Abstract Electric arc furnace (EAF) slag, a by-product of steelmaking recovered after the oxidizing process, is useful when employed as aggregate in hydraulic concrete and bituminous mixtures. Concrete made with EAF oxidizing slag as an aggregate shows good physical and mechanical properties and further study of its durability will ensure greater reliability in its usage. This paper details a systematic study of slag concrete behaviour under severe test conditions. The tests were designed to evaluate the internal expansivity of the slag, its chemical reactivity with some components of the cement and its resistance to environmental agents, ice and moisture. The results indicate that the durability of slag concrete is acceptable, though slightly lower than that of conventional concrete. When the mix proportions are adequate, both the mechanical strength and the durability of slag concrete are satisfactory, although in less care mixes durability is likely to be impaired. Finally, leaching tests were performed to determine the environmental impact of the concrete, which, in comparison to results obtained directly from the slag, confirmed an important cloistering effect of the cementitious matrix on contaminant elements.