Hydration reactions of the C₃A-CaSO₄.2H₂O system (1 : 1 mole ratio) at 30 and 50°C. Part I – effect of calcium lignosulfonate

The hydration characteristics of a tricalcium aluminate and gypsum mixture with a mole ratio of 1 : 1 in the presence and absence of calcium lignosulfonate at 30 and 50°C were investigated. Different ratios of calcium lignosulfonate were used namely 0, 1 and 3% by weight. The water-to-solid ratio used was 10. Hydration was carried out for various time intervals from 0·5 h up to 90 days. Ettringite and monosulfate hydrate were the only hydration products formed as indicated by X-ray diffraction analysis and scanning electron microscopy. The results of combined water content, X-ray diffraction and scanning electron microscopy indicate that calcium lignosulfonate retarded the formation of ettringite at early hydration ages. The extent of hydration was inversely proportional to the ratio of calcium lignosulfonate.