SI-29 AND AL-27 MASNMR STUDY OF STRATLINGITE

Stratlingite (2CaO . Al2O3 . SiO2 . 8H(2)O) is a complex calcium alumi nosilicate hydrate commonly associated with the hydration of slag-cont aining 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 struct ure and how aluminum is accommodated by the structure is important, Ph ase pure stratlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate ce ment, CaO, NaOH, and water, The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermograv imetric analysis (TGA) and then further examined using Si-29, With and without cross-polarization (CP), and Al-27 solid-state magic angle nu clear magnetic resonance spectroscopy (MASNMR), For the most part, NMR data for these stratlingites corroborate structural information avail able 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 affect s the structure of stratlingite in subtle ways, significantly reducing the AI(/)(IV)AI(VI) ratio.