Effect of some inorganic admixtures on the formation and properties of calcium silicate hydrates produced in hydrothermal conditions

Hydrated calcium silicates have been synthesized at 200 °C under saturated steam pressure, giving materials consisting of ill crystallized calcium silicate hydrates, formed as an initial product and/or more crystalline forms. Three series of samples having different CaOSiO2 ratios and doped with inorganic compounds such as CaCl2, AlCl3, CrCl3, Na2CrO4, NaOH and Al(OH)3 were produced. The phase composition of the samples was examined by XRD. The microstructure was observed with the SEM and porosity measurements. Their thermal behaviour was characterized by DTA/TG methods. It has been found that the CaOSiO2 lowering promoted the formation of poorly crystalline C-S-H with high surface area and porosity. The stabilizing effect of Al on tobermorite was generally confirmed. The formation of disordered C-S-H, with relatively high water content, surface area and porosity in the presence of CrCl3 was found. The formation of xonotlite was promoted by CaCl2 and NaOH.