Abstract: The liquid steel slag (2) is poured in at least four successive layers (6-8), comprising a lowermost layer (6), an uppermost layer (7) and at least two intermediate layers (8), in a reservoir (3) and the layers of liquid steel slag are allowed to solidify. After having applied the uppermost layer (7), the solidified steel slag is cooled down more quickly by means of water. The average temperature of each of the intermediate layers (8) is kept at least until the start of the water cooling step, and this for at least one hour, above a minimum temperature which is equal to or higher than the temperature at which ?-dicalcium silicate is formed. In this way, more crystalline phases different from dicalcium silicates are formed so that the formation of fines by the transition of ? into ?-dicalcium silicates can be considerably reduced. A glassy material and/or a phosphorus containing compound is preferably added to the liquid slag to further reduce the formation of fines.

Abstract: The carbonate bonded, press-moulded article is produced by press-moulding a particulate, carbonatable material that contains water and by carbonating the obtained compact with carbon dioxide gas. In order to be able to ensure an optimal compressive strength of the article two types of tests are provided. In the first type of test a sample of the particulate material is compressed with an increasing compaction pressure and when water starts to be expelled from the material as from a particular compaction pressure, the press-moulding step is performed with a compaction pressure which is at least 7 MPa smaller than this compaction pressure. In the second type of test different samples of the particulate material are press-moulded with different compaction pressures and, after having released the compaction pressure, the density of the compact is determined.

Abstract: The present invention relates to a method for recycling waste water from a stainless steel slag treatment process wherein stainless steel slag is brought into contact with water, in particular to neutralize the free lime contained therein, thereby producing said waste water. This waste water contains heavy metals, including at least chromium, and has a pH higher than or equal to 11. In accordance with the invention, it is used as production water for manufacturing mortar and/or concrete. In this way, the heavy metals, which are dissolved in the waste water and thus readily available, become bound in the newly formed cement phases so that they are prevented from leaching. Moreover, it has been found that the workability of the fresh mortar or concrete and also the quality of the final mortar or concrete materials is not negatively affected by the use of this alkaline waste water and that an accelerated setting could be achieved during the first hours.

Abstract: The present invention relates to a process for producing a granular material 26 for mixing with at least a hydraulic binding agent and with water to produce mortar or concrete. This process comprises at least an aggregation step and a carbonation step. In the aggregation step, steel slag particles from at least a fine fraction 24 of steel slag, in particular a fine fraction of steel slag containing a significant amount of ?-dicalcium silicate, are aggregated into larger grains so as to form a coarser granular material 25. In the carbonation step, said aggregated particles in said coarser granular material 25 are carbonated by means of carbon dioxide so as to produce a carbonated granular material 26. The present invention also relates to a carbonated granular material of aggregated steel slag particles containing a significant amount of ?-dicalcium silicate, in particular at least 3 wt. %, preferably at least 5 wt. % and more preferably at least 7 wt.

Abstract: The invention concerns a method of treating an alkaline granular carbonatable material which contains aluminium metal and which has in particular a pH of at least 10. The method comprises an oxidation step wherein at least a portion of said aluminium metal is oxidized by contact with moisture. The aluminium should be oxidized to avoid swelling problems when using the granular material as aggregate. In the method according to the invention this oxidation is accelerated by providing at least one oxidizing agent in said moisture, which oxidizing agent has a higher redox potential than the water contained in said moisture. The method further comprises a carbonation step wherein the granular carbonatable material is at least partially carbonated to lower the pH thereof. In this way the formation of ettringite, which may also release aluminium ions which causing further swelling problems, can be avoided in the granular material or any ettringite present therein can be destabilized.

Abstract: Process for preparing a foaming slag former for electric furnaces comprising the steps of aggregating solid slag particles into a coarser granular material and carbonating the solid slag particles to form the foaming slag former. The solid slag particles are preferably aggregated before carbonization, so that the carbonates form a solid matrix binding the particles together.