Recycling of steel slag in clay brick production

In the two last decades, that is since the enviromental sensibility strongly came out, a lot of studies have been carried out in order to appraise the possibility of waste disposal, in particular the recycling in ceramic manufacturing. This study is aimed at assessing the recycling potentialities of residues difficult to be disposed of: steel slags as raw materials in the brick industry. For this purpose, three specimens representative of the Italian production of common steel slags were selected. Moreover, three brickworks located near the steel plants were taken into account, in order to test the slag introduction in their productive cycle. Wastes and brick clays were characterized by chemical and physical point of view. The steel slags are mainly constituted by FeO (34-40%), CaO (18-27%) and SiO2 (11-15%); considerable are also the percentages of MnO, MgO and Cr2O3. They are characterized by an amorphous phase prevalent over w?stite and larnite. Afterwards mixtures of clay and slag, in growing percentages until 10%, were tested by reproducing in laboratory the whole manufacturing process (shaping, drying and firing) and performing the technological characterization of unfired and fired products. The analyses show that the use of steel slags caused the following effects: reduction of plasticity and mechanical strength in unfired articles; decrease of drying shrinkage and drying sensitivity; increase of porosity and reduction of bulk density and mechanical strength in fired products. These effects depend to a large extent on the clay composition: as a matter of fact, fine grained clays can accept in a better way the slags introduction. With this addition there is an improvement of the drying behaviour and tolerable changes of the final mechanical properties.