Utilization of carbonated steel slag as fine sand in OPC concrete and mortar

• The use of carbonated steel slag as partial or full replacement of fine aggregates. • Carbonation enhanced the performance of steel slag in concrete and mortar. • The comparable mechanical and durability properties of concrete were achieved. • Results showed that the use of natural resources could be reduced. • The SEM and EDS analysis of concrete made with carbonated steel slag is presented. Steel slag, a by-product of the steel industry, offers potential as a sustainable alternative in cement-based composites. However, the presence of free calcium and magnesium oxides in steel slag may increase the risk of alkali-silica reaction (ASR), impacting long-term stability. This study investigated carbonation treatment as a method to stabilize these reactive oxides, thereby reducing ASR risk and capturing carbon emissions. Furthermore, removing fine particles (<75 µm) was examined to enhance slag stability. In this study, four types of steel slag, including raw, raw classified, carbonated and carbonated classified, were used as replacements for natural fine aggregates in concrete and mortar. A total of nine mixes for both concrete and mortar were developed to assess the impact of steel slag on their strength and durability properties. The results indicated that carbonated steel slag, especially the classified ones, significantly reduced mortar shrinkage, ASR and water absorption while enhancing compressive and flexural strengths across all testing ages. Notably, the concrete mix incorporating carbonated classified steel slag as 50 % replacement for natural fine aggregates exhibited higher compressive strength at 56 days, lower water absorption at 28 days, and reduced shrinkage compared to control concrete. These findings highlight the high potential of carbonated classified slag as a fine aggregate, promoting sustainability. and the conservation of natural resources.