QUANTITATIVE X-RAY-DIFFRACTION ANALYSIS OF CHROMIUM(III) DOPED TRICALCIUM SILICATE PASTES

The hydration products of tricalcium silicate (C3S) pastes prepared w ith different concentrations of Cr-III solutions have been investigate d (w/s similar to 0.5). Tricalcium silicate is the main constituent of Portland cement responsible for the strength and stability of hardene d Portland cement paste. Cr(NO3)(3).9H(2)O and [Cr(H2O)(4)Cl-2]Cl.2H(2 )O, added as dopants to C3S, simulate trivalent chromium waste that ma y be stabilized in ordinary Portland cement. X-ray diffraction was use d to monitor the development of the hydration reaction products from t he early stages to the late reaction stages. Leaching studies were car ried out to evaluate the stability of the Cr-III containing phases in the hydrated C3S matrix. When added in the trivalent form, chromium ha s been found to be primarily contained in C3S pastes as calcium chromi um hydroxide complexes. The nature of the complex formed depended on t he ambient conditions within the reaction chamber. The concentration o f the chromium complexes were also found to vary considerably with bot h 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.