Influence of sulphate source on Portland cement hydration

Cements were synthesized by blending a Type I low alkali Portland cement clinker with sulphate salts. A quantitative X-ray diffraction method was developed to measure the rate at which the C₃A and C₄AFphases in these cements were consumed in pastes hydrated at 23°C. The initial high rate of aluminate phase consumption was influenced significantly by the rate of solubility of the sulphate source, and especially the rate at which it released CaSO₄ into solution. Interground gypsum was far more effective than interblended gypsum in controlling aluminate hydration. Better control of the initial aluminate hydration generally led to higher 28-day paste strengths.