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.