The steelmaking and manganese industries produce large amounts of slag which are little valorised today for the formulation of hydraulic binder in the field of civil engineering. The ground blast furnace slag (GGBFS) is commonly used in the building materials industry but the converter steel slag (BOF slag) is mainly used as aggregates and the silicomanganese slag (LSiMn) is currently not upgraded in this sector. The companies ArcelorMittal, Eramet and Ecocem produce or exploit these slags, which are very different in terms of origins and compositions and properties. They want to develop the valorisation of these by-products in the field of materials for building construction. Some studies have already suggested that the steel slag and the silicomanganese slag can be incorporated into cement matrix as component for cement industry. But few data exist about mechanism of hydration of these slags in cement systems, the sustainability of such systems and the environmental impact which involve the use of these slags. Our research concerns first the characterization of the selected slags, particularly the particle size distribution, the chemical composition and microstructure, and their reactivity. The results showed that the silicomanganese slag is comparable to the ground granulated blast furnace slag because of its latent hydraulic behaviour but it has a different chemical composition with lower calcium content and a small part of inert material (10%). The steel slag, which has 23% of inert portion (composed of iron rich compounds) is very basic due to the presence of lime and portlandite and has a slight hydraulic behaviour at early age. The formulation of binary systems (cement / slag) shows that the silicomanganese slag added to Portland cement forms, like blast furnace slag, hydrates (hydrated calcium silicates) which participate in the development of compressive strength. Thus, the utilization of silicomanganese slag can be a good alternative for the formulation of hydraulic binders in the field of building materials. The steel slag has a smaller hydraulic activity than both other hydraulic slags and has a limited contribution to the development of the compressive strength. However, the high alkalinity of steel slag makes it a good potential activator of latent hydraulic slags. Ternary cementitious systems (cement/steel slag/slag with latent hydraulic behaviour) have been made: the steel slag appears to be effective for activating the blast furnace and silicomanganese slags. These cementitious systems, composed of at least 80% of slags, have satisfying mechanical properties for hydraulic road binders. In addition to these works, an environmental study was conducted for the slags and the slag incorporated in cementitious matrix. The results show that the low leaching of pollutant allows the utilization of our slag as hydraulic road binders.
