Early hydration of hot-stuffy steel slag-cement composite pastes: isothermal calorimetry and phase evolution.

Hot stuffy self-disintegration has become an advanced and popular steel slag treatment method in recent years, presenting numerous advantages. Hot-stuffy steel slag (HSS) obtained by self-disintegration treatment technology with waste heat has different compositions and properties compared with ordinary steel slag (OSS). Although the properties of OSS as a mineral admixture have been reported by numerous articles, few researches focus on HSS, especially its effect on early cement hydration. In this paper, the early hydration of HSS-cement composite pastes is investigated from the insights of isothermal calorimetry and phase evolution. Effects of HSS on the setting time, hydration heat, reaction product, reaction degree, microstructure, and pore solution were systematically studied and compared with those of OSS. Results show that, unlike OSS, HSS hardly ever retards the early hydration of cement. This is caused by the differences in the composition of HSS and OSS due to the diversity in their production treatment processes. During the hot stuffy self-disintegration, the key retarding component in OSS, such as C₁₂A₇, reacts with water and their contents in HSS are reduced. It is found that hot stuffy self-disintegration is an effective method to mitigate the retardation effect of steel slag on the early hydration of cement. This study provides a better understanding of HSS, which is crucial for its utilization in cementitious materials. Highlights: The impact of HSS on the early hydration of cement paste was studied. Hydration kinetics and phase evolution of C-HSS paste were investgated. Unlike OSS, HSS hardly ever retards the early hydration of cement. During the hot stuffy process, the key retarding component in SS is reduced. Hot stuffy self-disintegration effectively mitigates the retarding effect of SS. [ABSTRACT FROM AUTHOR]