Formation and stability of C-S-H (I) of various degrees of crystallinity in the Ca(OH)2/CaO-Hi-Sil-H2O system

The stability and crystal morphology of C-S-H (I) in the CaO/Ca(OH)(2)-Hi-Sil-H2O systems and a sequence of formation of the intermediary compound has been examined. Two series of samples, with different ratios of CaO to SiO2 were used in the experimental tests. The molar ratio CaO/SiO2 of primary mixtures was 1.0. Hydrothermal synthesis was carried out under the saturated steam pressure at temperatures of 90, 110, 130, 150 and 175 degrees C; the duration of isothermal curing was 2-72 h. It was determined that an increase of temperature significantly influences the stability, morphology and degree of crystallinity of C-S-H (I). It was found that C-S-H (I) is stable in the ranhe 90-130 degrees C. The overall morphology of C-S-H varies from the common fibrous type to irregular grains forming a reticular network. The compositions of intermediate products and of final products can be changed by adding calcium containing components (Ca(OH)(2), CaO). In the mixtures with Ca(OH)(2), an intermediate compound is C-S-H (I) and the final product is xonotlite. Meanwhile, in the mixtures with CaO, the main intermediate compounds are Z phase and C-S-H (I), and the main product is gyrolite.