Ceramics-Silikáty 53 (2) 81-87 (2009)

FORMATION AND STABILITY OF C–S–H(I) IN Ca(OH)₂/CaO–THERMAL SILICA DENSIFIED–H₂O SYSTEM

K. Baltakys, R. Jauberthie, V. Kasperaviciute

The stability and crystals morphology of C–S–H(I) in the CaO/Ca(OH)₂–TSD–H₂O systems and a sequence of intermediary compound formation has been examined. Two series of samples, each being made with different forms of CaO and SiO₂, were used in the experimental tests. The molar ratio of primary mixtures was CaO/SiO₂ = 1.0. Hydrothermal synthesis has been carried out under the saturated steam pressure at temperatures of 90, 110, 130, 150 and 175ºC; the duration of isothermal curing was 2, 8, 24 or 72 hours. It was determined that thermal silica densified has negative influence on the formation of calcium silicate hydrates. Ca²⁺ containing components (Ca(OH)₂, CaO) change the composition of intermediate and final products of the synthesis. In the mixtures with Ca(OH)₂, intermediary and final compound is C–S–H(I) in different crystalline degree. Meanwhile, in the mixtures with CaO, the main intermediary compound is C–S–H(I) and the main product is xonotlite. It was estimated that the increment of temperature significantly influences the stability, morphology and crystalline degree of C–S–H(I).

Keywords: Calcium silicate hydrates; C–S–H(I); Xonotlite; X-Ray Diffraction