Hydration and mechanical properties of cement-steel slag system incorporating different activators

This study aims to improve the mechanical properties of cement-steel slag mortar by the addition of alkaline activators (NaOH, Na2CO3/NaOH and water glass) to promote the optimal utilization of steel slag. In this paper, the setting time, flexural and compressive strength, early-age hydration kinetics and microstructure are investigated to explore how the alkaline activators influence the hydration of cement-steel slag system. The results indicate that the incorporation alkaline activators shortens the setting time and enhances the mechanical strength of cement-steel slag composite binder, which are ranked from large to small in the order of water glass >Na2CO3/NaOH > NaOH. Moreover, the hydration exothermic action of cement-steel slag activated by alkaline activators is significantly accelerated in comparison to cement-steel slag. Furthermore, the incorporation of alkaline activators promotes the formation of amorphous gel products, such as C-S-H and C-A-S-H gel, of cement-steel slag system, which can fill the capillary pores and convert them into gel pores with a smaller pore size, leading to a denser microstructure. Based on the outcome of different analytical techniques, it is observed that alkaline activators can facilitate disintegration of steel slag's vitreous structure and can be applied to enhance the reactivity of steel slag in the cement-steel slag system to develop a sustainable composite cement.