Influence of some heavy metal nitrates on the hydration of C3A

Abstract

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. Hydration reaction was carried out at 30° C for various time intervals; 0.5, 3, 6, 24 hours, and 3 and 7 days. Hydration kinetics of the system 3CaO. Al2O3 – CaSO4. 2H2O in absence and presence of different nitrates salts was studied via the determination of the combined water contents. X-ray diffraction analysis (XRD) and Scanning electron microscope (SEM) 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.