Early Hydration Properties and Kinetics of Steel Slag-Cement Activated by Sodium Salts

The early hydration process, hydration properties, and kinetics of steel slag cement activited by different sodium salts were studied through hydration heat measurement, scanning electron microscope(SEM) analysis, and hydration kinetics simulation. The results show that the incorporation of sodium salt does not affect the hydration process, and the hydration exothermic process of steel slag-cement with or without sodium salt can be divided into five stages:initial rapid exothermic stage, induction stage, acceleration stage, deceleration and attenuation stage. The acceleration stage hydration reaction is controlled by nucleation reaction, which belongs to the autocatalytic reaction. During the deceleration stage, the hydration reaction is jointly controlled by the phase boundary reaction and diffusion mechanism. In the attenuation stage, the hydration reaction is also controlled by diffusion mechanism. The reaction rate constant in the acceleration stage is 6 to 8 times of that in the attenuation stage due to the different reaction mechanisms. However, the reaction rate constant of steel slag-cement doped with sodium salt is greater than that without sodium salt. The addition of sodium salt is conductive to the hydration reaction of steel slag-cement. The promotion effect of different sodium salt on hydration is different. The promotion effect of sodium aluminate on hydration is better before the acceleration stage, and the promotion effect of sodium silicate is better after the deceleration stage. Different sodium salts have different promotion effects on hydration. The sodium aluminate promotes hydration better before the acceleration stage, while sodium silicate performs better after the deceleration stage. © 2021, Editorial Department of Journal of Building Materials. All right reserved.