The use of electric arc furnace slag (EAF) aggregate as a replacement for natural aggregate can reduce the consumption of natural resources and promote the reuse of steelmaking by-products. However, the high density, rough surface texture, and angular shape of EAF particles may adversely affect concrete workability and fresh concrete stability against aggregate segregation. This study investigated the effect of calcium carbonate powder on the fresh-state behavior, mechanical properties, and durability indicators of concrete containing naturally weathered EAF aggregate. Eight concrete mixtures were prepared in two groups containing 9% and 13% calcium carbonate powder by the volume of total aggregates. In each group, fine and coarse natural aggregates were simultaneously replaced with EAF at levels of 0%, 50%, 75%, and 100%. The cement content, water-to-cement ratio, and superplasticizer dosage were kept constant at 420 kg/m³, 0.35, and 0.8%, respectively. The results showed that increasing EAF content in the 9% powder group increased the slump value; however, collapse slump and aggregate segregation occurred at high replacement levels. In contrast, the 13% powder group exhibited a more consistent slump response without visible segregation. The A100 mixture (13% powder and 100% EAF) achieved the highest 28-day compressive and splitting tensile strengths, reaching 81.55 and 5.59 MPa, respectively. The A75 mixture showed the highest flexural strength (8.43 MPa) and the lowest deicing salt scaling value (approximately 94 g/m²). Although A100 provided the highest compressive and splitting tensile strengths, its advantages over A75 were limited to 4% and 3.5%, respectively. Conversely, A75 exhibited the highest flexural strength among all mixtures and, compared with A100, reduced deicing salt scaling, 30-min water absorption, and 24-h water absorption by 19%, 26%, and 6%, respectively. Therefore, A75 provided a more balanced performance considering mechanical properties and durability indicators and was selected as the preferred mixture among the investigated mixtures.