Recrystallisation of granulated blast-furnace slags and the significance for the hydraulic reactivity

In this paper the recrystallisation reactions of granulated blast-furnace slags (GBS) with different chemical compositions were studied. The investigations were carried out with X-ray powder method on the chemically modified technical GBS. During the heating merwinite first crystallised at approximately 750°C and converted to melilite with rising temperatures. The concentrations of the crystallised mineral phases merwinite and melilite depend on the CaO content. The merwinite concentration increases and the melilite concentration decreases with rising CaO content. Depending on the chemical composition the structural parameters of the melilite vary in the range between gehlenite and åkmernite. Due to the good correlation between the gehlenite concentration and the reactivity of the GBS the gehlenite concentration can be regarded as an indicator for the reactivity of the GBS.