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

Abstract

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.