Abstract

The electric arc furnace (EAF) slag, generated from an alternative steel production route with lower carbon emissions, is projected as a by-product with increasing availability. This study investigated the feasibility of incorporating EAF slag aggregates carbonated by aqueous (EAF-A) and semi-aqueous (EAF-S) processes as full replacements for natural aggregates in Portland cement mortars, with the aim of evaluating their viability as a raw material in cementitious materials, with a view to enhancing their valorisation. Physical, mechanical, and microstructural properties of the mortars were assessed using thermogravimetric analysis, X-ray diffraction, ultrasonic pulse velocity (UPV), and capillary absorption tests. Results showed that mortars incorporating EAF-S aggregates exhibited superior workability and significantly higher compressive strength at 28 days, exceeding 35 MPa and outperforming both the control and EAF-A series. In contrast, EAF-A aggregates did not consistently improve mechanical strength. Microstructural analysis revealed increased formation of amorphous silica, C-S-H gels, and portlandite in mortars containing carbonated EAF aggregates compared to the control. These findings emphasise that the type of carbonation treatment critically influences the internal structure and performance of mortars, supporting the viability of semi-aqueous carbonated EAF aggregates for sustainable construction applications.