Enhanced mechanical property of steel slag through glycine-assisted hydration and carbonation curing

Steel slag, an industrial by-product from the steelmaking process, has limited utilities primarily due to its low reactivity and grindability. This study proposed a new method to actively utilize steel slag as a cementless binder by adding glycine to enhance the reactivity of steel slag under CO2 curing condition. Employing glycine as an activator under 1 day of hydration followed by 7 days of carbonation curing resulted in noticeable densification of the microstructure and significant improvement in compressive strength. The compressive strength of seven-day carbonated steel slag with 3 wt.% glycine reached 77.8 MPa. This improvement was due to the accelerated hydration of brownmillerite (C2F) and gradual carbonation during the carbonation period. While C2F was merely reactive without glycine, the hydration of C2F was significantly stimulated by glycine addition, producing hydrogarnet, CO32--bearing AFm phases, and amorphous phases. During the carbonation curing, AFm phases and hydrogarnet were carbonated and formed various polymorphs of CaCO3 and amorphous Al(OH)3. Adding 3 wt.% and 5 wt.% of glycine decreased the degree of carbonation, preserving the quantity of AFm phases and hydrogarnet. The use of glycine also made the pores finer and induced the reaction of RO phase to form pyroaurite.