SI-29 AND AL-27 MASNMR STUDY OF STRATLINGITE

Stratlingite (2CaO . Al2O3 . SiO2 . 8H(2)O) is a complex calcium aluminosilicate hydrate commonly associated with the hydration of slag-containing cements or other cements enriched in alumina, Stratlingite can coexist with the hydrogarnet solid solution [hydrogarnet (3CaO . Al2O2 . 6H(2)O)-katoite (3CaO . Al2O3 . SiO2 . 4H2O)] and calcium silicate hydrate (C-S-H). Since stratlingite is present in many blended cements, the knowledge of stratlingite's characteristic silicate anion structure and how aluminum is accommodated by the structure is important, Phase pure stratlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate cement, CaO, NaOH, and water, The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) and then further examined using Si-29, With and without cross-polarization (CP), and Al-27 solid-state magic angle nuclear magnetic resonance spectroscopy (MASNMR), For the most part, NMR data for these stratlingites corroborate structural information available in the literature, The aluminum atoms are both tetrahedrally and octahedrally coordinated, and the silicon atoms exist predominantly as Q(2), Q(2)(1A1), and Q(2)(2AI) species, The presence of alkali affects the structure of stratlingite in subtle ways, significantly reducing the AI(/)(IV)AI(VI) ratio.