Abstract Solidification / stabilization ( S S ) of chromium with Portland cement type I and tricalcium silicate (C 3S) was investigated by using the 29Si solid state magic angle spinning/nuclear magnetic resonance ( 29Si MAS NMR ), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The present study confirms that chromium nitrate can increase the extent of C 3S hydration. It also confirms that the chromium ion is easily incorporated into the C 3S 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 (CaCrSi 4O 10), calcium chromium oxide hydrate (CaCrO 4·2H 2O), and calcium dichromate (CaCr 2O 7) during the hydration of chromium-doped C 3S indicates the probable substitution of chromium for silicon in the calcium silicate hydrate (CSH) and the interaction between Cr and Si. Furthermore, formation of CaCrSi 4O 10, aluminum chromium oxide hydroxide hydrate (Al(OH)CrO 4·H 2O), aluminum chromium oxide hydroxide (Al 2(OH) 4CrO 4), and CaCr 2O 7 during the hydration of chromiumdoped cement reveals not only the probable substitution of chromium for silicon in the calcium silicate hydrate (CSH) but also the interaction among Cr, Si and Al. Apparently, the chromium iron (Cr 3+) may also be stabilized and solidified through these mechanisms in addition to those proposed by other investigators.