Early formation of belite in cement clinker raw materials with slag

Analytical methods for characterising cement raw meal during heating in different atmospheres were investigated. The effect of replacing limestone with 10 wt% slag on the formation of incipient belite and precursors of the clinker liquid in the temperature range 600–1050°C was quantified using thermogravimetry, X-ray diffraction and equilibrium calculations. The results showed that when calculating the lime saturation factor, slags were favoured to sand, resulting in lower amounts of quartz and C₂S in the samples containing slag than the reference sample. This suggests that silicon dioxide in slag minerals did not react in this temperature range. The multi-component equilibrium results supported the phase formation sequence established. Allowing for the possible kinetic influences the potential solids solutions offered with the software was a valuable asset. The results showed that the effect of using slags to reduce the carbonate and sand content in a raw meal on potential amounts of incipient C₂S was negative. At present, more detailed knowledge is needed regarding how blast-furnace slag and basic oxygen furnace slag contribute to the formation of intermediary compounds such as incipient C₂S, C₃A, C₂F and C₄AF in the solid phase at temperatures over 1050°C and affect the formation of C₃S.