An NMR, XRD and EDS study of solidification/stabilization of chromium with portland cement and C3S

Abstract

Solidification/stabilization (S/S) of chromium with Portland cement type I and tricalcium silicate (C3S) was investigated by using the Si-29 solid state magic angle spinning/nuclear magnetic resonance (Si-29 MAS/NMR), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The present study confirms that chromium nitrate can increase the extent of C3S hydration. It also confirms that the chromium ion is easily incorporated into the C3S paste and hydrated Portland cement, and that it affects the characteristics of the hydration processes and their hydration products, The formation of calcium chromium silicate (CaCrSi4O10), calcium chromium oxide hydrate (CaCrO4 . 2H(2)O), and calcium dichromate (CaCr2O7) during the hydration of chromium-doped C3S indicates the probable substitution of chromium for silicon in the calcium silicate hydrate (C-S-H) and the interaction between Cr and Si. Furthermore, formation of CaCrSi4O10, aluminum chromium oxide hydroxide hydrate (Al(OH)CrO4 . H2O), aluminum chromium oxide hydroxide (Al-2(OH)(4)CrO4), and CaCr2O7 during the hydration of chromium-doped cement reveals not only the probable substitution of chromium for silicon in the calcium silicate hydrate (C-S-H) but also the interaction among Cr, Si and Al, Apparently, the chromium iron (Cr3+) may also be stabilized and solidified through these mechanisms in addition to those proposed by other investigators. (C) 1997 Elsevier Science B.V.