Ground steel slag based cementless binder activated by sodium bicarbonate

The utilization of steel slag as a supplementary cementitious material has been limited due to its low hydraulic or pozzolanic reactivity. This study investigated the enhancement of the hydration property of steel slag paste and the significant strength development by employing NaHCO 3 in aqueous solution at various concentrations (0.5, 1, and 2 wt%). A noticeable increase in compressive strength of pasted sample was observed with the use of 1 % of NaHCO 3 (e.g., from 1.7 MPa to 19 MPa). It was confirmed that NaHCO 3 accelerated the formation of carbonate-AFm phases (hemicarbonate and monocarbonate) through reactions with mayenite and the consumption of porlandite. As the hydration of steel slag progressed, the addition of NaHCO 3 significantly enhanced the reaction of belite through internal carbonation, consequently increasing the production of calcium silicate hydrates and calcite. In this process, the polymorphs of calcium carbonate, such as aragonite and amorphous calcium carbonate, were confirmed. The gradational formation of hydration products has a positive effect on the steady enhancement of compressive strength by densifying the structure of steel slag.