Quantitative X-ray diffraction analysis of chromium(III) doped tricalcium silicate pastes

Abstract

The hydration products of tricalcium silicate (C₃S)^∗ pastes prepared with different concentrations of Cr^III solutions have been investigated ($\text{w}\text{s}\text{≈ 0.5}$). Tricalcium silicate is the main constituent of Portland cement responsible for the strength and stability of hardened Portland cement paste. Cr(NO₃)₃.9H₂O and [Cr(H₂O)₄Cl₂]Cl.2H₂O, added as dopants to C₃S, simulate trivalent chromium waste that may be stabilized in ordinary Portland cement. X-ray diffraction was used to monitor the development of the hydration reaction products from the early stages to the late reaction stages. Leaching studies were carried out to evaluate the stability of the Cr^III containing phases in the hydrated C₃S matrix.

When added in the trivalent form, chromium has been found to be primarily contained in C₃S pastes as calcium chromium hydroxide complexes. The nature of the complex formed depended on the ambient conditions within the reaction chamber. The concentration of the chromium complexes were also found to vary considerably with both age and the chromium concentration in the initial Cr^III/C₃S mixture. Cr^III was found to be totally stabilized in C₃S paste and immobile in the standard acetic acid leaching test.