Influence of Fineness on Activity Index of Blast Furnace Slag with Different SiO2/Al2O3

Granulated blast furnace slag (GBFS) is a by-product of ironmaking and widely used in the cement and concrete. GBFS samples with different ratio of SiO2/Al2O3 were prepared under the laboratory conditions and ground by the agate ball mill at different times. Then they were characterized by laser particle size analysis (LPSA), scanning electron microscopy (SEM), Bertrand surface method and mechanical testing. It was found that the activity index of GBFS clearly increased with the decrease of the GBFS particle size. In the case of the average particle size about 32μm, the activity indices were irregular with the increase of SiO2/Al2O3 ratio, whereas for the average particle size about 11μm, the activity indices decreased with the increase of SiO2/Al2O3 ratio.