Effects of the Chemical Composition of Synthetic Slags Compared to an Average Blast Furnace Slag

To study the effect of the main oxides and the minor components in slags on their reactivity as SCM, various glasses were synthesized to stepwise imitate a commercial slag of average chemical composition. First, a glass was produced from the main oxides CaO, Al₂O₃ and SiO₂. In a second step, the minor components MgO, Fe₂O₃, Na₂O and K₂O were added separately to the main oxide mix. A selection of two synthetic glasses was tested for their compressive strength contribution (up to 90 days) by substituting 20 wt.% of cement. After all testing times, the synthetic slags achieved a strength similar to that of the commercial product. The reactivities determined by heat flow calorimetry (R³ test) correlate with the calculation of NBO/T and the results of ²⁹Si MAS NMR showing that a decreased degree of polymerization enhances the reactivity. Apart from that, FTIR spectroscopy and ²⁷Al MAS NMR indicate a similar structure of the original and the synthetic slags.