Stabilization of steelmaking slag based by FMP S.r.l. patent and possible application in concrete production

Steel slag is an industrial by-product of steel manufacturing and can be categorized into basic oxygen furnace (BOF) slag, electric arc furnace (EAF) slag, and ladle furnace (LF) slag. The world slag production is about 203 Mt while in Europe slag production is about 21.8 Mt from steel and 23.5 Mt from cast iron. Steel slag is useful in many fields such as road construction, asphalt concrete, agricultural fertilizer, and soil improvement. However, better utilization for value-added purposes in cement and concrete products can be achieved. A massive utilization of the slag in concrete production is hindered by their high porosity, water adsorption and possible phenomena of artefact expansion due to the presence of free CaO and MgO. The slag subtracts the water from the hydraulic binder (sponge effect) and produces a destructive interference on the phenomenon of hydraulic binder hydration. Subsequent release of water interferes with the hardening and mechanical properties of the artefacts. In order to limit the risk of expansion, the steel slag is generally subjected to weathering in outdoor conditions during several months. These phenomena actually limit the use of slag in concrete at a maximum percentage of 25% w/w and this percentage requires a great increase of the chemical additives dosage (fluidifying agent). The way of valorisation of the slag in concrete production would help to achieve several aims: conservation of the natural aggregate resources and reduction of the high costs of slag processing and storage. This study focuses on the use of EAF slag for the production of concrete with a degree of substitution of natural inert up to 80% by weight without the use of chemical additives after treatment of inertization / stabilization of the EAF slag according to a procedure patented by FMP innovative start-up. After the chemical and mineralogical characterizations of the EAF slag, the operating parameter for inertization/stabilization of the artificial aggregate were optimized. Comparison tests were carried to determine the physico-chemical properties differences between the slag submitted to the inertization / stabilization process and the one not submitted to the treatment process used as aggregate in concrete design. A concrete with substitution of 50% and 70% w/w of natural aggregate were designed in order to highlight the influence of slag aggregate on the concrete behaviour. Apparent density, porosity, permeability, compressive strength, tensile strength, and elasticity modulus were measured to assess the influence on concrete mechanical properties with different substitution of natural aggregate. Durability of the concrete samples was evaluated by accelerate aging tests while the micro-properties by the characteristics of interfacial transition zone (ITZ).