CHARACTERIZATION OF C-S-H FROM HIGHLY REACTIVE BETA-DICALCIUM SILICATE PREPARED FROM HILLEBRANDITE

Beta-dicalcium silicate synthesized by thermal dissociation of hydroth ermally prepared hillebrandite (Ca2(SiO3)(OH)2) exhibits extremely hig h hydration activity. Characterization of the hydrates obtained and in vestigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, Si-29 magic angle spinning nuclear magn etic resonance, transmission electron microscopy selected area electro n diffraction, and XRD. The silicate anion structure of C-S-H consiste d mainly of a dimer and a single-chain polymer. Polymerization advance s with increasing curing temperature and curing time. The C-S-H has an oriented fibrous structure and exhibits a 0.73-nm dreierketten in the longitudinal direction. On heating, the C-S-H dissociates to form bet a-C2S. The temperature at which beta-C2S begins to form decreases with increasing chain length of the C-S-H or as the Ca/Si ratio becomes hi gher. The high activity of beta-C2S is due to its large specific surfa ce area and the fact that the hydration is chemical-reaction-rate-cont rolled until its completion. As a result, the hydration progresses in situ and C-S-H with a high Ca/Si ratio is formed.