Influence of some heavy metal nitrates on the hydration of C₃A

The influence of addition of some heavy metal salts such as Zn, Cu, Cr and Pb nitrates as admixtures on the hydration reaction of a mixture of C₃A and gypsum with molar ratio 1 : 3 was studied. Different ratios of each salt were used namely; 0·5, 1·5 and 3% by weight of the solid mixture. The hydration reaction was carried out at 30°C for various time intervals; 0·5, 3, 6, 24 h and 3 and 7 days. The hydration kinetics of the system 3CaO. Al₂O₃–CaSO₄. 2H₂O in absence and presence of different nitrate salts was studied via the determination of the combined water contents. X-ray diffraction analysis and scanning electron microscopy showed that the ettringite was the only hydration product formed in the different mixes. The results indicated that the rate of formation of ettringite and its microstructure depend on the admixture used and its dosage.