INFLUENCE OF SLAG COMPOSITION ON THE HYDRATION OF ALKALI-ACTIVATED SLAG

This contribution highlights the influence of the slag composition on the properties of alkali activated slags. The hydration of eight blast-furnace slags with different chemical compositions with sodium metasilicate or NaOH as activator was investigated. Sodium metasilicate shows poor strength after 1 day, but high strength after 7 days and beyond, whereas NaOH activation leads to high 1 day strength, but only moderate strength development at later ages. At the same hydration degree sodium metasilicate activation gives a much higher compressive strength than NaOH activation. This is due to the formation of a dense hydration product in the NaOH activated system at the early age, which leads to a more porous microstructure than in the case of sodium metasilicate. A higher MgO content in the slags was found to be beneficial with respect to faster hydration kinetics and a more rapid strength development. Increasing Al2O3 contents lead to slightly slower hydration kinetics and slightly lower compressive strengths.