Dicalcium silicate hydrate (hillebrandite) was prepared by hydrothermal treatment of lime/silica fume mixtures with (Ca + Ba)/Si = 2 at 110[degrees]C for 5 hours.
The first step is preparation of dicalcium silicate hydrate (hillebrandite, [Ca.sub.2](Si[O.sub.3])[(OH).sub.2]) by hydrothermal treatment of silica rich waste material/lime mixtures.
The specific surface area of [beta]-[C.sub.2]S depends on calcination temperature of hillebrandite. The hydration rate of [beta]-[C.sub.2]S enhanced with increasing surface area.
Preparation of hillebrandite by hydrothermal treatment of silica fume and lime with and without 2wt% Ba[Cl.sub.2] was carried out as described below.
The product of hydrothermal treatment (hillebrandite) was filtered, washed with distilled water, and dried under vacuum.
Preparation of Hillebrandite. Figures 5 and 6 illustrate the FTIR spectra of lime/silica mixture hydrothermally treated at 110-150[degrees]C for 2-5 hours.
Hillebrandite lost absorbed water at 109[degrees]C.
As determined by TGA/DTA results, hillebrandite completely dehydrates forming [alpha]'-[C.sub.2]S that transforms to [beta]-[C.sub.2]S and/or [gamma]-[C.sub.2]S after cooling.
Hillebrandite does not appear in the XRD analysis (Figure 9(a)) because of its gel structure.
The mixtures of silica fume and lime that were hydrothermally treated at 110[degrees]C for 2 hours contain little amount of hillebrandite of low density with web-like morphology (Figures 11(a) and 11(b)).