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

This paper describes the low temperature synthesis of belite (β-C(2)S) from silica fume. Mixtures of lime, BaCl(2), and silica fume with the ratio of (Ca + Ba)/Si = 2 were hydrothermally treated in stainless steel capsule at 110–150°C for 2–5 hours, calcined at 600–700°C for 3 hours, and analyzed by FTIR, XRD, TGA/DTA, and SEM techniques. Dicalcium silicate hydrate (hillebrandite) was prepared by hydrothermal treatment of lime/silica fume mixtures with (Ca + Ba)/Si = 2 at 110°C for 5 hours. Hillebrandite partially dehydrates in two steps at 422 and 508°C and transforms to γ-C(2)S at 734°C which in turn transforms to α′-C(2)S at 955°C which in turn transforms to β-C(2)S when cooled. In presence of Ba(2+) ions, β-C(2)S could be stabilized with minor transformation to γ-C(2)S. Mixture of silica fume, lime, and BaCl(2) with the ratio of (Ca + Ba)/Si = 2 was successfully utilized for synthesis of β-C(2)S by hydrothermal treatment at 110°C for 5 hours followed by calcination of the product at 700°C for 3 hours.