Utilization of steel slag for sustainable concrete blocks: Laboratory study on water absorption, flexural strength, carbon dioxide capture, and volumetric expansion

In this study, the applicability of steel slag in sustainable concrete blocks was experimentally evaluated by analyzing water absorption, flexural strength, carbon dioxide (CO₂) capture performance, and expansion behavior. Three types of steel slag were used: basic oxygen furnace (BOF) slag, electric arc furnace (EAF)-oxidizing slag, and EAF-reducing slag. These were incorporated into a conventional concrete block mix by partially replacing the binder or fine aggregate. The results show that replacing 10 % of the binder or 35 % of the fine aggregate with steel slag did not degrade the performance (such as by increasing water absorption) compared to the reference mix. In terms of flexural strength, a reduction was observed only when 10 % of the binder was replaced with EAF-oxidizing slag. In all other cases, the flexural strength increased, with improvements of up to 127.3 % over the reference mix. The results of thermogravimetric analysis and X-ray micro-computed tomography confirmed that sustainable concrete blocks with incorporated BOF slag therein exhibited superior CO₂ capture performance. Although volumetric expansion due to the reaction of free calcium oxide in BOF slag was observed when immersing the sustainable concrete blocks in water, the porous structure of the latter allowed internal voids to be filled, resulting in a denser microstructure. No negative effects, such as cracking or spalling, were observed. Therefore, the use of steel slag in sustainable concrete blocks demonstrates strong potential in terms of both mechanical performance and environmental benefits.