Influence of Al2O3 content on hydraulic reactivity of granulated blast-furnace slag, and the interaction between Al2O3 and CaO

This paper presents results of investigations on the influence of the Al2O3 content of granulated blast-furnace slag (GBFS) on its hydraulic reactivity. Al2O3 content up to 15% has a positive effect on the reactivity of GBFS. Due to the interaction between the Al2O3 and CaO contents the effectiveness of the Al2O3 depends also on the CaO content, which is clearly more significant in lime-rich slags than in slags that are poor in lime. For the optimisation of the quality of GBFS it is recommended to maintain Al2O3 over 10·5% and CaO over 40%. It was found by27 Al NMR investigation that aluminium in GBFS is mainly tetrahedrally coordinated. However with rising Al2O3 so-called ‘tricluster’ is formed in the slag glasses. This leads to a reactivity reduction.