing can stimulate the activity of steel slag significantly and accelerate the early hydration rate, but had little influence on the hydration products. When 30% cement is replaced by steel slag, the content of non-evaporable water at 3 days was increased by 59.9% and Ca(OH)2 increased by 25.0% compared with complex binder cured under standard condition; High temperature curing can make the slurry structure more compact, the greater the steel slag, the more obvious about excitation effect at later hydration age.The hydration process of steel slag cement binders has experienced 5 stages, that is the early induction, induction phase, accelerated phase, deceleration phase and stable phase,respectively. With the increase of steel slag, the hydration heat emission rate and quantity of cementitious materials are significantly reduced and the greater the amount of steel slag, the more obvious extension about the induction period; The hydration process of steel slag cement binders is not a single process, but controlled by three different reaction mechanisms,that is nucleation and crystal growth(NG), interactions at phase boundaries(I) and diffusion(D), respectively. And the overall development depends on the slowest hydration rate process. When 30% cement is replaced by steel slag, the hydration process sequence and reaction mechanism of steel slag cement binders is the NG-I-D. When the dosage of steel slag is 60%, the reaction mechanism changes and the Krustulovic-Dabic dynamics model is no longer applicable.CaCO3 can act as the crystal nucleus of hydration products, and thus have a contribution to accelerate the hydration of C3S, thereby increasing the early strength of composite binder. Along with the hydration process, part of the CaCO3 can react with C3A to generate a new single carbon calcium aluminate (Ca4Al2O6·CO3·11H2O), the type of which is layered and irregularly arranges in the slurry. Some unreacted CaCO3 can fill in the cracks of the slurry, creating a micro aggregation effect, which enhances the compactness of the cementitious materials; CaSO4·2H2O can make steel slag-cement complex binders generate more AFt, which can fill in the cracks and increase the strength of the pastes; Both CaCO3 and CaSO4·2H2O have a significant impact to the macro-performance and microstructure of composite pastes. Compared with the steel slag-cement composite binders without adding CaCO3 and CaSO4·2H2O, the compressive strength at 3 days was increased by 59.9%, and at 28 days by 17.8%. The combination of both makes the slurry structure more compact, beneficial to increase the intensity of the steel slag-cement composite binders. |
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