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

Abstract

P-dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca,(SiO,)(OH),) 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, 29Si 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 P-C,S. The temperature at which P-C,S begins to form decreases with increasing chain length of the C-S-H or as the CdSi ratio becomes higher. The high activity of p-C,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 CdSi ratio is formed.

Research review of cement clinker chemistry

“…It is possible to produce fly ash belite cements [64,65] or thermally activated hillebrandite (Ca 2 SiO 4 ⋅ H 2 O) [66][67][68]. These procedures result in the familiar β-α′-polymorphs and the reactivity is much lower compared to amorphousand x-C 2 S.…”

Low Temperature Synthesis of Belite Cement Based on Silica Fume and Lime

“…Hillebrandite starts to decompose at about 500°C producing low-crystalline β -C 2 S [15]. Moreover, 29 Si MAS NMR analysis illustrates that the temperature at which β -C 2 S begins to form decreases as the Ca/Si ratio of hillebrandite becomes higher [19] or as the temperature of hydrothermal synthesis of hillebrandite becomes higher [16]. On the other hand, XRD analysis illustrates that the crystallographic properties and density of dissociation products of α -C 2 SH depend on the calcination temperature [20].…”

“…The reactivity of β -C 2 S relates to its large specific surface area taking into consideration the fact that the hydration is chemical-reaction-rate-controlled until its completion [19]. The specific surface area of β -C 2 S depends on calcination temperature of hillebrandite.…”

Improvement in Hydration Reactivity of α‐Phase Belite by Remelting Reaction

“…In the laboratory, highly reactive ␤-Ca 2 SiO 4 crystals made without any foreign oxides were successfully synthesized. [3][4][5][6] The reactivity was increased by the high specific surface area of the powder specimens.…”

“…In the laboratory, highly reactive ␤-Ca 2 SiO 4 crystals made without any foreign oxides were successfully synthesized. [3][4][5][6] The reactivity was increased by the high specific surface area of the powder specimens.The hydration behavior has been compared between the ␣Ј Lphase and polysynthetically twinned ␤-phase with identical chemical compositions. 7 The twin boundaries behaved on the crystal surface like active centers of the reaction with water.…”