In metallurgy, slag refers to a glassy or crystalline solidified melt residue of non-metallic nature. It is a mixture of substances composed of different oxides.

Linz-Donawitz slag (LDS) is produced during the production of steel from pig iron. When operating, for example, three converters depending on the number of batches, about 65 - 80 bucket slag accrue per day (corresponds to about 2,000 t). The company Erich Friedrich Hüttenservice takes over the slag from the Salzgitter AG steel mill and processes it over several process steps into a usable building material. The slag must be stored on "maturity storage" in order to achieve a complete reaction of the available free lime and other constituents, thus achieving the usability of the slag.

LDS were previously used in road, track and track construction. The problem with current treatment methods is that they are lengthy (at least 2 years) and thus have a large space requirement (landfill space). Furthermore, in spite of relatively homogeneous compositions in an already built-in state, unwanted partial increases in volume due to subsequent hydration have occurred for some years. This phenomenon currently prevents the reuse of the slag. From a volume increase of> 5%, the slag must no longer be used according to DIN EN 1744-1 in road and road construction, as this can cause damage to roads and buildings. This currently leads to the fact that most of the LDS can only be stored. The existing landfill space is limited.

Slag can very well replace natural stones in many applications. However, in order to continue and accelerate the reuse of the largest part of the slag, a novel treatment process has to be developed to prevent a subsequent volume increase of> 5%.