Characterization of C‐S‐H from Highly Reactive β‐Dicalcium Silicate Prepared from Hillebrandite

Abstract

β‐dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca 2 (SiO 3 )(OH) 2 ) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, 29 Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C‐S‐H consisted mainly of a dimer and a single‐chain polymer. Polymerization advances 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 β‐C 2 S. The temperature at which βC 2 S begins to form decreases with increasing chain length of the C‐S‐H or as the Ca/Si ratio becomes higher. The high activity of β‐C 2 S is due to its large specific surface area and the fact that the hydration is chemical‐reaction‐rate‐controlled until its completion. As a result, the hydration progresses in situ and C‐S‐H with a high Ca/Si ratio is formed.