Carbonated Basic Oxygen Furnace Slag Fine Aggregate in Concrete (2026-02)¶

Basic oxygen furnace slag (BOFS) has attracted increasing attention as a sustainable alternative to natural aggregate, but its practical use in concrete is severely limited by volumetric expansion induced by the hydration of free CaO. Therefore, this study proposed a novel application of basic oxygen furnace slag aggregate (BOFSA) to mitigate volumetric instability through accelerated carbonation; the resulting carbonated BOFSA was subsequently applied in extrusion-based 3D concrete printing. Notably, the characteristics inherent to 3D concrete printing can facilitate CO2 diffusion and subsequent carbonation curing, thereby realizing environmentally stable BOFSA concrete. The expansion behavior and mechanical performance of BOFSA and BOFS mortar (BOFSM) were systematically evaluated together with their carbonation characteristics. In addition, the carbonation-induced evolution of CaCO3 was analyzed from thermal and compositional perspectives. Finally, the practical applicability of carbonated BOFSA at the component scale was evaluated by fabricating a sustainable 3D-printed concrete component and demonstrating its environmental stability. The results indicated that carbonation decreased the volumetric expansion of BOFSA by 17% and the volumetric expansion of BOFSM by 35.4% at 15 days of age. The surface leachate pH decreased from 12.74 to 11.85 after the 3D-printed component was carbonated for 1 day in a high-humidity environment. Thus, carbonation effectively mitigated the volumetric expansion of BOFSA and improved its environmental compatibility, demonstrating its potential for use as a sustainable and eco-efficient fine aggregate in concrete.