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The hydration of tricalcium aluminate (C_3A) has a significant effect on the effectiveness of cement-based systems. In addition, the carbonation of hydration products of C_3A is particularly important in respect of durability performance. The present work investigates the hydration and carbonation reactions of C_3A and the changes induced by the presence of the heavy metal ions such as Zn 2+, Pb 2+, Cu 2+ and Cr 3+ by X-ray diffractometry (XRD). During hydration of C_3A, gehlenite hydrate, hydrogarnet, calcium monoaluminate (C_4AH_x) and calcium carboaluminate were detected in C_3A pastes except the Zn 2+doped paste, where hydrogarnet did not form. The examinations revealed that heavy metals coexisted with gehlenite hydrate, calcium monoaluminate (C_4AH_x) and calcium carboaluminate, inhibiting the formation of hydrogarnet. Hydrating C_3A was liable to be carbonated on exposure to air and carbon dioxide, especially in the presence of heavy metals, resulting in the formation of carboaluminate and/or calcium carbonate. The presence of heavy metals in-fluenced the polymorphism of calcium carbonate,ndicating that heavy metals could co-precipitate with calcium to form a carbonate solid solution.
The hydration of tricalcium aluminate (C_3A) has a significant effect on the effectiveness of cement-based systems. In addition, the carbonation of hydration products of C_3A is particularly important in respect of durability performance. The present work investigates the hydration and carbonation reactions of C_3A and the changes induced by the presence of the heavy metal ions such as Zn 2+, Pb 2+, Cu 2+ and Cr 3+ by X-ray diffractometry (XRD). During hydration of C_3A, gehlenite hydrate, hydrogarnet, calcium monoaluminate (C_4AH_x) and calcium carboaluminate were detected in C_3A pastes except the Zn 2 + doped paste, where hydrogarnet did not form. The examinations revealed that heavy metals coexisted with gehlenite hydrate, calcium monoaluminate (C_4AH_x) and calcium carboaluminate, inhibiting the formation of Hydrogarnet. Hydrating C_3A was liable to be carbonated on exposure to air and carbon dioxide, especially in the presence of heavy metals, resulting in the formation of carboalu minate and / or calcium carbonate. The presence of heavy metals in-fluenced the polymorphism of calcium carbonate, ndicating that heavy metals could co-precipitate with calcium to form a carbonate solid solution.