Preparation and characterization of alkali-activated white belite cements

Activated white cement clinkers with a theoretical 60% (wt) belite (dicalcium silicate) content were prepared at a temperature 100 °C lower than used to manufacture conventional white Portland cement clinkers. Activation was achieved by adding variable amounts of K₂CO₃ or Na₂CO₃ to the raw mixes. Rietveld quantitative analysis of X-ray diffraction findings showed that adding the alkalis stabilized the high temperature belite polymorphs. When 2.0% (wt) of Na₂O was added, the composition (by wt) found was 16.4(4)% α-C₂S, 16.7(8)% α'H-C₂S, 23.2(6)% β-C₂S, 32.7(7)% total C₃S, 9.5(2)% orthorhombic C₃A and 1.50(5)% free lime. Due to the high volatilization rate of K₂O under the experimental conditions, it stabilized the alpha-type C₂S less effectively than Na₂O. A calorimetric study was likewise performed to correlate the phase composition with early age hydration (behaviour).