Abstract Natural clayey soils have often to be stabilized by mixing them with certain materials, such as cement, lime, or similar products, so that they acquire the necessary properties for civil works. Some industrial by-products can also be used for this purpose, among which steelmaking slags. Our research studies the properties of Ladle Furnace Slag (LFS) and the characteristics of several clayey soils susceptible to improvement with additions of this by-product. The behaviour of the different soil and slag mixes was similar to the behaviour of the soil and lime mixtures reported in the literature. The results of a series of test report improvements in various geotechnical properties, such as the plasticity index, expansiveness, bearing capacity and durability.